Cerebrovascular carbon dioxide reactivity is influenced by sex despite comparable hemodynamic and respiratory chemosensitivity in young fit individuals

Abstract

Cerebral blood flow (CBF) is generally higher in women compared to men at rest. Although accumulating evidence supports sex differences in CBF regulation, findings remain contradictory for dynamic cerebral autoregulation (dCA) and cerebrovascular reactivity to carbon dioxide (CVRCO2). Cardiorespiratory fitness represents an indicator of cardiovascular health. However, we have recently reported that dCA is reduced in young fit men compared to controls, and that dCA is attenuated in young fit women compared to fit men. However, the influence of sex on CVRCO2 in these young fit individuals remains misunderstood. The aim of this study was to examine the influence of sex on CVRCO2 in young fit individuals. Changes in middle cerebral artery mean blood velocity (MCAvmean; transcranial doppler), mean arterial pressure (MAP; photoplethysmography), heart rate (HR; ECG) and pulmonary ventilation (spirometer) were measured in 29 young fit individuals (women n=10, men n=19), in response to changes in end‐tidal partial pressure of carbon dioxide (PETCO2; gas analyzer) during the modified Duffin hyperoxic rebreathing test. Women were tested in the early follicular phase. CVRCO2, as well as hemodynamic and ventilatory chemosensitivity, were characterized using linear regressions on the rebreathing portion of the test after the determined ventilatory recruitment threshold. While age was not different between groups (26 ± 6 vs. 27 ± 5 years, P = 0.92), height: (1.64 ± 0.06 vs. 1.77 ± 0.08 m; P < 0.0001), body weight (60 ± 6 vs. 72 ± 10 kg; P = 0.0009) and maximal oxygen uptake (48.4 ± 3.8 vs. 57.9 ± 6.8 mL−1kg−1min−1; P < 0.0001) were lower in women. At rest, MCAvmean (72 ± 8 cm/s vs. 62 ± 11 cm/s; P = 0.02) and HR (73 ± 8 vs. 64 ± 11 bpm; P = 0.02) were higher in women, whereas MAP was not different between groups (100 ± 19 vs. 97 ± 10 mm Hg; P = 0.73). CVRCO2 was higher in women compared to men, both in absolute (1.59 ± 0.78 vs. 0.35 ± 1.51 cm/s/mm Hg, P = 0.01) and normalized terms (2.19 ± 0.97 vs. 0.54 ± 2.41 %/mm Hg, P = 0.02). Hemodynamic and respiratory chemosensitivity responses during CO2 rebreathing were not different between groups (all P > 0.05). These results indicate that the cerebrovasculature of young fit women is more sensitive to CO2 than men despite comparable hemodynamic and ventilatory chemosensitivity responses.Support or Funding InformationS.I., L.L. and S.M. have been supported by a doctoral training scholarship from the Fonds de recherche du Québec ‐ Santé (FRQS)