Maximal exercise as a countermeasure to orthostatic intolerance after spaceflight

Previous investigators have suggested that maximal exercise performed 24 h before the end of bed rest, a spaceflight analog, restores prebed rest plas ma volume, baroreflex responses, and orthostatic tolerance. Purpose: In thi s case report, we examined the effect of a similar exercise protocol 24 h b efore a Shuttle landing on the orthostatic responses of four crewmembers (E X) after spaceflights of 8-14 d. Four additional crewmembers (CON) served a s controls and did not perform exercise during the final day of the flight. Methods: Each crewmember performed a 10-min stand test approximately 10 d before launch (L-10) and within 1-2 h of landing (R+0). Cardiac stroke volu me was measured (Doppler ultrasound) supine and during each min of standing for three EX and three CON subjects. Results: Preflight, all crewmembers c ompleted the stand test and each group had similar heart rate and blood pre ssure responses. Postflight, all subjects also completed the 10-min stand t est. Each group had similarly elevated supine and standing heart rates, ele vated diastolic and mean arterial blood pressures, and reduced pulse pressu res compared to L-10. However, postflight cardiac output, mean +/- SEM, (EX : 4.5 +/- 0.6 L.min(-1); CON: 3.1 +/- 0.3 L.min(-1)) and stroke volume (EX: 43 +/- 7 mL.beat; CON: 30 +/- 6 mL.beat) were higher after 10 min standing in the EX subjects compared to CON subjects. Conclusions: For these four c rewmembers, maximal exercise performed 24 h before landing may have helped maintain stroke Volume but did not maintain heart rate and blood pressure r esponses during standing compared to preflight.