PRINCIPAL INVESTIGATOR (S ) : Raphael F. Smith, Kevin Stanton, David Stoop, 



Donald Brown, Walter Janusz, and Paul King 



EXPERIMENT TITLE/NUMBER : Vectorcardiographic Changes During Extended Space 



Flight, M093 



PROGRAM/MISSION : Skylab 2, 3, 4 



CLASSIFICATION : Human 



DISCIPLINE(S) : Cardiovascular 



OBJECTIVES : To measure electrocardiographic signals during space flight, to 

 elucidate the electrophysiological basis for the changes observed, and to 

 assess the effect of the change on the human cardiovascular system. 



PROTOCOL : Vectorcardiograms were taken at rest, during and after exercise in 

 each crewman in the preflight, inflight, and postf light phases. The crew 

 exercised on the bicycle ergometer at a work load of 150 watts for 2 min, and 

 then vectorcardiograms were obtained for 10 min. 



EQUIPMENT : Vectorcardiograph, bicycle ergometer. 



RESULTS : There was a statistically significant increase in QRS vector 

 magnitude, T maximum vector magnitude, and resting PR interval. During 

 exercise, the PR interval did not differ from preflight. Exercise heart rates 

 inflight were the same as preflight, but increased in the immediate postf light 

 period. No major changes in QRS, T, or ST vector direction occurred. During 

 the three flights cardiac arrythmias were occasionally observed. 



CONCLUSIONS : With the exception of the arrththmias, no adverse electrocardio- 

 graphic changes were observed during the Skylab missions. The increase in QRS 

 and T magnitude resembles the electrocardiographic changes associated with 

 athletic conditioning and may be related to increased ventricular volume 

 secondary to centripetal shifts of fluid and/or the inflight isotonic exercise 

 program. Prolongation of the PR interval at rest with normalization by 

 exercise suggests that there was increased vagal tone in those crewmen 

 exhibiting this response. 



PUBLICATIONS : 489, 490, 491, 492, 493 



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