Heat stress alters hemodynamic responses during the Valsalva maneuver.

The Valsalva maneuver can be used as a noninvasive index of autonomic control of blood pressure and heart rate. The purpose of this investigation was to test the hypothesis that sympathetic mediated vasoconstriction, as referenced by hemodynamic responses during late phase II (phase IIb) of the Valsalva maneuver, is inhibited during whole body heating. Seven individuals (5 men, 2 women) performed three Valsalva maneuvers (each at a 30-mmHg expiratory pressure for 15 s) during normothermia and again during whole body heating (increase sublingual temperature approximately 0.8 degrees C via water-perfused suit). Each Valsalva maneuver was separated by a minimum of 5 min. Beat-to-beat mean arterial blood pressure (MAP) and heart rate were measured during each Valsalva maneuver, and responses for each phase were averaged across the three Valsalva maneuvers for both thermal conditions. Baseline MAP was not significantly different between normothermic (88+/-11 mmHg) and heat stress (84+/-9 mmHg) conditions. The change in MAP (DeltaMAP) relative to pre-Valsalva MAP during phases IIa and IIb was significantly lower during heat stress (IIa=-20+/-8 mmHg; IIb=-13+/-7 mmHg) compared with normothermia (IIa=-1+/-15 mmHg; IIb=3+/-13 mmHg). DeltaMAP from pre-Valsalva baseline during phase IV was significantly higher during heat stress (25+/-10 mmHg) compared with normothermia (8+/-9 mmHg). Counter to the proposed hypothesis, the increase in MAP from the end of phase IIa to the end of phase IIb during heat stress was not attenuated. Conversely, this increase in MAP tended to be greater during heat stress relative to normothermia (P=0.06), suggesting that sympathetic activation may be elevated during this phase of the Valsalva while heat stressed. These data show that heat stress does not attenuate this index of vasoconstrictor responsiveness during the Valsalva maneuver.