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9 Electrical Impedance, a Sensory System for Detection of Rectal Filling After Anorectal Reconstruction [2001년 2월 DCR] 2011-11-12 2971
 
Experimental Study of Rectal Impedance Measurements and Defecation in Dogs
Eric Rullier, M.D.,*t Jean Fioramonti, Ph.D.,Jean Woloszko, M.D., Ph.D.,Lionel Bueno, Ph.D.
 
From the Department of Neurogastroenterology and Nutrition, Institut National de Recherche Agronomique, Toulouse, France, Department of Surgery, Saint-Andre Hospital, Bordeaux, France, and Bakken Research Center, Maastricht, the Netherlands
 
BACKGROUND: 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 m determine whether monitoring of rectal electric impedance can give information about fullness or motility of the rectum.
METHODS: Four aduk female beagle dogs underwent rectal electric impedance nmasurements using a
bipolar electrode implanted on the rectal wall. An alternating current of 1 /xA 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.
RESULTS: The basal rectal impedance was 682 + 19 fZ. During the period of observation (n= 4), 84 inapedance waves (amplitude, 72 + 2 ~; 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-dnration 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.
CONCLUSIONS: 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.
 
DISCUSSION
Current techniques for total anorectal reconstruction allow the anatomic restoration of the anorectum
but dramatically modify the physiologic functions of this area. Indeed, patients rarely have spontaneous
defecations, and most of them use enemas to be continent. This is due mainly to the complete loss
of sensitivity, which prevents coordination between the neosphincter and the colonic activity. The use of
colonic impedance measurements as an alternative sensory system after anorectal reconstruction is attractive for two reasons. First, impedance measurements allow detection of rectal filling or modifications of the rectum wall. 16, 19 Second, electric impedance may be integrated with the electrostimulated graciloplasty procedure because both systems depend on electric technology.
 
When fecal matter enters the rectum, impedance increases because the lumen is filled by formed stools
or because the rectal wall is distended. Changes of impedance during or after rectal emptying may be a
result of modifications of either the rectal wall or the rectal fullness. The former, i.e., contraction of the
rectum, would induce a very short impedance wave occurring before defecation. The latter would induce
a short or long impedance wave depending on volume of stools, and it would occur after defecation. In
the preliminary study (Woloszko et al., unpublished data) performed in pigs, it was shown that there is a
relationship between impedance variations and contractile activity of the colon, suggesting that detection
of a propulsive activity of the colon is possible and consequently a control of the neosphincter: activation
of the implanted pulse generator should be triggered by detection of propulsive activity to avoid uncontrolled evacuation of stools. Our results confirmed this observation. However, concurrent observation of rectal impedance and defecation in dogs showed that significant impedance variations occurred after defecation and not before. Moreover, most of the impedance waves occurring after defecation had a long duration, the latter probably being related to rectal refilling, as suggested by the impedance waves' profile showing a slow and progressive recovery. Thus, in our study, which used a bipolar intramural electrode, these two findings suggest that tile significant variations of impedance depend mainly on modifications of the rectal contents and not of the rectal wall.
 
Very few studies have demonstrated the relationships between electric or mechanical activities of the
colon and the actual transport or evacuation of feces. 20, 21 To our knowledge, the present study is the
first to demonstrate a relation between the electric impedance activity and stool movements. Moreover,
this was achieved using a single intramural bipolar electrode, whereas mukiple sensors are usually required to evaluate colonic motility. 22 Variations of rectal impedance in the dogs are characterized by two parameters, amplitude and duration, correlated with frequency and volume of defecation, respectively. Accordingly, two groups of impedance were isolated. The first group includes impedance waves of Types I, II, and III, related with eventual partial defecations. The second group includes waves of Type IV, related with complete defecations. These two groups of waves can be easily differentiated: waves of the first group had an amplitude that was positive or <10 percent, whereas waves of the second group were negative and >10 percent (Table 1).
 
Until now, total anorectal reconstruction by dynamic graciloplasty has been performed using a constant
continuous stimulation of the neosphincter. Electric activation of the muscle is manually stopped by the patient before defecation and restored afterward. Stimulation of the transposed muscle is not required continuously to the same degree. It depends on the fullness of the distal colon. Colonic electric
impedance measurements may provide automatic modulation of the neosphincter, giving a high pressure when the colon is full and a low pressure when the colon is empty. After anorectal reconstruction, patients would have an implantation of definitive impedance electrodes on the serosa of the distal colon. The neurostimulator would be connected to both the impedance electrodes and the neosphincter stimulation electrodes. Thus, the system would be a completely autonomous feedback loop, allowing us to determine the ideal time for defecation. Activation of the electric stimulator, i.e., of the neosphincter, should be stopped automatically after the occurrence of a Type IV impedance wave because in this case the rectum is empty. Afterward, an automatic activation of the stimulator should be triggered after rectal refilling, i.e., when a given percentage of the basal impedance, which remains to be determined, is restored. On the other hand, the stimulator should automatically be activated after the occurrence of Type I, II, or III impedance waves, even after a defecation, because in these cases the colon is never totally empty.
 
Automatic modulation of the neosphincter after total anorectat reconstruction may improve quality of
life of the patients. Continence should be improved by intermittent but significant increase of the pressure
of the neosphincter. Risk of ischemic colonic perforation induced by continuous high tension of the
graciloplasty observed in some series 5' 23 may be decreased by intermittent stimulation of the neosphincter. Impedance measurements may become a real sensory system that enables the patient to know when the colon is full (stimulator on: tension of the transposed gracilis muscle) and when the colon is empty (stimulator off. relaxation of the transposed gracilis muscle). Moreover, this system may allow a more rational use of the nonrenewable energy of the pulse generator.
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