Author and graduation date: Charlotte HALL, December, 2000

Committee members: Fred Kolkhorst (Chair), Michael Buono, James Noto, Warren Lockette

Thesis title: Blood Pressure Predicts Individual Responses to Thermal Stress

Baroreceptors are stimulated in response to decreases in blood pressure (BP). It has not been determined whether individuals susceptible to cold temperatures have decreased baroreceptor response when compared to individuals who do not respond adversely to cold. The purpose of this study was to investigate the relationship of forearm blood flow (FBF) and hand temperature during lower body negative pressure (LBNP) and cold-pressor testing. This was accomplished by comparing the differences in vascular reactivity to these stimuli. Twelve healthy male volunteers, between the ages of 19 and 34 years were studied during LBNP testing while FBF and BP were measured. Following recovery a cold-pressor test was administered while FBF was recorded. Changes in BP during LBNP were moderately inversely correlated with changes in temperature during cold-pressor testing (r = -0.758; p = 0.004). Participants who experienced the most vasoconstriction demonstrated larger decreases in temperature during cold-pressor testing and smaller decreases in BP during LBNP. Also, decreases in FBF during LBNP were moderately correlated with decreased hand temperature after cold-pressor testing (r = 0.700; p = 0.011). LBNP causes blood to be directed to the lower extremities of the body, resulting in a decreased BP and FBF. In response to cold, blood vessels in the hand and forearm also vasoconstrict, which contributed to decreases in BP and FBF. Furthermore, there were no significant correlations between the percent change in FBF during LBNP, percent change in FBF during cold-pressor test, and percent change in temperature. These results indicate that the mechanism involved in the regulation of BP during LBNP and cold-pressor testing in these individuals was functioning within normal parameters. Baroreceptors mediate HR and FBF in response to alterations of BP. Furthermore, participants who experienced the most vasoconstriction demonstrated the largest decreases in temperature during cold-pressor testing and the smallest decreases in BP during LBNP. However, these results do not conclusively support the use of LBNP and cold-pressor testing as a method for predicting individuals who may be susceptible to cold-induced illness among Naval Special Warfare trainees.

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