The influence of the carotid baroreflex on dynamic regulation of cerebral blood flow and cerebral tissue oxygenation in humans at rest and during exercise
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This preliminary study tested the hypothesis that the carotid baroreflex (CBR) mediated sympathoexcitation regulates cerebral blood flow (CBF) at rest and during dynamic exercise.
In seven healthy subjects (26 ± 1 years), oscillatory neck pressure (NP) stimuli of + 40 mmHg were applied to the carotid baroreceptors at a pre-determined frequency of 0.1 Hz at rest, low (10 ± 1W), and heavy (30 ± 3W) exercise workloads (WLs) without (control) and with α − 1 adrenoreceptor blockade (prazosin). Spectral power analysis of the mean arterial blood pressure (MAP), mean middle cerebral artery blood velocity (MCAV), and cerebral tissue oxygenation index (ScO2) in the low-frequency range (0.07–0.20 Hz) was estimated to examine NP stimuli responses.
From rest to heavy exercise, WLs resulted in a greater than three-fold increase in MCAV power (42 ± 23.8–145.2 ± 78, p < 0.01) and an almost three-fold increase in ScO2 power (0.51 ± 0.3–1.53 ± 0.8, p = 0.01), even though there were no changes in MAP power (from 24.5 ± 21 to 22.9 ± 11.9) with NP stimuli. With prazosin, the overall MAP (p = 0.0017), MCAV (p = 0.019), and ScO2 (p = 0.049) power was blunted regardless of the exercise conditions. Prazosin blockade resulted in increases in the Tf gain index between MAP and MCAV compared to the control (p = 0.03).
CBR-mediated changes in sympathetic activity contribute to dynamic regulation of the cerebral vasculature and CBF at rest and during dynamic exercise in humans.
KeywordsCerebral blood vessels Cerebral tissue oxygenation Dynamic exercise Power spectral density Sympathetic activity Transfer function gain
Analysis of variance
Cerebral blood flow
Mean arterial pressure
Middle cerebral artery blood velocity
Cerebral tissue oxygenation
Power spectral density
Conception and design of research: SP and PBR. Data collection and analyses: SP, KM, XZ, RZ, and PBR. Manuscript was drafted by SP, KM, XZ, RZ, and PBR. All authors contributed to data interpretation, editing, and revision of the manuscript. All authors approved the final version of the manuscript.
This study was supported in part by funds provided by the Cardiovascular Research Institute and the Department of Integrative Physiology at the University of North Texas Health Science Center at Fort Worth, TX. The authors also wish to thank the subjects for volunteering to undertake the study.
Compliance with ethical standards
Conflict of interest
The authors declare no competing financial interests.
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