Sex differences in changes in cerebral blood flow induced by short-term mild +Gz hypergravity in young males and females

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Understanding sex differences in the physiological changes resulting from exposure to hypergravity is important as the proportion of females participating in spaceflight continues to increase. To reveal possible sex differences in changes in CBF during mild hypergravity, the present study evaluated changes in mean cerebral blood velocity in the middle cerebral artery (MCAV) in healthy young males (n=20; age, 20–26 yr) and females (n=20; 20–32 yr) during 6-min exposure to +1.5 Gz hypergravity using a short-arm human centrifuge. Changes in mean arterial pressure at the middle cerebral artery level (MAP MCA ) were also evaluated. Mean MCAV showed different changes between sexes (analysis of variance, significant interaction effect, P=0.026, partial η 2 =0.124). Mean MCAV decreased significantly in males at +1.5 Gz hypergravity compared with pre-hypergravity +1.0 Gz baseline [46±8 → 43±8 cm/s (−6.5%), P<0.001], but did not change significantly in females [61±10 → 60±11 cm/s (−1.6%), P=0.148]. MAP MCA decreased significantly in both males [51±6 → 46±6 mmHg (−10.7%), P<0.001] and females [55±8 → 51±7 mmHg (−5.5%), P=0.002]. From the results for mean MCAV as an index of CBF, we identified for the first time that sex differences exist in the changes in CBF induced by acute short-term exposure to mild +Gz hypergravity. Specifically, our results suggest that CBF would be maintained in females, but reduced in males during +1.5 Gz hypergravity. Sex differences in changes in CBF induced by hypergravity should be considered when managing the health of astronauts and space travelers.