Colorectal Distention-Induced EMG Response

The EMG activity reflects the contraction of the external oblique muscle in response to colorectal distention (CRD). A balloon was inserted into the colorectum 5 cm from the anal verge. The balloon was then distended sequentially at a pressure of 20, 30, 40, 50 and 60 mmHg and maintained for 20 s with a 4 min interval between two distention pressures. The EMG was recorded with a frequency range of 10 to 5000 Hz using an EMG amplifier (EMG 100C; Biopac systems, Inc, Santa Barbara, CA, USA). The area under the curve (AUC) of EMG was calculated by the software (Acknowledge; Biopac System, Inc., Santa Barbara CA). The final EMG data were presented as a percent increase against the baseline value before each distention: the AUC of the EMG activity during the 20 s distention divided by the 20 s baseline was defined as the EMG response to CRD^{44 (link)}.