No abstract

The aim of the study was to further elucidate the pathophysiology of irritable bowel syndrome and its subgroups by examining and comparing alterations in small bowel motility, specifically phase II and phase III components of the migrating motor complex. Prolonged recordings of interdigestive small bowel motility were obtained during both diurnal and nocturnal periods in 20 patients with irritable bowel syndrome--10 with predominant constipation and 10 with predominant diarrhea--and in 10 healthy subjects. Diurnal amplitude (mean +/- SD) of phase III activity fronts was lower (P less than 0.05) in constipation-predominant patients (16.3 +/- 3.1 mm Hg) than in diarrhea-predominant patients (20.2 +/- 3.1) or controls (20.9 +/- 2.7). Similar findings were observed nocturnally. Phase III cycle length was also significantly prolonged diurnally in constipation-predominant patients when compared to the other groups. In the diarrhea-predominant group repetitive and rapidly propagated bursts of contractions were observed in eight patients, and this pattern occupied a significantly greater proportion of phase II motor activity than in controls. These alterations in phase II and in phase III components of the migrating motor complex suggest that both local (enteric) and more central mechanisms may operate to produce intestinal dysmotility in the irritable bowel syndrome and that these mechanisms differ according to the predominant alteration of bowel habit.

Psychologic stress may be a provoking factor in the alterations in phase-2 motor activity of the migrating motor complex (MMC) which have been recorded in patients with the irritable bowel syndrome (IBS). To test this, changes in phase-2 duodenojejunal motor activity during 20 min of psychologic stress in 10 patients with IBS were compared with those shown by 10 healthy subjects. Autonomic arousal in response to the stressor was assessed by cardiovascular responses and self-reported levels of anxiety and tension. IBS and controls showed a significant cardiovascular and subjective response to stress which was comparable in the two groups. In general, duodenal phase-2 motor activity was suppressed during stress in both IBS and controls. Jejunal motor activity showed a similar inhibitory response in both groups, but the change in motility index was significant for controls only. Qualitatively, stress did not cause clustered contractions in either the IBS or the control group. However, in IBS patients with clustered contractions in the basal period there was inhibition of this pattern during stress. These findings suggest that acute psychologic stress profoundly suppresses, rather than enhances, duodenojejunal MMC phase-2 motility in healthy subjects. IBS patients, irrespective of their underlying phase-2 motor pattern show similar, although less marked, changes in motility.

The acute effects of both cigarette smoking and nicotine on postprandial mouth-cecum transit were studied in 20 habitual smokers, 10 males and 10 females. Mouth-cecum transit time was measured by the breath hydrogen technique, following ingestion of a standard mixed liquid meal. Each subject was studied on four separate occasions, either (1) sham or actively smoking two standard cigarettes, commencing 20 min after the meal, or (2) chewing two placebo or nicotine tablets over a 60-min period, commencing immediately after the meal. The time of administration of these stimuli was designed to minimize the effects on mouth-cecum transit time of alterations in gastric emptying. Mouth-cecum transit time was prolonged in response to both smoking [median and interquartile range: 120 (95, 150) min vs 100 (75, 140) min, P = 0.01] and nicotine [120 (80, 170) min vs 100 (70, 140) min, P = 0.002]. No difference was observed between sexes with respect to nicotine; the effect of smoking on mouth-cecum transit time, however, was less pronounced in females compared to males [difference active-placebo: 10 (10, 20) min vs 35 (20, 60) min, P = 0.01]. We conclude that acute cigarette smoking delays mouth-cecum transit time, an effect most likely due to nicotine.

Recordings of fasting duodenojejunal motor activity were obtained during a controlled 20‐min period of psychological relaxation in 10 patients with irritable bowel syndrome (IBS) and 10 healthy subjects. The IBS group showed a significant decline in their level of arousal (on both cardiovascular and subjective measures) in response to relaxation; such alterations were minimal in the control group. Both groups, however, demonstrated significant inhibition of phase 2 activity (motility index, contractile frequency and amplitude) of the migrating motor complex in response to relaxation, and the magnitude of the response did not differ between the two groups. Clustered contractile activity present in 4 IBS patients was also suppressed during the relaxation period. There were no correlations between changes in the level of arousal and the degree of motor suppression in either IBS patients or controls. These findings demonstrate that psychological relaxation therapy can profoundly influence patterns of small bowel motility, and shed light on the mechanisms by which psychological intervention therapy appears to be effective in IBS.