title: Interactions between CO2 chemoreflexes and arterial baroreflexes.
abstract: We studied interactions between CO2 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 CO2 levels (3, 4, and 5%, fixed-frequency, large-tidal-volume breathing, CO2 plus O2). Our study supports three principal conclusions. First, although low levels of CO2 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 CO2 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.
authors.affiliation: Department of Medicine, Hunter Holmes McGuire Department of Veterans Affairs Medical Center, Richmond, Virginia 23249, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Henry
authors.forename: I L
authors.initials: IL
authors.lastname: Lu
authors.forename: L A
authors.initials: LA
authors.lastname: Beightol
authors.forename: D L
authors.initials: DL
authors.lastname: Eckberg
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001158:Arteries / Q000502:physiology; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D002245:Carbon Dioxide / Q000097:blood*; D002628:Chemoreceptor Cells / Q000502:physiology*; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D008955:Models, Cardiovascular; D015233:Models, Statistical; D009599:Nitroprusside / Q000008:administration & dosage; D010656:Phenylephrine / Q000008:administration & dosage; D017156:Photoplethysmography; D012965:Sodium Chloride / Q000008:administration & dosage; D016683:Supine Position; D014662:Vasoconstrictor Agents / Q000008:administration & dosage; D014665:Vasodilator Agents / Q000008:administration & dosage
chemical_list: D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D002245:Carbon Dioxide; D009599:Nitroprusside; D010656:Phenylephrine; D012965:Sodium Chloride