title: Controlled breathing protocols probe human autonomic cardiovascular rhythms.
abstract: The purpose of this study was to determine how breathing protocols requiring varying degrees of control affect cardiovascular dynamics. We measured 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 min each); 3) stepwise frequency breathing as above, but with prescribed tidal volumes; 4) random-frequency breathing (approximately 0.5-0.05 Hz) for 6 min; and 5) fixed-frequency breathing (0.25 Hz) for 5 min. During stepwise breathing, R-R interval and arterial pressure spectral power increased as breathing frequency decreased. Control of inspired volume reduced R-R interval spectral power during 0.1 Hz breathing (P < 0.05). Stepwise and random-breathing protocols yielded comparable coherence and transfer functions between respiration and R-R intervals and systolic pressure and R-R intervals. Random- and fixed-frequency breathing reduced end-tidal CO2 modestly (P < 0.05). Our data suggest that stringent tidal volume control attenuates low-frequency R-R interval oscillations 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 stepwise protocol without stringent control of inspired volume may allow for the most efficient assessment of short-term respiratory-mediated autonomic oscillations.
authors.affiliation: Department of Medicine, Medical College of Virginia of Virginia Commonwealth University, Richmond, USA.
authors.forename: W H
authors.initials: WH
authors.lastname: Cooke
authors.forename: J F
authors.initials: JF
authors.lastname: Cox
authors.forename: A M
authors.initials: AM
authors.lastname: Diedrich
authors.forename: J A
authors.initials: JA
authors.lastname: Taylor
authors.forename: L A
authors.initials: LA
authors.lastname: Beightol
authors.forename: J E
authors.initials: JE
authors.lastname: Ames
authors.forename: J B
authors.initials: JB
authors.lastname: Hoag
authors.forename: H
authors.initials: H
authors.lastname: Seidel
authors.forename: D L
authors.initials: DL
authors.lastname: Eckberg
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D001794:Blood Pressure; D002320:Cardiovascular Physiological Phenomena; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D010507:Periodicity; D012119:Respiration / Q000502:physiology*; D013990:Tidal Volume