The electrical activity of the human heart during ventricular repolarization under acute normobaric hypoxia before and after interval hypoxic training

Abstract

Morphological and functional differences in the heart, which have not resulted from a pathological process, do not cause specific changes in the traditional ECG, widely used for determining various functional disorders in the myocardium. The Body Surface Potential Mapping method (BSPM), known as noninvasive multichannel synchronous recording of electrical potentials of the heart on the thoracic surface from multiple unipolar leads, is a more informative method for studying the functional state of the heart, which makes it possible to obtain more data on the electrical processes in the myocardium compared to the standard electrocardiography. The aim of this research was to investigate the electrical activity of the human heart by the method of BSPM during the period of ventricular repolarization with acute normobaric hypoxia before and after a course of interval hypoxic training. The study population consisted of 14 practically healthy young men (19.7 ± 1.0 years , weight 74.4 ± 9.8 kg, height 177.2 ± 6.4 cm). All subjects gave information consent to participate in this study; study We studied the heart’s electrical activity in young men using traditional and multiple electrocardiography during the ventricle repolarization period of the heart to the acute normobaric hypoxia (gas mixture contains 12% of O 2 ) before and after a 19-day interval hypoxic training. BSPM with 64 unipolar leads covering the thorax was perfomed. Limb lead II was used as a reference. The electrodes located in the intercostal space on the torso with 3-5 cm distance were used. The electrodes were attached to 8 flexible strips each containing 8 electrodes. BSPM was recorded in the supine position at rest. We analyzed the amplitude characteristics of the positive and negative extrema (the amplitude of the maximum and the amplitude of the minimum, respectively) and the time they reach the maximum amplitudes at the period of the ventricular repolarization (the maximum time and the minimum time, respectively) ( See Fig. 1 ). In the initial state, at each minute of the acute hypoxia and the recovery period - normoxia (5 min) the heart rate (HR) and hemoglobin saturation (SpO 2 ) were measured in each subject by an oximeter (Nonin Medical Inc., USA). Systolic and diastolic blood pressure was registered by an automatic tonometer (OMRON, Japan). At each minute of the study, unipolar ECG from 64 electrodes located on the thorax surface was recorded. In limb lead II of ECG, the QT II , R-R II , J-Tpeak II and Tpeak-Tend II intervals were determined, the corrected QT interval (QTc) was calculated using the Bazett formula. The course of interval hypoxic training (IHT) consisted of 19 days of breathing with a hypoxic mixture with 10% oxygen content in the intermittent mode. The first day included 6 cycles (one cycle - 5 minutes of breathing with a hypoxic state. After hypoxic training, when exposed to acute hypoxia, the amplitude maximum and minimum decreased significantly (p<0.05). After interval training under the exposure of acute hypoxia in the subjects in the period corresponding to the ST-T interval, we revealed changes in the temporal parameters of the ECG in the limb leads and of the extrema of the heart’s electrical field on the torso surface in comparison with the initial state. The changes in amplitude-temporal characteristics of the extrema of the heart’s electrical field were revealed using the BSPM method, that was the result of the structural changes of ventricular repolarization of the heart of the subjects ( See Table ). Thus, using the BSPM method during acute hypoxia after the intermittent hypoxic training we identified the initial changes in the electrical activity of the heart which were not detected using traditional methods of studying cardiac electrophysiology. The paper contains 5 Figures, Table and 26