Effects of posture on cardiovascular responses to lower body positive pressure at rest and during dynamic exercise.

We tested the hypothesis that cardiovascular responses to lower body positive pressure (LBPP) would be dependent on the posture of the subject and also on the background condition (rest or exercise). We measured heart rate (HR), mean arterial blood pressure (MAP), and cardiac stroke volume in eight subjects at rest and during cycle ergometer exercise (76 +/- 3 W) with and without LBPP (25, 50, and 75 mmHg) in the supine and upright positions. At rest, the increase in MAP was proportional to the increase in LBPP and was greater in the supine (6 +/- 2, 15 +/- 3, and 26 +/- 3 mmHg) than in the upright (2 +/- 3, 9 +/- 3, and 17 +/- 3 mmHg) position. During dynamic exercise, the increases in MAP evoked by 25, 50, and 75 mmHg LBPP were greater in the supine (13 +/- 2, 28 +/- 3, and 40 +/- 3 mmHg) than in the upright (7 +/- 3, 12 +/- 3, and 25 +/- 3 mmHg) position. We conclude that the systemic pressure response to LBPP is clearly dependent on the body position, with the larger pressure responses being associated with the supine position both at rest and during dynamic leg exercise.