Fig. 3. Beat-to-beat arterial pressure and heart rate during upright posture after a short (top) and long (bottom) flight in a different subject from that in Figure 2. In the top panel the horizontal arrow indicates that upright posture was maintained for the entire 10-minute test. Upright heart rate was about 100 bpm. In contrast, after the long flight (bottom), the interrupted horizontal bar indicates that the subject was able to maintain upright posture for only about 2 minutes before presyncopal symptoms occurred. Unlike the subject in Figure 2, arterial pressure fell immediately on assumption of upright posture and continued to fall steadily and rapidly until presyncopal symptoms occurred. As with the subject in Figure 2, a simultaneous fall in heart rate and arterial pressure preceded presyncope.
