Abstract
Heat and cold stress influence cerebral blood flow (CBF) regulatory factors (e.g., arterial CO2 partial pressure). However, it is unclear whether the CBF response to a CO2 stimulus (i.e., cerebrovascular-CO2 responsiveness) is maintained under different thermal conditions. This study aimed to compare cerebrovascular-CO2 responsiveness between normothermia, passive heat and cold stress conditions. Sixteen participants (8 female; 25 ± 7 yrs) completed two experimental sessions (randomised) comprising of normothermic and either passive heat or cold stress conditions. Middle and posterior cerebral artery velocity (MCAv, PCAv) was measured during rest, hypercapnia (5% CO2 inhalation) and hypocapnia (voluntary hyperventilation to an end-tidal CO2 of 30 mmHg). The linear slope of the cerebral blood velocity (CBv) response to changing end-tidal CO2 was calculated to measure cerebrovascular-CO2 responsiveness, and cerebrovascular conductance (CVC) was used to examine responsiveness independent of blood pressure. CBv-CVC-CO2 responsiveness to hypocapnia was greater during heat stress compared to cold stress (MCA: +0.05 ± 0.08 cm/s/mmHg/mmHg, p = 0.04; PCA: +0.02 ± 0.02 cm/s/mmHg/mmHg, p = 0.002). CBv-CO2 responsiveness to hypercapnia decreased during heat stress (MCA: -0.67 ± 0.89 cm/s/mmHg, p = 0.02; PCA: -0.64 ± 0.62 cm/s/mmHg; p = 0.01) and increased during cold stress (MCA: +0.98 ± 1.33 cm/s/mmHg, p = 0.03; PCA: +1.00 ± 0.82 cm/s/mmHg; p = 0.01) compared to normothermia. However, CBv-CVC-CO2 responsiveness to hypercapnia was not different between thermal conditions (p > 0.08). Overall, passive heat, but not cold, stress challenges maintenance of cerebral perfusion. A greater cerebrovascular responsiveness to hypocapnia during heat stress likely reduces an already impaired cerebrovascular reserve capacity and may contribute to adverse events (e.g., syncope).
Original language | English |
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Pages (from-to) | 23–32 |
Number of pages | 10 |
Journal | Journal of Applied Physiology |
Volume | 136 |
Issue number | 1 |
Early online date | 16 Nov 2023 |
DOIs | |
Publication status | Published - 1 Jan 2024 |
Keywords
- cerebral blood flow
- cerebrovascular function
- cold stress
- heat stress