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Abstract

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