Cerebrovascular responsiveness to steady-state changes in end-tidal CO 2 during passive heat stress

David A. Low, Jonathan E. Wingo, David M. Keller, Scott L. Davis, Rong Zhang, Craig G. Crandall

Research output: Contribution to journalArticle

45 Scopus citations

Abstract

This study tested the hypothesis that passive heat stress alters cerebrovascular responsiveness to steady-state changes in end-tidal CO 2 (PETCO2). Nine healthy subjects (4 men and 5 women), each dressed in a water-perfused suit, underwent normoxic hypocapnic hyperventilation (decrease PETCO2 ∼20 Torr) and normoxic hypercapnic (increase in PETCO2 ∼9 Torr) challenges under normothermic and passive heat stress conditions. The slope of the relationship between calculated cerebrovascular conductance (CBVC; middle cerebral artery blood velocity/mean arterial blood pressure) and PETCO2 was used to evaluate cerebrovascular CO2 responsiveness. Passive heat stress increased core temperature (1.1 ± 0.2°C, P < 0.001) and reduced middle cerebral artery blood velocity by 8 ± 8 cm/s (P = 0.01), reduced CBVC by 0.09 ± 0.09 CBVC units (P = 0.02), and decreased PET CO2 by 3 ± 4 Torr (P = 0.07), while mean arterial blood pressure was well maintained (P = 0.36). The slope of the CBVC-PETCO2 relationship to the hypocapnic challenge was not different between normothermia and heat stress conditions (0.009 ± 0.006 vs. 0.009 ± 0.004 CBVC units/Torr, P = 0.63). Similarly, in response to the hypercapnic challenge, the slope of the CBVC-PETCO2 relationship was not different between normothermia and heat stress conditions (0.028 ± 0.020 vs. 0.023 ± 0.008 CBVC units/Torr, P = 0.31). These results indicate that cerebrovascular CO2 responsiveness, to the prescribed steady-state changes in PETCO2, is unchanged during passive heat stress.

Original languageEnglish (US)
Pages (from-to)976-981
Number of pages6
JournalJournal of applied physiology
Volume104
Issue number4
DOIs
StatePublished - Apr 2008

Keywords

  • Brain blood flow
  • Hypercapnia
  • Hyperthermia
  • Hypocapnia

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

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