Cardiovascular Responses To Passive Posture Change In Blood Pressure Regulation

INTRODUCTION: This study examined the possible effects of head-up and head-down passive tilt on cardiovascular parameters in blood pressure regulation to assess use of a head-down position post-exercise or for shock treatment. METHODS: 11 healthy males were set at 35°, 0° and -35° in a randomised sequence for 10 minutes. Systolic and diastolic blood pressures and cardiac output were measured at the end of each period. Heart rate and forearm blood flow were taken each minute and stroke volume was calculated from cardiac output and heart rate values. RESULTS: Cardiac output (48.96 ± 30.09 to 24.04 ± 24.72l·min-1) and stroke volume (0.82 ± 0.56 to 0.35 ± 0.35l) were reduced significantly (P=0.015 and 0.012, respectively). Blood pressures and forearm blood flow were unchanged in all conditions (P=0.778, 0.281 and 0.655). CONCLUSIONS: The data suggest mediation of forearm blood flow independent of the baroreflex. This study shows that no significant changes occurred in head-down tilt possibly due to unchanged central venous pressure. In addition, no cardiovascular symmetry was observed. Measurement of the present parameters in conjunction with non-invasive assessment of central venous pressure is recommended for future study.