Interactions between CO2 chemoreflexes and arterial baroreflexes

• Published in: American journal of physiology. Heart and circulatory physiology 1998-06, Vol.274 (6), p.H2177
• Main Authors: Henry, Rebecca A, Lu, I-Li, Beightol, Larry A, Eckberg, Dwain L
• Format: Article
• Language: English
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.1998.274.6.h2177

Departments of Medicine and Physiology, Hunter Holmes McGuire Department of Veterans Affairs Medical Center, and Medical College of Virginia of Virginia Commonwealth University, Richmond, Virginia 23249 We studied interactions between CO 2 chemoreflexes and arterial baroreflexes in 10 supine healthy young men and women. We measured vagal carotid baroreceptor-cardiac reflexes and steady-state fast Fourier transform R-R interval and photoplethysmographic arterial pressure power spectra at three arterial pressure levels (nitroprusside, saline, and phenylephrine infusions) and three end-tidal CO 2 levels (3, 4, and 5%, fixed-frequency, large-tidal-volume breathing, CO 2 plus O 2 ). Our study supports three principal conclusions. First, although low levels of CO 2 chemoreceptor stimulation reduce R-R intervals and R-R interval variability, statistical modeling suggests that this effect is indirect rather than direct and is mediated by reductions of arterial pressure. Second, reductions of R-R intervals during hypocapnia reflect simple shifting of vagally mediated carotid baroreflex responses on the R-R interval axis rather than changes of baroreflex gain, range, or operational point. Third, the influence of CO 2 chemoreceptor stimulation on arterial pressure (and, derivatively, on R-R intervals and R-R interval variability) depends critically on baseline arterial pressure levels: chemoreceptor effects are smaller when pressure is low and larger when arterial pressure is high. defense reaction; vagal baroreceptor; sympathetic innervation; hyperventilation