Abstract
Introduction and hypothesis
Locating the innervation zones (IZs) of the external anal sphincter (EAS) is helpful to obstetricians to identify areas particularly vulnerable to episiotomy in pregnant women. The aim was to investigate the motor unit (MU) properties of the EAS during voluntary contractions.
Methods
Electromyographic signals were detected, from 478 pregnant women, by means of an intra-anal cylindrical probe carrying a circumferential array of 16 electrodes. The signals were decomposed into the constituent MU action potential trains and 5,947 templates were extracted and analyzed in order to identify the IZ position.
Results
MUs innervated at one end are concentrated in the dorsal portion of the sphincter, while MUs innervated in the middle are distributed symmetrically in the left and right portions of the EAS. The angular propagation velocity was estimated for each MU resulting in 260 ± 45 rad/s, corresponding to 1.8 m/s on the probe surface and to about 4 m/s at a radial depth of 10 mm from the probe surface.
Conclusions
A novel method for identification and classification of MUs of the EAS is proposed and applied to a large-scale study. It is possible to distinguish MUs of the EAS in a minimally invasive way and identify their IZs. This information should be used to plan episiotomies and minimize risks of EAS denervation.
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Acknowledgments
This work was sponsored by Projects TASI (Else Kroner-Fresenius-Stiftung, Compagnia di San Paolo) and TASI-2 (Compagnia di San Paolo). The authors are grateful to Drs. Maggiorino Barbero, Diego Riva, Dace Rezeberga, Olesja Zelenova, Pier Dino Rattazzi, Adolf Lukanovic, Anna Maria Paoletti, Donatella Marongiu, Vicky Rabino, Olexander Protsepko, Lena Martynshyn, Marina Storoshuk, Kaven Baessler, and Milena Ludescher for their help in recruiting patients and making EMG measurements.
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Cescon, C., Raimondi, E.E., Začesta, V. et al. Characterization of the motor units of the external anal sphincter in pregnant women with multichannel surface EMG. Int Urogynecol J 25, 1097–1103 (2014). https://doi.org/10.1007/s00192-014-2356-3
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DOI: https://doi.org/10.1007/s00192-014-2356-3