Interactions between CO2 chemoreflexes and arterial baroreflexes.
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.
Henry
R A
RA
Department of Medicine, Hunter Holmes McGuire Department of Veterans Affairs Medical Center, Richmond, Virginia 23249, USA.
Lu
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IL
Beightol
L A
LA
Eckberg
D L
DL
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
D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D002245:Carbon Dioxide; D009599:Nitroprusside; D010656:Phenylephrine; D012965:Sodium Chloride