| The study is set to investigate whether normalization of the transmural pressure in the carotid sinus using neck chamber pressure (NP) during the -Gz phase of the Push Pull Manoeuvre (PPM) would attenuate the cardiovascular responses, and thus, improve +Gz-tolerance. Finally, we would like to examine to what extent the carotid baroreflex contributes to the overall cardiovascular responses to the PPM.; 10 male subjects first underwent acceleration exposures to determine their relaxed control G-tolerance and control PPM G-tolerance. Resting carotid cardiac baroreflex testing was also performed. Subjects were then exposed to three centrifuge run types: (1) a +1.4Gz baseline followed by 15s at relaxed G-tolerance level; (2) -1Gz for 5s followed by 15s of +Gz at relaxed control PPM G-tolerance level (PPM-C). (3) -Gz for 5s followed by 15s of +Gz at relaxed control PPM G-tolerance level with positive neck chamber pressure (PPM-NP). Carotid level systolic blood pressure (SBPc) was measured using Portapres(TM), and R-R interval (RRI) using electrocardiography. (Abstract shortened by UMI.)... |
