Watenpaugh DE, Buckey JC, Lane LD, Gaffney FA, Moore WE, Levine BD, Wright SJ, Blomqvist CG.

Circulation. 1998 Oct 27; 98: 1763.

UT Southwestern, Dallas, TX, USA.

The human leg circulation possesses adaptations to gravitational pressures, such as vasoconstriction in upright postures and low venous and tissue compliance. Space travel eliminates gravitational pressures, and may therefore compromise these adaptations. To assess effects of microgravity on the leg circulation, we measured resting leg compliance and blood flow with venous occlusion plethysmography, and arterial blood pressure with automated sphygmomanometry, in 7 healthy subjects before, during and after space flights of 9-14 days. Subjects were supine for pre- and post-flight measurements, and measurements were made between 4 and 12 days in space. Leg vascular resistance equaled mean arterial pressure divided by leg blood flow. Compliance equaled the slope of the leg volume change/venous occlusion pressure relationship for thigh cuff pressures of 20, 40, 60 and 80 mmHg held for 1, 2, 3 and 4 min, respectively, with 1 min breaks between occlusions. Leg blood flow decreased 41% in microgravity (p = 0.01) relative to supine Earthbound conditions, and arterial pressure tended to increase. Therefore, leg vascular resistance doubled in microgravity (pre-flight: 43 +/- 4 units, in-flight: 83 +/- 13 units, p < 0.01). Resistance returned to control levels post-flight. Although variability existed, mean leg compliance remained unchanged in microgravity, but tended to increase during the first week post-flight. The degree of leg vasoconstriction observed in microgravity parallels that seen upon standing from recumbent posture on Earth, and therefore supports the "upright setpoint" hypothesis of acclimation to microgravity, which holds that the circulation adopts conditions approximating those while in upright posture on Earth. However, leg vasoconstriction occurred in microgravity without the high gravitational pressures which produce vasoconstriction in upright posture on Earth. Possible mechanisms for microgravity-induced leg vasoconstriction include elevation of sympathetic nerve activity and reduction of leg tissue metabolism secondary to hypokinesia. Our results reveal no effect of space flight on leg hemodynamics to explain the secondary to orthostatic intolerance commonly seen after space flight.

Publication Types:

• Meeting Abstracts

Keywords:

• Animals
• Blood Pressure
• Hindlimb
• Humans
• Leg
• Posture
• Space Flight
• Sympathetic Nervous System
• Vascular Resistance
• Vasoconstriction
• Venous Pressure
• Weightlessness
• NASA Discipline Cardiopulmonary
• Non-NASA Center

Other ID:

• 20601440

UI: 102184898

From Meeting Abstracts