To investigate whether breathing more slowly modifies the sensitivity of the chemoreflex and baroreflex.
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.
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.
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.