- Email: [email protected]
Uterine electromyogram topography to represent synchronization of uterine contractions
International Journal of Gynecology and Obstetrics (2007) 97, 120–124
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / i j g o
CLINICAL ARTICLE
Uterine electromyogram topography to represent synchronization of uterine contractions Wei Jiang ⁎, Gang Li, Ling Lin College of Precision Instruments and Opto-electronic Engineering, Tianjin University, China Received 3 August 2006; received in revised form 5 November 2006; accepted 15 November 2006
KEYWORDS Relative energy; Synchronization topography; Uterine electromyogram
Abstract Objective: To image the synchronization of different parts of the uterus in relation to the abdominal surface during uterine contractions using uterine electromyogram topography. Methods: Of the 20 participants, 16 were in active labor at term, 1 was in preterm labor, and 3 were experiencing failed induced labor. The signals simultaneously collected by 16 digitized channels were in the frequency ranges of 0.2 to 0.45 Hz and 0.8 to 3 Hz. Relative energies were calculated for these 2 frequency ranges and imaged by means of interpolation and transformation. Results: Uterine topographic imaging during active labor suggested good synchronization in all participants, except in one of the 3 who were experiencing failed induced labor. Most notably, synchronization was as good in preterm labor as it was in labor at term. Conclusion: Uterine electromyogram topography provided good imaging of the synchronization of uterine contractions, and could be used for further research on uterine contractility during term and preterm labor. © 2006 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.
1. Introduction Uterine contractions have been monitored by tocodynamometer, intrauterine pressure catheter, and Doppler ultrasonography. The first 2 methods have been used to record the global pressure resulting from the uterine myometrial contractions, but they cannot reflect the contractions’ synchronization and concordance. And although the third method is capable of measuring uterine muscle contractions,
⁎ Corresponding author. Tel./fax: +86 22 27406535. E-mail address: [email protected] (W. Jiang).
it is unsuitable for long-term monitoring. Thus, another clinical method is needed for labor monitoring. A uterine electromyogram (EMG), even performed in a noninvasive way with abdominal probes, can be used to image the process of muscle-fiber excitation [1]. Technically, efficient uterine contractions include 3 main factors: intensity, frequency, and synchronization. However, most studies based on single-lead recordings can only reflect the intensity and frequency of uterine contractions. On the other hand, because of differences among the materials and methods used in the research on multi-lead recordings, conclusions are not consistent. Krishnamurti et al. [2] observed that electrical activity was more frequent in the body than in the horns of the uterus and Sigger et al. [3] found
0020-7292/$ - see front matter © 2006 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ijgo.2006.11.015
Uterine electromyogram topography to represent synchronization of uterine contractions
121
relative energies and transformation was used to map the results (the topography part).
2. Methods and study participants 2.1. Participants
Figure 1 Arrangement of the 16 electrodes on the participants’ abdomen.
no valid statistical concordance between an electrical activity measured in the uterus and another in the distal part of one of the uterine horns (parts that they see as completely separated from the rest of the uterus), whereas other scientists have found electrical activities to be usually well synchronized [4–7]. In particular, Méndez–Bauer et al. [6] suggested that the contractile wave originates near the right fallopian tube and spreads very slowly throughout the uterus, and Ramon et al. [7] suggested that the spatial patterns of synchronization change and follow the periodic pattern of the uterine contraction cycle. There is thus a need to establish controversies as well as points of agreement on a solid basis. The aim of this study was to test a simpler and more representative method of showing the synchronization of the different parts of the uterus in relation to abdominal surface during labor. First, 20 electrodes made of wire leads 16 centimeters long were placed over the participants’ abdominal surface to collect bipolar signals uterine (the EMG part of the method); then, the signals were calculated as
Figure 2
Parturition data were recorded for 1 woman in preterm labor and 19 women in spontaneous or induced labor at the Shandong Zibo Center Hospital, China, between June 2005 and August 2005. The women were between 26 and 32 years old. All had bishop scores higher than 7, and estimated pregnancy durations were all between 37 and 41 weeks except for the woman who was in preterm labor at 33 weeks. The recording session lasted between 1 and 2 h. The participants were enrolled in the study they gave informed consent.
2.2. Data collection After skin preparation by cleaning and mild abrasion, electrodes 8 mm in diameter (Beckman Coulter, Inc., Fullerton, CA, USA) were placed on the women’s abdomens, approximately 5 cm apart in an array of 5 rows and 4 columns (Fig. 1). Uterine EMG signals were collected between 2 vertical electrodes. Ground electrodes were set on the hips. First, the uterine EMG signals were amplified with a gain setting of 10 on the preamplifier and filtered by a second-order high-pass filter with a cut-off frequency of 0.1 Hz to remove direct current potential. After preamplification, the signals were amplified by the main amplifiers with a gain of 100, and then filtered by a fourth-order low-pass filter with a cut-off frequency of 25 Hz to remove high-frequency noise. Then the filtered signals flowed into an analog-to-digital converter (A/DC). To improve synchronization between separate channels, two 8-channel, 14-bit chips with an input range of −2.5 V to + 2.5 V were used (A/DC MAX126; Maxim Integrated Products, Inc. Sunnyvale, CA, USA). With its 14-bit precision and the gains of 1000 provided by its analog part, the system had a resolution power of 0.6 μV, which is adequate for uterine EMGs.
Transform function (the maximum for display increases with the increase of the maximum-to-minimum ratio).
122 Table 1
W. Jiang et al. Statistical results for the uterine EMG signals obtained from 297 contractions during labor Term labor
Preterm labor
Failed labor induction Lesser intensity of contractions
No. of participants No. of Contractions max:min ≤ 1.2 1.2 < max:min < 1.4 max:min ≥ 1.4 Total number of contractions Max:min contraction, mean
16 87 138 0 225 1.2239
1
1
14 5 0 19 1.1883
17 3 0 20 1.1625
Dis-synchronization of contractions 2 0 3 30 33 1.8163
Abbreviations: EMG, electromyogram; max:min, maximum-to-minimum ratio.
The digitized data were transferred by the microprocessor to a laptop computer through a parallel port. The application software on the laptop could process real-time data and present them in different ways.
2.3. Data analysis By recording uterine signals through 16 digitized channels simultaneously during the EMG, it was possible to obtain a 2dimensional 256 gray level display of uterine EMG values ranging from low (white) to high (black). The points located between 2 neighboring electrodes were calculated by interpolation (computing the intermediary value of those measured by the electrodes), so that a smooth grayscale image could be obtained. The computed parameters used in this uterine mapping were defined as the relative energy (H/L) of uterine EMG signals, where H stands for high-frequency bands ranging from 0.8 Hz to 3 Hz, and L stands for low frequency band ranging from 0.2 Hz to 0.45 Hz. Significant changes have been shown to exist in the relative power of 2 frequency bands owing to uterine EMG bursts during the progress of labor [8,9]. All 16 channels of the conventional uterine EMG were analyzed with the same method to obtain the relative energies of the 16 leads for uterine mapping.
To display uterine topography and clearly differentiate uterine synchronization from dis-sychronization, the parameters of the 16 leads involved in the imaging process were transformed to values between 0 and 255. The effect of display was optimized by a transform function as follows: 255T1:2 ðx−minÞ ; x V¼ int maxT1:2−min where x′ is a value between 0 and 255; x is the parameter value to be transformed; min and max are the minimum and maximum values of the 16-lead parameters, and int( ) is the function for the integer part in parenthesis. In this way, the value of x′ with respect to the minimum values of the 16 parameters was 0 (white), and the value retained for the maximum was determined by the minimum-tomaximum ratio, namely: 255T1:2 ð1−min=maxÞ xmax V ¼ int 1:2−min=max As shown in Fig. 2, xmax ′ is a monotonically increasing function of max/min. With a minimum-to-maximum ratio of 2 or greater, the maximum of 16 parameters is equal to twice the minimum or
Figure 3
Uterine electromyogram topography to represent synchronization of uterine contractions
123
Figure 4 greater, which means that the dis-synchronization of uterine ′ tends to be a constant contraction is obvious. In this case, the xmax and the corresponding area on the image is black. When the ratio is less than 1.2, the synchronization of uterine contractions is good and the whole topography is white or light gray. If the ratio is between 1.2 and 2, some areas appear medium gray or dark gray, which points to a risk of dis-synchronization.
3. Results Twenty women accepted the invitation to participate in this study. Among them, 16 were in active labor, 1 in preterm labor, and the remaining 3 had failed induced labor. A total of 297 contractions were observed from these participants.
Uterine EMG signals obtained from the contractions were analyzed and are listed in Table 1. Technically, these contractions were classified as synchronous, semisynchronous, and asynchronous. For each class, a representative contraction was used as an example in this article. The results for the 3 typical examples are shown in Figs. 3, 4, and 5, respectively. The participants were also divided into 3 groupsactive labor at term, active preterm labor, and failed induction of labor. Furthermore, the latter group was divided into 2 subgroups, a dis-synchronization and a lower-intensity group, to account for the reasons for the failed induction. There were a total of 225 contractions recorded in active labor, for which the mean ± S.D. of the computed value, i.e., the minimum-to-maximum ratio, was 1.2239 ± 0.0573 (Table 1). Of these 225 contractions, 87 were synchronous.
Figure 5
124 Fig. 3a shows the 16-lead EMG recordings for a typical synchronous uterine contraction. The recording duration was 4 s. All channels had active electrical activity, but the relation between channels still needed to be determined and the 16-lead relative energies (H/L) of the EMG signals were computed (Fig. 3b). The minimum-to-maximum ratio was less than 1.2. As the whole topographic image was white or light gray, it could be judged empirically that the synchronization of the uterine contraction was good. However, according to the recordings, 138 uterine contractions were not completely synchronous. Some channels away from the umbilicus and the median vertical axis of the uterus showed no electrical activity. In this situation, the minimum-tomaximum ratio was greater than 1.2 but less than 1.4. A typical example of such contractions, which might be called semisynchronous, is shown in Fig. 4a and b. Channels 1, 2, 3, and 4 could be distinguished from the other channels. In clinical practice, the process of labor is not influenced by this kind of semisynchronization. For the EMG recordings of 19 contractions in women in preterm labor, the mean minimum-to-maximum ratio was 1.1883, i.e., identical to that for active labor contractions. The remaining 53 contractions occurred in the 3 participants experiencing failed labor induction. Two of them had 30 asynchronous and 3 semi-synchronous contractions, for which the minimum-to-maximum ratio was 1.8163 ± 0.0482, indicating dis-synchronization. Furthermore, the difference between synchronization and dis-synchronization was statistically significant (P < 0.02). The uterine EMG signal and uterine topography for one of the women with asynchronous contractions are shown in Fig. 5a and b. On the topographic image (Fig. 5b), there is an obvious difference in shade between the 2 sides of uterus, which indicates strong dissynchronization. Since the intensity and frequency of the contractions were efficient, the failure of induced labor was probably related to dis-synchronization. No cervical dilatation was obtained after 4 h of oxytocin infusion (Bachem California Inc., Torrance, CA, USA) accompanied by asynchronous contractions, but it must be pointed out that asynchronous contractions are not the only factor related to failed induction. Other factors such as the intensity and frequency of uterine contractions could also affect the process of labor, which was the case for the third woman with failed induction (the failure was caused by the low intensity of her contractions).
4. Discussion The imaging of the synchronization of uterine contractions by means of uterine EMG topography can also help to detect the origin of dysfunctional uterine activity. In this study, analysis was restricted to the relative energy of uterine EMG signals, which is not averaged over the nearby channels. The energy was computed for each channel individually, and divided by the minimum of 16 channels. This method of representing the synchronization uses the relative amplitudes of uterine EMG signals in relation to the surface of uterus. To study the degree of phase synchronization of the whole uterus, other estimates of statistical entropy would probably be more appropriate for data analysis.
W. Jiang et al. Previous work has demonstrated that successful progress of labor is related to an increase in gap junction, which is thought to be responsible for improving electrical coupling between myometrical cells. The synchronization and coordination of contractile events of different uterine myometrial regions is the result of the increased gap junction, and helps fetal expulsion [10–12]. Therefore, uterine synchronization monitoring can be used in the clinical setting to display the progress of labor. To some extent, this study support the view that uterine electrical activity is usually well synchronized despite semisynchronization in channels away from the umbilicus and the median vertical axis of the uterus. Dis-synchronization reflects the poor electrical coupling of different part of uterus, and is related to induced labor failure. The uterine EMG topography is identical in preterm labor and labor at term because of the increased gap junction in preterm labor. Therefore, uterine EMG topography can be used in preterm labor detection. In addition, uterine EMG topography can be used to monitor the effects of medication in preterm or induced labor.
References [1] Devedeux D, Marque C, Mansour S, Germain G, Duchêne J. Uterine electromyography: a critical review. Am J Obstet Gynecol 1993;169(6):1636–53. [2] Krishnamurti CR, Kitts DD, Kitts WD, Tompkins JG. Myoelectrical changes in the uterus of the sheep around parturition. J Reprod Fertil 1982;64:59–67. [3] Sigger JN, Harding R, Jenkin G. Relationship between electrical activity of the uterus and surgically isolated myometrium in the pregnant and nonpregnant ewe. J Reprod Fertil 1984;70: 103–14. [4] Germain G, Carbrol D, Visser A, Sureau C. Electrical activity of the pregnant uterus in the cynomolgus monkey. Am J Obstet Gynecol 1982;142:513–9. [5] Harding R, Poore ER, Bailey A, Thorburn GD, Jansen CAM, Nathanielsz PW. Electromyographic activity of the nonpregnant and pregnant sheep uterus. Am J Obstet Gynecol 1982;142: 448–57. [6] Méndez-Bauer C, Fielitz C, Caldeyro-Barcia R. Recording of intramuscular pressure in the human myometrium. J Appl Physiol 1961;16:573–5. [7] Ramon C, Preissl H, Murphy P, Wilson JD, Lowery C, Eswaran H. Synchronization analysis of the uterine magnetic activity during contractions. Biomed Eng Online 2005;4:55. [8] Marque C, Duchene J, Leclercq S, Panczer GS, Chaumont J. Uterine EHG processing for obstetrical monitoring. IEEE Trans Biomed Eng 1986;33:1182–7. [9] Gondry J, Marque C, Duchene J, Cabrol D. Electrohysterography during pregnancy: preliminary report. Biomed Instrum Technol 1993;27:318–24. [10] Garfield RE, Blennerhasset MG, Miller SM. Control of myometrial contractility: role and regulation of gap junctions. Oxf Rev Reprod Biol 1988;10:436–90. [11] Demianczuk N, Towell ME, Garfield RE. Myometrial electrophysiologic activity and gap junctions in the pregnant rabbit. Am J Obstet Gynecol 1984;149:485–91. [12] Verhoeff A, Garfield RE, Ranmondt J, Wallenburg HC. Myometrial activity related to gap junction area in periparturient and in ovariectomized oestrogen treated sheep. Acta Physiol Hung 1986;67:117–29.
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / i j g o
CLINICAL ARTICLE
Uterine electromyogram topography to represent synchronization of uterine contractions Wei Jiang ⁎, Gang Li, Ling Lin College of Precision Instruments and Opto-electronic Engineering, Tianjin University, China Received 3 August 2006; received in revised form 5 November 2006; accepted 15 November 2006
KEYWORDS Relative energy; Synchronization topography; Uterine electromyogram
Abstract Objective: To image the synchronization of different parts of the uterus in relation to the abdominal surface during uterine contractions using uterine electromyogram topography. Methods: Of the 20 participants, 16 were in active labor at term, 1 was in preterm labor, and 3 were experiencing failed induced labor. The signals simultaneously collected by 16 digitized channels were in the frequency ranges of 0.2 to 0.45 Hz and 0.8 to 3 Hz. Relative energies were calculated for these 2 frequency ranges and imaged by means of interpolation and transformation. Results: Uterine topographic imaging during active labor suggested good synchronization in all participants, except in one of the 3 who were experiencing failed induced labor. Most notably, synchronization was as good in preterm labor as it was in labor at term. Conclusion: Uterine electromyogram topography provided good imaging of the synchronization of uterine contractions, and could be used for further research on uterine contractility during term and preterm labor. © 2006 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.
1. Introduction Uterine contractions have been monitored by tocodynamometer, intrauterine pressure catheter, and Doppler ultrasonography. The first 2 methods have been used to record the global pressure resulting from the uterine myometrial contractions, but they cannot reflect the contractions’ synchronization and concordance. And although the third method is capable of measuring uterine muscle contractions,
⁎ Corresponding author. Tel./fax: +86 22 27406535. E-mail address: [email protected] (W. Jiang).
it is unsuitable for long-term monitoring. Thus, another clinical method is needed for labor monitoring. A uterine electromyogram (EMG), even performed in a noninvasive way with abdominal probes, can be used to image the process of muscle-fiber excitation [1]. Technically, efficient uterine contractions include 3 main factors: intensity, frequency, and synchronization. However, most studies based on single-lead recordings can only reflect the intensity and frequency of uterine contractions. On the other hand, because of differences among the materials and methods used in the research on multi-lead recordings, conclusions are not consistent. Krishnamurti et al. [2] observed that electrical activity was more frequent in the body than in the horns of the uterus and Sigger et al. [3] found
0020-7292/$ - see front matter © 2006 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ijgo.2006.11.015
Uterine electromyogram topography to represent synchronization of uterine contractions
121
relative energies and transformation was used to map the results (the topography part).
2. Methods and study participants 2.1. Participants
Figure 1 Arrangement of the 16 electrodes on the participants’ abdomen.
no valid statistical concordance between an electrical activity measured in the uterus and another in the distal part of one of the uterine horns (parts that they see as completely separated from the rest of the uterus), whereas other scientists have found electrical activities to be usually well synchronized [4–7]. In particular, Méndez–Bauer et al. [6] suggested that the contractile wave originates near the right fallopian tube and spreads very slowly throughout the uterus, and Ramon et al. [7] suggested that the spatial patterns of synchronization change and follow the periodic pattern of the uterine contraction cycle. There is thus a need to establish controversies as well as points of agreement on a solid basis. The aim of this study was to test a simpler and more representative method of showing the synchronization of the different parts of the uterus in relation to abdominal surface during labor. First, 20 electrodes made of wire leads 16 centimeters long were placed over the participants’ abdominal surface to collect bipolar signals uterine (the EMG part of the method); then, the signals were calculated as
Figure 2
Parturition data were recorded for 1 woman in preterm labor and 19 women in spontaneous or induced labor at the Shandong Zibo Center Hospital, China, between June 2005 and August 2005. The women were between 26 and 32 years old. All had bishop scores higher than 7, and estimated pregnancy durations were all between 37 and 41 weeks except for the woman who was in preterm labor at 33 weeks. The recording session lasted between 1 and 2 h. The participants were enrolled in the study they gave informed consent.
2.2. Data collection After skin preparation by cleaning and mild abrasion, electrodes 8 mm in diameter (Beckman Coulter, Inc., Fullerton, CA, USA) were placed on the women’s abdomens, approximately 5 cm apart in an array of 5 rows and 4 columns (Fig. 1). Uterine EMG signals were collected between 2 vertical electrodes. Ground electrodes were set on the hips. First, the uterine EMG signals were amplified with a gain setting of 10 on the preamplifier and filtered by a second-order high-pass filter with a cut-off frequency of 0.1 Hz to remove direct current potential. After preamplification, the signals were amplified by the main amplifiers with a gain of 100, and then filtered by a fourth-order low-pass filter with a cut-off frequency of 25 Hz to remove high-frequency noise. Then the filtered signals flowed into an analog-to-digital converter (A/DC). To improve synchronization between separate channels, two 8-channel, 14-bit chips with an input range of −2.5 V to + 2.5 V were used (A/DC MAX126; Maxim Integrated Products, Inc. Sunnyvale, CA, USA). With its 14-bit precision and the gains of 1000 provided by its analog part, the system had a resolution power of 0.6 μV, which is adequate for uterine EMGs.
Transform function (the maximum for display increases with the increase of the maximum-to-minimum ratio).
122 Table 1
W. Jiang et al. Statistical results for the uterine EMG signals obtained from 297 contractions during labor Term labor
Preterm labor
Failed labor induction Lesser intensity of contractions
No. of participants No. of Contractions max:min ≤ 1.2 1.2 < max:min < 1.4 max:min ≥ 1.4 Total number of contractions Max:min contraction, mean
16 87 138 0 225 1.2239
1
1
14 5 0 19 1.1883
17 3 0 20 1.1625
Dis-synchronization of contractions 2 0 3 30 33 1.8163
Abbreviations: EMG, electromyogram; max:min, maximum-to-minimum ratio.
The digitized data were transferred by the microprocessor to a laptop computer through a parallel port. The application software on the laptop could process real-time data and present them in different ways.
2.3. Data analysis By recording uterine signals through 16 digitized channels simultaneously during the EMG, it was possible to obtain a 2dimensional 256 gray level display of uterine EMG values ranging from low (white) to high (black). The points located between 2 neighboring electrodes were calculated by interpolation (computing the intermediary value of those measured by the electrodes), so that a smooth grayscale image could be obtained. The computed parameters used in this uterine mapping were defined as the relative energy (H/L) of uterine EMG signals, where H stands for high-frequency bands ranging from 0.8 Hz to 3 Hz, and L stands for low frequency band ranging from 0.2 Hz to 0.45 Hz. Significant changes have been shown to exist in the relative power of 2 frequency bands owing to uterine EMG bursts during the progress of labor [8,9]. All 16 channels of the conventional uterine EMG were analyzed with the same method to obtain the relative energies of the 16 leads for uterine mapping.
To display uterine topography and clearly differentiate uterine synchronization from dis-sychronization, the parameters of the 16 leads involved in the imaging process were transformed to values between 0 and 255. The effect of display was optimized by a transform function as follows: 255T1:2 ðx−minÞ ; x V¼ int maxT1:2−min where x′ is a value between 0 and 255; x is the parameter value to be transformed; min and max are the minimum and maximum values of the 16-lead parameters, and int( ) is the function for the integer part in parenthesis. In this way, the value of x′ with respect to the minimum values of the 16 parameters was 0 (white), and the value retained for the maximum was determined by the minimum-tomaximum ratio, namely: 255T1:2 ð1−min=maxÞ xmax V ¼ int 1:2−min=max As shown in Fig. 2, xmax ′ is a monotonically increasing function of max/min. With a minimum-to-maximum ratio of 2 or greater, the maximum of 16 parameters is equal to twice the minimum or
Figure 3
Uterine electromyogram topography to represent synchronization of uterine contractions
123
Figure 4 greater, which means that the dis-synchronization of uterine ′ tends to be a constant contraction is obvious. In this case, the xmax and the corresponding area on the image is black. When the ratio is less than 1.2, the synchronization of uterine contractions is good and the whole topography is white or light gray. If the ratio is between 1.2 and 2, some areas appear medium gray or dark gray, which points to a risk of dis-synchronization.
3. Results Twenty women accepted the invitation to participate in this study. Among them, 16 were in active labor, 1 in preterm labor, and the remaining 3 had failed induced labor. A total of 297 contractions were observed from these participants.
Uterine EMG signals obtained from the contractions were analyzed and are listed in Table 1. Technically, these contractions were classified as synchronous, semisynchronous, and asynchronous. For each class, a representative contraction was used as an example in this article. The results for the 3 typical examples are shown in Figs. 3, 4, and 5, respectively. The participants were also divided into 3 groupsactive labor at term, active preterm labor, and failed induction of labor. Furthermore, the latter group was divided into 2 subgroups, a dis-synchronization and a lower-intensity group, to account for the reasons for the failed induction. There were a total of 225 contractions recorded in active labor, for which the mean ± S.D. of the computed value, i.e., the minimum-to-maximum ratio, was 1.2239 ± 0.0573 (Table 1). Of these 225 contractions, 87 were synchronous.
Figure 5
124 Fig. 3a shows the 16-lead EMG recordings for a typical synchronous uterine contraction. The recording duration was 4 s. All channels had active electrical activity, but the relation between channels still needed to be determined and the 16-lead relative energies (H/L) of the EMG signals were computed (Fig. 3b). The minimum-to-maximum ratio was less than 1.2. As the whole topographic image was white or light gray, it could be judged empirically that the synchronization of the uterine contraction was good. However, according to the recordings, 138 uterine contractions were not completely synchronous. Some channels away from the umbilicus and the median vertical axis of the uterus showed no electrical activity. In this situation, the minimum-tomaximum ratio was greater than 1.2 but less than 1.4. A typical example of such contractions, which might be called semisynchronous, is shown in Fig. 4a and b. Channels 1, 2, 3, and 4 could be distinguished from the other channels. In clinical practice, the process of labor is not influenced by this kind of semisynchronization. For the EMG recordings of 19 contractions in women in preterm labor, the mean minimum-to-maximum ratio was 1.1883, i.e., identical to that for active labor contractions. The remaining 53 contractions occurred in the 3 participants experiencing failed labor induction. Two of them had 30 asynchronous and 3 semi-synchronous contractions, for which the minimum-to-maximum ratio was 1.8163 ± 0.0482, indicating dis-synchronization. Furthermore, the difference between synchronization and dis-synchronization was statistically significant (P < 0.02). The uterine EMG signal and uterine topography for one of the women with asynchronous contractions are shown in Fig. 5a and b. On the topographic image (Fig. 5b), there is an obvious difference in shade between the 2 sides of uterus, which indicates strong dissynchronization. Since the intensity and frequency of the contractions were efficient, the failure of induced labor was probably related to dis-synchronization. No cervical dilatation was obtained after 4 h of oxytocin infusion (Bachem California Inc., Torrance, CA, USA) accompanied by asynchronous contractions, but it must be pointed out that asynchronous contractions are not the only factor related to failed induction. Other factors such as the intensity and frequency of uterine contractions could also affect the process of labor, which was the case for the third woman with failed induction (the failure was caused by the low intensity of her contractions).
4. Discussion The imaging of the synchronization of uterine contractions by means of uterine EMG topography can also help to detect the origin of dysfunctional uterine activity. In this study, analysis was restricted to the relative energy of uterine EMG signals, which is not averaged over the nearby channels. The energy was computed for each channel individually, and divided by the minimum of 16 channels. This method of representing the synchronization uses the relative amplitudes of uterine EMG signals in relation to the surface of uterus. To study the degree of phase synchronization of the whole uterus, other estimates of statistical entropy would probably be more appropriate for data analysis.
W. Jiang et al. Previous work has demonstrated that successful progress of labor is related to an increase in gap junction, which is thought to be responsible for improving electrical coupling between myometrical cells. The synchronization and coordination of contractile events of different uterine myometrial regions is the result of the increased gap junction, and helps fetal expulsion [10–12]. Therefore, uterine synchronization monitoring can be used in the clinical setting to display the progress of labor. To some extent, this study support the view that uterine electrical activity is usually well synchronized despite semisynchronization in channels away from the umbilicus and the median vertical axis of the uterus. Dis-synchronization reflects the poor electrical coupling of different part of uterus, and is related to induced labor failure. The uterine EMG topography is identical in preterm labor and labor at term because of the increased gap junction in preterm labor. Therefore, uterine EMG topography can be used in preterm labor detection. In addition, uterine EMG topography can be used to monitor the effects of medication in preterm or induced labor.
References [1] Devedeux D, Marque C, Mansour S, Germain G, Duchêne J. Uterine electromyography: a critical review. Am J Obstet Gynecol 1993;169(6):1636–53. [2] Krishnamurti CR, Kitts DD, Kitts WD, Tompkins JG. Myoelectrical changes in the uterus of the sheep around parturition. J Reprod Fertil 1982;64:59–67. [3] Sigger JN, Harding R, Jenkin G. Relationship between electrical activity of the uterus and surgically isolated myometrium in the pregnant and nonpregnant ewe. J Reprod Fertil 1984;70: 103–14. [4] Germain G, Carbrol D, Visser A, Sureau C. Electrical activity of the pregnant uterus in the cynomolgus monkey. Am J Obstet Gynecol 1982;142:513–9. [5] Harding R, Poore ER, Bailey A, Thorburn GD, Jansen CAM, Nathanielsz PW. Electromyographic activity of the nonpregnant and pregnant sheep uterus. Am J Obstet Gynecol 1982;142: 448–57. [6] Méndez-Bauer C, Fielitz C, Caldeyro-Barcia R. Recording of intramuscular pressure in the human myometrium. J Appl Physiol 1961;16:573–5. [7] Ramon C, Preissl H, Murphy P, Wilson JD, Lowery C, Eswaran H. Synchronization analysis of the uterine magnetic activity during contractions. Biomed Eng Online 2005;4:55. [8] Marque C, Duchene J, Leclercq S, Panczer GS, Chaumont J. Uterine EHG processing for obstetrical monitoring. IEEE Trans Biomed Eng 1986;33:1182–7. [9] Gondry J, Marque C, Duchene J, Cabrol D. Electrohysterography during pregnancy: preliminary report. Biomed Instrum Technol 1993;27:318–24. [10] Garfield RE, Blennerhasset MG, Miller SM. Control of myometrial contractility: role and regulation of gap junctions. Oxf Rev Reprod Biol 1988;10:436–90. [11] Demianczuk N, Towell ME, Garfield RE. Myometrial electrophysiologic activity and gap junctions in the pregnant rabbit. Am J Obstet Gynecol 1984;149:485–91. [12] Verhoeff A, Garfield RE, Ranmondt J, Wallenburg HC. Myometrial activity related to gap junction area in periparturient and in ovariectomized oestrogen treated sheep. Acta Physiol Hung 1986;67:117–29.