Treatment of irritable bowel syndrome with colonic pacing: evaluation of pacing parameters required for correction of the "tachyarrhythmia" of the IBS

BACKGROUND/AIMS: A recent study of the electromyographic (EMG) activity of irritable bowel syndrome (IBS) has shown that the frequency, amplitude and conduction velocity of the slow waves (SWs) of the sigmoid colon (SC) were significantly higher in IBS patients than in the healthy volunteers. The SW rhythm was irregular. A "tachyarrhythmic pattern" was characteristic of the IBS. The SC pressure in the IBS was also significantly higher than that of the healthy controls. We suggested that the cause of IBS is related to an aberrant focus in one or more of the colonic pacemakers which possibly triggers abnormal impulses to the colon. We hypothesized that stimulation of the pacemaker which delivers electric waves to the SC, may correct the abnormal electric waves and eliminate the IBS symptoms. In this communication we tried to define the adequate pacing parameters necessary for normalization of the tachyarrhythmic pattern of the electric waves in IBS. METHODOLOGY: Nineteen subjects with IBS were divided into a study group (age 48.6+/-9.8 years; 7 women, 4 men) and a control group (age 47.6+/-9.2 years; 5 women, 3 men). The study also included 8 healthy volunteers (47.9+/-9.7 years; 5 women). Three 28-gauge cardiac pacing electrodes were used: one for pacing applied to the pacemaker at the colosigmoid junction (CSJ) and 2 for recording applied to the SC mucosa. In the study group, the CSJ electrode was stimulated using an electrical stimulator which delivered a constant current. The optimal pacing parameters had been determined after repeated trials with different variables. In the control group, recording was done without pacemaker activation. The SC pressure was measured by a 10-F saline-perfused tube. RESULTS: In the healthy volunteers, the basal SWs were regular and followed or superimposed by action potentials (APs). Pacing produced a significant increase in the SW variables and SC pressure; the latency was 20.3+/-3.6 s. The study and the control group exhibited a basal tachyarrhythmic pattern and a significantly higher SC pressure than the healthy volunteers. Pacing of the study group effected lowering of the SW variables and SC pressure which did not show a significant difference against those of the healthy volunteers at rest. The optimal pacing parameters comprised an amplitude of 6 mA, a pulse width of 150 ms and a 25% higher frequency than that of the already recorded basal colonic waves. The control group showed no change in the tachyarrhythmic pattern. CONCLUSIONS: CS pacing parameters were identified and succeeded in normalizing the tachyarrhythmic pattern of the IBS. We suggest that this method be used for the treatment of patients with IBS when other measures have failed to cure the condition.     

On the pathogenesis of rectocele: the concept of the rectovaginal pressure gradient

Coughing or straining evokes reflex bulbocavernosus (BCM) and puborectalis (PRM) muscle contraction, which apparently transforms the vagina into a closed high-pressure cavity [13]. This elevated vaginal pressure counteracts the increased intra-abdominal pressure and the tendency of the uterus to prolapse, and also supports the rectovaginal septum against the high straining-induced intrarectal pressure and possible consequent rectocele (posterior vaginal prolapse) formation. We investigated the hypothesis that a weak BCM and PRM share in the genesis of rectocele by changing the rectovaginal pressure gradient. Twenty-three women with rectocele (mean age 43.2±6.6 years) and 12 healthy women volunteers (mean age 41.6±6.2 years) were studied. The response of the intrarectal (intra-abdominal) and intravaginal pressure, as well as the EMG activity of the BCM and PRM to straining or coughing, was recorded. In the healthy volunteers the rectal and vaginal pressures showed a significant increase on coughing or straining, with no significant difference between the rectal or vaginal pressures. Also, the BCM and PRM EMG activity exhibited a significant increase. Rectocele patients showed a significantly low resting vaginal pressure. The increase in rectal and vaginal pressure, as well as of the EMG activity of the BCM and PRM on straining or coughing, was significantly lower and the latency of the EMG response was significantly longer than those of the healthy volunteers. A difference in the rectovaginal pressure gradient showing a significant increase in the rectal against the vaginal pressure, particularly on coughing or straining, is suggested to be the basic factor in the genesis of rectocele. This pressure difference appears to be caused by diminished BCM and PRM contractile activity. A disrupted rectovaginal septum is not a prerequisite for rectocele formation, as the septum appears normal in obstructed defecation despite the common occurrence of rectocele. A histopathologic study of the septum in rectocele seems necessary.Abbreviations BCM Bulbocavernosus muscle - PRM Puborectalis muscle - EMG Electromyogram Editorial Comment: The investigation demonstrated decreased EMG activity and vaginal pressure in the women with rectoceles, especially during increased intra-abdominal pressure, compared to normal controls. Based on these data, the authors theorize that the decreased vaginal pressure results from poor tone and blunted reflex contraction of the BCM and PRMS during increases in intra-abdominal pressure, which in normal women closes the vaginal hiatus causing an equilibration of increased intra-abdominal pressure on the rectal and vaginal sides of the rectovaginal septum. This is a novel theory for the pathogenesis of rectocele and is supported by these preliminary data. The fact that the subjects had a stool frequency of less than twice weekly is more consistent with defecatory dysfunction secondary to a motility disorder rather than outlet obstruction. This raises the question of whether the rectocele is a result of the defecatory dysfunction rather than causative, and affects the external validity of the study population. Additionally, the theory fails to explain the association of paradox with rectocele. Nevertheless, this theory merits further investigation as one of several potential etiologies of rectocele.     

Study of the role of the second defecation reflex: anorectal excitatory reflex in the pathogenesis of constipation

BACKGROUND: Previous studies have shown that anal distension caused rectal contraction, an action mediated through the anorectal excitatory reflex. Anal anesthetization aborted rectal contraction and rectal evacuation was induced by excessive straining. We investigated the hypothesis that inhibition or absence of the anorectal excitatory reflex could lead to constipation. METHODS: We studied 18 patients (mean age +/- SD: 40.6 +/- 5.8 years, 14 women) with rectal inertia, 14 (41.7 +/- 6.6 years, 12 women) with puborectalis paradoxical syndrome, and 10 healthy volunteers (37.9 +/- 4.8 years, 8 women). The rectum was filled with normal saline until urge and then evacuated; residual fluid was calculated. The anal and rectal pressure response to anal balloon distension in increments of 2 mL of saline was recorded by a two-channel microtip catheter. RESULTS: In the healthy volunteers, saline was evacuated as a continuous stream without straining except occasionally at the start of evacuation; no residual fluid was encountered. Anal balloon distension effected notable rectal pressure increase. In rectal inertia patients, evacuation occurred in small fluid gushes produced with excessive straining; residual fluid of large volume was collected. Anal balloon distension up to 10 mL produced no notable rectal pressure changes. The patients with PPS failed to evacuate more than a few mL of fluid despite excessive straining; the volume of residual fluid was considerable. Anal balloon distension caused a notable rectal pressure rise. The results were reproducible. CONCLUSIONS: These results suggest that the defecation reflexes (rectoanal and anorectal) are absent in rectal inertia patients and this presumably denotes a neurogenic disorder. The anorectal reflex is active in puborectalis paradoxical syndrome, but the rectoanal reflex is not, indicating a possible myogenic defect in the puborectalis muscle.     

Role of sympathetic innervation in the defecation mechanism: a novel concept of its function

BACKGROUND/OBJECTIVE: Because the role of sympathetic innervation in the defecation mechanism is still vague and unidentified, this study was performed to investigate this issue. METHODS: The effect of individual administration of alpha- and beta-adrenoceptor blocking agents (3 mg/kg phentolamine mesylate and 1 mg/kg propranolol hydrochloride, respectively) and the effect of thoracolumbar sympathectomy on anal and rectal pressures was studied in 13 mongrel dogs. Pressures were measured by a 2-channel microtip catheter. Bilateral thoracolumbar sympathectomy was performed by excising the sympathetic ganglia from T11 to L2. Incremental rectal filling using a rectal balloon with simultaneous anal and rectal pressure measurements was continued until balloon expulsion was achieved. RESULTS: Rectal balloon distension with 30 to 40 mL of saline affected rectal pressure increase (P < 0.001 ), anal pressure decrease (P < 0.01), and balloon expulsion. Following administration of either phentolamine or propranolol or after thoracolumbar sympathectomy, rectal pressure declined (P < 0.05), but anal pressure showed no change (P > 0.05). At a rectal balloon volume of 50 to 60 mL of saline, rectal pressure increased (P < 0.001), anal pressure decreased (P < 0.01), and the balloon was expelled. CONCLUSION: Sympathetic rectal innervation may have a role during both the filling and evacuation phases of the defecation mechanism. During rectal filling, it most likely maintains rectal compliance. During evacuation in cases of rectal sympathetic block or denervation, a larger volume than usual of rectal distension is needed to induce rectal contraction and evacuation.     

Role of tunica albuginea in erection: is it a dynamic or a static role?

The tunica albuginea (TA) of the penis is claimed to share in erectile mechanism by compressing the emissary veins passing through it. Apparently this claim is theoretical as no experimental studies could be traced in literature proving this concept. We investigated the hypothesis that TA acts as a cover to corpora cavernosa (CC) and spongiosa (CS) and does not have an active role in erectile mechanism. Penises of 9 dogs were degloved and TA was divided at upper, middle and lower 1/3 of the penis. The intracorporal and glans penis (GP) pressures were measured in the TA-covered and non-covered parts of CC and CS in the flaccid and erectile phases. Sham operation, without performing the TA incisions, was done in 7 control animals. In the test animals, intracorporal pressure (ICP) in the non-TA covered corpora and in GP recorded in flaccid phase a mean of 12.2 +/- 0.8 cmH2O for CC and 11.3 +/- 0.7 cmH2O for the CS and GP, and in the erectile phase 98.4 +/- 8.6 and 76.2 +/- 9.3 cmH2O, respectively. There was no significant difference between covered and non-covered corpora or between test and control animals. In conclusion, the TA seems to act as a cover to the corporal tissue. Its absence did not change ICP.     

Does the composition of voided urine reflect that of the renal pelvis?

Studies have shown that the urothelium has a transport function and that urine composition changes on its way through the urinary tract. In this study, we investigated the hypothesis that the composition of voided urine differs from and does not reflect that of the renal pelvis. Urine samples were obtained from the renal pelvis and voided urine of 18 healthy volunteers (mean age 36.2 ± 5.1 SD years, 10 men, 8 women). The pH was determined using a pH electrode, osmolality by means of micro-osmometry and Na and K using flame photometry. In comparison to the urine of the renal pelvis, voided urine showed significant increases in pH, osmolality and Na and K concentrations (P < 0.05 for each). There were no significant differences in gender and age. This study has demonstrated that the pH, osmolality, Na and K of voided urine differ significantly from the values in the renal pelvis. Urine composition is thus modified as it passes through the urinary tract, which would support the concept of a dynamic urothelium. The composition of voided urine does not seem to compare to renal pelvic urine. This concept needs to be considered in urine analysis evaluation and its relation to renal function.     

Role of the rectosigmoidal junction in fecal continence: concept of the primary continent mechanism

HYPOTHESIS: At mass contraction of the descending colon, the colonic contents stop at the sigmoid colon (SC) and do not pass directly to the rectum. We investigated the hypothesis that a continent mechanism seems to exist at the rectosigmoidal junction (RSJ), preventing the direct passage of stools from the descending colon to the rectum. METHODS: The SC in 16 healthy volunteers (mean +/- SD age, 38.6 +/- 10.2 years; 9 men and 7 women) was distended with an isotonic sodium chloride solution-filled balloon, and the pressure response of the RSJ and the rectum was recorded at rapid and gradual filling of the balloon. The test was repeated after the SC and RSJ were anesthetized separately. RESULTS: Rapid SC balloon distension with a mean +/- SD of 52.1 +/- 3.6 mL of isotonic sodium chloride solution effected an RSJ pressure increase to a mean +/- SD of 67.8 +/- 18.4 cm H(2)O (P<.01) with no rectal pressure response (P>.05). Slow SC filling produced a progressive increase in RSJ pressure but no rectal pressure change. At a mean +/- SD SC distending volume of 86.3 +/- 4.1 mL, the RSJ pressure decreased to 9.6 +/- 2.8 (P<.01), and the balloon was dispelled to the rectum; rectal pressure increased (P<.001), and the balloon was expelled to the exterior. The RSJ pressure did not respond to distension of the anesthetized SC. CONCLUSIONS: Contraction of the RSJ at rapid SC distension with big volumes implies a reflex relationship that we call the RSJ guarding reflex. This reflex seems to prevent the descending colon contents from passing directly to the rectum. It is considered the first continent reflex and may serve as an investigative tool in the study of fecal incontinence.