Dr.Biol., Professor R.R. Khalfina¹
PhD, Associate Professor T.V. Timchenko²
PhD, Associate Professor A.V. Danilov^2
1Ufa Law Institute of the Ministry of Internal Affairs of Russia, Ufa
²M. Akmullah Bashkir State Pedagogical University, Ufa

Keywords: short-term hypoxia, athletes, visual system.

Relevance. One of the most important parts of successful performance in many sports is the ability to analyze information quickly and effectively in extreme conditions including hypoxia. The level of development of modern electrophysiology of vision allows to evaluate the functional state of different visual system parts, to reveal many  reasons for perception change, to verify the processors of visual information transition. It should be noted that according to numerous clinical and experimental data hypoxia results in deep and very often irreversible vision impairment. At the same time physiological hypoxia may influence on organism resulting in expressed functional changes without pathological processes. Specifically, such states are developing while practicing sports when oxygen transportation system of the body does not meet increasing oxygen demands. In such cases the functional changes of  the visual system may take place and its mechanisms are not investigated enough [1, 4].

So, taking into consideration that sports activities take place against the background of pronounced hypoxia and at the same time require highly effective visual functions, further research of the visual system in athletes with hypoxia by means of clinical electrophysiological methods is one of the actual problems of modern physiology.

Organization and research methods. The research was carried out with 16 active athletes without ophthalmic pathologies of 18-23 years of age on a voluntary basis. The average age was 19,5 years. Bioelectrical activity of different parts of the visual system was studied using generally accepted electrophysiological methods: electroretinography (ERG) and visual evoked potential record (VEPR). ERG was recorded by means of research report of cone ERG to single stimulus. Before breath-holding ERG was recorded three times with 2 minute interval to obtain data at rest (test №1-3). Then the subject without lung hyperventilation held his breath as long as he could. ERG was recorded twenty minutes before breath recovery (test №4). After breath recovery four ERG were recorded with two-minute intervals (test № 5-8).

VEP pattern was recorded using the Neuro-MEP-4 («Neurosoft», Ivanovo, Russia) neuromyograph with electrodes placed at O1-Cz,O2-CZ (2-200 Hz bandpass). The epoch of the analysis was 350 ms, quantitative period on each channel was 180 ms.

In order to build a model of hypoxia the voluntary external breath – holding (VEBH) test

of maximum duration was applied. Statistic data processing was performed using Student’s t-test.

It is the choice of these research methods that made it possible to obtain valid experimental data about electrophysiological mechanisms of processes of visual information processing. So, high sensibility of mechanisms of visual information processing to the lack of oxygen was shown.

Thus, electrophysiological research including ERG, VEP is one of the vital areas in studying adaptation processors of athletes to extreme information and energy conditions. 

Results and discussion.

The role of ERG in retina research is determined by the fact that using its amplitude-time characteristics one can make quantitative evaluation of the functional state of photoreceptors and  neurons. The method is sensitive enough and reveals insignificant changes in the neuroreceptor apparatus, the mechanisms of ERG generation in the norm have been well studied.

The results obtained in the statistic analysis of significant data differences between amplitude-time parameters of ERG in different tests were as follows. The ERG amplitude for the breath-holding peak (test 4) declined statistically significantly in relation to the initial level. The largest differences were discovered between the b-wave amplitudes of ERG in tests № 4 and № 5. Moreover, significant differences in the b-wave amplitudes of ERG were detected in tests № 5 and №7 as well as №5 and №8. The peak time of the b-wave of ERG in different tests didn’t differ significantly (Table 1).

Taking into consideration the depth and duration of hypoxia in VEBH of maximum duration as well as features of organization of the breathing mechanism and the visual system the most probable reason for the b-wave amplitude decline of ERG is the intensification of inhibitory effects on retina in the nonspecific activating brain system.

Table 1. Average values of amplitude-time parameters of the b-wave of ERG and coefficient of variation in different tests

Thus, in the study the b-wave amplitude of ERG changed in the following way. At the initial stage prior to hypoxia steady amplitude of ERG was recorded. At VEHB the decline of the b-wave amplitude of ERG was recorded. After breath recovery the dynamics of the b-wave amplitude of ERG had a phase nature. In the initial post-hypoxic period the amplitude of responses increased, exceeding the initial level and then declined smoothly below the initial level.

Central visual mechanisms to short-term hypoxia in athletes were studied using the method of evoked potentials. Unlike phosphene and ERG perception the VEP dynamics at the initial stage with hypoxia and recovery was of more expressed individual manner. So elite athletes having longer VEBH resulting in deeper hypoxia, more significant changes of the late components of VEP was observed. This fact may be explained by the changes in intercentral interrelationship in short-term hypoxia in athletes in the system of central breathing  mechanism – reticular formation – subcortical  and cortical parts of visual brain.

Data about VEP intensification in focusing attention on visual stimuli became classical, the founders of elecrtroneurophysiology of the brain highlighted the processes of activation involving diffuse nonspecific forms. Physiological explanation of our results is more verified  from these positions.

It is known that timed inspiratory capacity test is an integral indicator of the functional state of the body exerting strong influence on it which results in activation of the ponto-bulbar breathing mechanism [2,3]. Such activation is due to numerous central and peripheral mechanisms participating in the process (central and peripheral chemoreceptors, baroreceptors, proprireceptors of muscles etc.). We believe that the influence of the central breathing mechanism on the cerebral cortex through rising reticular activating brain system results in changes of the VEP pattern in transient hypoxia, evoked by VEBH of maximum duration.

Conclusions. The dynamics of  indicators changes of the b-wave amplitude and late components  of evoked potentials in athletes under short-term hypoxic stress testifies to activation of urgent protective-compensatory mechanisms resulting in the development of inhibitory processors in the peripheral and central parts of the visual analyzer.

Taking into consideration the morpho-functional features of the visual system organization we may suppose that the detected dynamics of electrophysiological parameters in inhibition hypoxia is due to the neuronal interaction in the system of breathing center - reticular formation – peripheral and cortical parts of the visual system.

References

1. Girfatullina R.R., Akhmadeev R.R., Koshelev D.I. Modal'no-nespetsifichnye vyzvannye potentsialy kak pokazatel' kratkosrochnoy psikhofiziologicheskoy adaptatsii u sportsmenov [Modal-nonspecific evoked potentials as an indicator of short-term psychophysiological adaptation in athletes]. Teoriya i praktika fizicheskoy kultury, 2009, no. 4, pp. 33-35.
2. Krylov I.N. Shuvayev V.T., Tretiyakov D.A. Stabilizatsiya vyzvannykh potentsialov kory mozga pri selektivnom zritel'nom vnimanii [Stabilization of cerebral evoked potential in selective visual attention]. Zhurnal vysshey nervnoy deyatelnosti [Journal of Higher Nervous Activity], 1998, vol. 48, no. 6, pp. 926-935.
3. Rutman E.I. Vyzvannyie potentsialy v psikhologii i psikhofiziologii [Evoked potentials in psychology and psychophysiology]. Moscow, 1979. 213 p.
4. Khalfina R.R. Elektrofiziologicheskie aspekty reaktsii zritel'noy sistemy na tranzitornye nagruzki [Electrophysiological aspects of visual system reaction to transient loads]. Vestnik Tomskogo gosudarstvennogo pedagogicheskogo universiteta, 2003, no. 4. (132), pp. 187 – 189.

Corresponding author: riga23@mail.ru

Abstract. The dynamics of the main electrophysiological indicators of the functional  state of the  visual system at rest and under extreme short-term loading is presented in the article. The voluntary external breath-holding test  (VEBH) of maximum duration was applied to make a model of hypoxia. It has been established that the dynamics of change of  the  b-wave amplitude  and late components indicators of the evoked potentials in athletes under short-term hypoxemic stress testifies to activation of urgent protective and compensatory mechanisms expressed in the development of inhibition processes in peripheral and central parts of the visual analyzer.