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Human cutaneous vascular responses to whole-body tilting, G_z centrifugation, and LBNP

Gravitational Research Branch, NASA Ames Research Center, Moffett Field, California 94035-1000

Submitted 25 February 2003 ; accepted in final form 1 February 2004

We hypothesized that gravitational stimuli elicit cardiovascular responses in the following order with gravitational stress equalized at the level of the feet, from lowest to highest response: short-(SAC) and long-arm centrifugation (LAC), tilt, and lower body negative pressure (LBNP). Up to 15 healthy subjects underwent graded application of the four stimuli. Laser-Doppler flowmetry measured regional skin blood flow. At 0.6 G_z (60 mmHg LBNP), tilt and LBNP similarly reduced leg skin blood flow to 36% of supine baseline levels. Flow increased back toward baseline levels at 80–100 mmHg LBNP yet remained stable during 0.8–1.0 G_z tilt. Centrifugation usually produced less leg vasoconstriction than tilt or LBNP. Surprisingly, SAC and LAC did not differ significantly. Thigh responses were less definitive than leg responses. No gravitational vasoconstriction occurred in the neck. All conditions except SAC increased heart rate, according to our hypothesized order. LBNP may be a more effective and practical means of simulating cardiovascular effects of gravity than centrifugation.

gravity; cutaneous circulation; hemodynamics; short- and long-arm centrifuges; microgravity countermeasures; lower body negative pressure

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