Comparison of cardiovascular responses between lower body negative pressure and head-up tilt

To investigate local blood-flow regulation during orthostatic maneuvers, 10 healthy subjects were exposed to −20 and −40 mmHg lower body negative pressure (LBNP; each for 3 min) and to 60° head-up tilt (HUT; for 5 min). Measurements were made of blood flow in the brachial (BFbrachial) and femoral arteries (BFfemoral) (both by the ultrasound Doppler method), heart rate (HR), mean arterial pressure (MAP), cardiac stroke volume (SV; by echocardiography), and left ventricular end-diastolic volume (LVEDV; by echocardiography). Comparable central cardiovascular responses (changes in LVEDV, SV, and MAP) were seen during LBNP and HUT. During −20 mmHg LBNP, −40 mmHg LBNP, and HUT, the following results were observed: 1) BFbrachial decreased by 51, 57, and 41%, and BFfemoral decreased by 40, 53, and 62%, respectively, 2) vascular resistance increased in the upper limb by 110, 147, and 85%, and in the lower limb by 76, 153, and 250%, respectively. The increases in vascular resistance were not different between the u...