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

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 (MAPMCA) were also evaluated. Mean MCAV showed different changes between sexes (analysis of variance, significant interaction effect, P = 0.026, partial η2 = 0.124). Mean MCAV decreased significantly in males at +1.5 Gz hypergravity compared with prehypergravity +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]. MAPMCA 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.NEW & NOTEWORTHY Previous studies have shown that cerebral blood flow (CBF) was reduced by hypergravity in males, and we obtained similar results from young males in the present study. Moreover, we identified for the first time that CBF in young females was maintained and higher than in young males during acute short-term mild +Gz hypergravity.