Submitted on January 30, 2007
Accepted on October 10, 2007
Lower body negative pressure (LBNP) exercise plus brief post-exercise LBNP improves post-bed rest orthostatic tolerance
Donald E. Watenpaugh1*, Deborah D. O'Leary2, Suzanne M. Schneider3, Stuart M.C. Lee4, Brandon R. Macias5, Kunihiko Tanaka6, Richard L. Hughson7, and Alan R. Hargens8
1 Sleep Consultants, Inc., Fort Worth, Texas, United States
2 Community Health Sciences, Brock University, St. Catharines, Canada
3 Dept of Exercise, NASA, Albuquerque, New Mexico, United States
4 NASA Johnson Space Center, Houston, Texas, United States
5 Orthopaedic Surgery, UCSD, San Diego, California, United States
6 Department of Physiology, Gifu University, Graduate School of Medicine, Gifu, Japan
7 University of Waterloo, Waterloo, Canada
8 Dept. of Orthop Surg, University of California, San Diego, San Diego, California, United States
* To whom correspondence should be addressed. E-mail: dwatenpaugh{at}texaspulmonary.com.
Orthostatic intolerance follows actual weightlessness and weightlessness simulated by bed rest. Orthostasis immediately after acute exercise imposes greater cardiovascular stress than orthostasis without prior exercise. We hypothesized that 5 min per day of simulated orthostasis (supine LBNP) immediately following LBNP exercise maintains orthostatic tolerance during bed rest. Identical twins (14 women, 16 men) underwent 30 days of 6° head-down tilt bed rest. One of each pair was randomly selected as a control, and their sibling performed 40 min x day-1 of treadmill exercise while supine in 53 mm Hg (SD 4) (7.05 kPa (SD 0.50)) LBNP. LBNP continued for 5 min after exercise stopped. Head-up tilt at 60° plus graded LBNP assessed orthostatic tolerance before and after bed rest. Hemodynamic measurements accompanied these tests. Bed rest decreased orthostatic tolerance time to a greater extent in control (34% (SD 10)) than in countermeasure subjects (13% (SD 20); P < 0.004). Controls exhibited the cardiac stroke volume reduction and relative cardioacceleration typically seen after bed rest, yet no such changes occurred in the countermeasure group. These findings demonstrate that 40 min per day of supine LBNP treadmill exercise followed immediately by 5 min of post-exercise LBNP attenuates, but does not fully prevent, the orthostatic intolerance associated with 30 days of bed rest. We speculate that longer post-exercise LBNP may improve results. Together with our earlier related studies, these ground-based results support space flight evaluation of post-exercise orthostatic stress as a time-efficient countermeasure against post-flight orthostatic intolerance.
