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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
identify whether whole body heating alters arterial baroreflex
control of muscle sympathetic nerve activity (MSNA), MSNA and
beat-by-beat arterial blood pressure were recorded in seven healthy
subjects during acute hypotensive and hypertensive stimuli in both
normothermic and heat stress conditions. Whole body heating significantly increased sublingual temperature (P < 0.01), MSNA (P < 0.01), heart rate (P < 0.01), and skin blood flow (P < 0.001), whereas
mean arterial blood pressure did not change significantly (P > 0.05). During both normothermic and heat stress
conditions, MSNA increased and then decreased significantly when blood
pressure was lowered and then raised via intravenous bolus infusions of sodium nitroprusside and phenylephrine HCl, respectively. The slope of
the relationship between MSNA and diastolic blood pressure during heat
stress (
128.3 ± 13.9 U · beats
1 · mmHg1) was
similar (P = 0.31) with normothermia (140.6 ± 21.1 U · beats1 · mmHg1).
Moreover, no significant change in the slope of the relationship between heart rate and systolic blood pressure was observed. These data
suggest that arterial baroreflex modulation of MSNA and heart rate are
not altered by whole body heating, with the exception of an upward
shift of these baroreflex curves to accommodate changes in these
variables that occur with whole body heating.
baroreflex sensitivity; muscle sympathetic nerve activity; heart rate; heat stress
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