Selective elevation in external carotid artery flow during acute gravitational transition to microgravity during parabolic flight.

This study sought to determine to what extent acute exposure to microgravity (0G) and related increases in central blood volume (CBV) during parabolic flight influence the regional redistribution of intra and extra cranial cerebral blood flow (CBF). Eleven healthy participants performed during two PF campaigns aboard the Airbus A310-ZERO G aircraft. The response of select variables for each of the 15 parabolas involving exposure to both 0G and hypergravity (1.8G) were assessed in the seated position. Mean arterial blood pressure (MAP) and heart rate (HR) were continuously monitored and used to calculate stroke volume (SV), cardiac output (Q ̇) and systemic vascular resistance (SVR). Changes in CBV were measured using an impedance monitor. Extracranial flow through the internal carotid, external carotid, vertebral artery (Q ̇ICA, Q ̇ECA and Q ̇VA) and intracranial blood velocity was measured by duplex ultrasound. Compared to 1G baseline condition, 0G increased CBV (+375 ± 98 mL, P = 0.004) and Q ̇ (+16% ± 14, P = 0.024) and decreased SVR (-7.3 ± 5 mmHg.min.L-1, P = 0.002) and MAP (-13 ± 4 mmHg, P = 0.001). Q ̇ECA increased by 43% ± 46 in 0G (P = 0.030) while no change was observed for CBF, Q ̇ICA or Q ̇VA (respectively P = 0.102, P = 0.637 and P = 0.095).