Relationship between ultrasound measurements of tissue thickness, manometry and multichannel sEMG of the external anal sphincter

Cescon, Corrado and Destefano, Ines and Ferronato, Marco and Scaglia, Marco and Merletti, Roberto (2009) Relationship between ultrasound measurements of tissue thickness, manometry and multichannel sEMG of the external anal sphincter. In: 19th World Congress on Ultrasound in Obstetrics and Gynecology, 13-17 Sept 2009, Hamburg, Germany.

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Abstract

The probability of sphincter damage and the prevalence of anal incontinence have been estimated in the literature in relation to episiotomy rates. Injury to the pudendal nerve from prior obstetric trauma is described as the principal risk factor in women (Wheeler et al. 2007). The current knowledge of the external anal sphincter (EAS) is limited to global strength indexes (manometry), to structural data (ultrasonography, MRI, and anatomical studies on cadavers) and to local electrophysiological properties. This work focuses on detection and interpretation of multichannel surface electromyography (sEMG) of the EAS. We investigated the relationship between sEMG parameters, manometric measurements and anatomical parameters measured with endoanal 3D ultrasound. The study was conducted on 32 female patients (Age:48.7±12yrs). A novel anal probe was used to record multichannel sEMG signals at different depths during maximal voluntary contractions. The probe holds three circumferential arrays of 16 equally spaced silver bar electrodes. Manometric measurements were performed on a subset of 29 patients. Endoanal 3D ultrasound images were detected on a subset of 18 patients. Information about innervation zone position, sEMG amplitude, and motor unit discharge rate was obtained with innovative signal processing techniques. Knowledge of innervation zone location could be valuable in performing episiotomy with minimal risk of EAS denervation. Negative correlation was observed between sEMG amplitude and the thickness of anal mucosa and internal sphincter with Pearson's linear correlation coefficient r=-0.48 (p<0.05). Positive correlation was observed between sEMG amplitude and the maximum sphincter pressure r=0.37 (p<0.05). The information extracted from sEMG signals is complementary to that provided by ultrasound images and manometry. The technological innovation described in this work is promising for the investigation of pelvic floor pathologies and for episiotomy planning.

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