In this project, we are applying the most powerful technologies available to determine, in a ground-based study of long duration spaceflight, the mechanisms by which spaceflight affects cardiovascular function, and then on the basis of an understanding of these mechanisms to develop rational and specific countermeasures. However, the effects of spaceflight and the associated physiologic stresses on cardiac conduction processes are not known, and an increase in cardiac susceptibility to arrhythmias has never been quantified. In addition, numerous reports from the past 30 years suggest that the incidence of ventricular arrhythmias among astronauts is increased during spaceflight. Perhaps, as a result, effective countermeasures have yet to be developed. However, the precise physiologic mechanisms responsible for these alterations remain to be fully elucidated. These alterations are manifested, for example, by reduced orthostatic tolerance upon reentry to the Earth's gravity from space. This collaborative study is making many of the same measurements, however much less frequently, on subjects who are exposed to a much longer duration of simulated microgravity.Īlterations in cardiovascular regulation and function that occur during and after space flight have been reported. In these studies very intensive measurements are made during a short duration of bed rest. The Cardiovascular Alterations Team is conducting studies of hemodynamic regulation and susceptibility to arrhythmias resulting from 16 days of simulated microgravity exposure.
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