CO2 supplementation dissociates cerebral oxygenation and middle cerebral artery blood velocity during maximal cycling

Abstract

This study evaluated whether the reduction of prefrontal cortex oxygenation (ScO2) during maximal exercise depends on the hyperventilation-induced hypocapnic attenuation of middle cerebral artery blood velocity (MCA Vmean). Twelve endurance-trained males (age: 25 ± 3 years, height: 183 ± 8 cm, weight: 75 ± 9 kg; mean ± SD) performed in three separate laboratory visits, a maximal oxygen uptake (VO2max) test, an isocapnic (end-tidal CO2 tension (PetCO2) clamped at 40 ± 1 mmHg), and an ambient air controlled-pace constant load high-intensity ergometer cycling to exhaustion, while MCA Vmean (transcranial Doppler ultrasound) and ScO2 (near-infrared spectroscopy) were determined. Duration of exercise (12 min 25 s ± 1 min 18 s) was matched by performing the isocapnic trial first. Pulmonary VO2 was 90 ± 6% versus 93 ± 5% of the maximal value (P =.012) and PetCO2 40 ± 1 versus 34 ± 4 mmHg (P