Fig. 2.

Heart rate at normothermia, heat stress, peak orthostatic challenge, and at test termination. Heat stress increased heart rate, while heart rate was further elevated during combined heat stress and LBNP/upright tilt. However, at test termination heart rate was reduced, indicative of a vagal response often accompanying a syncopal symptom limited orthostatic stress test. Peak represents the highest heart rate during combined heat and LBNP/upright tilt. Test termination represents heart rate immediately before ending LBNP or returning subject to the supine position due to syncopal symptoms. All values are significantly different from each other. bpm, Beats/min.