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Am J Physiol Regul Integr Comp Physiol 283: R1221-R1226, 2002. First published August 15, 2002; doi:10.1152/ajpregu.00195.2002
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Vol. 283, Issue 5, R1221-R1226, November 2002

Phenylephrine-induced elevations in arterial blood pressure are attenuated in heat-stressed humans

Jian Cui1, Thad E. Wilson1, and Craig G. Crandall1,2

1 Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas 75231; and 2 Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390

To test the hypothesis that phenylephrine-induced elevations in blood pressure are attenuated in heat-stressed humans, blood pressure was elevated via steady-state infusion of three doses of phenylephrine HCl in 10 healthy subjects in both normothermic and heat stress conditions. Whole body heating significantly increased sublingual temperature by ~0.5°C, muscle sympathetic nerve activity (MSNA), heart rate, and cardiac output and decreased total peripheral vascular resistance (TPR; all P < 0.005) but did not change mean arterial blood pressure (MAP; P > 0.05). At the highest dose of phenylephrine, the increase in MAP and TPR from predrug baselines was significantly attenuated during the heat stress [Delta MAP 8.4 ± 1.2 mmHg; Delta TPR 0.96 ± 0.85 peripheral resistance units (PRU)] compared with normothermia (Delta MAP 15.4 ± 1.4 mmHg, Delta TPR 7.13 ± 1.18 PRU; all P < 0.001). The sensitivity of baroreflex control of MSNA and heart rate, expressed as the slope of the relationship between MSNA and diastolic blood pressure, as well as the slope of the relationship between heart rate and systolic blood pressure, respectively, was similar between thermal conditions (each P > 0.05). These data suggest that phenylephrine-induced elevations in MAP are attenuated in heat-stressed humans without affecting baroreflex control of MSNA or heart rate.

baroreflex sensitivity; vasoconstrictor agents; muscle sympathetic nerve activity; heart rate; whole body heating


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