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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
The purpose of this project was to test
the hypothesis that baroreceptor modulation of muscle sympathetic nerve
activity (MSNA) and heart rate is altered during the cold pressor test.
Ten subjects were exposed to a cold pressor test by immersing a hand in
ice water for 3 min while arterial blood pressure, heart rate, and MSNA
were recorded. During the second and third minute of the cold pressor
test, blood pressure was lowered and then raised by intravenous bolus
infusions of sodium nitroprusside and phenylephrine HCl, respectively.
The slope of the relationship between MSNA and diastolic blood pressure
was more negative (P < 0.005) during the cold pressor
test (
244.9 ± 26.3 units · beat
1 · mmHg
1) when
compared with control conditions (
138.8 ± 18.6 units · beat
1 · mmHg
1),
whereas no significant change in the slope of the relationship between
heart rate and systolic blood pressure was observed. These data suggest
that baroreceptors remain capable of modulating MSNA and heart rate
during a cold pressor test; however, the sensitivity of baroreflex
modulation of MSNA is elevated without altering the sensitivity of
baroreflex control of heart rate.
baroreflex sensitivity; heart rate; nitroprusside; phenylephrine
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