The importance of the orientation of the electrode plates in recording the external anal sphincter EMG by non-invasive anal plug electrodes

Abstract

Two non-invasive anal plug electrodes of similar size have been compared, one with the electrode plates orientated circularly in the anal canal and the other with the plates in the long axis of the anal canal. There was a significant increase in the amplitude in the EMG signals recorded at rest and during squeeze from the external anal sphincter with a longitudinally placed electrode in 117 patients. Inappropriate contraction of the external anal sphincter when straining at stool was more readily detected using the longitudinal electrode in 52 patients investigated for intractable constipation. The longitudinal electrode detected the amplitude of the response to the elicitation of a pudeno-anal reflex more readily than the circular electrode. When in 12 of the 117 the pudeno-anal reflex EMG signal was either absent or not detected with the circumferential plug electrode, the longitudinal electrode detected the presence of a low amplitude response in 11 of these. When the non-invasive longitudinal electrode was compared to invasive fine wire stainless steel electrodes, a correlation was found for external anal sphincter resting EMG (r = 0.99, p less than 0.01), voluntary squeeze EMG (r = 0.99, p less than 0.001) and strain EMG (r = 0.91, p less than 0.01). The longitudinal anal plug electrode thus facilitates surface acquisition of EMG activity.

Multichannel Surface EMG for the Non-Invasive Assessment of the Anal Sphincter Muscle

“…When single electrode bar pairs or pads are adopted, their position with respect to the anatomical characteristics of the sphincter muscles is of pivotal importance [7]. Binnie et al [7], comparing the use of two rings placed transversally in the sphincter canal with respect to the use of two flat bars placed longitudinally, concluded that the latter was better than the former since higher signal amplitude was recordable with that arrangement.…”

“…The multichannel method allows getting additional information with respect to classic bipolar recordings. The use of an internal plug, as required in the technique herein presented, does not significantly alter the muscle functions and the contractile mechanisms [7]. …”

“…Comparison between recordings obtained by different systems has also been reported [7, 8, 9], with emphasis on the relevant effect that the type of recording has on the signal features [7]. The sensitivity of the recording to these factors limits the applicability of the method.…”

“…This detection modality has been used in many studies on the assessment of the external anal sphincter (EAS) functions [7, 8, 9, 10], with a variety of electrode shapes, sizes, and locations. Signals recorded by the bipolar configuration are affected by anatomical, geometrical, physical and detection system parameters [11].…”

Standard characteristics of functional state of the rectal obturator muscles obtained from neurophysiological examination

“…Одним из самых распространенных и хорошо вос-производимых методов остается неинвазивная оценка функционального состояния ЗАПК и тазового дна с помощью интерференционной ЭМГ [9,11,12,[20][21][22][23][24]. Для регистрации биоэлектрической активности (БЭА) мышц ЗАПК и тазового дна используются вну-трианальные или игольчатые электроды.…”