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Effects of gender and posture on thoraco-abdominal kinematics during quiet breathing in healthy adults
Respiratory Physiology & Neurobiology 172 (2010) 184–191
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Effects of gender and posture on thoraco-abdominal kinematics during quiet breathing in healthy adults M. Romei a,∗ , A. Lo Mauro b , M.G. D’Angelo a , A.C. Turconi a , N. Bresolin a,c , A. Pedotti b , A. Aliverti b a b c
IRCCS E.Medea, Bosisio Parini (Lc), Italy TBM Lab, Dipartimento di Bioingegneria, Politecnico di Milano, Milano, Italy Fondazione Policlinico – Mangiagalli – Regina Elena, IRCCS Ospedale Maggiore, Università degli Studi di Milano, Istituto di Clinica Neurologica, Milano, Italy
a r t i c l e
i n f o
Article history: Accepted 19 May 2010 Keywords: Chest wall Posture Abdomen Opto-electronic plethysmography Gender Thorax
a b s t r a c t To investigate the effects of posture and gender on thoraco-abdominal motion and breathing pattern, 34 healthy men and women were studied by Opto-Electronic Plethysmography during quiet breathing in five different postures from seated (with and without back support) to supine position. Chest wall kinematics and breathing pattern were significantly influenced by position and gender. The progressively increased inclination of the trunk determined a progressive reduction of rib cage displacement, tidal volume, and minute ventilation and a progressive increase of abdominal contribution to tidal volume. Female subjects were characterized by smaller dimensions of the rib cage compartment and during quiet breathing by lower tidal volume, minute ventilation and abdominal contribution to tidal volume than males. The effect of posture on abdominal kinematics was significant only in women. The presence of a back support in seated position determined differences in breathing pattern. In conclusion, posture and gender have a strong influence on breathing and on chest wall kinematics. © 2010 Elsevier B.V. All rights reserved.
1. Introduction It is well known that posture influences thoraco-abdominal kinematics during spontaneous quiet breathing. Previous studies (Wade, 1954; Fugl-Meyer, 1974; Sharp et al., 1975; Verschakelen and Demedts, 1995; Lee et al., 2010) have investigated both erect (sitting or standing) and supine positions in healthy subjects, and have shown that quiet breathing is predominantly abdominal in the former and thoracic in the latter position. On the other hand, the effect of gender on chest wall kinematics is still controversial. While some authors (Fugl-Meyer, 1974; Gilbert et al., 1981) reported a relatively greater rib cage motion in women, others (Sharp et al., 1975; Verschakelen and Demedts, 1995) did not. There is evidence in the literature, however, that the differences in pulmonary function (namely, lung volumes, maximal expiratory flow rates, diffusion surfaces and maximal pulmonary ventilation) between females and males are mostly due to the smaller height and trunk size in women (McClaran et al., 1998). These controversies remain when considering possible interactions between posture and gender on thoraco-abdominal motion during quiet breathing.
∗ Corresponding author at: IRCCS “E. Medea”, Via Don Luigi Monza, 20, 23842 Bosisio Parini (Lc), Italy. Tel.: +39 031 877351; fax: +39 031 877499. E-mail address: [email protected] (M. Romei). 1569-9048/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.resp.2010.05.018
In the previous studies, different measurement techniques such as mercury-in-rubber strain gauges (Wade, 1954), linear differential transducers (Konno and Mead, 1967), magnetometers (Fugl-Meyer, 1974; Sharp et al., 1975; Gilbert et al., 1981), and respiratory inductive plethysmography (Verschakelen and Demedts, 1995) were used. The differences in experimental methods, particularly in the kind of measurement they provide (changes of diameters, perimeters, transversal sections), could contribute to the different findings regarding the effects of gender and possible interactions between posture and gender on chest wall kinematics. Opto-Electronic Plethysmography (OEP, Cala et al., 1996) has been proposed as a new method that, starting from the threedimensional coordinates of markers positioned on a subject’s trunk and acquired by an opto-electronic system for motion analysis, allows the accurate measurement of the kinematics and the volume variations of the chest wall and its compartments (rib cage and abdomen) in different positions: standing, seated, supine (Aliverti et al., 2000), and prone (Aliverti et al., 2001). The present study was conducted in order to prove the hypothesis that posture, gender and their interaction all have significant effects on rib cage and abdominal kinematics during quiet breathing and to clarify which are the limits of validity of chest wall kinematics measurements when considering different geometrical parameters. For these purposes, we used the novel OEP technique to study a group of healthy female and male subjects in different postures, i.e., different inclinations of the trunk from seated
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Table 1 Subjects’ characteristics (data are expressed as mean ± SD). M: males; F: females; M + F: overall group. In the last column on the right, the p-value of the comparison between males and females are shown.
Size group Age (years) Weight (kg) Height (cm)
M+F
M
F
p-Value (M vs F)
34 32.1 ± 8 (range: 22–52) 64.6 ± 11.4 (range: 46–83) 172.9 ± 8.2 (range: 157–187)
17 31.5 ± 9.4 (range: 22–52) 72.1 ± 6.5 (range: 60–83) 177 ± 5.4 (range: 165–187)
17 32.8 ± 6.6 (range: 22–50) 56.3 ± 8.4 (range 46–76) 164.9 ± 5.4 (range: 157–180)
0.65 <0.01 <0.01
(with and without back support) to supine position. By using the same set of three-dimensional coordinates measured by the same opto-electronic system for motion analysis, we calculated simultaneous variations in diameters, perimeters, transversal sections and volumes at the levels of the rib cage and the abdomen as different descriptors of chest wall kinematics. In this way we aimed to exclude all the possible differences between these parameters due to measurement errors introduced by the different sensors and/or devices, which in part may explain the controversial results reported in the literature.
2. Materials 2.1. Subjects 34 healthy adults (17 females, 17 males) were recruited for the present study. The inclusion criteria were: absence of cardiac and pulmonary disease, no smokers, no endurance-trained athletes, and age higher than 18 years. Subjects’ characteristics are shown in Table 1. The study was approved by the local Ethical committee of IRCCS “E. Medea” Institute where all the data acquisitions were performed and all subjects gave informed consent.
2.2. Protocol For each subject, the data acquisition protocol consisted of five trials performed in a single session. Each session took about 45 min in total, including both the time for the subject’s adaptation on the different positions and data acquisition. All subjects were asked to maintain a spontaneous breathing pattern for the whole duration of the experimental session. Five different positions were considered (Fig. 1) and measurements were repeated five times (one for each position) in which data were acquired during at least 3 min of quite breathing. In the first position (position A in Fig. 1), the subject was seated on a rigid bed without back support. In the three other positions (positions B–D in Fig. 1), the subject was seated on a wheelchair, with the back support position adjusted to one of three different inclinations (B: ∼80◦ , C: ∼65◦ , D: ∼40◦ with respect to the floor). Finally, the subject lay supine on a rigid bed.
2.3. Opto-Electronic Plethysmography analysis Opto-Electronic Plethysmography (OEPSystem BTS, Italy) was based on an eight-infrared cameras system working at 60 Hz. For positions A–C, four cameras were positioned in front of the subject, and four were behind. For position D and supine, four cameras were positioned to the right of the subject, and four to the left. For position A, 89 passive markers were placed on the anterior and posterior side of the trunk, according to the protocol described by Cala et al. (1996). For positions B–D and supine, the markers on the posterior trunk surface were removed, and 52 markers were left on the anterior and lateral trunk surface. In these cases, 45 markers were positioned according to the protocol described by Aliverti et al. (2001), adding a row of 7 markers at the nipple level, in order to have the same anterior surface arrangement in all the 5 positions. The same operator identified the anatomical positions, and placed the passive retro-reflective markers on the chest wall surface. 2.4. Data analysis 2.4.1. Total chest wall volume As previously described, total chest wall volume was calculated from the 3D coordinates of the markers, surface triangulation, and Gauss’ theorem (Cala et al., 1996; Aliverti et al., 2001). In the case of the seated position without back support (A) the whole trunk was visible, whereas for the positions with back support (B–D and supine), the posterior part of the trunk was defined by a virtual plane. This was obtained by calculating a reference plane defined by the co-ordinates of the markers positioned laterally on the trunk (Aliverti et al., 2001). 2.4.2. Compartmental volumes As in previous studies, the total chest wall was divided into three compartments (Ward et al., 1992), namely Pulmonary Rib Cage, Abdominal Rib Cage and Abdomen (Kenyon et al., 1997). For the purposes of the present study, the Pulmonary and Abdominal Rib Cage compartments were considered as a single compartment (Rib Cage), given by their sum (Grimby et al., 1976) (Fig. 2a). 2.4.3. Chest dimensions and displacement From 3D marker coordinates measured by OEP, the mediolateral (ML) diameters, the antero-posterior (AP) diameters, the
Fig. 1. Schematic representation of the five postures adopted by the subjects. From left to right: seated on a rigid bed without back support (position A); seated with three different back support inclinations (position B: ∼80◦ , position C: ∼65◦ , position D: ∼40◦ with respect to the floor) and supine on a rigid flat bed.
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Fig. 2. Schematic diagrams showing marker positioning on the front of the subject and the thoraco-abdominal surface triangulation defined to compute rib cage and abdominal volumes (a). Cross-sectional areas (b), medio-lateral (ML) diameters (c) and antero-posterior (AP) diameters (d and e) at Angle of Louis, xiphoid and umbilical levels. The definition of AP diameters is shown both for position A (d) and for positions B–D and supine (e). The crosses shown in (b) and (e) are ‘virtual’ markers positioned on the back support.
perimeters and the cross-sectional areas were calculated for rib cage and abdomen (Fig. 2). For the rib cage, the following dimensions were calculated: AP diameters at angle of Louis and xiphoid levels, ML diameter, perimeter, cross-sectional area at xiphoid level. For the abdomen the following dimensions were calculated: AP diameter, ML diameter, perimeter and cross-sectional area at umbilical level. Antero-posterior diameters at the angle of Louis, xiphoid and umbilicus levels were calculated as the distance between the anterior and posterior central markers placed at the same level in position A (Fig. 2d). In all positions with back support (i.e., B–D and supine), they were calculated as the distance between the anterior central markers and the reference plane (Fig. 2e). Medio-lateral diameters at xiphoid and umbilicus levels were calculated as the distance between the two more lateral markers at the xiphoid and umbilical line, respectively (Fig. 2c). Perimeters were obtained by summing the 3D distances of all the contiguous markers placed at the same level (Fig. 2b). Cross-sectional areas were calculated by summing the areas of the triangles each formed by two contiguous markers and the baricenter of all the markers positioned at the considered level (Fig. 2b). Xiphoid and umbilical levels were considered respectively for the rib cage and the abdomen. To characterize subject chest size and configuration, the above defined diameters, perimeters, cross-sectional areas, total and compartmental volumes were assessed as the mean value at endexpiration in position A. Rib cage and abdominal volumes were expressed both as absolute values and percentage of total chest wall volume. To assess thoraco-abdominal dimensional variations during quiet spontaneous breathing, we calculated the mean variations of the above defined diameters, perimeters, cross-sectional areas, and volumes for the rib cage and the abdomen in all the considered positions. 2.4.4. Ventilatory pattern From total and compartmental chest wall volume tracings, the following parameters were considered for the analysis of the ventilatory pattern: Tidal Volume as the average total chest wall volume variations, Respiratory Rate, Minute Ventilation (as Tidal Volume × Respiratory Rate) and contribution of the Rib Cage and Abdomen to Tidal Volume (expressed as percentage of Tidal Volume). In addition, Tidal Volume and Minute Ventilation were
normalized by body weight in order to correct for sex-differences in body size, metabolic rate and vital capacity. 2.5. Statistical analysis For respiratory and anthropometric parameters, mean values ± standard deviation (SD) were calculated for the entire group, and for the female and male subgroups for each positions (A–D and supine). For the comparison between anthropometric data, volumes and displacement, tests of normality were performed, followed by either parametric (unpaired Student’s t) or nonparametric (Mann–Whitney) tests between data of Male and Female subjects. For respiratory parameters (Tidal Volume, Minute Ventilation, Respiratory Rate and Abdominal Contribution) and chest displacement (AP diameters, ML diameters, perimeters and crosssectional areas) a general linear model for repeated measures with gender as between-subjects factor was performed. The level of significance was set at p < 0.05 for all statistical comparisons. Values in text and tables are group means ± SD and in figures are group means ± Standard Error of the Mean (SEM). All computations were performed with SPSS version 11.0 for Windows; SPSS, Chicago, IL. 3. Results The anthropometric characteristics of the entire group and of the two subgroups were divided according to their gender (Table 1). The two gender subgroups were homogeneous in age but not in weight and height (p < 0.01). 3.1. Chest dimensions and displacement AP and ML diameters, perimeters, cross-sectional areas and volumes for rib cage and abdomen calculated in position A and averaged at end-expiration are shown in Table 2. In general, the total dimension of the chest wall was higher in male than in female subjects. This was mainly due to the rib cage which in males was characterized by longer AP diameters and perimeter and larger cross-sectional area and volume. In the abdomen, only AP diameter and volume were larger in males compared to females. The subdivision of the total chest wall volume into the two compartments, however, was similar when they were expressed as a percentage of total chest wall volume.
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Table 2 Antero-posterior (AP) and medio-lateral (ML) diameters, perimeters, cross-sectional areas and volumes in the overall group of subjects (M + F) and in the two gender groups (M: males; F: females) for the rib cage and the abdomen. All the presented values are group means ± SD obtained at end-expiration in position A. In the last column on the right, the p-value of the comparison between males and females are shown.
Total chest wall (CW) Volume (L) Rib cage AP (Angle of Louis level) (mm) AP (xiphoid level) (mm) ML (mm) Perimeter (mm) Area (cm2 ) Volume (L) Volume (% of CW) Abdomen AP (mm) ML (mm) Perimeter (mm) Area (cm2 ) Volume (L) Volume (% of CW)
M+F
M
F
p-Value (M vs F)
18.7 ± 4.0
21.7 ± 2.6
15.7 ± 2.6
<0.001
188 208 245 855 419 14.0 75.1
± ± ± ± ± ± ±
17 24 21 116 93 3.0 3.0
197 219 250 911 471 16.4 76.0
± ± ± ± ± ± ±
14 21 15 51 62 1.7 3.3
179 197 240 799 355 11.6 74.2
± ± ± ± ± ± ±
15 23 26 136 82 2 2.5
0.001 0.006 0.189 0.001 <0.001 <0.001 0.081
226 260 864 466 4.65 24.9
± ± ± ± ± ±
26 28 123 99 1.2 3.0
239 264 876 497 5.2 24.0
± ± ± ± ± ±
24 22 78 96 1.2 3.3
214 257 851 424 4.1 25.8
± ± ± ± ± ±
21 33 157 89 0.9 2.5
0.003 0.505 0.245 0.071 0.003 0.082
The dimensional variations of the rib cage and abdomen during quiet breathing in the different positions are shown in Figs. 3 and 4, respectively. 3.1.1. Effects of posture on the rib cage Posture strongly influenced the displacement of the rib cage, which in general gradually decreased from position A to the supine position with increasing inclination of the back, both in male and in female subjects. In fact, all but one the considered dimensional parameters were significantly dependent on posture (Fig. 3), being the AP diameter at the xiphoid level the only exception. This was true both considering the overall group of subjects and the two gender groups separately. 3.1.2. Effects of posture on the abdomen On the other hand, the effect of posture on the abdomen (Fig. 4) was much less evident. When considering the overall group of subjects, the volume change of the abdomen was the only parameter significantly influenced by posture (p < 0.01). Conversely, when considering male and female subjects as two separate groups, the effect of posture on abdominal dimensional changes was present only in the women and became statistically significant (p < 0.001) not only for the volume, but also for perimeter and cross-sectional area variations. All dimensional variations but ML diameter changes increased with increasing inclination of the back support (Fig. 4). 3.1.3. Effects of gender Variations of rib cage dimensional parameters during breathing were not significantly different between male and female subjects in all the considered positions, with very few exceptions (AP diameter in two positions and perimeter in four positions, see Fig. 3). Conversely, the displacement of the abdomen was significantly greater in male than in female subjects for all the dimensional parameters in all the positions (Fig. 4). 3.2. Ventilatory pattern Data of ventilatory parameters in the different positions are reported in Table 3. The only parameter that was independent on posture was Respiratory Rate (p > 0.05). For the entire group and for the two gender-subgroups, Tidal Volume and Minute Ventilation presented the highest values in seated position without back support (position A) (p < 0.05). Absolute Tidal Volume and Minute Ventilation values were significantly higher (p < 0.05) in
males than in females in all the considered positions, but when normalized with respect to body weight these differences did not persist. Fig. 5 shows Rib Cage and Abdominal contributions to Tidal Volume for Males and Females expressed as percentage of tidal volume. Posture significantly influenced the contribution of abdomen to Tidal Volume, which gradually increased with increasing inclination of the back, from position A to supine position (p < 0.05). Consequently, the contribution of rib cage to Tidal Volume gradually decreased with increasing inclination of the back. Also gender significantly influenced the contribution of abdomen to Tidal Volume. In all the considered postures from A to D, males had significantly greater abdominal contribution than females (p < 0.05), with a similar increasing trend related to the different trunk inclinations (p > 0.05). In the supine position, males still showed higher abdominal contribution than females, although this difference did not reach statistical significance. 4. Discussion The main result of the present study is that chest wall kinematics and breathing pattern are significantly influenced by the position of the trunk and by gender. A progressively increased inclination of the trunk determines a progressive reduction of rib cage displacement, tidal volume, and minute ventilation and a progressive increase of abdominal contribution to tidal volume. Female subjects are characterized by smaller dimensions confined in the rib cage compartment and during quiet breathing by lower tidal volume, minute ventilation and abdominal contribution to tidal volume than males. The effect of posture on abdominal kinematics is present only in women. From a methodological point of view, the original aspect of this study is that the different parameters used to describe thoracoabdominal kinematics (i.e., antero-posterior and medio-lateral diameters, perimeters, cross-sectional areas and volumes) have been assessed simultaneously starting from the same set of threedimensional coordinates measured by the same opto-electronic system for motion analysis. In this way we excluded all the possible differences between these descriptors of chest wall kinematics due to measurement errors introduced by the different sensors and/or devices (i.e., magnetometers, strain gauges, inductive plethysmography), which in part may explain controversial results reported in the literature. In the approach adopted in the present study, the volume variations of the rib cage and the abdomen can be considered as
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Fig. 3. Dimensional variations of the rib cage during quiet spontaneous breathing in the five different considered postures (A–D and supine, see Fig. 1) in male (closed circles) and female (open circles) subjects. Upper left: antero-posterior diameter changes at the angle of Louis level; upper center: antero-posterior diameter changes at the xiphoid level; upper right: medio-lateral diameter changes at the xiphoid level; lower left: perimeter changes at the xiphoid level; lower center: cross-sectional area changes at the xiphoid level; lower right: rib cage volume changes. Data are shown as mean values ± SEM. *, **, ***: p < 0.05, 0.01, 0.001 male vs female subjects.
the most complete parameter describing the kinematics of each compartment. In fact, such volume measurements are obtained by integrating the three-dimensional motion of multiple surface markers and therefore include and integrate changes of dimensions in multiple directions.
The results obtained in this study demonstrate that variations of perimeters and cross-sectional areas generally follow variations of volumes, both in the rib cage and in the abdomen, with only minor differences. Therefore, the effects of gender and different trunk positions can be reliably detected by using these parameters. Con-
Table 3 Ventilatory pattern in the five different positions (A–D and supine, see Fig. 1). All data are expressed as mean ± SD. M: males; F: females; M + F: overall group. In the last column on the right, p-values regarding position effect significance are shown. All data are mean ± SD. Positions A Tidal volume (L)
M+F M F
Tidal volume/weight (ml kg−1 )
M F
Minute ventilation (L/min)
M+F M F
Minute ventilation/weight (ml min−1 kg−1 )
M F
Respiratory rate (min−1 )
M+F M F
p-Value B
0.6 ± 0.2◦ ◦ ◦ 0.7 ± 0.3**, ◦ ◦ ◦ 0.5 ± 0.1◦ ◦ ◦
C
D
Supine
0.5 ± 0.2 0.5 ± 0.2** 0.4 ± 0.1
0.4 ± 0.2 0.5 ± 0.2** 0.4 ± 0.1
0.4 ± 0.1 0.5 ± 0.1*** 0.4 ± 0.1
0.5 ± 0.1 0.5 ± 0.1*** 0.4 ± 0.1
8.1 ± 3.1 6.8 ± 1.8
7.7 ± 3.4 6.7 ± 1.8
7.2 ± 2.1 6.6 ± 1.6
7.8 ± 2.1 7 ± 2.1
7.4 ± 2.7 8.6 ± 3.4** 6.1 ± 0.8
7.2 ± 3.6 8.5 ± 4.7** 5.9 ± 0.9
6.6 ± 1.9 7.6 ± 2*** 5.6 ± 1
7.2 ± 3.5 8.4 ± 2.4*** 6.1 ± 1.2
162.8 ± 99.1 140.2 ± 33.8
127.9 ± 62.5 109.8 ± 16.7
125.9 ± 84.6 105.9 ± 16.9
111.8 ± 44.2 99.3 ± 16.8
123.1 ± 47.3 109.9 ± 23.1
15.9 ± 3.5 15.2 ± 3 16.7 ± 3.8
16.4 ± 3.5 15.9 ± 3.5 17 ± 3.4
16.4 ± 3.9 16.2 ± 4 16.6 ± 3.8
15.9 ± 4.0 15.8 ± 4 16 ± 4.1
16.3 ± 4.5 16 ± 4.3 16.6 ± 4.7
10.7 ± 5.4 8.9 ± 2.8 9.4 ± 4.4◦ ◦ ◦ 11 ± 5.7**, ◦ ◦ ◦ 7.8 ± 1.6◦ ◦ ◦
<0.001
<0.001
n.s.
A: seated without back support, B: seated with back support reclined at about 80◦ , C: seated with back support reclined at about 65◦ , D: seated with back support reclined at about 40◦ and supine. Last column: p-value indicated the statistically significance of the different positions on each parameter for the entire group. Post hoc pairwise comparisons. —◦ ◦ ◦ p < 0.001 in the pairwise comparisons of position A with position B–D and supine; **: p < 0.01 in the pairwise comparisons with the corresponding female values in the same position; ***: p < 0.001 in the pairwise comparisons with the corresponding female values in the same position.
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Fig. 4. Dimensional variations of the abdomen during quiet spontaneous breathing in the five different considered postures (A–D and supine, see Fig. 1) in male (closed circles) and female (open circles) subjects. Upper left: antero-posterior diameter changes at umbilical level; upper right: medio-lateral diameter changes at the umbilical level; lower left: perimeter changes at the umbilical level; lower center: cross-sectional area changes at the umbilical level; lower right: abdominal volume changes. Data are shown as mean values ± SEM. *, **, ***: p < 0.05, 0.01, 0.001 male vs female subjects.
versely, antero-posterior and medio-lateral diameter changes are not always in agreement with volume variations and provide different results regarding gender and postural effects. As an example, for the rib cage the variations of antero-posterior diameters are different between men and women when assessed at the Angle of Louis or at xiphoid level (Fig. 3). As another example, for the abdomen the variations of antero-posterior diameters in the various positions are different when assessed as either changes of antero-posterior or medio-lateral diameter (Fig. 4). 4.1. Effect of posture The present study shows that chest wall kinematics are significantly influenced by posture. A progressively increased inclination of the trunk determines a progressive reduction of rib cage displacement and a progressive increase of abdominal contribution to tidal volume, which is particularly evident in women. The results of our study are generally in agreement with previous studies which, by using different measurement devices, showed that in erect or seated position the relative contribution of the rib cage to tidal breathing is higher than in supine position (Wade, 1954; Konno and Mead, 1967; Sharp et al. (1975); Verschakelen and Demedts, 1995). Original measurements of rib cage and abdominal volume obtained by OEP considering four different trunk inclinations from erect to supine position are now here reported. The experimental protocol allowed to systematically study the effect of gravity on breathing by considering different orientations of its vector with respect of the body. The increasing abdominal component to tidal volume passing from erect to supine position (Fig. 5) can be explained by the elastic properties
of rib cage and abdominal compartments (Konno and Mead, 1968). In fact, in the region of quiet breathing, in the standing posture the abdomen is nearly as compliant as the rib cage, while in the supine position only the abdomen varies its static characteristic by increasing the compliance (Agostoni and Rahn, 1960). This is due to the fact that, while seated, the weight of the abdominal content distends the abdominal wall and therefore the elastances of diaphragm-abdomen and belly wall are higher than in the supine posture (Barnas et al., 1993). Moreover, it is well known that posture strongly influences the geometry of the respiratory muscles, particularly the diaphragm. In supine position, the weight of the abdominal content lengthens the diaphragm’s fibers, and this may result in a different ability to generate a given trans-diaphragmatic pressure for a given respiratory neural central drive. An important additional issue here reported is that, until now, the seated position has been studied without considering possible effects due to the presence of a support for the back. Therefore, in this study it was investigated if back support had any effect on breathing in seated position. Significant differences were found, namely that the contribution of abdominal compartment to tidal volume in seated position with back support is significantly greater than without back support (Fig. 5, position A compared to position B) with a corresponding lower displacement of the rib cage (in terms of perimeter, cross-sectional area and volume changes, Fig. 3, position A compared to position B). These differences may be explained, at least in part, by the effect of tonic contraction of abdominal muscles for postural maintenance and trunk stabilization. In the absence of a back support the abdominal compliance is reduced, and the motion of the abdominal compartment increases. Moreover, not only abdominal muscles, but also the diaphragm, are
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Fig. 5. Percentage contribution of rib cage (left) and abdomen (right) to tidal volume in the five different postures (A–D and supine, see Fig. 1) in male (closed circles) and female (open circles) subjects. Data are shown as mean values ± SEM. *, **, ***: p < 0.05, 0.01, 0.001 male vs female subjects.
involved in the control of postural stability in erect postures, and diaphragmatic contraction minimizes displacement of abdominal contents into the thorax as well (Hodges et al., 1997). 4.2. Effect of gender The present study shows that chest wall kinematics is significantly influenced by gender, namely women have a lower abdominal contribution to tidal volume and smaller abdominal dimensional changes than males during quiet breathing. Our results are in agreement with those obtained by Fugl-Meyer (1974) and Gilbert et al. (1981), who found a relatively greater abdominal motion in men than in women. The different results obtained by Sharp et al. (1975) and Verschakelen and Demedts (1995), who did not find any sex-related differences in thoraco-abdominal motion during quiet breathing in different postures, may be attributed to the positioning and the kind of the measurements devices. More recently, Binazzi et al. (2006) found a more costal pattern in females than in males during quiet breathing at rest with the subjects seated in a comfortable armchair. Their data, obtained by OEP (abdominal contribution to tidal volume equal to about 45% for males and 31% in females), are very similar to the ones presented in this study measured in a similar position (Fig. 5, position B). By using esophageal and gastric pressure measurements, Bellemare et al. (2003) showed that female subjects exhibit a greater inspiratory rib cage muscle contribution during resting breathing than male. In the same study, these authors reported significant gender-related differences in thoracic dimensions and configuration as assessed by chest radiographs. Females have smaller radial rib cage dimensions in relationship to height than males and a greater inclination of the ribs. Bellemare et al. hypothesized that this could confer a mechanical advantage to the rib cage muscles for male subjects. Our findings regarding both thoraco-abdominal contributions to breathing and chest dimensions confirm these observations. Female subjects showed more rib cage breathing pattern when compared to males, and this difference was maintained in all the considered positions passing from seated to supine (Fig. 5). In addition to Bellemare’s data, we have now shown that, despite different thoraco-abdominal diameters, women and men are characterized by similar distribution of chest wall volumes in the different compartments at end-expiration (Table 2). Regarding the ventilatory pattern, our data are in agreement with those reported by Kilbride et al. (2003) who showed that at rest minute ventilation is lower in women than in men and this is entirely due to the lower tidal volume at a similar respiratory rate. These differences disappear, however, when minute venti-
lation and tidal volume are corrected for differences in body size between women and men. 4.2.1. Implications of the study Our study shows that considering different geometrical parameters could bring to different results. This is important to define the limit of validity of chest wall kinematics measurements in different positions and different genders when using different devices. Our results demonstrate, moreover, significant differences in chest wall kinematics due to the presence of back support in the seated position. This is of particular interest in several clinical situations, as many patients with respiratory involvement (e.g., those affected by neuromuscular disorders) are often bound on a wheelchair and are not able to maintain a seated position without back support. For these patients, the assessment by OEP of thoraco-abdominal behavior in the position adopted during their daily life provides useful early indicators of respiratory impairment (Lo Mauro et al., 2010). The effects of posture and gender on chest wall shape and kinematics are strong. Therefore, they may contribute to individual variations and must be carefully controlled when the impairment of respiratory muscle function, namely the diaphragm, is assessed by kinematic measurements, e.g., by respiratory inductive Plethysmography or Opto-Electronic Plethysmography (Lo Mauro et al., 2010). 4.2.2. Limitations of the study A possible limitation of our analysis is represented by the use of a different number of markers in position A compared to all the other positions. In order to allow an appropriate comparison of the different geometrical parameters in the different postures, in our results we have therefore only considered their variations rather than their absolute values, with the assumption that the back surface was not moving with respect to its support. Another limitation of this study was that we did not directly compare different measurement devices, but we preferred to derive the different geometrical parameters from the same set of data and to avoid problems related to the simultaneous use of different devices. Finally, we did not systematically studied potentially confounding effects of female breast size, and its possible mass loading effects on chest wall kinematics and activation of postural muscles respectively in supine and seated position. In conclusion, in the present study we confirm that posture plays a fundamental role on breathing and we provide original data regarding chest wall volumes and kinematics. In addition, we demonstrate that the presence of a support for the back in seated position leads to differences in breathing pattern, and this should be carefully taken into consideration when respiratory function is
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evaluated in patients who are not able to maintain an erect position without a support (e.g., patients affected by neuromuscular diseases seated in a wheelchair). Finally, our findings suggest that gender also has a strong influence on breathing, particularly on thoraco-abdominal contribution to tidal volume. All these findings should be considered as a reference when studying breathing patterns in disease. Acknowledgement The authors gratefully acknowledge M.H. Schwartz for the language revision. References Agostoni, E., Rahn, H., 1960. Abdominal and thoracic pressures at different lung volumes. J. Appl. Physiol. 15, 1087–1092. Aliverti, A., Dellacà, R., Pelosi, P., Chiumello, D., Pedotti, A., Gattinoni, L., 2000. Optoelectronic plethysmography in intensive care patients. Am. J. Respir. Crit. Care Med. 161 (5), 1546–1552. Aliverti, A., Dellacà, R., Pelosi, P., Chiumello, D., Gattinoni, L., Pedotti, A., 2001. Compartmental analysis of breathing in the supine and prone positions by optoelectronic plethysmography. Ann. Biomed. Eng. 29 (1), 60–70. Barnas, G.M., Green, M.D., MacKenzie, C.F., Fletcher, S.J., Campbell, N., Runcie, C., Broderick, G.E., 1993. Effect of posture on lung and regional chest wall mechanics. Anesthesiology 78, 251–259. Binazzi, B., Lanini, B., Bianchi, R., Romagnoli, I., Nerini, M., Gigliotti, F., Duranti, R., Milic-Emili, J., Scano, G., 2006. Breathing pattern and kinematics in normal subjects during speech, singing and loud whispering. Acta Physiol. 186, 233–246. Bellemare, F., Jeanneret, A., Couture, J., 2003. Sex differences in thoracic dimensions and configuration. Am. J. Respir. Crit. Care Med. 168, 305–312. Cala, S.J., Kenyon, C.M., Ferrigno, G., Carnevali, P., Aliverti, A., Pedotti, A., Macklem, P.T., Rochester, D.F., 1996. Chest wall and lung volume estimation by optical reflectance motion analysis. J. Appl. Physiol. 81, 2680–2689.
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Fugl-Meyer, A.R., 1974. Relative respiratory contribution of the rib cage and the abdomen in males and females with special regard to posture. Respiration 31, 240–251. Gilbert, R., Auchincloss, J.H., Peppi, D., 1981. Relationship of rib cage and abdomen motion to diaphragm function during quiet breathing. Chest 80, 607–612. Grimby, G., Goldman, M., Mead, J., 1976. Respiratory muscle action inferred from rib cage and abdominal V–P partitioning. J. Appl. Physiol. 41 (5), 739–751. Hodges, P.W., Butler, J.E., McKenzie, D.K., Gandevia, S.C., 1997. Contraction of the human diaphragm during rapid postural adjustments. J. Physiol. 505 (2), 539–548. Kenyon, C.M., Cala, S.J., Yan, S., Aliverti, A., Scano, G., Duranti, R., Pedotti, A., Macklem, P.T., 1997. Rib cage mechanics during quiet breathing and exercise in humans. J. Appl. Physiol. 83, 1242–1255. Kilbride, E., McLoughin, P., Gallagher, C.G., Harty, H.R., 2003. Do gender differences exist in the ventilatory response to progressive exercise in males and females of average fitness? Eur. J. Appl. Physiol. 89, 595–602. Konno, K., Mead, J., 1967. Measurement of the separate volume changes of rib cage and abdomen to ventilation during exercise. J. Appl. Physiol. 22, 407–422. Konno, K., Mead, J., 1968. Static volume–pressure characteristics of the rib cage and abdomen. J. Appl. Physiol. 24, 544–548. Lee, L.J., Chang, A.T., Coppieters, M.W., Hodges, P.W., 2010. Changes in sitting posture induce multiplanar changes in chest wall shape and motion with breathing. Respir. Physiol. Neurobiol. 170 (3), 236–245. Lo Mauro, A., D’Angelo, M.G., Romei, M., Motta, F., Colombo, D., Comi, G., Pedotti, A., Marchi, E., Turconi, A.C., Bresolin, N., Aliverti, A., 2010. Abdominal tidal volume as an early indicator of respiratory impairment in DMD. Eur. Respir. J. 35 (5), 1118–1125. McClaran, S.R., Harms, C.A., Pegelow, D.F., Dempsey, J.A., 1998. Smaller lungs in women affect exercise hyperpnea. J. Appl. Physiol. 84 (6), 1872–1881. Sharp, J.T., Goldberg, N.B., Druz, W.S., Danon, J., 1975. Relative contributions of rib cage and abdomen to breathing in normal subjects. J. Appl. Physiol. 39 (4), 608–618. Verschakelen, J.A., Demedts, M.G., 1995. Normal thoracoabdominal motion, influence of sex, age, posture, and breath size. Am. J. Respir. Crit. Care Med. 151, 399–405. Wade, O.L., 1954. Movements of the thoracic cage and diaphragm in respiration. J. Physiol. 124, 193–212. Ward, M.E., Ward, J.W., Macklem, P.T., 1992. Analysis of human chest wall motion using a two-compartment rib cage model. J. Appl. Physiol. 72 (4), 1338–1347.
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Respiratory Physiology & Neurobiology journal homepage: www.elsevier.com/locate/resphysiol
Effects of gender and posture on thoraco-abdominal kinematics during quiet breathing in healthy adults M. Romei a,∗ , A. Lo Mauro b , M.G. D’Angelo a , A.C. Turconi a , N. Bresolin a,c , A. Pedotti b , A. Aliverti b a b c
IRCCS E.Medea, Bosisio Parini (Lc), Italy TBM Lab, Dipartimento di Bioingegneria, Politecnico di Milano, Milano, Italy Fondazione Policlinico – Mangiagalli – Regina Elena, IRCCS Ospedale Maggiore, Università degli Studi di Milano, Istituto di Clinica Neurologica, Milano, Italy
a r t i c l e
i n f o
Article history: Accepted 19 May 2010 Keywords: Chest wall Posture Abdomen Opto-electronic plethysmography Gender Thorax
a b s t r a c t To investigate the effects of posture and gender on thoraco-abdominal motion and breathing pattern, 34 healthy men and women were studied by Opto-Electronic Plethysmography during quiet breathing in five different postures from seated (with and without back support) to supine position. Chest wall kinematics and breathing pattern were significantly influenced by position and gender. The progressively increased inclination of the trunk determined a progressive reduction of rib cage displacement, tidal volume, and minute ventilation and a progressive increase of abdominal contribution to tidal volume. Female subjects were characterized by smaller dimensions of the rib cage compartment and during quiet breathing by lower tidal volume, minute ventilation and abdominal contribution to tidal volume than males. The effect of posture on abdominal kinematics was significant only in women. The presence of a back support in seated position determined differences in breathing pattern. In conclusion, posture and gender have a strong influence on breathing and on chest wall kinematics. © 2010 Elsevier B.V. All rights reserved.
1. Introduction It is well known that posture influences thoraco-abdominal kinematics during spontaneous quiet breathing. Previous studies (Wade, 1954; Fugl-Meyer, 1974; Sharp et al., 1975; Verschakelen and Demedts, 1995; Lee et al., 2010) have investigated both erect (sitting or standing) and supine positions in healthy subjects, and have shown that quiet breathing is predominantly abdominal in the former and thoracic in the latter position. On the other hand, the effect of gender on chest wall kinematics is still controversial. While some authors (Fugl-Meyer, 1974; Gilbert et al., 1981) reported a relatively greater rib cage motion in women, others (Sharp et al., 1975; Verschakelen and Demedts, 1995) did not. There is evidence in the literature, however, that the differences in pulmonary function (namely, lung volumes, maximal expiratory flow rates, diffusion surfaces and maximal pulmonary ventilation) between females and males are mostly due to the smaller height and trunk size in women (McClaran et al., 1998). These controversies remain when considering possible interactions between posture and gender on thoraco-abdominal motion during quiet breathing.
∗ Corresponding author at: IRCCS “E. Medea”, Via Don Luigi Monza, 20, 23842 Bosisio Parini (Lc), Italy. Tel.: +39 031 877351; fax: +39 031 877499. E-mail address: [email protected] (M. Romei). 1569-9048/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.resp.2010.05.018
In the previous studies, different measurement techniques such as mercury-in-rubber strain gauges (Wade, 1954), linear differential transducers (Konno and Mead, 1967), magnetometers (Fugl-Meyer, 1974; Sharp et al., 1975; Gilbert et al., 1981), and respiratory inductive plethysmography (Verschakelen and Demedts, 1995) were used. The differences in experimental methods, particularly in the kind of measurement they provide (changes of diameters, perimeters, transversal sections), could contribute to the different findings regarding the effects of gender and possible interactions between posture and gender on chest wall kinematics. Opto-Electronic Plethysmography (OEP, Cala et al., 1996) has been proposed as a new method that, starting from the threedimensional coordinates of markers positioned on a subject’s trunk and acquired by an opto-electronic system for motion analysis, allows the accurate measurement of the kinematics and the volume variations of the chest wall and its compartments (rib cage and abdomen) in different positions: standing, seated, supine (Aliverti et al., 2000), and prone (Aliverti et al., 2001). The present study was conducted in order to prove the hypothesis that posture, gender and their interaction all have significant effects on rib cage and abdominal kinematics during quiet breathing and to clarify which are the limits of validity of chest wall kinematics measurements when considering different geometrical parameters. For these purposes, we used the novel OEP technique to study a group of healthy female and male subjects in different postures, i.e., different inclinations of the trunk from seated
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Table 1 Subjects’ characteristics (data are expressed as mean ± SD). M: males; F: females; M + F: overall group. In the last column on the right, the p-value of the comparison between males and females are shown.
Size group Age (years) Weight (kg) Height (cm)
M+F
M
F
p-Value (M vs F)
34 32.1 ± 8 (range: 22–52) 64.6 ± 11.4 (range: 46–83) 172.9 ± 8.2 (range: 157–187)
17 31.5 ± 9.4 (range: 22–52) 72.1 ± 6.5 (range: 60–83) 177 ± 5.4 (range: 165–187)
17 32.8 ± 6.6 (range: 22–50) 56.3 ± 8.4 (range 46–76) 164.9 ± 5.4 (range: 157–180)
0.65 <0.01 <0.01
(with and without back support) to supine position. By using the same set of three-dimensional coordinates measured by the same opto-electronic system for motion analysis, we calculated simultaneous variations in diameters, perimeters, transversal sections and volumes at the levels of the rib cage and the abdomen as different descriptors of chest wall kinematics. In this way we aimed to exclude all the possible differences between these parameters due to measurement errors introduced by the different sensors and/or devices, which in part may explain the controversial results reported in the literature.
2. Materials 2.1. Subjects 34 healthy adults (17 females, 17 males) were recruited for the present study. The inclusion criteria were: absence of cardiac and pulmonary disease, no smokers, no endurance-trained athletes, and age higher than 18 years. Subjects’ characteristics are shown in Table 1. The study was approved by the local Ethical committee of IRCCS “E. Medea” Institute where all the data acquisitions were performed and all subjects gave informed consent.
2.2. Protocol For each subject, the data acquisition protocol consisted of five trials performed in a single session. Each session took about 45 min in total, including both the time for the subject’s adaptation on the different positions and data acquisition. All subjects were asked to maintain a spontaneous breathing pattern for the whole duration of the experimental session. Five different positions were considered (Fig. 1) and measurements were repeated five times (one for each position) in which data were acquired during at least 3 min of quite breathing. In the first position (position A in Fig. 1), the subject was seated on a rigid bed without back support. In the three other positions (positions B–D in Fig. 1), the subject was seated on a wheelchair, with the back support position adjusted to one of three different inclinations (B: ∼80◦ , C: ∼65◦ , D: ∼40◦ with respect to the floor). Finally, the subject lay supine on a rigid bed.
2.3. Opto-Electronic Plethysmography analysis Opto-Electronic Plethysmography (OEPSystem BTS, Italy) was based on an eight-infrared cameras system working at 60 Hz. For positions A–C, four cameras were positioned in front of the subject, and four were behind. For position D and supine, four cameras were positioned to the right of the subject, and four to the left. For position A, 89 passive markers were placed on the anterior and posterior side of the trunk, according to the protocol described by Cala et al. (1996). For positions B–D and supine, the markers on the posterior trunk surface were removed, and 52 markers were left on the anterior and lateral trunk surface. In these cases, 45 markers were positioned according to the protocol described by Aliverti et al. (2001), adding a row of 7 markers at the nipple level, in order to have the same anterior surface arrangement in all the 5 positions. The same operator identified the anatomical positions, and placed the passive retro-reflective markers on the chest wall surface. 2.4. Data analysis 2.4.1. Total chest wall volume As previously described, total chest wall volume was calculated from the 3D coordinates of the markers, surface triangulation, and Gauss’ theorem (Cala et al., 1996; Aliverti et al., 2001). In the case of the seated position without back support (A) the whole trunk was visible, whereas for the positions with back support (B–D and supine), the posterior part of the trunk was defined by a virtual plane. This was obtained by calculating a reference plane defined by the co-ordinates of the markers positioned laterally on the trunk (Aliverti et al., 2001). 2.4.2. Compartmental volumes As in previous studies, the total chest wall was divided into three compartments (Ward et al., 1992), namely Pulmonary Rib Cage, Abdominal Rib Cage and Abdomen (Kenyon et al., 1997). For the purposes of the present study, the Pulmonary and Abdominal Rib Cage compartments were considered as a single compartment (Rib Cage), given by their sum (Grimby et al., 1976) (Fig. 2a). 2.4.3. Chest dimensions and displacement From 3D marker coordinates measured by OEP, the mediolateral (ML) diameters, the antero-posterior (AP) diameters, the
Fig. 1. Schematic representation of the five postures adopted by the subjects. From left to right: seated on a rigid bed without back support (position A); seated with three different back support inclinations (position B: ∼80◦ , position C: ∼65◦ , position D: ∼40◦ with respect to the floor) and supine on a rigid flat bed.
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Fig. 2. Schematic diagrams showing marker positioning on the front of the subject and the thoraco-abdominal surface triangulation defined to compute rib cage and abdominal volumes (a). Cross-sectional areas (b), medio-lateral (ML) diameters (c) and antero-posterior (AP) diameters (d and e) at Angle of Louis, xiphoid and umbilical levels. The definition of AP diameters is shown both for position A (d) and for positions B–D and supine (e). The crosses shown in (b) and (e) are ‘virtual’ markers positioned on the back support.
perimeters and the cross-sectional areas were calculated for rib cage and abdomen (Fig. 2). For the rib cage, the following dimensions were calculated: AP diameters at angle of Louis and xiphoid levels, ML diameter, perimeter, cross-sectional area at xiphoid level. For the abdomen the following dimensions were calculated: AP diameter, ML diameter, perimeter and cross-sectional area at umbilical level. Antero-posterior diameters at the angle of Louis, xiphoid and umbilicus levels were calculated as the distance between the anterior and posterior central markers placed at the same level in position A (Fig. 2d). In all positions with back support (i.e., B–D and supine), they were calculated as the distance between the anterior central markers and the reference plane (Fig. 2e). Medio-lateral diameters at xiphoid and umbilicus levels were calculated as the distance between the two more lateral markers at the xiphoid and umbilical line, respectively (Fig. 2c). Perimeters were obtained by summing the 3D distances of all the contiguous markers placed at the same level (Fig. 2b). Cross-sectional areas were calculated by summing the areas of the triangles each formed by two contiguous markers and the baricenter of all the markers positioned at the considered level (Fig. 2b). Xiphoid and umbilical levels were considered respectively for the rib cage and the abdomen. To characterize subject chest size and configuration, the above defined diameters, perimeters, cross-sectional areas, total and compartmental volumes were assessed as the mean value at endexpiration in position A. Rib cage and abdominal volumes were expressed both as absolute values and percentage of total chest wall volume. To assess thoraco-abdominal dimensional variations during quiet spontaneous breathing, we calculated the mean variations of the above defined diameters, perimeters, cross-sectional areas, and volumes for the rib cage and the abdomen in all the considered positions. 2.4.4. Ventilatory pattern From total and compartmental chest wall volume tracings, the following parameters were considered for the analysis of the ventilatory pattern: Tidal Volume as the average total chest wall volume variations, Respiratory Rate, Minute Ventilation (as Tidal Volume × Respiratory Rate) and contribution of the Rib Cage and Abdomen to Tidal Volume (expressed as percentage of Tidal Volume). In addition, Tidal Volume and Minute Ventilation were
normalized by body weight in order to correct for sex-differences in body size, metabolic rate and vital capacity. 2.5. Statistical analysis For respiratory and anthropometric parameters, mean values ± standard deviation (SD) were calculated for the entire group, and for the female and male subgroups for each positions (A–D and supine). For the comparison between anthropometric data, volumes and displacement, tests of normality were performed, followed by either parametric (unpaired Student’s t) or nonparametric (Mann–Whitney) tests between data of Male and Female subjects. For respiratory parameters (Tidal Volume, Minute Ventilation, Respiratory Rate and Abdominal Contribution) and chest displacement (AP diameters, ML diameters, perimeters and crosssectional areas) a general linear model for repeated measures with gender as between-subjects factor was performed. The level of significance was set at p < 0.05 for all statistical comparisons. Values in text and tables are group means ± SD and in figures are group means ± Standard Error of the Mean (SEM). All computations were performed with SPSS version 11.0 for Windows; SPSS, Chicago, IL. 3. Results The anthropometric characteristics of the entire group and of the two subgroups were divided according to their gender (Table 1). The two gender subgroups were homogeneous in age but not in weight and height (p < 0.01). 3.1. Chest dimensions and displacement AP and ML diameters, perimeters, cross-sectional areas and volumes for rib cage and abdomen calculated in position A and averaged at end-expiration are shown in Table 2. In general, the total dimension of the chest wall was higher in male than in female subjects. This was mainly due to the rib cage which in males was characterized by longer AP diameters and perimeter and larger cross-sectional area and volume. In the abdomen, only AP diameter and volume were larger in males compared to females. The subdivision of the total chest wall volume into the two compartments, however, was similar when they were expressed as a percentage of total chest wall volume.
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Table 2 Antero-posterior (AP) and medio-lateral (ML) diameters, perimeters, cross-sectional areas and volumes in the overall group of subjects (M + F) and in the two gender groups (M: males; F: females) for the rib cage and the abdomen. All the presented values are group means ± SD obtained at end-expiration in position A. In the last column on the right, the p-value of the comparison between males and females are shown.
Total chest wall (CW) Volume (L) Rib cage AP (Angle of Louis level) (mm) AP (xiphoid level) (mm) ML (mm) Perimeter (mm) Area (cm2 ) Volume (L) Volume (% of CW) Abdomen AP (mm) ML (mm) Perimeter (mm) Area (cm2 ) Volume (L) Volume (% of CW)
M+F
M
F
p-Value (M vs F)
18.7 ± 4.0
21.7 ± 2.6
15.7 ± 2.6
<0.001
188 208 245 855 419 14.0 75.1
± ± ± ± ± ± ±
17 24 21 116 93 3.0 3.0
197 219 250 911 471 16.4 76.0
± ± ± ± ± ± ±
14 21 15 51 62 1.7 3.3
179 197 240 799 355 11.6 74.2
± ± ± ± ± ± ±
15 23 26 136 82 2 2.5
0.001 0.006 0.189 0.001 <0.001 <0.001 0.081
226 260 864 466 4.65 24.9
± ± ± ± ± ±
26 28 123 99 1.2 3.0
239 264 876 497 5.2 24.0
± ± ± ± ± ±
24 22 78 96 1.2 3.3
214 257 851 424 4.1 25.8
± ± ± ± ± ±
21 33 157 89 0.9 2.5
0.003 0.505 0.245 0.071 0.003 0.082
The dimensional variations of the rib cage and abdomen during quiet breathing in the different positions are shown in Figs. 3 and 4, respectively. 3.1.1. Effects of posture on the rib cage Posture strongly influenced the displacement of the rib cage, which in general gradually decreased from position A to the supine position with increasing inclination of the back, both in male and in female subjects. In fact, all but one the considered dimensional parameters were significantly dependent on posture (Fig. 3), being the AP diameter at the xiphoid level the only exception. This was true both considering the overall group of subjects and the two gender groups separately. 3.1.2. Effects of posture on the abdomen On the other hand, the effect of posture on the abdomen (Fig. 4) was much less evident. When considering the overall group of subjects, the volume change of the abdomen was the only parameter significantly influenced by posture (p < 0.01). Conversely, when considering male and female subjects as two separate groups, the effect of posture on abdominal dimensional changes was present only in the women and became statistically significant (p < 0.001) not only for the volume, but also for perimeter and cross-sectional area variations. All dimensional variations but ML diameter changes increased with increasing inclination of the back support (Fig. 4). 3.1.3. Effects of gender Variations of rib cage dimensional parameters during breathing were not significantly different between male and female subjects in all the considered positions, with very few exceptions (AP diameter in two positions and perimeter in four positions, see Fig. 3). Conversely, the displacement of the abdomen was significantly greater in male than in female subjects for all the dimensional parameters in all the positions (Fig. 4). 3.2. Ventilatory pattern Data of ventilatory parameters in the different positions are reported in Table 3. The only parameter that was independent on posture was Respiratory Rate (p > 0.05). For the entire group and for the two gender-subgroups, Tidal Volume and Minute Ventilation presented the highest values in seated position without back support (position A) (p < 0.05). Absolute Tidal Volume and Minute Ventilation values were significantly higher (p < 0.05) in
males than in females in all the considered positions, but when normalized with respect to body weight these differences did not persist. Fig. 5 shows Rib Cage and Abdominal contributions to Tidal Volume for Males and Females expressed as percentage of tidal volume. Posture significantly influenced the contribution of abdomen to Tidal Volume, which gradually increased with increasing inclination of the back, from position A to supine position (p < 0.05). Consequently, the contribution of rib cage to Tidal Volume gradually decreased with increasing inclination of the back. Also gender significantly influenced the contribution of abdomen to Tidal Volume. In all the considered postures from A to D, males had significantly greater abdominal contribution than females (p < 0.05), with a similar increasing trend related to the different trunk inclinations (p > 0.05). In the supine position, males still showed higher abdominal contribution than females, although this difference did not reach statistical significance. 4. Discussion The main result of the present study is that chest wall kinematics and breathing pattern are significantly influenced by the position of the trunk and by gender. A progressively increased inclination of the trunk determines a progressive reduction of rib cage displacement, tidal volume, and minute ventilation and a progressive increase of abdominal contribution to tidal volume. Female subjects are characterized by smaller dimensions confined in the rib cage compartment and during quiet breathing by lower tidal volume, minute ventilation and abdominal contribution to tidal volume than males. The effect of posture on abdominal kinematics is present only in women. From a methodological point of view, the original aspect of this study is that the different parameters used to describe thoracoabdominal kinematics (i.e., antero-posterior and medio-lateral diameters, perimeters, cross-sectional areas and volumes) have been assessed simultaneously starting from the same set of threedimensional coordinates measured by the same opto-electronic system for motion analysis. In this way we excluded all the possible differences between these descriptors of chest wall kinematics due to measurement errors introduced by the different sensors and/or devices (i.e., magnetometers, strain gauges, inductive plethysmography), which in part may explain controversial results reported in the literature. In the approach adopted in the present study, the volume variations of the rib cage and the abdomen can be considered as
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Fig. 3. Dimensional variations of the rib cage during quiet spontaneous breathing in the five different considered postures (A–D and supine, see Fig. 1) in male (closed circles) and female (open circles) subjects. Upper left: antero-posterior diameter changes at the angle of Louis level; upper center: antero-posterior diameter changes at the xiphoid level; upper right: medio-lateral diameter changes at the xiphoid level; lower left: perimeter changes at the xiphoid level; lower center: cross-sectional area changes at the xiphoid level; lower right: rib cage volume changes. Data are shown as mean values ± SEM. *, **, ***: p < 0.05, 0.01, 0.001 male vs female subjects.
the most complete parameter describing the kinematics of each compartment. In fact, such volume measurements are obtained by integrating the three-dimensional motion of multiple surface markers and therefore include and integrate changes of dimensions in multiple directions.
The results obtained in this study demonstrate that variations of perimeters and cross-sectional areas generally follow variations of volumes, both in the rib cage and in the abdomen, with only minor differences. Therefore, the effects of gender and different trunk positions can be reliably detected by using these parameters. Con-
Table 3 Ventilatory pattern in the five different positions (A–D and supine, see Fig. 1). All data are expressed as mean ± SD. M: males; F: females; M + F: overall group. In the last column on the right, p-values regarding position effect significance are shown. All data are mean ± SD. Positions A Tidal volume (L)
M+F M F
Tidal volume/weight (ml kg−1 )
M F
Minute ventilation (L/min)
M+F M F
Minute ventilation/weight (ml min−1 kg−1 )
M F
Respiratory rate (min−1 )
M+F M F
p-Value B
0.6 ± 0.2◦ ◦ ◦ 0.7 ± 0.3**, ◦ ◦ ◦ 0.5 ± 0.1◦ ◦ ◦
C
D
Supine
0.5 ± 0.2 0.5 ± 0.2** 0.4 ± 0.1
0.4 ± 0.2 0.5 ± 0.2** 0.4 ± 0.1
0.4 ± 0.1 0.5 ± 0.1*** 0.4 ± 0.1
0.5 ± 0.1 0.5 ± 0.1*** 0.4 ± 0.1
8.1 ± 3.1 6.8 ± 1.8
7.7 ± 3.4 6.7 ± 1.8
7.2 ± 2.1 6.6 ± 1.6
7.8 ± 2.1 7 ± 2.1
7.4 ± 2.7 8.6 ± 3.4** 6.1 ± 0.8
7.2 ± 3.6 8.5 ± 4.7** 5.9 ± 0.9
6.6 ± 1.9 7.6 ± 2*** 5.6 ± 1
7.2 ± 3.5 8.4 ± 2.4*** 6.1 ± 1.2
162.8 ± 99.1 140.2 ± 33.8
127.9 ± 62.5 109.8 ± 16.7
125.9 ± 84.6 105.9 ± 16.9
111.8 ± 44.2 99.3 ± 16.8
123.1 ± 47.3 109.9 ± 23.1
15.9 ± 3.5 15.2 ± 3 16.7 ± 3.8
16.4 ± 3.5 15.9 ± 3.5 17 ± 3.4
16.4 ± 3.9 16.2 ± 4 16.6 ± 3.8
15.9 ± 4.0 15.8 ± 4 16 ± 4.1
16.3 ± 4.5 16 ± 4.3 16.6 ± 4.7
10.7 ± 5.4 8.9 ± 2.8 9.4 ± 4.4◦ ◦ ◦ 11 ± 5.7**, ◦ ◦ ◦ 7.8 ± 1.6◦ ◦ ◦
<0.001
<0.001
n.s.
A: seated without back support, B: seated with back support reclined at about 80◦ , C: seated with back support reclined at about 65◦ , D: seated with back support reclined at about 40◦ and supine. Last column: p-value indicated the statistically significance of the different positions on each parameter for the entire group. Post hoc pairwise comparisons. —◦ ◦ ◦ p < 0.001 in the pairwise comparisons of position A with position B–D and supine; **: p < 0.01 in the pairwise comparisons with the corresponding female values in the same position; ***: p < 0.001 in the pairwise comparisons with the corresponding female values in the same position.
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Fig. 4. Dimensional variations of the abdomen during quiet spontaneous breathing in the five different considered postures (A–D and supine, see Fig. 1) in male (closed circles) and female (open circles) subjects. Upper left: antero-posterior diameter changes at umbilical level; upper right: medio-lateral diameter changes at the umbilical level; lower left: perimeter changes at the umbilical level; lower center: cross-sectional area changes at the umbilical level; lower right: abdominal volume changes. Data are shown as mean values ± SEM. *, **, ***: p < 0.05, 0.01, 0.001 male vs female subjects.
versely, antero-posterior and medio-lateral diameter changes are not always in agreement with volume variations and provide different results regarding gender and postural effects. As an example, for the rib cage the variations of antero-posterior diameters are different between men and women when assessed at the Angle of Louis or at xiphoid level (Fig. 3). As another example, for the abdomen the variations of antero-posterior diameters in the various positions are different when assessed as either changes of antero-posterior or medio-lateral diameter (Fig. 4). 4.1. Effect of posture The present study shows that chest wall kinematics are significantly influenced by posture. A progressively increased inclination of the trunk determines a progressive reduction of rib cage displacement and a progressive increase of abdominal contribution to tidal volume, which is particularly evident in women. The results of our study are generally in agreement with previous studies which, by using different measurement devices, showed that in erect or seated position the relative contribution of the rib cage to tidal breathing is higher than in supine position (Wade, 1954; Konno and Mead, 1967; Sharp et al. (1975); Verschakelen and Demedts, 1995). Original measurements of rib cage and abdominal volume obtained by OEP considering four different trunk inclinations from erect to supine position are now here reported. The experimental protocol allowed to systematically study the effect of gravity on breathing by considering different orientations of its vector with respect of the body. The increasing abdominal component to tidal volume passing from erect to supine position (Fig. 5) can be explained by the elastic properties
of rib cage and abdominal compartments (Konno and Mead, 1968). In fact, in the region of quiet breathing, in the standing posture the abdomen is nearly as compliant as the rib cage, while in the supine position only the abdomen varies its static characteristic by increasing the compliance (Agostoni and Rahn, 1960). This is due to the fact that, while seated, the weight of the abdominal content distends the abdominal wall and therefore the elastances of diaphragm-abdomen and belly wall are higher than in the supine posture (Barnas et al., 1993). Moreover, it is well known that posture strongly influences the geometry of the respiratory muscles, particularly the diaphragm. In supine position, the weight of the abdominal content lengthens the diaphragm’s fibers, and this may result in a different ability to generate a given trans-diaphragmatic pressure for a given respiratory neural central drive. An important additional issue here reported is that, until now, the seated position has been studied without considering possible effects due to the presence of a support for the back. Therefore, in this study it was investigated if back support had any effect on breathing in seated position. Significant differences were found, namely that the contribution of abdominal compartment to tidal volume in seated position with back support is significantly greater than without back support (Fig. 5, position A compared to position B) with a corresponding lower displacement of the rib cage (in terms of perimeter, cross-sectional area and volume changes, Fig. 3, position A compared to position B). These differences may be explained, at least in part, by the effect of tonic contraction of abdominal muscles for postural maintenance and trunk stabilization. In the absence of a back support the abdominal compliance is reduced, and the motion of the abdominal compartment increases. Moreover, not only abdominal muscles, but also the diaphragm, are
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Fig. 5. Percentage contribution of rib cage (left) and abdomen (right) to tidal volume in the five different postures (A–D and supine, see Fig. 1) in male (closed circles) and female (open circles) subjects. Data are shown as mean values ± SEM. *, **, ***: p < 0.05, 0.01, 0.001 male vs female subjects.
involved in the control of postural stability in erect postures, and diaphragmatic contraction minimizes displacement of abdominal contents into the thorax as well (Hodges et al., 1997). 4.2. Effect of gender The present study shows that chest wall kinematics is significantly influenced by gender, namely women have a lower abdominal contribution to tidal volume and smaller abdominal dimensional changes than males during quiet breathing. Our results are in agreement with those obtained by Fugl-Meyer (1974) and Gilbert et al. (1981), who found a relatively greater abdominal motion in men than in women. The different results obtained by Sharp et al. (1975) and Verschakelen and Demedts (1995), who did not find any sex-related differences in thoraco-abdominal motion during quiet breathing in different postures, may be attributed to the positioning and the kind of the measurements devices. More recently, Binazzi et al. (2006) found a more costal pattern in females than in males during quiet breathing at rest with the subjects seated in a comfortable armchair. Their data, obtained by OEP (abdominal contribution to tidal volume equal to about 45% for males and 31% in females), are very similar to the ones presented in this study measured in a similar position (Fig. 5, position B). By using esophageal and gastric pressure measurements, Bellemare et al. (2003) showed that female subjects exhibit a greater inspiratory rib cage muscle contribution during resting breathing than male. In the same study, these authors reported significant gender-related differences in thoracic dimensions and configuration as assessed by chest radiographs. Females have smaller radial rib cage dimensions in relationship to height than males and a greater inclination of the ribs. Bellemare et al. hypothesized that this could confer a mechanical advantage to the rib cage muscles for male subjects. Our findings regarding both thoraco-abdominal contributions to breathing and chest dimensions confirm these observations. Female subjects showed more rib cage breathing pattern when compared to males, and this difference was maintained in all the considered positions passing from seated to supine (Fig. 5). In addition to Bellemare’s data, we have now shown that, despite different thoraco-abdominal diameters, women and men are characterized by similar distribution of chest wall volumes in the different compartments at end-expiration (Table 2). Regarding the ventilatory pattern, our data are in agreement with those reported by Kilbride et al. (2003) who showed that at rest minute ventilation is lower in women than in men and this is entirely due to the lower tidal volume at a similar respiratory rate. These differences disappear, however, when minute venti-
lation and tidal volume are corrected for differences in body size between women and men. 4.2.1. Implications of the study Our study shows that considering different geometrical parameters could bring to different results. This is important to define the limit of validity of chest wall kinematics measurements in different positions and different genders when using different devices. Our results demonstrate, moreover, significant differences in chest wall kinematics due to the presence of back support in the seated position. This is of particular interest in several clinical situations, as many patients with respiratory involvement (e.g., those affected by neuromuscular disorders) are often bound on a wheelchair and are not able to maintain a seated position without back support. For these patients, the assessment by OEP of thoraco-abdominal behavior in the position adopted during their daily life provides useful early indicators of respiratory impairment (Lo Mauro et al., 2010). The effects of posture and gender on chest wall shape and kinematics are strong. Therefore, they may contribute to individual variations and must be carefully controlled when the impairment of respiratory muscle function, namely the diaphragm, is assessed by kinematic measurements, e.g., by respiratory inductive Plethysmography or Opto-Electronic Plethysmography (Lo Mauro et al., 2010). 4.2.2. Limitations of the study A possible limitation of our analysis is represented by the use of a different number of markers in position A compared to all the other positions. In order to allow an appropriate comparison of the different geometrical parameters in the different postures, in our results we have therefore only considered their variations rather than their absolute values, with the assumption that the back surface was not moving with respect to its support. Another limitation of this study was that we did not directly compare different measurement devices, but we preferred to derive the different geometrical parameters from the same set of data and to avoid problems related to the simultaneous use of different devices. Finally, we did not systematically studied potentially confounding effects of female breast size, and its possible mass loading effects on chest wall kinematics and activation of postural muscles respectively in supine and seated position. In conclusion, in the present study we confirm that posture plays a fundamental role on breathing and we provide original data regarding chest wall volumes and kinematics. In addition, we demonstrate that the presence of a support for the back in seated position leads to differences in breathing pattern, and this should be carefully taken into consideration when respiratory function is
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