Carotid baroreflex responsiveness during dynamic exercise in humans

J. T. Potts, Xiangrong Shi, P. B. Raven

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Abstract

We utilized 5-s changes of neck pressure and neck suction (from 40 to -80 Torr) to alter carotid sinus transmural pressure in seven men with peak oxygen uptake (V̇O2(peak)) of 41.4 ± 3.6 ml O2 · kg-1 · min-1. Peak responses of heart rate (HR) and mean arterial pressure (MAP) to each carotid sinus perturbation were used to construct open-loop baroreflex curves at rest and during exercise at 25.7 ± 1.1 and 47.4 ± 1.9% V̇O2(peak). The baroreflex curves were fit to a logistic function describing the sigmoidal nature of the carotid sinus baroreceptor reflex. Maximal gain for baroreflex control of HR (-0.31 ± 0.05 beats · min-1 · mmHg-1) and MAP (-0.30 ± 0.08 mmHg/mmHg) at rest was the same as during exercise at 25 and 50% V̇O2(peak) (-0.30 ± 0.05, -0.39 ± 0.13 beats · min-1 · mmHg-1 for HR, P = NS; -0.23 ± 0.04, -0.60 ± 0.38 mmHg/mmHg for MAP, P = NS). Resetting of the baroreflex occurred during exercise at 50% V̇O2(peak). The centering point, threshold, and saturation pressures were significantly increased for baroreflex control of HR (Δpressure = 26.3 ± 6.8, 19.6 ± 10.4, 33.0 ± 5.6 mmHg, P < 0.05) and MAP (Δpressure = 27.1 ± 7.7, 16.1 ± 14.8, 38.2 ± 8.5 mmHg, P < 0.05). The operating point (steady-state HR and MAP) was shifted closer to threshold of the baroreflex during exercise at 50% V̇O2(peak), as reflected by differences in HR and MAP between the centering and operating points (ΔHR = 12.5 ± 4.7 beats/min, P = 0.10; ΔMAP = 7.6 ± 1.3 mmHg, P < 0.05). These findings suggest a resetting of the carotid baroreflex during exercise with no attenuation in maximal sensitivity. A shift in operating point toward threshold of the baroreflex enables effective buffering of elevations in systemic blood pressure via reflex alterations in HR and MAP.

Original languageEnglish
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume265
Issue number6 34-6
StatePublished - 1 Dec 1993

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Keywords

  • blood pressure
  • carotid baroreceptors
  • centering point pressure
  • heart rate
  • operating point pressure
  • saturation pressure
  • threshold pressure

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