Electrical impedance, a sensory system for detection of rectal filling after anorectal reconstruction: experimental study of rectal impedance measurements and defecation in dogs.

Abstract

Total anorectal reconstruction with dynamic graciloplasty is an alternative to a permanent colostomy; however, perfect continence cannot be achieved because of loss of sensitivity. This study was designed in dogs to determine whether monitoring of rectal electric impedance can give information about fullness or motility of the rectum. Four adult female beagle dogs underwent rectal electric impedance measurements using a bipolar electrode implanted on the rectal wall. An alternating current of 1 microA at a frequency of 4 kHz was applied between the two wires. Variations of impedance (called impedance waves), defecations, and weight of stools were recorded and analyzed. The basal rectal impedance was 682+/-19 omega. During the period of observation (n = 4), 84 impedance waves (amplitude, 72+/-2 omega; duration, 58+/-11 minutes) were observed and 33 defecations (weight of stools, 74+/-6 g) occurred. Four types of impedance waves were identified and classified into two groups: low-amplitude or short-duration waves (Types I, II, and III), and high-amplitude and long-duration waves (Type IV). Frequency of defecation was associated with the amplitude of the waves. The weight of stools was correlated with the duration of the waves (r = 0.574, n = 27, P = 0.002). Types I, II, and III waves were correlated with eventual partial defecations, whereas Type IV waves were correlated with complete defecations. After defecation, no spontaneous new defecation occurred before recovering at least 80 percent of the basal impedance. Rectal impedance variations are correlated with defecation in a canine model, and single bipolar measurements provide a suitable evaluation of rectum fullness. This suggests the possible use of impedance signals to control electrostimulated graciloplasty after anorectal reconstruction.