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Fu, Q1; Arbab-Zadeh, A1; Perhonen, M A.1; Zhang, R1; Zuckerman, J H.1; Levine, B D. FACSM1

Medicine & Science in Sports & Exercise: May 2003 - Volume 35 - Issue 5 - p S309
G-15D Free Communication/Slide Hypotension and Orthostasis

1Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75231

(Sponsor: Benjamin D. Levine, FACSM)

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To test the hypothesis that a greater incidence of orthostatic intolerance in young women compared with men is related to hemodynamics rather than to a reduced vascular responsiveness during orthostatic stress.

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We constructed Frank-Starling curves from pulmonary capillary wedge pressure (PCWP) and stroke volume (SV) during lower body negative pressure (LBNP) and rapid saline infusion in 10 healthy, sedentary women (29.6 ± 1.9 yrs, mean ± SE) and 13 control men (25.5 ± 1.4 yrs). Orthostatic tolerance was determined by progressive LBNP to presyncope with continuous hemodynamic monitoring including PCWP and right atrial pressure.

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LBNP tolerance was significantly lower in females than males (626.8 ± 55.0 vs. 927.7 ± 53.0 mmHg x min, P <0.01). Women had steeper slopes of the linear portion of Frank-Starling curves than men (12.5 ± 2.0 vs. 7.1 ± 1.5 ml/mmHg, P <0.05). During progressive LBNP, PCWP dropped quickly at low levels of LBNP, then more slowly and reached a plateau at high levels of LBNP near presyncope in all the subjects. At presyncope, SV was 35% and stroke index was 29% lower for the females compared with the males (both P <0.05). Coincident with the smaller SV, females had higher heart rates (P <0.05), but similar mean arterial pressures compared with males at the onset of presyncope. Vascular resistance was similar and plasma norepinephrine concentration did not differ between the genders.

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These results suggest that lower orthostatic tolerance in women is associated with a smaller SV at any given cardiac filling pressure, rather than a lower responsiveness of vascular resistance during an orthostatic challenge. Thus, the Frank-Starling relationship may be an important mechanism underlying the gender difference in orthostatic tolerance. Supported by NASA SCORT grant NAGW-3582, and NASA OLMSA grant NAG5–4846.

©2003The American College of Sports Medicine