The relationship between widespread changes in gravity and cerebral blood flow

Area of Science:

• Human physiology
• Aerospace medicine
• Cardiovascular research

Background:

• Gravity significantly impacts physiological systems, particularly cardiovascular and cerebrovascular regulation.
• Understanding cerebral blood flow (CBF) responses to altered gravity is crucial for spaceflight and high-G environments.

Purpose of the Study:

• To investigate the dose-response relationship between varying gravitational loads (0 to 2.0 Gz) and cerebral blood flow (CBF).
• To test the hypothesis that CBF exhibits a linear correlation with gravitational force.

Main Methods:

• Ten healthy males were exposed to simulated gravity levels (0, 0.5, 1.0, 1.5, 2.0 Gz) using a tilt chair and centrifuge.
• Cerebral blood flow velocity (CBFV) in the middle cerebral artery was measured using transcranial Doppler ultrasonography.
• Mean arterial pressure at heart level (MAPHeart), heart rate, stroke volume, cardiac output, and end-tidal carbon dioxide pressure (ETCO2) were recorded.

Main Results:

• Steady-state CBFV demonstrated a stepwise decrease from 0.5 to 2.0 Gz.
• Estimated mean arterial pressure in the middle cerebral artery (MAPMCA) and ETCO2 also decreased stepwise with increasing gravity.
• MAPHeart and cardiac output showed no significant changes, while CBFV positively correlated with MAPMCA and ETCO2.

Conclusions:

• Gravity-induced increases from 0.5 to 2.0 Gz cause stepwise reductions in CBF, independent of stable MAPHeart.
• Decreased MAPMCA and ETCO2 are identified as key contributors to the reduction in CBF under hypergravity conditions.
• Even mild increases in gravity can compromise CBF, highlighting the importance of maintaining cerebral perfusion pressure.