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Influence of core body temperature on cerebral blood flow during exercise

University of British Columbia

Introduction: Cerebral blood flow (CBF) decreases by approximately 10-15% for every 1°C rise in core temperature (Tc) during passive heat stress. Acute moderate-intensity exercise (e.g., 30- 60 mins at 50-60% workload max) also increases Tc (+0.7-0.8°C); however, likely due to small elevations in arterial PCO₂ and metabolism, such exercise increases CBF (+10-20%). This study aimed to isolate the role of Tc from PCO₂ on CBF regulation during submaximal exercise. Methods: Healthy adults (n=11; 10M/ 1F; 26±4 yrs) participated in two separate interventions: 1) 60 mins semi-recumbent cycling (EX; 50% workload max); and 2) passive heat stress (HS; 49°C water-perfused suit) timed to match the exercise-induced increases in Tc. Blood flow in the internal and external carotid (ICA and ECA, respectively) and vertebral (VA) arteries (Duplex ultrasound) was measured. End-tidal PCO₂ and PO₂ were effectively “clamped” to resting values within each condition. Results: The changes in Tc with EX and HS were matched between conditions (Δ0.76±0.24°C, P=0.855). Chest skin temperature was higher during the HS intervention (HS: Δ2.91±1.21°C vs. EX: Δ0.53±1.17°C, respectively, P<0.001), whereas increases in cheek temperature (Δ1.17±0.92°C) were not different between conditions (P=0.221). Related to this, although ECA blood flow increased during both EX and HS for thermoregulatory heat dissipation (EX: Δ42±58% vs. HS: Δ53±28%, time effect: P<0.001), there was no difference between conditions (P=0.628). Blood flow in the ICA was unchanged with EX and HS interventions (P=0.665), consistent with the unchanged end-tidal PCO₂ (P=0.327). In contrast, blood flow in the VA was higher throughout both EX and HS (EX: Δ16±21% vs. HS: Δ16±23%, time effect: P=0.006) with no between condition differences (P=0.514). These increases in VA blood flow contributed to higher global CBF throughout both EX and HS (EX: Δ12±20% vs. HS: Δ14±14%, time effect: P=0.029). Including blood pressure as a covariate did not influence these CBF findings (all P>0.05). Conclusions: These data indicate a selective influence of Tc in mediating elevations in posterior CBF during exercise that is independent of changes in PCO₂ and blood pressure.

Text

2019-08-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/71419

Health and Exercise Sciences

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/