PRINCIPAL INVESTIGATOR (S ): William E. Thornton, and G. Wyckliffe Hoffler 



EXPERIMENT TITLE/NUMBER : Hemodynamic Studies of the Legs Under Weightlessness 



PROGRAM/MISSION : Skylab 3, 4 



CLASSIFICATION : Human 



DISCIPLINE(S) : Cardiovascular 



OBJECTIVES : To investigate the hemodynamic mechanisms involved in the 

 alterations in the return of blood from the legs after weightlessness which 

 play a crucial role in orthostatic tolerance. 



PROTOCOL : Venous compliance and arterial blood flow were determined by 

 occluding venous flow with a pressure cuff above the knee and recording the 

 resulting change in volume from a midcuff segment. Muscle pumping action was 

 studied by placing the subject in lower body negative pressure at -30 mmHg and 

 recording volume change from a calf segment. The studies were performed 3 

 times pref light, 7 times inflight, and 3 times postf light. 



EQUIPMENT : Capacitance volume transducer, lower body negative pressure 

 device. 



RESULTS : There was an increase in blood flow in all crewmen inflight, but 

 there were no apparent trends. After flight there was an immediate sharp 

 reduction, almost to pref light values. Venous compliance showed a gradual 

 increase which reached a factor of five in 2 of the 3 crewmen by mission day 

 15, a slowly decreasing trend in all three crewmen after mission day 40, and a 

 sharp drop to less than pref light values at recovery. After muscle pumping 

 under negative pressure, the relative amount of blood remaining in leg veins 

 was about the same during flight as before flight, but the absolute amount 

 collected and remaining was increased several times. 



CONCLUSIONS : The most likely cause of increased blood flow was an increase in 

 the cardiac output secondary to increasing central venous pressure caused by 

 blood redistribution. Changes in the venous compliance are thought be be 

 primarily changes in the somatic musculature which is postulated to primarily 

 determine venous compliance of the legs. This was also thought to be demon- 

 strated by the changes in muscle pumping. It is thought that these 

 compliance changes, when taken with the decreased blood volume, provide a 

 basis for the changes seen in orthostatic tolerance, work capacity, and lower 

 body negative pressure response. 



PUBLICATIONS : 522, 523 



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