[Response of regional vascular tone to orthostatic and gravitational effects]

The effect of active orthostasis and +Gz acceleration on regional vessels was investigated with the participation of 6 test subjects. Using photoplethysmography, the arterial pulse and venous blood filling of vessels of the finger at the level of the right atrium and at 41 cm above and below it were measured. This corresponded to variations of the intravascular hydrostatic pressure within the range +/- 30 mm Hg. This test was performed before and after exposure to acceleration of 5, 7, 8 and 9 G for 30 s at an onset rate of 1.0 G/s in the horizontal and vertical position. Arterial and venous responses were determined by comparing the results obtained at extreme levels of hydrostatic pressure. In all cases, increase in hydrostatic pressure led to enhancement of arterial tone and venous blood filling. After exposure to acceleration arterial tone and venous blood filling grew to a greater extent, particularly in the horizontal position. It is believed that the above method of measuring responses of regional vessels may prove useful to assess the vascular function after orthostatic, gravitational and other effects.