CUTANEOUS MICROVASCULAR FLOW IN THE FOOT DURING SIMULATED VARIABLE GRAVITIES

Our objective was to understand how weight bearing with varying gravit ational fields affects blood perfusion in the sole of the foot. Human subjects underwent whole body tilting at four angles: upright [1 gravi tational vector from head to foot (G(z))], 22 degrees (0.38 G(z)), 10 degrees (0.17 G(z)), and supine (0 G(z)), simulating the gravitational fields of Earth, Mars, Moon, and microgravity, respectively. Cutaneou s capillary blood flow was monitored on the plantar surface of the hee l by laser Doppler flowmetry while weight-bearing load was measured. A t each tilt angle, subjects increased weight bearing on one foot in gr aded load increments of 1 kg beginning with zero. The weight bearing a t which null flow first occurred was determined as the closing load. S ubsequently, the weight bearing was reduced in reverse steps until blo od flow returned (opening load). Mean closing loads for simulated Eart h 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(fo ot)) calculated for each simulated gravitational field were 192, 127, 106, and 87 mmHg, respectively. Closing load and opening load were sig nificantly correlated with MAP(foot) (r = 0.70, 0.72, respectively) an d were significantly different (P < 0.001) from each other. The data s uggest that decreased local arterial pressure in the foot lowers toler ance to external compression. Consequently, the human foot sole may be more prone to cutaneous ischemia during load bearing in microgravity than on Earth.