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An Aerodynamic Study of Labial Stop Consonants After Laser Cordectomy of Types II-III
An Aerodynamic Study of Labial Stop Consonants After Laser Cordectomy of Types II-III Lucille Wallet, Paris, France Summary: Objectives. The aim of this paper is to compare the aerodynamic parameters of intraoral pressure (IOP), oral airflow (OAF), and estimated transglottal pressure of 10 French patients treated by a cordectomy of types II-III with a group of 10 French healthy subjects. Study Design. Prospective. Methods. The collection of the aerodynamic data was conducted with EVA2. Parameters were measured using logatomes of the type CV1$CV2$CVC3 where C represents [p,b] and V is one of the vowels [a,i,u] in the positions one and two (n ¼ 240). The maximum peaks of IOP of the plosives [p] and [b] and the maximum peaks of OAF at their releases were extracted. Finally, the transglottal pressure was estimated, necessary for the voicing of [b], to establish the difference in the IOP mean peak of [p] and [b] at the same intensity. Subsequently, the differences in IOP for both positions and each vocalic contexts, ‘‘IOP(p-b)’’ were calculated, and the reports of these differences for the IOP of [p], viz ‘‘IOP(p-b)/IOP(p)’’, were established for a normalization of the results. Results. This study highlights an increase of the IOP and the OAF in voiceless contexts for both groups. The elevation of both parameters observed for the patients—confirmed by the calculation of the estimated transglottal pressure—does show some degree of laryngeal incompetence. Conclusions. The patients treated by cordectomy of types II-III maintain a relatively good voicing contrast. A certain difficulty in the execution of this articulatory feature is found. Key Words: Aerodynamic–Intraoral pressure–Oral airflow–Estimated transglottic pressure–Cordectomies. INTRODUCTION Besides the correspondence between the vertical laryngeal positions and the voice frequencies,1 laryngeal control occurs at the segmental level for the production of consonants to maintain a contrast between voiced and voiceless consonants in languages, like French, which have that contrast. The mechanisms involved in the laryngeal control may differ from one language to another. According to Ladefoged2 and Stevens,3 voicing of speech sounds corresponds to a state of relaxation of the laryngeal structures and the lowering of the larynx, which together cause, on the one hand, the shortening and the adduction of the vocal folds and, on the other hand, the maintenance of a sufficiently high transglottal pressure to uphold the vibratory cycles necessary for voicing. Rothenberg4 distinguishes three types of pressures that interact in the production of speech: subglottal pressure (SGP), which corresponds to the pressure of the pulmonary airflow beneath the vocal folds, supraglottal or intraoral pressure (IOP), which corresponds to the pressure above the vocal folds, and the atmospheric pressure (AP), which represents the external pressure. From an aerodynamic point of view, voicing depends both on the subglottal pressure (SGP) and the supraglottal or intraoral pressure (IOP). The open state of the glottis, necessary to the production of voiceless stops does not prevent the passage of the airflow. Consequently, a balance between the SGP and the IOP—higher Accepted for publication July 22, 2014. From the Laboratoire de Phonetique et Phonologie, UMR 7018 (CNRS/SorbonneNouvelle), Paris, France. Address correspondence and reprint requests to Lucille Wallet, Laboratoire de Phonetique et Phonologie, UMR 7018 (CNRS/Sorbonne-Nouvelle), 19, rue des Bernardins, Paris 75005, France. E-mail: [email protected] Journal of Voice, Vol. 29, No. 2, pp. 247-255 0892-1997/$36.00 Ó 2015 The Voice Foundation http://dx.doi.org/10.1016/j.jvoice.2014.07.011
than the AP—is established before the point of constriction in the vocal tract and until the release of stops. Finally, the closure causes a rapid increase of the IOP which reaches a plateau and a gradual decrease of the pulmonary airflow. Both pharyngeal walls and cheeks inflate slightly in order to fight against this pressure. The release phase, which corresponds to an immediate evacuation of the airflow outside the mouth, involves a drop of the IOP and a faster decrease of the lung volume.3 With regard to the production of voiced stops, two antagonist gestures must be coupled, which make these consonants difficult to produce. Ohala5 highlights a certain incompatibility between the voicing and the occlusion phase for these consonants. Ideally, the production of a voiced stop requires a vibration of the vocal folds maintained throughout the consonant. The specific disposition of the vocal folds necessary to cause voicing sets a resistance to the pulmonary airflow, which tends to decrease the IOP compared to the SGP. However, vocal fold vibrations require a transglottal airflow which only can be maintained as long as there is a difference between the SGP and the IOP. According to Chao6 and Ohala & Riordan7 among others, this pressure difference is mainly preserved by (i) a passive expansion, namely a slight swelling of the tissues which causes the relaxation of the vocal tract and (ii) an active expansion characterized by an enlargement of the supraglottal cavities which allows the preservation of the IOP in the vocal tract and, thus, a persistence of the airflow. The concept of laryngeal tumor resection through endoscopic intervention is not new. Even before the appearance of the laser, this type of intervention was common practice. Since the 70s, endoscopic laser cordectomy was introduced for tumors limited to the vocal fold.8,9 Nowadays, this surgery is experiencing an expansion because of its many advantages, such as the reduction of the period of hospitalization, the degree of morbidity, and the medico-economic costs, among others.
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In addition, recent studies report positive oncologic and vocal results, which argue in favor of the excision by endoscopic laser. This surgery, which is the usual one for precancerous states, in situ carcinomas, and T1 tumors, is used more and more for tumors classified as T2 or T3. The in-situ cancers include tumors limited to the epithelium. The T1 cancers are limited to the vocal folds which present a normal mobility. The invasion of the anterior or the posterior commissures is possible. The T2 cancers are limited to the larynx with an involvement of the sub or supraglottal area and/or a reduction of the affected vocal fold mobility. Finally, the T3 cancers are limited to the larynx with a chordal fixation. While this technique allows a rapid functional recovery, the resulting of voice quality depends on the extent of the resection. Generally, several types of laser cordectomies are distinguished, the simplest one involving only the epithelium, while the most complex one removes the entire vocal fold. The European Society of Laryngology recognizes five types of cordectomies.10 The study presented here is mainly interested in cordectomy of types II-III. Cordectomy of type II (or sub-ligamental) is an intervention indicated for in situ or micro invasive carcinomas of the lamina propria. The resection includes the epithelium, the vocal ligament and the three layers of the lamina propria (Figure 1). Cordectomy of type III (or transmuscular) is a surgery indicated for T1a lesions of the middle third of the vocal fold with a normal chordal mobility. It corresponds to the resection of the epithelium, the lamina propria and a variable part of the vocal muscle. In addition, the intervention may be extended from the vocal process of the arytenoid to the anterior commissure (Figure 2). In a previous study, we have shown that the modification of the internal structure of the affected vocal fold is responsible for an asymmetry, a desynchronized vibration and a decrease of the vibrating mass, which together cause a perturbation of the frequency and the amplitude of the vibratory cycles.11
More specifically, the glottis configuration resulting from the operation involves a change in the vocal gesture, especially in the acoustic properties of the mucosal wave. Therefore, one could foresee a deterioration of the phonetic implementation of the voicing feature ([±voice]), which is crucial for the discrimation of voiced and voiceless consonants in French. Based on an aerodynamic analysis of the IOP of the labial stops, the OAF during the release of the consonants and the estimated transglottal pressure, we will show that the phonetic implementation of the voicing feature is preserved after cordectomy of types II-III. According to us, no studies have taken the IOP and OAF into value and especially as parameters related to the voicing opposition after cordectomy of types II-IIIThus, this study is very important and welcomed because it focuses on the vibration characteristics of the vocal folds but considering the vibration not only as a ‘‘vocal’’ fact but as a phonological and articulatory fact.
FIGURE 1. Laser cordectomy of type II (Brasnu et al9).
METHODS Participants This research is a prospective study of 10 French male patients aged 47–80 years (average 66.7 years of age). All patients had come to seek medical advice because of a persistent hoarseness of 2 months or more. The diagnosis was made with the use of a nasofibroscopy. glottal lesions were classified into precancerous states or in situ carcinomas of type T1aN0. In fact, despite the fact that only one vocal fold was affected, chordal and arytenoid mobility were normal and without lymph node involvement. The subjects were recorded between 6 months and 1 year postoperatively after a cordectomy of types II-III, without any reconstructive or medialization procedures. A healthy population of 10 French males, aged between 34 and 67 years (average of 49.2 years) was selected to represent the control group. These persons had no history of speech or voice problems, laryngeal pathology or neuropathology.
FIGURE 2. Laser cordectomy of type III (Brasnu et al9).
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Study of Aerodynamic Parameters After Laser Cordectomy
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The data acquisition was performed with Phonedit.15 This software, used for acoustic and aerodynamic studies of voice and speech, was developed by the company SQLab (Aix en Provence). It allows to view acoustic, aerodynamic and EGG files simultaneously. Its main advantage is that we can obtain both the average measurements of a given segment and the exact values of OAF or IOP at any point of the curves. It is also possible to perform a manual labeling of the measurements in order to facilitate analysis.
FIGURE 3. Handpiece of EVA2 (user manual, Ghio15). Instrumentation Aerodynamic data collection was conducted with the Evaluation Voice Assisted EVA2 (Figure 3).12,13 This platform allows the collection of simultaneous acoustic data due to the availability of a microphone and a sonometer, of aerodynamic data through various aerodynamic sensors, and of EGG data through a connected portable laryngograph. We assume that to compare the aerodynamic data of our subjects, it is crucial to control reliably the loudness level. The sonometer remains the ideal instrument to control the loudness because it provides an SPL measure calibrated. In our case, speech was recorded with a headset microphone (AKG C 420), placed 6 cm away from the lip corner. We used the sonometer provided by the EVA system to measure the true SPL (dB SPL) of the speech wave in order to compare the root mean square intensity between utterances.14 We settled and determined the gain level of the sonometer from the first recording of the subjects for consistent comparisons. According to EVA two datasheet, the measurement of the oral airflow was made possible by a wide-range, grid pneumotachograph featuring low dead space and high linearity. All sensors are disposed on a handpiece mounted on an adjustable foot, positioned in front of the subject. This one is connected directly to a computer (PC). The sampling frequency is 25 000 Hz for the acoustic signal and 6250 Hz for the aerodynamic data. To collect the OAF, a silicone mask adapted to the subject’s morphology was placed over the mouth in such a way that air leaks were avoided. To measure the IOP, a tube of about 4 cm long and 5 mm in diameter was placed inside the mask. Pressures were measured using highly linear piezoelectric sensors with short response time. The subjects were told to keep their teeth tightened on the tip of the tube during the entire recording session, without crushing it. Throughout the session, subjects were seated, the breast right up in order to facilitate phonation. Most subjects held the handpiece by the back, slightly pressing the mask to the mouth. For the speaker’s comfort, breaks were scheduled between the different recording sequences.
Speech task Our corpus was composed of repetitions of logatomes of the type CV1$CV2$CVC3 where C represents the six oral stop consonants of French [p, t, k, b, d, g] and V is one of the three vowels [a, i, u]. These logatomes were constructed with the aim of estimating the consonant’s qualities in two syllable onset positions: absolute initial position (#_) and intervocalic position (V_V). The task of the participants was to read each logatomes three times at a moderate speech tempo and with conversational pitch and loudness. These types of stimuli were selected because of its advantage of reflecting normal phonation situations. It requires dynamic and successive articulation tasks that involve all the laryngeal muscles relevant for phonation. Thus, the different vocal folds phases of adduction and abduction associated with melodic variations, the rapid formant transitions, and the speaker-specific variations are characteristic of this type of corpus.16 Moreover, De Krom17 states that the natural speech situation highlights the pathology more efficiently than an isolated vowel quality analysis. Nevertheless, the natural speech analysis is more difficult to achieve because of the many disturbances. Moreover, according to this author, the chosen experiment type is essential in clinical analysis, because patients presenting voice disorders can not hide their dysphonia or adopt a compensatory behavior. Measurements The measurements of the intraoral pressure (IOP) and the oral airflow (OAF) were realized using the criteria shown in Figure 4. M€uller et Brown18 have proposed a segmentation according to the evolution of the two curves. The Tc phase corresponds to
FIGURE 4. IOP and OAF curves during the production of [p] (M€ uller et Brown18).
250 the stops closure. It starts at the moment when the IOP leaves its zero point to begin its ascent and ends when the OAF has reached its baseline. Therefore, these authors highlight a holding of this occlusion during which the OAF remains at zero and the IOP continues to increase to reach its maximum value (Pp phase). Finally, the Tr phase corresponds to the release of the consonant. It starts when the IOP begins to decrease while the OAF leaves its baseline to reach its maximum value (Pu). For the aerodynamic study of consonantal voicing, we have restricted our measurements to the logatomes composed of labial stops (ie, [p, b]). We have extracted the maximum peaks of IOP on plosives [p] and [b] (Pp phase). Regarding the OAF, we have taken the maximum peak of OAF during the release of the consonants (Pu phase). The relevant measures were performed manually using a mobile cursor with Phonedit software. We have analyzed 720 items (2 consonants x three vowels x three repetitions x two positions x 20 subjects). An average of the measurements of the three repetitions was calculated for each of the parameters and for all subjects. Consequently, the statistical analysis is based on 240 occurrences for each parameter (an average of our measurements x two consonants x three vowels x two positions x 20 subjects). Finally, we have considered the transglottal pressure necessary for the voicing. According to Kitajima et Fujita19 and Baken et Orlikoff,20 the difference in IOP peaks during the articulation of the consonants [p] and [b] is an estimation of the transglottal pressure and it can be used as an approximation of the phonatory threshold pressure (PTP, Kitajima & Fujita,19 Smitheran & Hixon21). Thus, we have calculated the difference for the IOP mean peaks of [p] and [b] for each of the two syllable-onset positions and each vocalic context at the same intensity, viz IOP(p-b). In order to standardize the results, we have also made the ratios of these differences for the IOP of [p], viz IOP(p-b)/IOP(p). The interest of this parameter is to normalize IOP(p-b) with respect to the sound intensity emitted during the production of the given corpus. In fact, as Hans22 pointed out, the SGP increases with the sound intensity emitted. In our point of view, even if the intensity was automatically calibrated with EVA, we assumed the standardization of the data was somehow needed. Statistical analysis We have noticed that the mean age of the two subject groups is substantially different. In order to rule out the explanation of age for between group differences rather than the surgery as the explanatory group difference factor, we have conducted some initial statistical analysis. F test of Fisher. It was first essential to check that the two populations had homogeneous variances in order to compare pairs. Based on an F-test of Fisher, we have calculated the ratio of the estimated variances (s2) between the ages of the two populations: F ¼ 1.102; P ¼ 0.59. Since the significance level was higher than 0.05, we can conclude that H0 must not be rejected (the variances of the two distributions were homogeneous) and that both populations must be considered as two independent groups in terms of age.
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Lilliefors test. The Lilliefors normality test, which checks the normality of the distributions of the ages of both groups, has also been applied on the data. The null hypothesis (H0) for this test is that the error isnormally distributed, that is to say that there is no difference between the observed error distribution and the normal distribution. The alternative hypothesis (H1) is that the error is not normally distributed. In the table of critical values of the Lilliefors test, the computed value of D must not be greater or equal to 0.0812 to accept H0 with a size n ¼ 120 and a threshold a ¼ .05. The results of these tests showed that the distributions of the ages of both groups (controls: D ¼ 0.1559, P < 0.0001 and patients: D ¼ 0.2108, P < 0.0001) did not fit a normal distribution. Since the values of P are less than 0.05, the null hypothesis should be rejected. In conclusion, the distributions of the ages being abnormal, we can not consider this parameter as a factor in our statistical analysis. The problem of the age. It is also important to confirm that age is not involved in the differences in IOP and OAF between the two groups (cf. Results part), we have retained five controls and five patients (M ¼ 58.6 years and M ¼ 57.8 years respectively) by removing the younger and older subjects in order to obtain two groups of the same age. Two one-way ANOVAs have been conducted with IOP and OAF values as the dependent variables and with the groups (patients vs controls) as the independent variable. The results were considered significant at an alpha level of 5% (P < 0.05). The IOP values were higher in patients than in controls (M ¼ 8.5 hPa and M ¼ 5.33 hPa respectively). The ANOVA conduced on this parameter showed a significant difference between the two groups of the same age (F (1, 118) ¼ 28.96, P < 0.0001). We can also note that the OAF values were higher in patients than in controls (M ¼ 0.34 dm3/s and M ¼ 0.26 dm3/ s respectively). The ANOVA conduced on this second parameter also showed a significant difference between the two groups of the same age (F (1, 118) ¼ 16.87, P < 0.0001). Thus, we can conclude that the observed differences on both IOP and OAF values are not induced by the age of the two groups. Indeed, we assume that these differences are a direct consequence of the surgery. Regular statistical analysis. In the remaining part of this study – since the effect of age has been ruled out –, we have conducted four-way ANOVAs, with IOP and OAF values as the dependent variables and with all subjects of the two groups (ie, 10 patients and 10 controls), the voicing context, the type of vowel, and the position of the labial stops in the logatomes as the independent variables. The results were considered significant at an alpha level of 5% (P < 0.05).
RESULTS IOP values We have observed that the values of the voicing parameters were always higher in patients than in controls (M ¼ 9.7 hPa and M ¼ 6.16 hPa respectively). The ANOVA showed a significant difference between the two groups (F (1, 216) ¼ 132.731,
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Study of Aerodynamic Parameters After Laser Cordectomy
P < 0.0001). In addition, we noted that for both groups, IOP values were higher for voiceless [p] than for voiced [b] (F (1, 216) ¼ 222.684, P < 0.0001). Furthermore, for both subject groups the vocalic contexts influenced the mean IOP values for both [p] and [b] (F (2, 216) ¼ 5.46, P ¼ 0.0049). In particular, their IOP values tended to be higher when these consonants were surrounded by high vowels, as the Fisher PLSD test showed significant differences between [a] and [i, u], with P ¼ 0.0152 for [a], and P ¼ 0.0019 for [i, u]. On the other hand, the position of the consonants in the logatomes had no significant effect on their IOP values (F (1, 216) ¼ 0.902, P ¼ 0.3434). Finally, we noted significant interactions between the factors ‘‘subjects’’ and ‘‘voicing’’, as well as between the factors ‘‘voicing’’ and ‘‘position’’, with statistical results equal to F (1, 216) ¼ 29.267, P < 0.0001 and F (1, 216) ¼ 4.338, P ¼ 0.0385 respectively. For the first interaction (ie, subjects:voicing), post-hoc analysis using Tukey’s HSD indicated that the IOP of patients (M ¼ 6.57, SD ¼ 1.79) is greater than the IOP of controls (M ¼ 4.69, SD ¼ 1.97) during the voiced labial stop, P ¼ 0.00012. In fact, for that consonant, the IOP of patients was 1.88 hPa higher than controls (95% CI: 0.76–3). Moreover, the test also showed that the IOP of patients (M ¼ 12.83, SD ¼ 2.73) is greater than the IOP of controls (M ¼ 7.62, SD ¼ 2.9) during the voiceless labial stop, P < 0.0001. For that consonant, the IOP of patients was 5.21 hPa higher than controls (95% CI: 4.09–6.33). These results confirmed that there is a difference between the two groups due to the surgery but it also underlined the fact that the IOP values between voiceless and voiced stops are still contrastive for both groups (cf. Discussion). Regarding the second interaction (ie, voicing:position), post-hoc analysis using Tukey’s HSD indicated that there is no effect of the position on the IOP values for a same consonant. In fact, there is no difference between a voiced labial consonant in initial and intervocalic positions, P ¼ 0.85. For that consonant, the difference between the two positions was 0.35 hPa (95% CI: 0.77 to 1.47). Further, there is no difference between a voiceless labial consonant in initial and intervocalic positions, P ¼ 0.14. For that consonant, the difference between these two positions was 0.93 hPa (95% CI: 0.19 to 2.05).
These results confirmed the first ANOVA which showed that the position of the consonants in the logatomes had no significant effect on their IOP values. Finally, the test indicated that the interaction observed is due to all other pairwise comparisons, such as [p] in initial position versus [b] in intervocalic position, which showed a significant difference (P < 0.0001). OAF values We noticed that whatever the consonant voicing was, the OAF values of patients were always higher than those of our controls (M ¼ 0.349 dm3/s and M ¼ 0.258 dm3/s respectively). The ANOVA showed a significant difference between the two groups (F (1, 216) ¼ 57.819, P < 0.0001). Besides, for both groups, OAF values tended to be higher in the voiceless context as compared to the voiced context (F (1, 216) ¼ 6.731, P ¼ 0.0101). We also noted a significant effect of vocalic contexts on the mean values of OAF (F (2, 216) ¼ 6.538, P ¼ 0.0018), which appeared to be more important for the low vowel [a] than for the two high vowels [i, u]. Indeed, the Fisher PLSD test showed significant differences between the vowels [a, i] and [a, u], with P-values equal to P ¼ 0.0004 and P ¼ 0.0297 respectively. Finally, the syllable position of the consonants in the logatomes had no influence on the mean values of OAF (F (1, 216) ¼ 2.212, P ¼ 0.1384). In addition, no interaction was found between these four factors. The mean data are displayed in Table 1 for both groups and the two syllabic positions. Moreover, the significant findings are summarized in Table 2. Estimated transglottal pressure Tables 3–5 summarize the estimated transglottal pressure necessary for the voicing for the two syllabic positions and each vocalic contexts. DISCUSSIONS IOP values We have demonstrated that, independently of the specific consonantal or vocalic contexts, the IOP measures of the patients were always significantly higher than those of the
TABLE 1. Means and Standard Deviations of IOP and OAF for the Controls and Patients in Function of the Voicing Context, the Type of Vowels and the Syllable Position During the Production of Logatomes [voix] #_ Controls IOP peaks (hPa) St. Dev. OAF (dm3/s) St. Dev. Patients IOP peaks (hPa) St. Dev. OAF (dm3/s) St. Dev.
[+voix]
[voix]
[pa]
[pi]
[pu]
[ba]
[bi]
[bu]
6.91 2.45 0.304 0.093
7.63 3.04 0.237 0.052
7.98 3.45 0.282 0.07
4.22 2.18 0.308 0.109
5.07 1.66 0.221 0.049
12.72 2.38 0.377 0.088
6.57 2.28 0.421 0.097
6.83 1.32 0.329 0.079
11.01 2.44 0.382 0.133
12.32 2.5 0.32 0.09
V_V
[+voix]
[apa]
[ipi]
[upu]
[aba]
[ibi]
[ubu]
4.92 2.03 0.224 0.069
6.69 2.58 0.325 0.152
8.09 3.04 0.242 0.066
8.44 3.06 0.283 0.073
4.12 2.62 0.341 0.07
4.57 1.44 0.215 0.058
5.25 1.89 0.212 0.073
7.24 1.08 0.343 0.092
12.47 2.6 0.374 0.134
14.31 2.74 0.339 0.123
14.17 2.86 0.364 0.097
5.82 2.32 0.299 0.069
6.38 2.1 0.33 0.111
6.61 1.34 0.31 0.087
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TABLE 2. Summary of Significant Findings where ‘‘**’’ Corresponds to Highly Significant Differences (P < 0.0001); ‘‘*’’ Corresponds to Significant Differences (P < 0.05) and ‘‘ns’’means ‘‘not significant’’
Groups Patients > Controls Voicing context [voix] > [+voix] Type of vowels [i,u] > [a] (IOP) [a] > [i,u] (OAF) Position V_V > #_ (IOP) #_ > V_V (OAF)
IOP
OAF
**
**
**
**
*
*
ns
ns
TABLE 4. Calculation of the Estimated Transglottal Pressure (in hPa) for the Two Syllabic Positions (Initial Onset and Intervocalic Onset) for Controls and Patients in Vowel Context [i] (n ¼ 80)
Controls Patients
IOP (pi-bi)
IOP(pi-bi)/ IOP(pi)
IOP (ipi-ibi)
IOP(ipi-ibi)/ IOP(ipi)
2.56 5.49
0.34 0.45
3.52 7.93
0.44 0.55
controls. In this respect, our findings are consistent with those of Hans,22 Zeitels et al,23 and Mirghani.24 Hans22 has shown, for different types of partial laryngectomies, that the IOP values in patients were always higher than those of the control group and that, moreover, this parameter is the most relevant for discriminating between these two groups for all types of laryngectomies. In fact, in the group of patients, the IOP tends to increase with the extent of resection. Similarly, for different types of cordectomies, Zeitels et al23 and Mirghani24 have shown that the IOP values of the patients were significantly higher than those of the control subjects. This increase of the IOP for the group of patients is possibly the consequence of a compensatory behavior. Koufman25 highlights two types of supraglottal compensatory behaviors: (i) the hyperadduction of the ventricular bands and (ii) the anteroposterior contraction of the larynx characterized by an anterior tilting of the arytenoids to the epiglottis. At this moment, we are unable to propose any specific hypothesis about the type of compensation adopted by the patients. A videolaryngostroboscopic examination would be necessary to establish whether our suggestion of a compensatory strategy is correct and, if so, to determine its precise nature. Nevertheless, we know that the elevated IOP in patients may be caused by one of these two reactions: (i) the development of a forced voice leading to a greater tension of the laryngeal muscles and, more broadly, by an increased tension of the vocal tract as a whole, or (ii) the increase of the pressure related to the surgery which allows the development of a supraglottal behavior.
Moreover, we assume that the IOP is equivalent to the SGP during the unvoiced labial stop because the vocal folds are in abduction (Holmberg et al,26 Rothenberg,4 among others). As a consequence, we postulate that the increase of the IOP values of the patients is also correlated with an increase of the SGP values. In our point of view, the high estimated subglottal values should be a compensation to the glottal inefficiency related to the surgery and should facilitate the initiation of the vibrations. We have also shown that for both groups the IOP values were statistically higher for voiceless stops, independently of the nature of the vocalic contexts. These results are in total agreement with the studies of Subtelny et al,27 Arkebauer et al,28 Lisker,29 Miller and Daniloff,30 Stathopoulos31 and Holmberg et al26 among others for normal speakers. We have already mentioned that during the production of a voiceless stop, the glottis remains open and the differential between SGP and IOP is constant. On the other hand, the articulation of voiced stops requires two antagonist gestures in the vocal tract: at first, a total obstruction of the air passage realized at some precise point in the vocal tract and in second, the maintenance of a sustained airflow in order to guarantee the vibration of the vocal folds. The glottal closure is responsible for resistance to the passage of the airflow, which tends to reduce the IOP in the vocal tract compared to the SGP. Except the results of normal speakers, it is important to underline that even after anatomical changes due to the surgery, our study results show that the IOP values between voiceless and voiced stops are still contrastive. An interesting result of our research is the observation that the mean IOP values of our two groups tend to be higher in the context of high vowels. Karnell & Willis32 had already concluded that the IOP values of [p] were greater between the high back vowel ([u]) than between the low vowel ([a]). Klich33 found the same dichotomy in whispered voice. Moreover, in a study of 11 men and 10 women involving various acoustic
TABLE 3. Calculation of the Estimated Transglottal Pressure (in hPa) for the Two Syllabic Positions (Initial Onset and Intervocalic Onset) for Controls and Patients in Vowel Context [a] (n ¼ 80)
TABLE 5. Calculation of the Estimated Transglottal Pressure (in hPa) for the Two Syllabic Positions (Initial Onset and Intervocalic Onset) for Controls and Patients in Vowel Context [u] (n ¼ 80)
IOP IOP(pa-ba)/ IOP IOP(apa-aba)/ (pa-ba) IOP(pa) (apa-aba) IOP(apa)
IOP IOP(pu-bu)/ IOP IOP(upu-ubu)/ (pu-bu) IOP(pu) (upu-ubu) IOP(upu)
Controls Patients
2.69 4.44
0.39 0.4
2.57 6.65
0.38 0.53
Controls Patients
3.06 5.48
0.38 0.43
3.19 7.56
0.38 0.53
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Study of Aerodynamic Parameters After Laser Cordectomy
and aerodynamic parameters—which includes the estimated subglottal pressure (ESGP) — Higgins et al34 concluded that there is an effect of the vocalic context on ESGP measures from IOP measurements. The mean IOP values of stops also appear to be higher before [i] than before [a]. Karnell & Willis32 suggested two hypotheses to explain these changes: (i) a higher impedance of the oral cavity due to the greater constriction of the high vowels as compared to the mid or low vowels and (ii) a greater tension of the vocal folds for these vowels which requires an increase of the pressure in order to maintain the vocal fold vibration. The fact that this effect is found in both modal voice and whispered voice suggests that the vibration of the vocal folds is independent of the second hypothesis. The rise of the IOP in contact with the high vowels compared to the low vowels is due solely to differences in the oral cavity impedance between these two vowel types. Thus, for the production of high vowels, the vocal tract is more tense, which has the effect of increasing the impedance of the vocal tract.34 In addition, various articulations for the production of vowels change the size and the volume of the pharyngeal and oral cavities, implying differences in terms of impedance in the vocal tract. OAF values We have noticed that, the mean OAF values of patients were always significantly higher than those of the controls, independently of the segmental contexts. Our findings corroborate those of Zeitels et al,23 Tamura et al35 and Mirghani24 studies for cordectomies. This increase in airflow is directly related to the glottal leak caused by the surgery. In fact, the resection of a part of the vocal fold is responsible for a vibratory asymmetry and an incomplete apposition of the mucosa. Therefore, we suggest that the surgical intervention reduces the glottal resistance in phonation, which causes a permanent loss of airflow through the vocal folds and explains the increase of the OAF.11 We have also shown that the OAF values were systematically higher for the voiceless stops in normal speakers. These results confirm the observations made by Emanuel & Counihan,36 Gilbert,37 Trullinger & Emanuel,38 Stathopoulos & Weismer39 and Higgins et al.34 For example, in a study involving 25 men and 25 women, Emanuel & Counihan36 have found that the voicing tends to reduce the airflow measurements for stops from 26 to 53% compared to their voiceless counterparts. Trullinger & Emanuel38 have found the same pattern for a child population of 15 boys and 15 girls. In our case, the differences in the OAF measures for the release of [p, b] can be attributed to the resistance imposed by the laryngeal vibrations of the vocal folds during the production of voiced stops. Indeed, we know that the voiceless stops involve a glottal opening characterized by an abduction of the vocal folds. Therefore, the lung airflow is not slowed down and can escape directly into the vocal tract. In contrast, the production of voiced stops requires a sustained vibration of the vocal folds, which increases the resistance against the oral airflow. Besides our study results are consistent with prior studies on normal speech, one of the most important finding of our study is that even after significant anatomical alterations due
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to cordectomy, the OAF values contrast between voiceless and voiced stops still occurs. Consequently, we can conclude that the voicing contrast is well maintained after these surgeries. We could finally note that, in general, the mean OAF values for the release of the consonant tends to be higher in the context of a low vowel for both groups. This conclusion is consistent with the studies of Emanuel & Counihan,36 Trullinger & Emanuel,38 and Higgins et al,34 among others for normal speakers. We have already explained that the elevation of the tongue necessary for the articulation of the high vowels causes a higher impedance in the oral cavity, which tends to reduce the oral airflow. Instead, the articulation combining a maximum aperture and a low tongue body position for the open vowel [a] entails a low resistance to the oral airflow. For Higgins et al,34 with regard to the different effects of vowel classes, the glottal width and the glottal resistance may also contribute to these airflow differences. Indeed, the elevation of the larynx necessary to create the vocal fold tension and, more specifically, the anterior vertical adjustment of the thyroid cartilage and hyoid bone, tends to reduce the glottal width and thereby increases the resistance in anticipation of the articulation of high vowels. Estimated transglottal pressure Remember that according to Kitajima & Fujita19 and Baken & Orlikoff,20 the difference in IOP peaks during the articulation of the consonants [p] and [b] is an estimation of the transglottal pressure during [b] (henceforth ETP) and has been claimed to be a possible substitute for the oscillation threshold pressure or phonatory threshold pressure (PTP, Kitajima & Fujita,19 Smitheran & Hixon21). The PTP has been defined by Titze40 as the minimum degree of lung pressure required for the initiation and maintenance of voicing when the vocal folds are slightly abducted. This phonatory threshold is in a range of two to four hPa with an usual SGP equal to seven hPa.40,41 The level of PTP depends on the stiffness of the vibrating portion of the vocal folds, their thickness, their viscosity, the width of the prephonatory glottis and the quality of the mucosal wave during the phonation.40 If the mucosal wave, the glottal width, and the stiffness of the vocal folds decrease, then PTP will follow the decline. Besides, Chan et al42 state that an increase of the tissues, the thickness of the vocal folds, or the stiffness of the epithelial membrane are indicators of an increase of the PTP. Since there is no evidence nor reliable recent studies that support a relationship between ETP and PTP, we will focus on the ETP method results only. For the control group, we note that the results of the ETP fall in an interval of two to four hPa in both positions. This interval is consistent with the transglottal pressure range required for initiation of phonation.20 In addition, we note that the minimum pressures are higher in the context of high vowels compared to the low vowel. In fact, during the release of the consonant, adjustments related to the coarticulation effect of the vowels on the consonant take place upstream. For the production of high vowels, the vocal folds will stretch more, which will reduce their vibrating mass, increase the glottal impedance and finally results in an increase of their intrinsic fundamental frequency.11 Consequently, the vibration will be more difficult
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TABLE 6. Results of the Main Studies on Estimated Transglottal Pressure (in cmH2O) in Healthy Subjects (1 cmH20 ¼ 0.98 hPa) Authors
Corpus
IOP(p-b)
IOP(p-b)/ IOP(p)
Subtelny et al27 /ipi/,/ibi/ 2.06 0.32 Murry et Brown43 /apa/,/aba/ 3.48 0.42 Stathopoulos31 /pap/,/bab/ 2.68 0.23 Kitajima et Fujita19 /ipi/,/ibi/ 4.7 0.44 Hans22 /pi/,/bi/and/ 2.4 and 2.8 0.35 and 0.29 ipi/,/ibi/
to maintain, which will lead, through a compensation phenomenon, to the rise of the ETP. Finally, our results are more or less identical to those of Subtelny et al,27 Murry & Brown,43 Stathopoulos,31 Kitajima & Fujita19 and Hans23 studies, abstracting away from individual variations (Table 6). Regarding the patients, we note that, just like the controls, the pressures remain higher in the context of high vowels. Besides the fact that the normalized transglottal pressure values of [b] in the low vowel context were almost identical for both groups in initial position, we observe that in the high vowel contexts the values are much higher than those of the healthy subjects in both initial and intervocalic positions. This finding is consistent with Hans22 who has highlighted the existence of pressure differences that are higher for patients treated with partial laryngectomies than for control subjects, which fact this author interpreted as a proof for the difficulty of creating voicing after these surgeries. It is well known that cordectomies change the glottal configuration in postoperative. Thus, one or more layers of the vocal fold are resected during the surgery, which results in an increase in the stiffness, a greater tension of the vocal fold and a reduction of the vibrating mass. In addition, a vibratory asymmetry is observed, implying an imprecise mucosal wave. The Hirano’s ‘‘body-cover’’ model, which is based on three histological sections of the vocal fold and mainly characterized by a ‘‘body’’ (vocal ligament and muscle) and a ‘‘cover’’ (vocal fold mucosa) separated by a drift space (Reinke space), explains the triple horizontal, vertical, and mucosal movements of the vocal folds during phonation.44 Changes in the anatomical structures, particularly the ‘‘cover’’, cause a reduction in the vibratory surface and, in extenso, the damping of the vibratory amplitude. Consequently, the results of this study definitively confirm that the patients tend to increase their ETP compared to the controls in order to initiate and sustain oscillations as a compensation for this chordal mutilation. Our results are also consistent with the experiment of Kitajima & Fujita19 which shows that the transglottal pressure can be considered as an index for the vibratory efficiency of the vocal folds and, therefore, it allows to classify the voice quality of the healthy subjects compared to dysphonic subjects with pathological voices. Thus, in their study of Japanese patients with diverse laryngeal pathologies, they claim that
the difference IOP(p-b) allows to objectify the condition: if the difference is less than the normal values, then the power of adduction of the vocal folds is considered insufficient, as it is typical for unilateral paralysis. Conversely, if the difference is greater than the normal values, abnormal stiffness of the vocal folds must be considered and an ineffective glottal closure is allowed, which is typical of cancers of the vocal fold. To the best of our knowledge, no studies examining this type of surgery had not yet shown the impact of anatomical changes on aerodynamic parameters selected here. The result probably the most robust of this study is that the voicing contrast is maintained despite obvious difficulties, compensated by an increase of the ETP. Finally, the results definitively confirm the existing clinical impressions. CONCLUSIONS The more relevant and original result of this study is that patients appear to mark the voicing contrast between/p/and/b/ with the highest IOP and OAF values for the voiceless labial stop. More in general, we observe that all the values for the parameters studied here are always higher for the patients than the control subjects, which reflects the glottal inefficiency of the former group. We interpret these measurements as either a vocal forcing behavior, or as a difficulty in the creation or maintenance of voicing. The latter hypothesis is supported by the estimated transglottal pressure measurements, obtained by the difference IOP(p-b), which are much more important in the patients than in the controls. The higher values observed in patients for all aerodynamic parameters indicate (i) the persistence of stiffness and tension of the resected vocal fold, (ii) a partial glottal closure (glottal leakage) and (iii) a difficulty regarding the realization of the voicing feature. Consequently, the increase in these different pressures in the values of the different parameters shows a compensatory mechanism applied to fight against the major laryngeal resistance and thereby facilitate the initiation and maintenance of voicing where it is necessary. Acknowledgments I wish to thank Jean-Marc Beltzung for his careful reading of the text and useful suggestions as well as for his encouragement throughout the redaction of this paper. I also thank Leo Wetzels for our discussions and his precious corrections and the members of the HEGP’s unit ‘‘Voice’’, Daniel Brasnu, Stephane Hans and Lise Crevier Buchman, for their hospitality during my stays at the ORL department, where I could meet the patients. I am alone responsible for any errors this paper may contain. REFERENCES 1. Shipp T. Vertical laryngeal position during continuous and discrete vocal frequency change. J Speech Hear Res. 1975;18:707–718. 2. Ladefoged P. The linguistic use of different phonation types. In: Bless D, Abbs J, eds. Vocal Fold Physiology: Contemporary Research and Clinical Issues. San Diego, CA: College Hill Press; 1983:351–360. 3. Stevens KN. Vocal fold vibration for obstruent consonants. In: Gauffin J, Hammarberg B, eds. Vocal Fold Physiology: Acoustic, Perceptual and
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Physiological Aspects of Voice Mechanisms. San Diego, CA: Singular Publishing Group; 1991:29–36. Rothenberg M. Breath-stream dynamics of simple-released-plosive production. Bibliotheca Phonetica. 1968;6:6–22. Ohala J. The origin of sound patterns in vocal tract constraints. In: MacNeilage PF, ed. The Production of Speech. New York, NY: Springer Verlag; 1983:189–216. Chao YR. Types of plosives in Chinese. In: Proceedings of the 2nd International Congress of Phonetic Sciences. Cambridge, UK: Cambridge University Press; 1936:106–110. Ohala JJ, Riordan CJ. Passive vocal tract enlargement during voiced stops. In: Wolf JJ, Klatt DH, eds. Speech Communication Papers. New York, NY: Acoustic Society. of America; 1979:89–92. Strong MS. Laser excision of carcinoma of the larynx. Laryngoscope. 1975; 85:1286–1289. Brasnu D, Laccourreye O, Hans S, Menard M, De Mones E, Behm E. La chirurgie conservatrice des cancers du larynx et du pharynx. Paris, France: Amplifon; 2005. Remacle M, Eckel HE, Antonelli A. Endoscopic cordectomy. A proposal for a classification by the working committee, European Laryngological society. Eur Arch Otorhinolaryngol. 2000;257:227–231. Wallet L. Etudes multiparametriques de la voix et de la parole apres cordectomie laser par voie endoscopique de type II-III; Ph.D. thesis: Universite Paris 3; 2012. Galindo B, Teston B. Physiologia, une station de travail qui etudie des parametres physiologiques de la voix. Travaux interdisciplinaires du laboratoire Parole et Langage d’Aix-en-Provence. 1989;13:197–217 [in French]. Teston B, Galindo B, Ghio A. A multisensor data acquisition and processing system for speech production investigation. In: Proceedings of 14th ICPhS. Vol 3. San Francisco, CA: University of California; 1999: 2251–2254. Lagier A, Vaugoyeau M, Ghio A, Legou T, Giovanni A, Assaiante C. Coordination between Posture and Phonation in Vocal Effort Behavior. Folia Phoniatr Logop. 2010;62:195–202. Ghio A. Phonedit: Multiparametric speech analysis. LPL: Universite d’Aix-en-Provence; 2002. Available at: www.lpl.univ-aix.fr. Schoentgen J, Bensaid M, Bucella F, Ciocea S. Issues in the acoustic evaluation of laryngeal disorders. In: Proceedings VOICEDATA98, Symposium on Databases in Voice Quality Research and Education. Pays-Bas, The Netherlands: University of Utrecht; 1998:16–21. De Krom G. Consistancy and reliability of voice quality ratings for different types of speech fragments. J Speech Hear Res. 1994;37:985–1000. Muller EM, Brown WS. Variations in the supraglottal air pressure waveform and their articulatory interpretation. In: Lass N, ed. Speech and Language: Advances in Basic Research and Practice, 1980;Vol 4. New York, NY: Academic Press; 1980:318–389. Kitajima K, Fujita F. Clinical report on preliminary data on intraoral pressure in the evaluation of laryngeal pathology. J Voice. 1992;6:79–85. Baken RJ, Orlikoff RF. Clinical measurement of speech and voice. San Diego, CA: Singular Publishing Group; 2000. Smitheran JR, Hixon T. A clinical method for estimating laryngeal airway resistance during vowel production. J Speech Hear Res. 1981;46:138–146. Hans S. Etude aerodynamique comparee de logatomes chez 120 sujets normaux et 38 patients avec resection d’un ou des deux plis vocaux; Ph.D. thesis: Universite Paris 3; 2003.
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23. Zeitels SM, Hillman RE, Franco RA, Bunting GW. Voice and treatment outcome from phonosurgical management of early glottal cancer. Ann Otol Rhinol Laryngol. 2002;190:3–20. 24. Mirghani H. Evolution de la voix apres cordectomie de type I par voie endoscopique au laser; Master’s thesis: Universite Paris 3; 2009. 25. Koufman J. Approach to the patient with a voice disorder. Otolaryngol Clin North Am. 1991;24:989–998. 26. Holmberg E, Hillman R, Perkell J. Glottal airflow and transglottal air pressure measurements for male and femal speakers in low, normal and high pitch. J Voice. 1988;3:294–305. 27. Subtelny JD, Worth JH, Sakuda M. Intraoral pressure and rate of flow during speech. J Speech Hear Res. 1966;9:498–518. 28. Arkebauer HJ, Hixon T, Hardy JC. Peak intraoral air pressure during speech. J Speech Hear Res. 1967;10:196–208. 29. Lisker L. Supraglottal air pressure in the production of English stops. Lang Speech. 1970;13:215–230. 30. Miller CJ, Daniloff R. Aerodynamics of stops in continuous speech. J Phonetics. 1977;5:351–360. 31. Stathopoulos ET. Relationship between intraoral air pressure and vocal intensity in children and adults. J Speech Hear Res. 1986;29: 71–74. 32. Karnell MP, Willis CR. The effect of vowel context on consonantal intraoral air pressure. Folia Phoniatr (Basel). 1982;34:1–8. 33. Klich RJ. Effects of speech level and vowel context on intraoral air pressure in vocal and whispered speech. Folia Phoniatr (Basel). 1982; 34:33–40. 34. Higgins MB, Netsell R, Schulte L. Vowel-related differences in laryngeal articulatory and phonatory function. J Speech Hear Res. 1998;41: 712–724. 35. Tamura E, Kitahara S, Oqura M, Kohno N. Voice quality after laser surgery or radiotherapy for T1a glottic carcinoma. Laryngoscope. 2003;113: 910–914. 36. Emanuel FW, Counihan DT. Some characteristics of oral and nasal airflow during plosive consonant production. Cleft Palate J. 1970;7: 249–260. 37. Gilbert H. Oral airflow during stop consonant production. Folia Phoniatr. 1973;25:288–296. 38. Trullinger RW, Emanuel FW. Airflow characteristics of stop-plosive productions of normal-speaking children. J Speech Hear Res. 1983;26: 202–208. 39. Stathopoulos E, Weismer G. Oral airflow and air pressure during speech production: a comprative study of children, youths and adults. Folia Phoniatr (Basel). 1985;37:152–159. 40. Titze IR. The physics of small-amplitude oscillation of the vocal folds. J Acoust Soc Am. 1988;83:1536–1552. 41. Verdolini K, Titze IR, Fennell A. Dependance of phonatory effort on hydration level. J Speech Hear Res. 1994;37:1001–1007. 42. Chan R, Titze IR, Titze M. Further studies on phonation threshold pressure in a physical model of the vocal fold mucosa. J Acoust Soc Am. 1997;10: 3722–3727. 43. Murry T, Brown WS. Intraoral air pressure in whispered stop consonants. J Phonetics. 1976;4:183–187. 44. Hirano M. Structure and vibratory behavior of the vocal folds. In: Sawashima M, Cooper FS, eds. Dynamic Aspects of Speech Production. Tokyo, Japan: University of Tokyo Press; 1977:13–27.
than the AP—is established before the point of constriction in the vocal tract and until the release of stops. Finally, the closure causes a rapid increase of the IOP which reaches a plateau and a gradual decrease of the pulmonary airflow. Both pharyngeal walls and cheeks inflate slightly in order to fight against this pressure. The release phase, which corresponds to an immediate evacuation of the airflow outside the mouth, involves a drop of the IOP and a faster decrease of the lung volume.3 With regard to the production of voiced stops, two antagonist gestures must be coupled, which make these consonants difficult to produce. Ohala5 highlights a certain incompatibility between the voicing and the occlusion phase for these consonants. Ideally, the production of a voiced stop requires a vibration of the vocal folds maintained throughout the consonant. The specific disposition of the vocal folds necessary to cause voicing sets a resistance to the pulmonary airflow, which tends to decrease the IOP compared to the SGP. However, vocal fold vibrations require a transglottal airflow which only can be maintained as long as there is a difference between the SGP and the IOP. According to Chao6 and Ohala & Riordan7 among others, this pressure difference is mainly preserved by (i) a passive expansion, namely a slight swelling of the tissues which causes the relaxation of the vocal tract and (ii) an active expansion characterized by an enlargement of the supraglottal cavities which allows the preservation of the IOP in the vocal tract and, thus, a persistence of the airflow. The concept of laryngeal tumor resection through endoscopic intervention is not new. Even before the appearance of the laser, this type of intervention was common practice. Since the 70s, endoscopic laser cordectomy was introduced for tumors limited to the vocal fold.8,9 Nowadays, this surgery is experiencing an expansion because of its many advantages, such as the reduction of the period of hospitalization, the degree of morbidity, and the medico-economic costs, among others.
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In addition, recent studies report positive oncologic and vocal results, which argue in favor of the excision by endoscopic laser. This surgery, which is the usual one for precancerous states, in situ carcinomas, and T1 tumors, is used more and more for tumors classified as T2 or T3. The in-situ cancers include tumors limited to the epithelium. The T1 cancers are limited to the vocal folds which present a normal mobility. The invasion of the anterior or the posterior commissures is possible. The T2 cancers are limited to the larynx with an involvement of the sub or supraglottal area and/or a reduction of the affected vocal fold mobility. Finally, the T3 cancers are limited to the larynx with a chordal fixation. While this technique allows a rapid functional recovery, the resulting of voice quality depends on the extent of the resection. Generally, several types of laser cordectomies are distinguished, the simplest one involving only the epithelium, while the most complex one removes the entire vocal fold. The European Society of Laryngology recognizes five types of cordectomies.10 The study presented here is mainly interested in cordectomy of types II-III. Cordectomy of type II (or sub-ligamental) is an intervention indicated for in situ or micro invasive carcinomas of the lamina propria. The resection includes the epithelium, the vocal ligament and the three layers of the lamina propria (Figure 1). Cordectomy of type III (or transmuscular) is a surgery indicated for T1a lesions of the middle third of the vocal fold with a normal chordal mobility. It corresponds to the resection of the epithelium, the lamina propria and a variable part of the vocal muscle. In addition, the intervention may be extended from the vocal process of the arytenoid to the anterior commissure (Figure 2). In a previous study, we have shown that the modification of the internal structure of the affected vocal fold is responsible for an asymmetry, a desynchronized vibration and a decrease of the vibrating mass, which together cause a perturbation of the frequency and the amplitude of the vibratory cycles.11
More specifically, the glottis configuration resulting from the operation involves a change in the vocal gesture, especially in the acoustic properties of the mucosal wave. Therefore, one could foresee a deterioration of the phonetic implementation of the voicing feature ([±voice]), which is crucial for the discrimation of voiced and voiceless consonants in French. Based on an aerodynamic analysis of the IOP of the labial stops, the OAF during the release of the consonants and the estimated transglottal pressure, we will show that the phonetic implementation of the voicing feature is preserved after cordectomy of types II-III. According to us, no studies have taken the IOP and OAF into value and especially as parameters related to the voicing opposition after cordectomy of types II-IIIThus, this study is very important and welcomed because it focuses on the vibration characteristics of the vocal folds but considering the vibration not only as a ‘‘vocal’’ fact but as a phonological and articulatory fact.
FIGURE 1. Laser cordectomy of type II (Brasnu et al9).
METHODS Participants This research is a prospective study of 10 French male patients aged 47–80 years (average 66.7 years of age). All patients had come to seek medical advice because of a persistent hoarseness of 2 months or more. The diagnosis was made with the use of a nasofibroscopy. glottal lesions were classified into precancerous states or in situ carcinomas of type T1aN0. In fact, despite the fact that only one vocal fold was affected, chordal and arytenoid mobility were normal and without lymph node involvement. The subjects were recorded between 6 months and 1 year postoperatively after a cordectomy of types II-III, without any reconstructive or medialization procedures. A healthy population of 10 French males, aged between 34 and 67 years (average of 49.2 years) was selected to represent the control group. These persons had no history of speech or voice problems, laryngeal pathology or neuropathology.
FIGURE 2. Laser cordectomy of type III (Brasnu et al9).
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The data acquisition was performed with Phonedit.15 This software, used for acoustic and aerodynamic studies of voice and speech, was developed by the company SQLab (Aix en Provence). It allows to view acoustic, aerodynamic and EGG files simultaneously. Its main advantage is that we can obtain both the average measurements of a given segment and the exact values of OAF or IOP at any point of the curves. It is also possible to perform a manual labeling of the measurements in order to facilitate analysis.
FIGURE 3. Handpiece of EVA2 (user manual, Ghio15). Instrumentation Aerodynamic data collection was conducted with the Evaluation Voice Assisted EVA2 (Figure 3).12,13 This platform allows the collection of simultaneous acoustic data due to the availability of a microphone and a sonometer, of aerodynamic data through various aerodynamic sensors, and of EGG data through a connected portable laryngograph. We assume that to compare the aerodynamic data of our subjects, it is crucial to control reliably the loudness level. The sonometer remains the ideal instrument to control the loudness because it provides an SPL measure calibrated. In our case, speech was recorded with a headset microphone (AKG C 420), placed 6 cm away from the lip corner. We used the sonometer provided by the EVA system to measure the true SPL (dB SPL) of the speech wave in order to compare the root mean square intensity between utterances.14 We settled and determined the gain level of the sonometer from the first recording of the subjects for consistent comparisons. According to EVA two datasheet, the measurement of the oral airflow was made possible by a wide-range, grid pneumotachograph featuring low dead space and high linearity. All sensors are disposed on a handpiece mounted on an adjustable foot, positioned in front of the subject. This one is connected directly to a computer (PC). The sampling frequency is 25 000 Hz for the acoustic signal and 6250 Hz for the aerodynamic data. To collect the OAF, a silicone mask adapted to the subject’s morphology was placed over the mouth in such a way that air leaks were avoided. To measure the IOP, a tube of about 4 cm long and 5 mm in diameter was placed inside the mask. Pressures were measured using highly linear piezoelectric sensors with short response time. The subjects were told to keep their teeth tightened on the tip of the tube during the entire recording session, without crushing it. Throughout the session, subjects were seated, the breast right up in order to facilitate phonation. Most subjects held the handpiece by the back, slightly pressing the mask to the mouth. For the speaker’s comfort, breaks were scheduled between the different recording sequences.
Speech task Our corpus was composed of repetitions of logatomes of the type CV1$CV2$CVC3 where C represents the six oral stop consonants of French [p, t, k, b, d, g] and V is one of the three vowels [a, i, u]. These logatomes were constructed with the aim of estimating the consonant’s qualities in two syllable onset positions: absolute initial position (#_) and intervocalic position (V_V). The task of the participants was to read each logatomes three times at a moderate speech tempo and with conversational pitch and loudness. These types of stimuli were selected because of its advantage of reflecting normal phonation situations. It requires dynamic and successive articulation tasks that involve all the laryngeal muscles relevant for phonation. Thus, the different vocal folds phases of adduction and abduction associated with melodic variations, the rapid formant transitions, and the speaker-specific variations are characteristic of this type of corpus.16 Moreover, De Krom17 states that the natural speech situation highlights the pathology more efficiently than an isolated vowel quality analysis. Nevertheless, the natural speech analysis is more difficult to achieve because of the many disturbances. Moreover, according to this author, the chosen experiment type is essential in clinical analysis, because patients presenting voice disorders can not hide their dysphonia or adopt a compensatory behavior. Measurements The measurements of the intraoral pressure (IOP) and the oral airflow (OAF) were realized using the criteria shown in Figure 4. M€uller et Brown18 have proposed a segmentation according to the evolution of the two curves. The Tc phase corresponds to
FIGURE 4. IOP and OAF curves during the production of [p] (M€ uller et Brown18).
250 the stops closure. It starts at the moment when the IOP leaves its zero point to begin its ascent and ends when the OAF has reached its baseline. Therefore, these authors highlight a holding of this occlusion during which the OAF remains at zero and the IOP continues to increase to reach its maximum value (Pp phase). Finally, the Tr phase corresponds to the release of the consonant. It starts when the IOP begins to decrease while the OAF leaves its baseline to reach its maximum value (Pu). For the aerodynamic study of consonantal voicing, we have restricted our measurements to the logatomes composed of labial stops (ie, [p, b]). We have extracted the maximum peaks of IOP on plosives [p] and [b] (Pp phase). Regarding the OAF, we have taken the maximum peak of OAF during the release of the consonants (Pu phase). The relevant measures were performed manually using a mobile cursor with Phonedit software. We have analyzed 720 items (2 consonants x three vowels x three repetitions x two positions x 20 subjects). An average of the measurements of the three repetitions was calculated for each of the parameters and for all subjects. Consequently, the statistical analysis is based on 240 occurrences for each parameter (an average of our measurements x two consonants x three vowels x two positions x 20 subjects). Finally, we have considered the transglottal pressure necessary for the voicing. According to Kitajima et Fujita19 and Baken et Orlikoff,20 the difference in IOP peaks during the articulation of the consonants [p] and [b] is an estimation of the transglottal pressure and it can be used as an approximation of the phonatory threshold pressure (PTP, Kitajima & Fujita,19 Smitheran & Hixon21). Thus, we have calculated the difference for the IOP mean peaks of [p] and [b] for each of the two syllable-onset positions and each vocalic context at the same intensity, viz IOP(p-b). In order to standardize the results, we have also made the ratios of these differences for the IOP of [p], viz IOP(p-b)/IOP(p). The interest of this parameter is to normalize IOP(p-b) with respect to the sound intensity emitted during the production of the given corpus. In fact, as Hans22 pointed out, the SGP increases with the sound intensity emitted. In our point of view, even if the intensity was automatically calibrated with EVA, we assumed the standardization of the data was somehow needed. Statistical analysis We have noticed that the mean age of the two subject groups is substantially different. In order to rule out the explanation of age for between group differences rather than the surgery as the explanatory group difference factor, we have conducted some initial statistical analysis. F test of Fisher. It was first essential to check that the two populations had homogeneous variances in order to compare pairs. Based on an F-test of Fisher, we have calculated the ratio of the estimated variances (s2) between the ages of the two populations: F ¼ 1.102; P ¼ 0.59. Since the significance level was higher than 0.05, we can conclude that H0 must not be rejected (the variances of the two distributions were homogeneous) and that both populations must be considered as two independent groups in terms of age.
Journal of Voice, Vol. 29, No. 2, 2015
Lilliefors test. The Lilliefors normality test, which checks the normality of the distributions of the ages of both groups, has also been applied on the data. The null hypothesis (H0) for this test is that the error isnormally distributed, that is to say that there is no difference between the observed error distribution and the normal distribution. The alternative hypothesis (H1) is that the error is not normally distributed. In the table of critical values of the Lilliefors test, the computed value of D must not be greater or equal to 0.0812 to accept H0 with a size n ¼ 120 and a threshold a ¼ .05. The results of these tests showed that the distributions of the ages of both groups (controls: D ¼ 0.1559, P < 0.0001 and patients: D ¼ 0.2108, P < 0.0001) did not fit a normal distribution. Since the values of P are less than 0.05, the null hypothesis should be rejected. In conclusion, the distributions of the ages being abnormal, we can not consider this parameter as a factor in our statistical analysis. The problem of the age. It is also important to confirm that age is not involved in the differences in IOP and OAF between the two groups (cf. Results part), we have retained five controls and five patients (M ¼ 58.6 years and M ¼ 57.8 years respectively) by removing the younger and older subjects in order to obtain two groups of the same age. Two one-way ANOVAs have been conducted with IOP and OAF values as the dependent variables and with the groups (patients vs controls) as the independent variable. The results were considered significant at an alpha level of 5% (P < 0.05). The IOP values were higher in patients than in controls (M ¼ 8.5 hPa and M ¼ 5.33 hPa respectively). The ANOVA conduced on this parameter showed a significant difference between the two groups of the same age (F (1, 118) ¼ 28.96, P < 0.0001). We can also note that the OAF values were higher in patients than in controls (M ¼ 0.34 dm3/s and M ¼ 0.26 dm3/ s respectively). The ANOVA conduced on this second parameter also showed a significant difference between the two groups of the same age (F (1, 118) ¼ 16.87, P < 0.0001). Thus, we can conclude that the observed differences on both IOP and OAF values are not induced by the age of the two groups. Indeed, we assume that these differences are a direct consequence of the surgery. Regular statistical analysis. In the remaining part of this study – since the effect of age has been ruled out –, we have conducted four-way ANOVAs, with IOP and OAF values as the dependent variables and with all subjects of the two groups (ie, 10 patients and 10 controls), the voicing context, the type of vowel, and the position of the labial stops in the logatomes as the independent variables. The results were considered significant at an alpha level of 5% (P < 0.05).
RESULTS IOP values We have observed that the values of the voicing parameters were always higher in patients than in controls (M ¼ 9.7 hPa and M ¼ 6.16 hPa respectively). The ANOVA showed a significant difference between the two groups (F (1, 216) ¼ 132.731,
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Study of Aerodynamic Parameters After Laser Cordectomy
P < 0.0001). In addition, we noted that for both groups, IOP values were higher for voiceless [p] than for voiced [b] (F (1, 216) ¼ 222.684, P < 0.0001). Furthermore, for both subject groups the vocalic contexts influenced the mean IOP values for both [p] and [b] (F (2, 216) ¼ 5.46, P ¼ 0.0049). In particular, their IOP values tended to be higher when these consonants were surrounded by high vowels, as the Fisher PLSD test showed significant differences between [a] and [i, u], with P ¼ 0.0152 for [a], and P ¼ 0.0019 for [i, u]. On the other hand, the position of the consonants in the logatomes had no significant effect on their IOP values (F (1, 216) ¼ 0.902, P ¼ 0.3434). Finally, we noted significant interactions between the factors ‘‘subjects’’ and ‘‘voicing’’, as well as between the factors ‘‘voicing’’ and ‘‘position’’, with statistical results equal to F (1, 216) ¼ 29.267, P < 0.0001 and F (1, 216) ¼ 4.338, P ¼ 0.0385 respectively. For the first interaction (ie, subjects:voicing), post-hoc analysis using Tukey’s HSD indicated that the IOP of patients (M ¼ 6.57, SD ¼ 1.79) is greater than the IOP of controls (M ¼ 4.69, SD ¼ 1.97) during the voiced labial stop, P ¼ 0.00012. In fact, for that consonant, the IOP of patients was 1.88 hPa higher than controls (95% CI: 0.76–3). Moreover, the test also showed that the IOP of patients (M ¼ 12.83, SD ¼ 2.73) is greater than the IOP of controls (M ¼ 7.62, SD ¼ 2.9) during the voiceless labial stop, P < 0.0001. For that consonant, the IOP of patients was 5.21 hPa higher than controls (95% CI: 4.09–6.33). These results confirmed that there is a difference between the two groups due to the surgery but it also underlined the fact that the IOP values between voiceless and voiced stops are still contrastive for both groups (cf. Discussion). Regarding the second interaction (ie, voicing:position), post-hoc analysis using Tukey’s HSD indicated that there is no effect of the position on the IOP values for a same consonant. In fact, there is no difference between a voiced labial consonant in initial and intervocalic positions, P ¼ 0.85. For that consonant, the difference between the two positions was 0.35 hPa (95% CI: 0.77 to 1.47). Further, there is no difference between a voiceless labial consonant in initial and intervocalic positions, P ¼ 0.14. For that consonant, the difference between these two positions was 0.93 hPa (95% CI: 0.19 to 2.05).
These results confirmed the first ANOVA which showed that the position of the consonants in the logatomes had no significant effect on their IOP values. Finally, the test indicated that the interaction observed is due to all other pairwise comparisons, such as [p] in initial position versus [b] in intervocalic position, which showed a significant difference (P < 0.0001). OAF values We noticed that whatever the consonant voicing was, the OAF values of patients were always higher than those of our controls (M ¼ 0.349 dm3/s and M ¼ 0.258 dm3/s respectively). The ANOVA showed a significant difference between the two groups (F (1, 216) ¼ 57.819, P < 0.0001). Besides, for both groups, OAF values tended to be higher in the voiceless context as compared to the voiced context (F (1, 216) ¼ 6.731, P ¼ 0.0101). We also noted a significant effect of vocalic contexts on the mean values of OAF (F (2, 216) ¼ 6.538, P ¼ 0.0018), which appeared to be more important for the low vowel [a] than for the two high vowels [i, u]. Indeed, the Fisher PLSD test showed significant differences between the vowels [a, i] and [a, u], with P-values equal to P ¼ 0.0004 and P ¼ 0.0297 respectively. Finally, the syllable position of the consonants in the logatomes had no influence on the mean values of OAF (F (1, 216) ¼ 2.212, P ¼ 0.1384). In addition, no interaction was found between these four factors. The mean data are displayed in Table 1 for both groups and the two syllabic positions. Moreover, the significant findings are summarized in Table 2. Estimated transglottal pressure Tables 3–5 summarize the estimated transglottal pressure necessary for the voicing for the two syllabic positions and each vocalic contexts. DISCUSSIONS IOP values We have demonstrated that, independently of the specific consonantal or vocalic contexts, the IOP measures of the patients were always significantly higher than those of the
TABLE 1. Means and Standard Deviations of IOP and OAF for the Controls and Patients in Function of the Voicing Context, the Type of Vowels and the Syllable Position During the Production of Logatomes [voix] #_ Controls IOP peaks (hPa) St. Dev. OAF (dm3/s) St. Dev. Patients IOP peaks (hPa) St. Dev. OAF (dm3/s) St. Dev.
[+voix]
[voix]
[pa]
[pi]
[pu]
[ba]
[bi]
[bu]
6.91 2.45 0.304 0.093
7.63 3.04 0.237 0.052
7.98 3.45 0.282 0.07
4.22 2.18 0.308 0.109
5.07 1.66 0.221 0.049
12.72 2.38 0.377 0.088
6.57 2.28 0.421 0.097
6.83 1.32 0.329 0.079
11.01 2.44 0.382 0.133
12.32 2.5 0.32 0.09
V_V
[+voix]
[apa]
[ipi]
[upu]
[aba]
[ibi]
[ubu]
4.92 2.03 0.224 0.069
6.69 2.58 0.325 0.152
8.09 3.04 0.242 0.066
8.44 3.06 0.283 0.073
4.12 2.62 0.341 0.07
4.57 1.44 0.215 0.058
5.25 1.89 0.212 0.073
7.24 1.08 0.343 0.092
12.47 2.6 0.374 0.134
14.31 2.74 0.339 0.123
14.17 2.86 0.364 0.097
5.82 2.32 0.299 0.069
6.38 2.1 0.33 0.111
6.61 1.34 0.31 0.087
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TABLE 2. Summary of Significant Findings where ‘‘**’’ Corresponds to Highly Significant Differences (P < 0.0001); ‘‘*’’ Corresponds to Significant Differences (P < 0.05) and ‘‘ns’’means ‘‘not significant’’
Groups Patients > Controls Voicing context [voix] > [+voix] Type of vowels [i,u] > [a] (IOP) [a] > [i,u] (OAF) Position V_V > #_ (IOP) #_ > V_V (OAF)
IOP
OAF
**
**
**
**
*
*
ns
ns
TABLE 4. Calculation of the Estimated Transglottal Pressure (in hPa) for the Two Syllabic Positions (Initial Onset and Intervocalic Onset) for Controls and Patients in Vowel Context [i] (n ¼ 80)
Controls Patients
IOP (pi-bi)
IOP(pi-bi)/ IOP(pi)
IOP (ipi-ibi)
IOP(ipi-ibi)/ IOP(ipi)
2.56 5.49
0.34 0.45
3.52 7.93
0.44 0.55
controls. In this respect, our findings are consistent with those of Hans,22 Zeitels et al,23 and Mirghani.24 Hans22 has shown, for different types of partial laryngectomies, that the IOP values in patients were always higher than those of the control group and that, moreover, this parameter is the most relevant for discriminating between these two groups for all types of laryngectomies. In fact, in the group of patients, the IOP tends to increase with the extent of resection. Similarly, for different types of cordectomies, Zeitels et al23 and Mirghani24 have shown that the IOP values of the patients were significantly higher than those of the control subjects. This increase of the IOP for the group of patients is possibly the consequence of a compensatory behavior. Koufman25 highlights two types of supraglottal compensatory behaviors: (i) the hyperadduction of the ventricular bands and (ii) the anteroposterior contraction of the larynx characterized by an anterior tilting of the arytenoids to the epiglottis. At this moment, we are unable to propose any specific hypothesis about the type of compensation adopted by the patients. A videolaryngostroboscopic examination would be necessary to establish whether our suggestion of a compensatory strategy is correct and, if so, to determine its precise nature. Nevertheless, we know that the elevated IOP in patients may be caused by one of these two reactions: (i) the development of a forced voice leading to a greater tension of the laryngeal muscles and, more broadly, by an increased tension of the vocal tract as a whole, or (ii) the increase of the pressure related to the surgery which allows the development of a supraglottal behavior.
Moreover, we assume that the IOP is equivalent to the SGP during the unvoiced labial stop because the vocal folds are in abduction (Holmberg et al,26 Rothenberg,4 among others). As a consequence, we postulate that the increase of the IOP values of the patients is also correlated with an increase of the SGP values. In our point of view, the high estimated subglottal values should be a compensation to the glottal inefficiency related to the surgery and should facilitate the initiation of the vibrations. We have also shown that for both groups the IOP values were statistically higher for voiceless stops, independently of the nature of the vocalic contexts. These results are in total agreement with the studies of Subtelny et al,27 Arkebauer et al,28 Lisker,29 Miller and Daniloff,30 Stathopoulos31 and Holmberg et al26 among others for normal speakers. We have already mentioned that during the production of a voiceless stop, the glottis remains open and the differential between SGP and IOP is constant. On the other hand, the articulation of voiced stops requires two antagonist gestures in the vocal tract: at first, a total obstruction of the air passage realized at some precise point in the vocal tract and in second, the maintenance of a sustained airflow in order to guarantee the vibration of the vocal folds. The glottal closure is responsible for resistance to the passage of the airflow, which tends to reduce the IOP in the vocal tract compared to the SGP. Except the results of normal speakers, it is important to underline that even after anatomical changes due to the surgery, our study results show that the IOP values between voiceless and voiced stops are still contrastive. An interesting result of our research is the observation that the mean IOP values of our two groups tend to be higher in the context of high vowels. Karnell & Willis32 had already concluded that the IOP values of [p] were greater between the high back vowel ([u]) than between the low vowel ([a]). Klich33 found the same dichotomy in whispered voice. Moreover, in a study of 11 men and 10 women involving various acoustic
TABLE 3. Calculation of the Estimated Transglottal Pressure (in hPa) for the Two Syllabic Positions (Initial Onset and Intervocalic Onset) for Controls and Patients in Vowel Context [a] (n ¼ 80)
TABLE 5. Calculation of the Estimated Transglottal Pressure (in hPa) for the Two Syllabic Positions (Initial Onset and Intervocalic Onset) for Controls and Patients in Vowel Context [u] (n ¼ 80)
IOP IOP(pa-ba)/ IOP IOP(apa-aba)/ (pa-ba) IOP(pa) (apa-aba) IOP(apa)
IOP IOP(pu-bu)/ IOP IOP(upu-ubu)/ (pu-bu) IOP(pu) (upu-ubu) IOP(upu)
Controls Patients
2.69 4.44
0.39 0.4
2.57 6.65
0.38 0.53
Controls Patients
3.06 5.48
0.38 0.43
3.19 7.56
0.38 0.53
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Study of Aerodynamic Parameters After Laser Cordectomy
and aerodynamic parameters—which includes the estimated subglottal pressure (ESGP) — Higgins et al34 concluded that there is an effect of the vocalic context on ESGP measures from IOP measurements. The mean IOP values of stops also appear to be higher before [i] than before [a]. Karnell & Willis32 suggested two hypotheses to explain these changes: (i) a higher impedance of the oral cavity due to the greater constriction of the high vowels as compared to the mid or low vowels and (ii) a greater tension of the vocal folds for these vowels which requires an increase of the pressure in order to maintain the vocal fold vibration. The fact that this effect is found in both modal voice and whispered voice suggests that the vibration of the vocal folds is independent of the second hypothesis. The rise of the IOP in contact with the high vowels compared to the low vowels is due solely to differences in the oral cavity impedance between these two vowel types. Thus, for the production of high vowels, the vocal tract is more tense, which has the effect of increasing the impedance of the vocal tract.34 In addition, various articulations for the production of vowels change the size and the volume of the pharyngeal and oral cavities, implying differences in terms of impedance in the vocal tract. OAF values We have noticed that, the mean OAF values of patients were always significantly higher than those of the controls, independently of the segmental contexts. Our findings corroborate those of Zeitels et al,23 Tamura et al35 and Mirghani24 studies for cordectomies. This increase in airflow is directly related to the glottal leak caused by the surgery. In fact, the resection of a part of the vocal fold is responsible for a vibratory asymmetry and an incomplete apposition of the mucosa. Therefore, we suggest that the surgical intervention reduces the glottal resistance in phonation, which causes a permanent loss of airflow through the vocal folds and explains the increase of the OAF.11 We have also shown that the OAF values were systematically higher for the voiceless stops in normal speakers. These results confirm the observations made by Emanuel & Counihan,36 Gilbert,37 Trullinger & Emanuel,38 Stathopoulos & Weismer39 and Higgins et al.34 For example, in a study involving 25 men and 25 women, Emanuel & Counihan36 have found that the voicing tends to reduce the airflow measurements for stops from 26 to 53% compared to their voiceless counterparts. Trullinger & Emanuel38 have found the same pattern for a child population of 15 boys and 15 girls. In our case, the differences in the OAF measures for the release of [p, b] can be attributed to the resistance imposed by the laryngeal vibrations of the vocal folds during the production of voiced stops. Indeed, we know that the voiceless stops involve a glottal opening characterized by an abduction of the vocal folds. Therefore, the lung airflow is not slowed down and can escape directly into the vocal tract. In contrast, the production of voiced stops requires a sustained vibration of the vocal folds, which increases the resistance against the oral airflow. Besides our study results are consistent with prior studies on normal speech, one of the most important finding of our study is that even after significant anatomical alterations due
253
to cordectomy, the OAF values contrast between voiceless and voiced stops still occurs. Consequently, we can conclude that the voicing contrast is well maintained after these surgeries. We could finally note that, in general, the mean OAF values for the release of the consonant tends to be higher in the context of a low vowel for both groups. This conclusion is consistent with the studies of Emanuel & Counihan,36 Trullinger & Emanuel,38 and Higgins et al,34 among others for normal speakers. We have already explained that the elevation of the tongue necessary for the articulation of the high vowels causes a higher impedance in the oral cavity, which tends to reduce the oral airflow. Instead, the articulation combining a maximum aperture and a low tongue body position for the open vowel [a] entails a low resistance to the oral airflow. For Higgins et al,34 with regard to the different effects of vowel classes, the glottal width and the glottal resistance may also contribute to these airflow differences. Indeed, the elevation of the larynx necessary to create the vocal fold tension and, more specifically, the anterior vertical adjustment of the thyroid cartilage and hyoid bone, tends to reduce the glottal width and thereby increases the resistance in anticipation of the articulation of high vowels. Estimated transglottal pressure Remember that according to Kitajima & Fujita19 and Baken & Orlikoff,20 the difference in IOP peaks during the articulation of the consonants [p] and [b] is an estimation of the transglottal pressure during [b] (henceforth ETP) and has been claimed to be a possible substitute for the oscillation threshold pressure or phonatory threshold pressure (PTP, Kitajima & Fujita,19 Smitheran & Hixon21). The PTP has been defined by Titze40 as the minimum degree of lung pressure required for the initiation and maintenance of voicing when the vocal folds are slightly abducted. This phonatory threshold is in a range of two to four hPa with an usual SGP equal to seven hPa.40,41 The level of PTP depends on the stiffness of the vibrating portion of the vocal folds, their thickness, their viscosity, the width of the prephonatory glottis and the quality of the mucosal wave during the phonation.40 If the mucosal wave, the glottal width, and the stiffness of the vocal folds decrease, then PTP will follow the decline. Besides, Chan et al42 state that an increase of the tissues, the thickness of the vocal folds, or the stiffness of the epithelial membrane are indicators of an increase of the PTP. Since there is no evidence nor reliable recent studies that support a relationship between ETP and PTP, we will focus on the ETP method results only. For the control group, we note that the results of the ETP fall in an interval of two to four hPa in both positions. This interval is consistent with the transglottal pressure range required for initiation of phonation.20 In addition, we note that the minimum pressures are higher in the context of high vowels compared to the low vowel. In fact, during the release of the consonant, adjustments related to the coarticulation effect of the vowels on the consonant take place upstream. For the production of high vowels, the vocal folds will stretch more, which will reduce their vibrating mass, increase the glottal impedance and finally results in an increase of their intrinsic fundamental frequency.11 Consequently, the vibration will be more difficult
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Journal of Voice, Vol. 29, No. 2, 2015
TABLE 6. Results of the Main Studies on Estimated Transglottal Pressure (in cmH2O) in Healthy Subjects (1 cmH20 ¼ 0.98 hPa) Authors
Corpus
IOP(p-b)
IOP(p-b)/ IOP(p)
Subtelny et al27 /ipi/,/ibi/ 2.06 0.32 Murry et Brown43 /apa/,/aba/ 3.48 0.42 Stathopoulos31 /pap/,/bab/ 2.68 0.23 Kitajima et Fujita19 /ipi/,/ibi/ 4.7 0.44 Hans22 /pi/,/bi/and/ 2.4 and 2.8 0.35 and 0.29 ipi/,/ibi/
to maintain, which will lead, through a compensation phenomenon, to the rise of the ETP. Finally, our results are more or less identical to those of Subtelny et al,27 Murry & Brown,43 Stathopoulos,31 Kitajima & Fujita19 and Hans23 studies, abstracting away from individual variations (Table 6). Regarding the patients, we note that, just like the controls, the pressures remain higher in the context of high vowels. Besides the fact that the normalized transglottal pressure values of [b] in the low vowel context were almost identical for both groups in initial position, we observe that in the high vowel contexts the values are much higher than those of the healthy subjects in both initial and intervocalic positions. This finding is consistent with Hans22 who has highlighted the existence of pressure differences that are higher for patients treated with partial laryngectomies than for control subjects, which fact this author interpreted as a proof for the difficulty of creating voicing after these surgeries. It is well known that cordectomies change the glottal configuration in postoperative. Thus, one or more layers of the vocal fold are resected during the surgery, which results in an increase in the stiffness, a greater tension of the vocal fold and a reduction of the vibrating mass. In addition, a vibratory asymmetry is observed, implying an imprecise mucosal wave. The Hirano’s ‘‘body-cover’’ model, which is based on three histological sections of the vocal fold and mainly characterized by a ‘‘body’’ (vocal ligament and muscle) and a ‘‘cover’’ (vocal fold mucosa) separated by a drift space (Reinke space), explains the triple horizontal, vertical, and mucosal movements of the vocal folds during phonation.44 Changes in the anatomical structures, particularly the ‘‘cover’’, cause a reduction in the vibratory surface and, in extenso, the damping of the vibratory amplitude. Consequently, the results of this study definitively confirm that the patients tend to increase their ETP compared to the controls in order to initiate and sustain oscillations as a compensation for this chordal mutilation. Our results are also consistent with the experiment of Kitajima & Fujita19 which shows that the transglottal pressure can be considered as an index for the vibratory efficiency of the vocal folds and, therefore, it allows to classify the voice quality of the healthy subjects compared to dysphonic subjects with pathological voices. Thus, in their study of Japanese patients with diverse laryngeal pathologies, they claim that
the difference IOP(p-b) allows to objectify the condition: if the difference is less than the normal values, then the power of adduction of the vocal folds is considered insufficient, as it is typical for unilateral paralysis. Conversely, if the difference is greater than the normal values, abnormal stiffness of the vocal folds must be considered and an ineffective glottal closure is allowed, which is typical of cancers of the vocal fold. To the best of our knowledge, no studies examining this type of surgery had not yet shown the impact of anatomical changes on aerodynamic parameters selected here. The result probably the most robust of this study is that the voicing contrast is maintained despite obvious difficulties, compensated by an increase of the ETP. Finally, the results definitively confirm the existing clinical impressions. CONCLUSIONS The more relevant and original result of this study is that patients appear to mark the voicing contrast between/p/and/b/ with the highest IOP and OAF values for the voiceless labial stop. More in general, we observe that all the values for the parameters studied here are always higher for the patients than the control subjects, which reflects the glottal inefficiency of the former group. We interpret these measurements as either a vocal forcing behavior, or as a difficulty in the creation or maintenance of voicing. The latter hypothesis is supported by the estimated transglottal pressure measurements, obtained by the difference IOP(p-b), which are much more important in the patients than in the controls. The higher values observed in patients for all aerodynamic parameters indicate (i) the persistence of stiffness and tension of the resected vocal fold, (ii) a partial glottal closure (glottal leakage) and (iii) a difficulty regarding the realization of the voicing feature. Consequently, the increase in these different pressures in the values of the different parameters shows a compensatory mechanism applied to fight against the major laryngeal resistance and thereby facilitate the initiation and maintenance of voicing where it is necessary. Acknowledgments I wish to thank Jean-Marc Beltzung for his careful reading of the text and useful suggestions as well as for his encouragement throughout the redaction of this paper. I also thank Leo Wetzels for our discussions and his precious corrections and the members of the HEGP’s unit ‘‘Voice’’, Daniel Brasnu, Stephane Hans and Lise Crevier Buchman, for their hospitality during my stays at the ORL department, where I could meet the patients. I am alone responsible for any errors this paper may contain. REFERENCES 1. Shipp T. Vertical laryngeal position during continuous and discrete vocal frequency change. J Speech Hear Res. 1975;18:707–718. 2. Ladefoged P. The linguistic use of different phonation types. In: Bless D, Abbs J, eds. Vocal Fold Physiology: Contemporary Research and Clinical Issues. San Diego, CA: College Hill Press; 1983:351–360. 3. Stevens KN. Vocal fold vibration for obstruent consonants. In: Gauffin J, Hammarberg B, eds. Vocal Fold Physiology: Acoustic, Perceptual and
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