title: Vagal dysfunction in irritable bowel syndrome assessed by rectal distension and baroreceptor sensitivity.
abstract: Autonomic nervous system dysfunction has been implicated in the pathophysiology of irritable bowel syndrome (IBS). This study characterized the autonomic response to rectal distension in IBS using baroreceptor sensitivity (BRS), a measure of autonomic function. Rectal bag pressure, discomfort, pain, ECG, blood pressure and BRS were continuously measured before, during and after rectal distension in 98 healthy volunteers (34 +/- 12 years old, 52 females) and 39 IBS patients (39 +/- 11 years old, 35 females). In comparison with the healthy volunteers, IBS patients experienced significantly more discomfort (69 +/- 2.2% vs 56 +/- 3.6%; P < 0.05), but not pain (9 +/- 1.4% vs 6 +/- 2.4%; ns) with rectal distension despite similar distension pressures (51 +/- 1.4 vs 54 +/- 2.4 mmHg; ns) and volumes (394 +/- 10.9 vs 398 +/- 21.5 mL; ns). With rectal distension, heart rate increased in both healthy volunteers (66 +/- 1 to 71 +/- 1 bpm; P < 0.05) and IBS patients (66 +/- 2 to 74 +/- 3 bpm; P < 0.05). Systolic blood pressure also increased in both healthy volunteers (121 +/- 2 to 143 +/- 2 mmHg; P < 0.05) and patients (126 +/- 3 to 153 +/- 4 mmHg (P < 0.05) as did diastolic blood pressure, 66 +/- 2 to 80 +/- 2 mmHg (P < 0.05), compared with 68 +/- 3 to 84 +/- 3 mmHg (P < 0.05) in IBS patients. The systolic blood pressure increase observed in IBS patients was greater than that seen in healthy volunteers and remained elevated in the post distension period (139 +/- 3 mmHg vs 129 +/- 2 mmHg; P < 0.05). IBS patients had lower BRS (7.85 +/- 0.4 ms mmHg(-1)) compared with healthy volunteers (9.4 +/- 0.3; P < 0.05) at rest and throughout rectal distension. Greater systolic blood pressure response to rectal distension and associated diminished BRS suggests a compromise of the autonomic nervous system in IBS patients.
authors.affiliation: Department of Medicine, McMaster University, Hamilton, ON, Canada. spaziar@mcmaster.ca
authors.forename: R
authors.initials: R
authors.lastname: Spaziani
authors.forename: A
authors.initials: A
authors.lastname: Bayati
authors.forename: K
authors.initials: K
authors.lastname: Redmond
authors.forename: H
authors.initials: H
authors.lastname: Bajaj
authors.forename: S
authors.initials: S
authors.lastname: Mazzadi
authors.forename: J
authors.initials: J
authors.lastname: Bienenstock
authors.forename: S M
authors.initials: SM
authors.lastname: Collins
authors.forename: M V
authors.initials: MV
authors.lastname: Kamath
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D004108:Dilatation, Pathologic; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D043183:Irritable Bowel Syndrome / Q000503:physiopathology*; D008297:Male; D017288:Pain Threshold; D011311:Pressoreceptors / Q000503:physiopathology*; D012007:Rectum / Q000294:innervation*; D012677:Sensation / Q000502:physiology; D020421:Vagus Nerve Diseases / Q000503:physiopathology*