Bioelectric heart processes in healthy men at different levels of acute normobaric hypoxia

The aim was to study cardiac bioelectric features across different levels of acute normobaric hypoxia (ANH) in healthy young men. Methods: We studied cardiac functions in response to exposure to ANH of mild (14.5 % O2) and medium (12.3 % O2) degrees for 20 minutes among 30 and 29 young men, respectively. Results. With mild and medium degree of ANH, SpO2 decreases to (91.6 ± 4.2) % and to (78.2 ± 5.2) %, respectively. An initial increase in the P1II wave was common for all ANH exposures. On average, during the period of mild ANH, the total BAL and BAR of the heart compartments decreased, only at the beginning the RR and QT intervals decreased, and in the end QT increased. Medium ANH was associated with more pronounced changes in ECG characteristics. On average, during the ANH period of 12.3 % O2, the RII wave (by 0.078 mV, p < 0.001), T1II (0.074 mV, p < 0.001), BAL (0.26 mV, р < 0.001) and BAR (at 0.12 mV, p < 0.001) of the heart decreased, RR intervals (at 100 ms, p < 0.001), QT (11 ms, p < 0.001), and Pc, PQc, QRSc, QTc increased. Correlations between QT deviations and SpO2, СО, SVR, VIK increased. For ANH of 14.5 % O2, the factor "positive chronotropic effect" dominated in the general structure of the ECG, while for 12.3 % O2 it was "chrono-inotropic conjugation". Conclusions. Changes in ECG parameters seem to be more pronounced in exposure to moderate than mild ANH. Possible extracardiac and myogenic regulation mechanisms in the organization of heart bioelectric processes with a mild and medium degree of hypoxia are proposed in the paper.