Impaired cerebrovascular autoregulation and CO2 response are related to changes in systolic pressure after long‐duration spaceflight

Abstract

Intracranial hypertension has been identified as a risk for long‐duration spaceflight. We monitored changes in cerebral blood flow velocity (CBFV) in response to changes in blood pressure (autoregulation) and CO2 before and after spaceflight (147±49 days) in 5 men and 1 woman to determine if changes in CBFV or cerebrovascular resistance index (CVRi) related to changes in systolic blood pressure (SBP). Autoregulation and CO2 reactivity were measured during a test where two breaths of 10% CO2 were given 4 times during a 5min period. The autoregulatory index of the CVRi response to BP was reduced post‐flight (0.035±0.007 to 0.029±0.005, p<0.05) with a trend to a greater CBFV response to a change in BP (p=0.128). The post‐flight CVRi response to CO2 was significantly reduced (−0.038±0.018 to −0.028±0.012, p<0.05) with a simultaneous reduction in the CBFV response to CO2 (p=0.056). The change in SBP from pre‐ to post‐flight was correlated with the change in CBFV per mmHg change in BP (r=0.66) and the change in CBFV per mmHg change in CO2 (r=0.71). Individuals with elevated post‐flight SBP were more likely to have impairment of autoregulation and of cerebrovascular health as indicated by CO2 reactivity. With short‐flights no impairment was found in non‐syncopal astronauts; it is unknown if sustained intracranial hypertension and/or elevated environmental CO2 contributed to these changes. Funded by Canadian Space Agency.