Background and Purpose Sex and fitness have been suggested to influence cerebrovascular function across the lifespan, but the effects of sex and fitness in healthy young adults remains debated. The purpose of this study was to investigate the effects of sex, cardiorespiratory fitness and anaerobic capacity on cerebrovascular reactivity (CVR) and dynamic cerebral autoregulation (dCA) in healthy young adults.
Methods 13 males (mean ± SD age, height and weight: 23.1±2.5 years, 178.0±5.3 cm and 73.7±9.4 kg, respectively) and 11 females (22.1±2.1 years, 165.2±6.5 cm and 61.6±9.5 kg) volunteered to take part in this study. Participants visited the laboratory on two occasions. During the first visit, participants completed a ramp incremental and verification test to determine maximal oxygen uptake (V̇O2max). In the second visit, dCA was assessed using a single sit-to-stand manoeuvre, and CVR to hypocapnia was determined during 60 seconds of voluntary hyperventilation. Middle cerebral artery blood velocity (MCAv) was measured via transcranial Doppler ultrasound, mean arterial pressure (MAP) via finger plethysmography and breath-by-breath end-tidal carbon dioxide (PETCO2) through a gas analyser. dCA was quantified as the percentage fall in MCAv relative to the percentage fall in MAP upon standing (∆%MCAv/∆%MAP). CVR was calculated as both the absolute (cm.s-1) and relative (%) change in MCAv from baseline per 1 mmHg change in PETCO2, taken from the final 10 seconds of hyperventilation. Participants then completed a maximal, 30 second Wingate test on a cycle ergometer. Peak power output (PPO) and mean power output (MPO) from the Wingate test were recorded and expressed relative to body weight (.kg-1). Independent samples t-tests explored differences in MCAv, dCA and CVR responses between males and females, and Pearson’s correlation explored relationships between V̇O2max and Wingate performance with dCA and CVR responses.
Results Males had a significantly greater V̇O2max (49.5±8.0 vs 39.1±8.5 ml.kg-1.min-1, P=0.01), PPO (12.6±2.7 vs 9.5±2.0 W.kg-1, P<0.01) and MPO (8.1±1.0 vs 6.3±1.1 W.kg-1, P<0.01), compared to females. There were no significant differences between males and females in resting MCAv (62.5±10.9 vs 70.4±9.7 cm.s-1, respectively, P=0.08), dCA (0.9±0.7 vs 0.8±0.4, P=0.76), absolute CVR (1.8± 0.3 vs 2.1± 0.5 cm.s-1.mmHg-1, P=0.08) nor relative CVR (2.8±0.5 vs 3.0± 0.8%.mmHg-1, P=0.53). V̇O2max was not significantly correlated with dCA, relative CVR or absolute CVR across the whole sample (r=-0.12 to 0.34, P≥0.12), in males (r=-0.19 to 0.50, P≥0.10) or in females (r=0.07 to 0.33, P≥0.32). MPO was also not significantly associated with dCA or CVR across the whole sample (r=-0.16 to 0.07, P≥0.45), in males (r=-0.16 to 0.25, P≥0.41) or in females (r=-0.27 to 0.35, P≥0.30).
Conclusion These findings indicate that, in healthy young adults, dCA and CVR are not different in males and females. Furthermore, cardiorespiratory fitness and anaerobic capacity were not associated with dCA or CVR in healthy young adults.