Slow breathing reduces chemoreflex response to hypoxia and hypercapnia, and increases baroreflex sensitivity

Objective To investigate whether breathing more slowly modifies the sensiti vity of the chemoreflex and baroreflex. Design Setting: University of Pavia, IRCCS Policlinico S. Matteo. Participa nts: Fifteen healthy individuals. Interventions: Progressive isocapnic hypo xia 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 sensit ivity (by monitoring ventilation, oxygen saturation, end-tidal carbon dioxi de, 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 hyperca pnic chemoreflex responses, compared with spontaneous or 15 b.p.m. controll ed breathing. Hypoxic and hypercapnic responses during spontaneous breathin g 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 inhib iting the chemoreflex during slow breathing. A slowing breathing rate may b e of benefit in conditions such as chronic heart failure that are associate d with inappropriate chemoreflex activation. J Hypertens 19:2221-2229 (C) 2 001 Lippincott Williams & Wilkins.