The aim of our study was to conduct comparative analysis of functional activity of the regulatory systems of organism in the early stages after the short-term acute hypoxia of different degrees, as well as under the conditions of long-term adaptation to hypoxia caused by exercises in endurance, using methods of heart rate variability research (HRV).

The research was carried out on the non-linear male rats. Each animal was trained individually by swimming with the load attached to the base of the tail (10 % of body weight).

Single training was carried out during the 10 – day period. In other series of research we simulated the rats raising under the conditional "altitude" of 6000 m or 9000 m above the sea level. Recording of pulse was performed by using photopletismographic transformer.

We investigated the HRV, based on the obtained data of the cardiac cycle duration. After exposure to the short-term acute hypoxia we could see the increasing of statistical and spectral parameters under the conditional "altitude" of 6000 m and 9000 m above the sea level. SDNN and RMSSD were increased depending on the intensity of hypoxia. We found significant decrease of the variation range (MxDMn) in both "altitudes".

Under these conditions all parameters of the spectral analysis (HF, MF, LF, TP) characteristically increased, depending on the intensity of hypoxia. The most significant spectrum oscillations increased within the range of MF at the "altitude" of 9000 m both concerning the control and relating to the hypoxia of 6000 m.

To study the effect of the long-term adaptation to hypoxia caused by physical exercise for endurance, at the beginning and the end of the experiment we conducted testing of animals on the resistance to hypoxia during their stay in the chamber under the conditional "altitude" of 11,000 meters. It was found that after the course of training that time changed from values of 7–12 minutes to 20–30 minutes. This led to the conclusion about the increase of the non-specific resistance of the organism of rats as a result of adaptation. During the training, we observed the change of the average length of the rats swimming until they were tired: the smallest was recorded after the 5th session and largest was recorded after the 10th. In these terms, the results of the HRV analysis also changed significantly. Especially, in the period the lowest endurance of an organism, we are able to note the decrease of the parameters of statistical (SDNN, CV, RMSSD), of spectral analysis (HF, MF, LF, TP), and of the separate data of variation pulsometry (MxDMn and AMo). It is significant that after the 10th day of training, when the length of swimming of the rats increased twice, we recorded a highly significant increase of all statistical and spectral parameters related to the control and, especially, concerning the 5th session.

The redistribution of the spectrum at that time provided the largest share for HF.

We observed the increasing to the control level of the variation range (MxDMn). The increase in the parameters of statistical and spectral analysis that we registered after a course of endurance training was much more expressive than under the conditions of short-term hypobaric hypoxia.

Added 05.12.2016

Keywords: hypoxia, adaptation, heart rate variability

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