EFFECTS OF POSTURE ON CARDIOVASCULAR-RESPONSES TO LOWER-BODY POSITIVEPRESSURE AT REST AND DURING DYNAMIC EXERCISE

We tested the hypothesis that cardiovascular responses to lower body p ositive pressure (LBPP) would be dependent on the posture of the subje ct and also on the background condition (rest or exercise). We measure d heart rate (HR), mean arterial blood pressure (MAP), and cardiac str oke volume in eight subjects at rest and during cycle ergometer exerci se (76 +/- 3 W) with and without LBPP (25, 50, and 75 mmHg) in the sup ine and upright positions. At rest, the increase in MAP was proportion al 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 1 7 +/- 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 l arger pressure responses being associated with the supine position bot h at rest and during dynamic leg exercise.