Controlled breathing protocols probe human autonomic cardiovascular rhythms

TLDR

The study aimed to assess how different breathing protocols influence cardiovascular dynamics. Ten volunteers underwent five breathing protocols while inspiratory volume, end‑tidal CO₂, R‑R interval, and arterial pressure spectral power were recorded. Stepwise breathing increased R‑R interval and arterial pressure spectral power as frequency decreased, while strict tidal‑volume control reduced low‑frequency R‑R oscillations; random and fixed‑rate protocols modestly lowered end‑tidal CO₂, and overall the protocols shared similar autonomic rhythms, with stepwise breathing without stringent volume control providing the most efficient assessment of short‑term respiratory‑mediated autonomic oscillations.

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 CO 2 , 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 (∼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 CO 2 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 CO 2 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.