Cardiorespiratory response to lower body negative pressure.
The cardiovascular effects of supine lower body negative pressure (LBNP, 0 mm Hg, -8 mm Hg, -15 mm Hg, -25 mm Hg, -35 mm Hg, and -45 mm Hg) were studied in humans (n = 10). The LBNP's were applied in a random order (three per session) for 20 min, with 15 min between each LBNP. Leg blood flow, cardiac output (Q), stroke volume (SV) and estimated lung blood volume were significantly reduced at -15 mm Hg. Increasing LBNP to -35 mm Hg did not result in further changes. When the LBNP was increased to -45 mm Hg, Q and SV were lower than comparable values at -15 mm Hg. Heart rate was unchanged up to -25 mm Hg, after which it increased proportionally to the LBNP. Systolic blood pressure was maintained throughout. Diastolic blood pressure was unchanged below -45 mm Hg, but was significantly elevated at -45 mm Hg. Mean arterial pressure was maintained up to LBNP's of -35 mm Hg by increased vascular resistance, in spite of reduced thoracic blood volume, as indicated by reduced central venous pressure and Q. Greater levels of LBNP were outside the physiological adjustment range and blood pressure dropped progressively.
Chang
C M
CM
Hermann Rahn Laboratory for Environmental Physiology, Department of Physiology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo 14214.
Cassuto
Y
Y
Pendergast
D R
DR
Farhi
L E
LE
D000328:Adult; D001794:Blood Pressure; D002302:Cardiac Output; D006439:Hemodynamics; D006801:Humans; D007866:Leg / Q000098:blood supply; D008150:Lower Body Negative Pressure; D008297:Male; D011652:Pulmonary Circulation; D012039:Regional Blood Flow; D014655:Vascular Resistance