Dynamic cerebral autoregulation during passive heat stress in humans
- 1 May 2009
- journal article
- research article
- Published by American Physiological Society in American Journal of Physiology-Regulatory, Integrative and Comparative Physiology
- Vol. 296 (5), R1598-R1605
- https://doi.org/10.1152/ajpregu.90900.2008
Abstract
This study tested the hypothesis that passive heating impairs cerebral autoregulation. Transfer function analyses of resting arterial blood pressure and middle cerebral artery blood velocity (MCA Vmean), as well as MCA Vmean and blood pressure responses to rapid deflation of previously inflated thigh cuffs, were examined in nine healthy subjects under normothermic and passive heat stress (increase core temperature 1.1 ± 0.2°C, P < 0.001) conditions. Passive heating reduced MCA Vmean [change (Δ) of 8 ± 8 cm/s, P = 0.01], while blood pressure was maintained (Δ −1 ± 4 mmHg, P = 0.36). Coherence was decreased in the very-low-frequency range during heat stress (0.57 ± 0.13 to 0.26 ± 0.10, P = 0.001), but was >0.5 and similar between normothermia and heat stress in the low- (0.07–0.20 Hz, P = 0.40) and high-frequency (0.20–0.35 Hz, P = 0.12) ranges. Transfer gain was reduced during heat stress in the very-low-frequency (0.88 ± 0.38 to 0.59 ± 0.19 cm·s−1·mmHg−1, P = 0.02) range, but was unaffected in the low- and high-frequency ranges. The magnitude of the decrease in blood pressure (normothermia: 20 ± 4 mmHg, heat stress: 19 ± 6 mmHg, P = 0.88) and MCA Vmean (13 ± 4 to 12 ± 6 cm/s, P = 0.59) in response to cuff deflation was not affected by the thermal condition. Similarly, the rate of regulation of cerebrovascular conductance (CBVC) after cuff release (0.44 ± 0.22 to 0.38 ± 0.13 ΔCBVC units/s, P = 0.16) and the time for MCA Vmean to recover to precuff deflation baseline (10.0 ± 7.9 to 8.7 ± 4.9 s, P = 0.77) were not affected by heat stress. Counter to the proposed hypothesis, similar rate of regulation responses suggests that heat stress does not impair the ability to control cerebral perfusion after a rapid reduction in perfusion pressure, while reduced transfer function gain and coherence in the very-low-frequency range during heat stress suggest that dynamic cerebral autoregulation is improved during spontaneous oscillations in blood pressure within this frequency range.Keywords
This publication has 46 references indexed in Scilit:
- Analysis of nonstationarity in renal autoregulation mechanisms using time-varying transfer and coherence functionsAmerican Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2008
- Autonomic Neural Control of the Cerebral VasculatureStroke, 2008
- Cerebrovascular responsiveness to steady-state changes in end-tidal CO2 during passive heat stressJournal of Applied Physiology, 2008
- Cerebral Autoregulation: From Models to Clinical ApplicationsCardiovascular Engineering, 2007
- MYPT1 mutants demonstrate the importance of aa 888–928 for the interaction with PKGIαAmerican Journal of Physiology-Cell Physiology, 2007
- Heat stress reduces cerebral blood velocity and markedly impairs orthostatic tolerance in humansAmerican Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2006
- Estimation of Time-Varying Coherence Function Using Time-Varying Transfer FunctionsAnnals of Biomedical Engineering, 2005
- Comparison of Static and Dynamic Cerebral Autoregulation MeasurementsStroke, 1995
- Assessment of Autoregulation by Means of Periodic Changes in Blood PressureStroke, 1995
- The frequency-dependent behavior of cerebral autoregulationNeurosurgery, 1990