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IMPAIRED PARASYMPATHETIC FUNCTION IN RESPONSE TO COLORECTAL DISTENSION IN PATIENTS WITH IBS

R Spaziani, K Redmond, A Bayati*, H Larsson*, S Ganguli, SM Collins, MV Kamath
McMaster University, Hamilton, Ontario; *AstraZeneca R&D, Molndal, Sweden

Autonomic (ANS) dysfunction may play a role in the etiology of Irritable Bowel Syndrome (IBS) and can be assessed using power spectral analysis of heart rate variability (PS/HRV).
AIMS: To study ANS response to colorectal distension (CRD) in patients with IBS and healthy volunteers (HV).
METHODS: After a 20-min baseline, a barostat-controlled rectal bag (max volume 863 mL) was distended (0.5 mmHg/s), to a max pressure of 70 mmHg, or 50% discomfort (whichever came first), and maintained in this tonic state for 3 mins. A 20-mi. recovery period was recorded. Subjects continuously indicated discomfort and pain. ECG was monitored throughout. PS/HRV was computed using autoregressive modeling. The ratio of low frequency (LF) power (0.02-0.15Hz) to high frequency (HF) power (0.15-0.5Hz) represents sympathetic to vagal modulation of the HR.
RESULTS: 98 HV (34±12 yrs, 52F) and 38 IBS patients (38±11 yrs, 35F) were studied. Patients had significantly more discomfort (69±22% vs. 56±21%), but not pain (9±14% vs. 6±14%) despite similar CRD pressure (51±14 vs 54±15 mmHg; NS) and volumes (394±108 vs 398±134 mL; NS). With CRD, HR (BPM) and BP (mmHg) significantly increased in both HV and IBS, respectively: HR (66±10 to 71±10; 66±9 to 74±13), SBP (121±18 to 143±21; 126±20 to 153±24), and DBP (66±13 to 80±15; 68±14 to 84±16). SBP increase during CRD was significantly greater in IBS and remained significantly elevated during the recovery phase (139±21) compared with HV (129±19).

Table: PS/HRV

Control Power Spectra Control Power Spectra Control Power Spectra Patient Power Spectra Patient Power Spectra Patient Power Spectra
LF HF Ratio LF HF Ratio
Base 5928±1042 5030±1116 1.30±0.49 5761±1040 5093±1217 1.26±0.47
Tonic 6536±1349* 4716±1401* 1.58±0.70* 6759±1324* 4978±1153 1.46±0.54*
Post 6006±1070 4920±1205 1.37±0.52 6180±1508 4901±1208 1.44±0.63
*p<0.05 vs. baseline

DISCUSSION: CRD increased sympathetic tone (increased HR, BP, LF:HF). SBP increase was greatest in IBS and did not recover post-distension. Vagal tone did not decrease significantly with CRD in IBS compared with HV suggesting impaired vagal modulation of the HR. Vagal dysfunction may play a role in the underlying etiology of IBS.
Support: NSERC, DeGroote, AstraZeneca

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Table: PS/HRV
	Control Power Spectra	Control Power Spectra	Control Power Spectra	Patient Power Spectra	Patient Power Spectra	Patient Power Spectra
	LF	HF	Ratio	LF	HF	Ratio
Base	5928±1042	5030±1116	1.30±0.49	5761±1040	5093±1217	1.26±0.47
Tonic	6536±1349*	4716±1401*	1.58±0.70*	6759±1324*	4978±1153	1.46±0.54*
Post	6006±1070	4920±1205	1.37±0.52	6180±1508	4901±1208	1.44±0.63
*p<0.05 vs. baseline