AJP - Regulatory, Integrative and Comparative Physiology, Vol 271, Issue 4 961-R966, Copyright © 1996 by American Physiological Society
Cutaneous microvascular flow in the foot during simulated variable gravities
D. S. Chang, G. A. Breit, J. R. Styf and A. R. Hargens
Life Science Division, National Aeronautics and Space Administration, Ames Research Center, Moffett Field, California 94035-1000, USA.
Our objective was to understand how weight bearing with varying
gravitational fields affects blood perfusion in the sole of the foot. Human
subjects underwent whole body tilting at four angles: upright [1
gravitational vector from head to foot (Gz)], 22 degrees (0.38 Gz), 10
degrees (0.17 Gz), and supine (0 Gz), simulating the gravitational fields
of Earth, Mars, Moon, and microgravity, respectively. Cutaneous capillary
blood flow was monitored on the plantar surface of the heel by laser
Doppler flowmetry while weight-bearing load was measured. At each tilt
angle, subjects increased weight bearing on one foot in graded load
increments of 1 kg beginning with zero. The weight bearing at which null
flow first occurred was determined as the closing load. Subsequently, the
weight bearing was reduced in reverse steps until blood flow returned
(opening load). Mean closing loads for simulated Earth gravity, Mars
gravity, Moon gravity, and microgravity were 9.1, 4.6, 4.4, and 3.6 kg,
respectively. Mean opening loads were 7.9, 4.1, 3.5, and 3.1 kg,
respectively. Mean arterial pressures in the foot (MAP(foot)) calculated
for each simulated gravitational field were 192, 127, 106, and 87 mmHg,
respectively. Closing load and opening load were significantly correlated
with MAP(foot) (r =0.70, 0.72, respectively) and were significantly
different (P < 0.001) from each other. The data suggest that decreased
local arterial pressure in the foot lowers tolerance to external
compression. Consequently, the human foot sole may be more prone to
cutaneous ischemia during load bearing in microgravity than on Earth.
