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Slow breathing reduces chemoreflex response to hypoxia and hypercapnia, and increases baroreflex sensitivity
L Bernardi1, A Gabutti, C Porta
1Department of Internal Medicine, University of Pavia and IRCCS Ospedale S. Matteo, Pavia, Italy. lbern1ps@unipv.it
Objective:
To investigate whether breathing more slowly modifies the sensitivity of the chemoreflex and baroreflex.
Design Setting:
University of Pavia, IRCCS Policlinico S. Matteo.
Participants:
Fifteen healthy individuals.
Interventions:
Progressive isocapnic hypoxia and progressive hyperoxic hypercapnia were measured during spontaneous breathing and during a breathing rate fixed at 6 and 15 breaths per minute (b.p.m.).
Main Outcome Measures:
Variations in chemo- and baroreflex sensitivity (by monitoring ventilation, oxygen saturation, end-tidal carbon dioxide, R-R interval and blood pressure) induced by different breathing rates.
Results:
Breathing at 6 b.p.m. depressed (P < 0.01) both hypoxic and hypercapnic chemoreflex responses, compared with spontaneous or 15 b.p.m. controlled breathing. Hypoxic and hypercapnic responses during spontaneous breathing correlated with baseline spontaneous breathing rate (r = -0.52 and r = +0.51, respectively; P = 0.05). Baroreflex sensitivity was greater (P < 0.05) during slow breathing at baseline and remained greater at end rebreathing.
Conclusions:
Slow breathing reduces the chemoreflex response to both hypoxia and hypercapnia. Enhanced baroreflex sensitivity might be one factor inhibiting the chemoreflex during slow breathing. A slowing breathing rate may be of benefit in conditions such as chronic heart failure that are associated with inappropriate chemoreflex activation.