CONTROLLED BREATHING PROTOCOLS PROBE HUMAN AUTONOMIC CARDIOVASCULAR RHYTHMS

The purpose of this study was to determine how breathing protocols req uiring varying degrees of control affect cardiovascular dynamics. We m easured inspiratory volume, end-tidal CO2, R-R interval, and arterial pressure spectral power in 10 volunteers who followed the following 5 breathing protocols: 1) uncontrolled breathing for 5 min; 2) stepwise frequency breathing (at 0.3, 0.25, 0.2, 0.15, 0.1, and 0.05 Hz for 2 m in each); 3) stepwise frequency breathing as above, but with prescribe d tidal volumes; 4) random-frequency breathing (similar to 0.5-0.05 Hz ) for 6 min; and 5) fixed-frequency breathing (0.25 Hz) for 5 min. Dur ing stepwise breathing, R-R interval and arterial pressure spectral po wer increased as breathing frequency decreased. Control of inspired vo lume reduced R-R interval spectral power during 0.1 Hz breathing (P < 0.05). Stepwise and random-breathing protocols yielded comparable cohe rence and transfer functions between respiration and R-R intervals and systolic pressure and R-R intervals. Random-and fixed-frequency breat hing reduced end-tidal CO2 modestly (P < 0.05). Our data suggest that stringent tidal volume control attenuates low-frequency R-R interval o scillations and that fixed-and random-rate breathing may decrease CO2 chemoreceptor stimulation. We conclude that autonomic rhythms measured during different breathing protocols have much in common but that a s tepwise protocol without stringent control of inspired volume may allo w for the most efficient assessment of short-term respiratory-mediated autonomic oscillations.