Initial cardiovascular response on change of posture from squatting to standing

SummaryThe immediate cardiovascular responses on active change from the squatting (control) to the standing position differ from those obtained in the lying-to-standing manoeuvre. Without exception, the first beat after changing from squatting to standing showed a decrease in systolic, diastolic and mean pressure by 2.0±1.1 kPa (14.6±8.3 mm Hg), 1.4±1.7 kPa (10.6±12.6 mm Hg) and 1.9±1.0 kPa (13.9±7.3 mm Hg), respectively. During the 4th or 5th pulse after standing the pulse pressure was significantly higher than when lying (P<0.01). Mean pressure reached a minimum of 7.7±1.9 kPa (57.8±14.4 mm Hg) after 7.1±1.1s. Thereafter the blood pressure increased to a new level within about 15 s. 11 of 16 subjects demonstrated a biphasic heart rate (HR) response. The maximum HR was reached after 11.0±2.4 s of standing. In all experiments, the peaks in HR were distinctly delayed after the blood pressure clips. We conclude that an arterial baroreflex could be implicated in the immediate HR increase after a squatting-tostanding manoeuvre. The subsequent time course of the initial HR response, however, might be induced by other mechanisms.