The influence of combined effects of hyperbaria and hyperoxia on human heart rate variability during exercise strain

With the participation of 8 male volunteers, the dynamics of values of heart rate autonomic regulation were studied at response to physical load on a bicycle ergometer twice: both respirating by the room air under normobaric environment and simulating effects of the altered hyperoxic respiratory gas mixture (HRGM) by the rebreathe respiration methods from a rebreather at the high-pressure chamber (at «depth» 7 m). The devices and methods of Holter electrocardiogram monitoring were used under 24 hours research. The specialized software to analyze the data was used. The electrocardiogram (ECG) and calculated time series of cardiac intervals data obtained were subjected to mathematical processing to calculate statistical and spectral values of heart rate variability (HRV). Additionally, the geometric and nonlinear analysis methods of HRV were investigated. It has been established that influencing factors (compound and pressure of the HRGM) affect the autonomic regulation of heartbeats both at rest and during physical load. Clinical practitioners the HRV values are studied at rest and during strictly regulated tests, i.e. in stationary conditions. The analysis of non-stationary processes, for example, when it is necessary to continuously analyze data, the so-called transient processes under increasing psychological stress, to assess changes in the autonomic regulation of the heart during breathing of gas mixtures with different compositions (hypoxic therapy, hyperbaric oxygenation, etc.), and, especially during physically upload are used the methods of nonlinear and geometric analysis of HRV that are independent of the degree of nonstationary processes and, to some extent, of artifactual cardiac intervals. During the breathing the respiratory gas mixtures with an increased substance of O2 under conditions of high pressure, the activity of the parasympathetic branches of the autonomic nervous system (ANS) significantly increases. The nonlinear dynamics indexes reflect significant differences in the activity of autonomic components under experimental conditions in the direction of strengthening the parasympathetic links of the ANS. The use of nonlinear analysis values is more acceptable when evaluating obtained of non-stationary processes. In general, the study confirms that the regulatory response to the effects of hyperbaria and hyperoxia when performing a bicycle ergometer test with stepwise increase exercise strain is manifested by the prevalence of the activity of the parasympathetic part of the ANS autonomic regulation of cardiac rhythm compared to regular room air and barometric pressure.