Reflex responses to regional venous pooling during lower body negative pressure in humans. Halliwill, John R., Lori A. Lawler, Tamara J. Eickhoff, Michael J. Joyner, and Sharon L. Mulvagh. Departments of Anesthesiology and Physiology & Biophysics, Mayo Medical School, and Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic and Foundation, Rochester, Minnesota 55905
APStracts 4:0436A, 1997.
Lower body negative pressure is frequently used to simulate orthostasis. Prior data suggests that venous pooling in abdominal or pelvic regions may have major hemodynamic consequences. Therefore, we developed a simple paradigm for assessing regional contributions to venous pooling during lower body negative pressure. Sixteen healthy men and women underwent graded lower body negative pressure protocols to 60 mmHg while wearing medical anti-shock trousers to prevent venous pooling under three randomized conditions: 1) no trouser inflation (control), 2) only the legs inflated, and 3) with the legs and abdominopelvic region inflated. Without trouser inflation, heart rate increased 28 +/- 4 beats min-1, mean arterial pressure fell -3 +/- 2 mmHg, and forearm vascular resistance increased 51 +/- 9 units at 60 mmHg lower body negative pressure. With inflation of either the legs or the legs and abdominopelvic region of the trousers, heart rate and mean arterial pressure did not change during lower body negative pressure. By contrast, while the forearm vasoconstrictor response to lower body negative pressure was attenuated by inflation of the legs (_ forearm vascular resistance 33 +/- 10 units, P < 0.05 vs control), attenuation was greater with the inflation of the legs and abdominopelvic region (_ forearm vascular resistance 16 +/- 5 units, P < 0.05 vs control and legs only). Thus, the hemodynamic consequences of pooling in the abdominal and pelvic regions during lower body negative pressure appear to be less than in the legs in healthy individuals. 

Received 9 June 1997; accepted in final form 15 September 1997.
APS Manuscript Number A528-7.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 29 October 1997