Changes in lower limb volume in humans during parabolic flight.
Variations in gravity [head-to-foot acceleration (Gz)] induce hemodynamic alterations as a consequence of changes in hydrostatic pressure gradients. To estimate the contribution of the lower limbs to blood pooling or shifting during the different gravity phases of a parabolic flight, we measured instantaneous thigh and calf girths by using strain-gauge plethysmography in five healthy volunteers. From these circumferential measurements, segmental leg volumes were calculated at 1, 1.7, and 0 Gz. During hypergravity, leg segment volumes increased by 0.9% for the thigh (P < 0.001) and 0.5% for the calf (P < 0.001) relative to 1-Gz conditions. After sudden exposure to microgravity following hypergravity, leg segment volumes were reduced by 3.5% for the thigh (P < 0.001) and 2.5% for the calf (P < 0.001) relative to 1.7-Gz conditions. Changes were more pronounced at the upper part of the leg. Extrapolation to the whole lower limb yielded an estimated 60-ml increase in leg volume at the end of the hypergravity phase and a subsequent 225-ml decrease during microgravity. Although quantitatively less than previous estimations, these blood shifts may participate in the hemodynamic alterations observed during hypergravity and weightlessness.
Bailliart
O
O
Services des Explorations Fonctionnelles et d'Anesthésie-Réanimation, Hôpital Lariboisière, 75010 Paris, France.
Capderou
A
A
Cholley
B P
BP
Kays
C
C
Rivière
D
D
Téchoueyres
P
P
Lachaud
J L
JL
Vaïda
P
P
D000328:Adult; D000337:Aerospace Medicine; D005260:Female; D006801:Humans; D018471:Hypergravity; D018472:Hypogravity; D007866:Leg / Q000033:anatomy & histology* / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D010991:Plethysmography