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Marked Exacerbation of Orthostatic Intolerance After Long- vs. Short-Duration Spaceflight in Veteran Astronauts

From Space Life Sciences Research Laboratories (J.V.M.), NASA, Johnson Space Center, and Wyle Laboratories (C.J.R., S.A.P.), Houston, TX; Beth Israel Deaconess Medical Center/Harvard Medical School (A.L.G.), Boston, MA; and University of California, San Diego (M.G.Z.), La Jolla, CA.

View larger version (29K): [in a new window]   Fig. 1. Incidence of presyncope during stand and tilt testing after short- and long-duration flights. Presyncope is defined as the failure to complete 10 minutes of 80° upright tilt without symptoms.

View larger version (35K): [in a new window]   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.

View larger version (33K): [in a new window]   Fig. 2. Beat-to-beat arterial pressure and heart rate during a stand test after a short flight (top) and a tilt test after a long flight (bottom) in one subject. In the top panel the horizontal arrow indicates that the entire 10 minutes of upright posture was maintained without presyncopal symptoms or hemodynamic instability. Note that after an initial rise and recovery, heart rate varied around 50 to 60 bpm during upright posture. In contrast, after the long flight (bottom), the interrupted horizontal line indicates that presyncopal symptoms occurred, associated with a sudden drop in both pressure and heart rate. (No blood work was available on this subject.)

View larger version (19K): [in a new window]   Fig. 4. Supine and standing plasma norepinephrine (left) and epinephrine levels (right) in the subject presented in Figure 3. Measurements were taken on landing day after this subject’s short (top) and long (bottom) flights.

View larger version (29K): [in a new window]   Fig. 5. Systolic and diastolic pressures and heart rates in six subjects before flight, on landing day, and 2 to 4 days after landing for their short- (left) and long-duration (right) missions. Short-duration data were obtained during stand tests. Long-duration data were obtained during tilt tests.

View larger version (17K): [in a new window]   Fig. 6. Pre- to postflight changes in plasma volume (A) and red blood cell (RBC) volume (B) associated with short- and long-duration flights. Short-duration plasma volumes are reproduced with permission (6).