EVALUATION OF THE PERIPHERAL HEMODYNAMICS REACTION TO G-LOADS IN THE HEAD-TO-LEGS DIRECTION (+Gz) ON A SHORT-ARM CENTRIFUGE WITH THE METHOD OF DOPPLER FLOWMETRY

We investigated peripheral arterial blood flow during exposure to the head-to-legs g-loads (+Gz) on a short-arm centrifuge (SAC). Purpose was to use some objective monitoring instruments for testing the hypothesis that the hemodynamic reaction to +Gz would be analogous to the reactions observed in the tilt test and/or the lower body negative pressure (LBNP) test. Six normal male subjects participated in 6 SAC runs with alternating interval g-loads of +1.27 Gz and +2.7 Gz. Blood flow in the femoral (FA) and medial cerebral (MCA) arteries was recorded continuously before, during and after runs with the use of Doppler flowmetry (Kardiomed device). It was found that +Gz centrifugation produced typical anti-gravity changes in hemodynamics, i.e. an increase in FA resistance and decrease in MCR resistance. In comparison to the records at rest, FA blood flow decreased 60 %; MCA blood flow changed insignificantly - no more than 10 % down. It was borne out that +Gz centrifugation has same effects as the Earth's gravity in standing humans, produces orthostatic blood pressure in the lower part of the body, and initiates the totality of anti-gravity hemodynamic reactions. Doppler recording was a quite useful source of data about the blood flow reaction to +Gz centrifugation.