CARDIOVASCULAR BARORECEPTORS MEDIATE



Number of Pages: 16

Number of Words: 4,865

Number of References: 26

Number of Figures: 8

MS #82040 revised

CARDIOVASCULAR BARORECEPTORS MEDIATE

SUSCEPTIBILITY TO HYPOTHERMIA IN MAN

1,2W. Christopher Fox, 3Charlotte Hall, 2Eric Hall, 3Fred Kolkhorst, and 1,2,4,5Warren Lockette

Running Head: Blood flow in the Cold

1Department of Physiology, University of Michigan Medical School, Ann Arbor; 2Naval Special Warfare Command, San Diego; 3Department of Exercise Science, San Diego State University, San Diego; 4Department of Neurosurgery, Wayne State University School of Medicine, Detroit; and 5Department of Medicine, University of California, San Diego. This work was supported by National Institutes of Health 2RO1 HL50849 and 1T35 HL07862, and the Naval Special Warfare Command. These views represent those of the authors and not necessarily those of the Department of Defense or U.S. Navy. Address correspondence to: Warren Lockette, M.D., Medical Officer, Naval Special Warfare Command, Building 624, 2000 Trident Way, San Diego, CA 92155-5599. E-mail: ridiculo@umich.edu.

1W. Christopher Fox is currently a fourth year medical student at the University of Michigan.

revised 10 October 02

Abstract

Background: The maintenance of excessively high peripheral blood flow through dilated blood vessels during immersion in cold water could explain some individuals’ predisposition to hypothermia. We hypothesized that interpersonal differences in vascular reactivity could account for contrasting susceptibility to hypothermia.

Method: Twenty-two highly fit, volume replete subjects undergoing Navy SEAL training were recruited for this study. Vascular reactivity in these trainees was determined in a thermal-neutral environment by measuring changes in forearm blood flow (FBF) while decreasing their blood pressure with the application of lower body negative pressure (LBNP). FBF was also measured during exposure of these subjects to ice cold water. Blood pressure, heart rate, stroke volume, and skin temperatures were also recorded.

Results: Changes in FBF induced by a fall in blood pressure correlated with an individual’s reduction in FBF caused by ice water immersion (n=17, r=0.84, p < 0.001). A subject’s decrement in blood pressure induced with LBNP correlated inversely with the fall in skin temperature in response to cold water immersion (n=19, r=0.70, p ................
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