[Cardiac bioelectrical activity in healthy men during 370-day head-down tilt hypokinesia]

Nine men, aged 27-42 yrs, have been examined during a 370-day head-down tilt (HDT) experiment. The group A test subjects (4 persons) used the countermeasures involving exercises, pharmacological means to correct metabolism, bone tissue and digestive function. The group B test subjects (5 individuals) have embarked on exercising only in 120 days of bedrest. The electrocardiographic changes in the group A test subjects were insignificant, manifested mainly as a moderately decreased T-wave amplitudes in the most leads. In the group B test subjects at early HDT stages there was a negative dynamics: an elevated heart rate (HR) at rest, an increased time of atrioventricular transmission, decreased T-wave amplitudes followed in some cases by its widening and deformations. After the onset of physical training there appeared a tendency toward normalizing the values although T-wave amplitudes till terminating a bedrest period never reached baseline levels. In a rehabilitation period, both groups displayed the dynamics similarity: initially the HR lability and certain decrease in T-wave amplitudes were noted. By the end of 2nd month of rehabilitation the ECGs in all the test subjects of both groups practically normalized, but in Group B this process developed more slower. Thus, a year-long HDT experiment exerted a moderately adverse effect on myocardium metabolism and HR control mainly in the Group B test subjects. The observed changes are reversible and can be regarded as functional.