Changes in lower limb volume in humans during parabolic flight

Area of Science:

• Physiology
• Aerospace Medicine

Background:

• Gravity variations, such as during parabolic flight, alter hydrostatic pressure gradients.
• These hemodynamic alterations affect blood pooling and shifting within the body.
• Understanding lower limb volume changes is crucial for assessing physiological responses to altered gravity.

Purpose of the Study:

• To quantify the contribution of lower limbs to blood volume shifts during different gravity phases.
• To estimate changes in thigh and calf volumes during hypergravity and microgravity.

Main Methods:

• Strain-gauge plethysmography was used to measure instantaneous thigh and calf girths in five healthy volunteers.
• Segmental leg volumes were calculated from girth measurements under 1 Gz, 1.7 Gz, and 0 Gz conditions.
• Data were analyzed to determine volume changes relative to baseline 1 Gz and hypergravity conditions.

Main Results:

• Leg segment volumes increased during hypergravity (thigh +0.9%, calf +0.5%) compared to 1 Gz.
• Upon exposure to microgravity, leg segment volumes decreased significantly (thigh -3.5%, calf -2.5%) relative to 1.7 Gz.
• Volume changes were more pronounced in the thigh, with an estimated 60-ml increase during hypergravity and a 225-ml decrease during microgravity.

Conclusions:

• Lower limb blood volume shifts occur during altered gravity conditions.
• These shifts, particularly the decrease in microgravity, contribute to hemodynamic alterations.
• The findings provide quantitative data on blood pooling in the lower extremities during spaceflight analog conditions.