Submitted on August 16, 2006
Accepted on June 16, 2007
Effect of Spaceflight on the Subcutaneous Venoarteriolar Reflex in the Human Lower Leg
Anders Gabrielsen1 and Peter Norsk2*
1 Center of Molecular Medicine, Karolinska Hospital, Stockholm, Sweden
2 Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
* To whom correspondence should be addressed. E-mail: pnorsk{at}mfi.ku.dk.
Whenever the legs are lowered in humans, a venoarteriolar reflex is activated by the hydrostatic distension of the venules. Through local axon reflexes, the adjacent arterioles are contracted to decrease blood flow and prevent formation of edema. Because the venoarteriolar reflex is activated by gravity, we tested the hypothesis that longterm weightlessness would attenuate it. The reduction in subcutaneous blood flow was measured by the 133Xenon wash-out technique just proximal to the ankle joint in dependent lower legs of 8 supine astronauts, where the knee joint was passively bent by 90°. The measurements were conducted before spaceflight and 3 - 6 hrs upon landing following 4 - 6.5 months in space. Activation of the venoarteriolar reflex reduced subcutaneous blood flow by 37 ± 9% (p=0.016) before flight and by 64 ± 8% (p<0.001) following landing with no statistical significant difference between the two reductions (p=0.062). Therefore, our results show that the venoarteriolar reflex is not attenuated by weightlessness and therefore does not need the everyday stimulus of gravity to maintain efficiency.
