Fainting (i.e. orthostatic intolerance), or symptoms associated with fainting account for 3% of all emergency room visits and 6% of all hospital admissions. A combination of the heat stress with orthostasis leads to pronounced and consistent reductions in orthostatic tolerance during upright tilt, gravitational acceleration, and lower-body negative pressure. Despite clear evidence of marked reductions in orthostatic tolerance in hyperthermic individuals, the mechanisms responsible for the reduction in orthostatic tolerance in heat stressed individuals is incompletely understood. It has been suggested that increased muscle temperature may attenuate alpha-adrenergic vasoconstriction; however, the effect of heat on baroreflex-mediated vasoconstriction and specifically the alpha-adrenergic responsiveness in human limbs is incompletely understood. Although redistribution of cardiac output to the skin is likely to contribute in part to the reduction in orthostatic tolerance with whole-body heating, it remains unknown as to whether autonomic control (i.e. the baroreflex) of the vasculature supplying other organs such as skeletal muscle is reduced, further challenging the maintenance of arterial blood pressure during heat stress. Therefore, the goal of the projects outlined in this proposal is to test the hypothesis that increased temperature attenuates baroreflex-mediated vasoconstriction and that this event occurs through reduced alpha-adrenergic receptor responsiveness in human limbs. ? ? ?

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Postdoctoral Individual National Research Service Award (F32)
Project #
5F32HL082426-02
Application #
7221281
Study Section
Special Emphasis Panel (ZRG1-F10-H (20))
Program Officer
Meadows, Tawanna
Project Start
2006-04-01
Project End
2007-08-31
Budget Start
2007-04-01
Budget End
2007-08-31
Support Year
2
Fiscal Year
2007
Total Cost
$20,915
Indirect Cost
Name
University of Texas Sw Medical Center Dallas
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
800771545
City
Dallas
State
TX
Country
United States
Zip Code
75390
Keller, David M; Low, David A; Wingo, Jonathan E et al. (2009) Acute volume expansion preserves orthostatic tolerance during whole-body heat stress in humans. J Physiol 587:1131-9
Keller, David M; Davis, Scott L; Low, David A et al. (2006) Carotid baroreceptor stimulation alters cutaneous vascular conductance during whole-body heating in humans. J Physiol 577:925-33