CARDIOVASCULAR AND VALSALVA RESPONSES DURING PARABOLIC FLIGHT

We investigated the integrated cardiovascular responses of 15 human su bjects to the acute gravitational changes (micro- and hypergravity por tions) of parabolic flight. Measurements were made with subjects quiet ly seated and while subjects performed controlled Valsalva maneuvers. During quiet, seated, parabolic flight, mean arterial pressure increas ed during the transition into microgravity but decreased as microgravi ty was sustained. The decrease in mean arterial pressure was accompani ed by immediate reflexive increases in heart rate but by absent (or la ter-than-expected) reflexive increases in total vascular resistance. M ean arterial pressure responses in Valsalva phases II1, III, and IV we re accentuated in hypergravity relative to microgravity (P < 0.01, P < 0.01, and P < 0.05, respectively), but accentuations differed qualita tively and quantitatively from those induced by a supine-to-seated pos tural change in 1 G. This study is the first systematic evaluation of temporal and Valsalva-related changes in cardiovascular parameters dur ing parabolic flight. Results suggest that arterial baroreflex control of vascular resistance may be modified by alterations of cardiopulmon ary, vestibular, and/or other receptor activity.