Indices of electrocardiogram dispersion mapping during five-day exposure to dry immersion

The results of the dispersion mapping of the electrocardiograms (ECGs) of 13 healthy young subjects recorded during five-day dry immersion (DI) are presented. This was the first study of 24-h variations of the dispersion of ECG microoscillations. For this purpose, 20- to 30-min fragments were “cut out” of every hour of Holter monitoring recordings to analyze their means after averaging over every 4 h. The heart rate (HR) and QRS amplitude were analyzed simultaneously. The index of metabolic adaptation (HRmax/MMImax, where MMI is myocardial mass index) was calculated. The results showed that alterations in the ECG signal became distinct on DI day 3. They started with a considerable rise of the amplitudes of the main ECG waves, especially at night (from 11 p.m. to 6 a.m.). The Myocardium index significantly increased in the period from 10 p.m. to 2 a.m. This index reached its maximum values on DI day 5, in the time intervals from 3 p.m to 6 p.m. and from 10 p.m. to 10 a.m. On DI day 5, of particular interest was a marked HR growth in the interval from 10 p.m. to 2 a.m. and in the post-sleep hours (from 7 a.m. to 10 a.m.). Thus, the general pattern of changes consisted in successive involvement of electrical, and, later, energy metabolism processes into the myocardium response to DI. Finally, the pulse rate increased, which suggests an integrated cardiovascular response. This pattern of alterations gives grounds for hypothesizing energy metabolism origin of the observed responses.