Subnormal norepinephrine release relates to presyncope in astronauts after spaceflight. Fritsch-Yelle, Janice M., Peggy A. Whitson, Roberta L. Bondar, and Troy E. Brown. Medical Sciences Division, NASA Johnson Space Center, Houston, Texas 77058, Centre for Advanced Technology Education, Ryerson Polytechnic University, Toronto, Ontario, Canada KRUG Life Sciences, Houston, Texas 77058
APStracts 3:0365A, 1996.
Postflight orthostatic intolerance is experienced by virtually all astronauts, but differs greatly in degree of severity. We studied cardiovascular responses to upright posture in 40 astronauts before and after spaceflights lasting up to 16 days. We separated individuals according to their ability to remain standing without assistance for 10 minutes on landing day. Astronauts who could not remain standing on landing day had significantly smaller increases in plasma norepinephrine levels with standing than those who could remain standing (105 + 41 vs 340 + 62 pg/ml, P = 0.05). In addition, they had significantly lower standing peripheral vascular resistance (23 + 3 vs 34 + 3 mmHg/l/min, P = 0.01) and greater decreases in systolic (-28 + 4 vs -11 + 3 mmHg, P = 0.002) and diastolic (-14 + 7 vs +3 + 2 mmHg, P = 0.0003) pressures. The presyncopal group also had significantly lower supine (16 + 1 vs. 21 + 2 mmHg/l/min, P = 0.04)and standing (23 + 2 vs. 32 + 2 mmHg/l/min, P = 0.038)vascular resistance, supine (66 + 2 vs. 73 + 2 mmHg, P = 0.008) and standing (69 + 4 vs. 77 + 2 mmHg, P = 0.007) diastolic pressure, and supine(109 + 3 vs. 114 + 2 mmHg, P = 0.05) and standing (99 + 4 vs. 108 + 3 mmHg, P = 0.006) systolic pressures before flight. This is the first study to clearly document these differences among presyncopal and non-presyncopal astronauts after spaceflight, and also offer the possibility of preflight prediction of postflight susceptibility. These results clearly point to hypoadrenergic responsiveness, possibly centrally mediated, as a contributing factor in postflight orthostatic intolerance. They may provide insights into autonomic dysfunction in Earthbound patients. 

Received 24 January 1996; accepted in final form 21 July 1996.
APS Manuscript Number A83-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996