Dr.Med., Professor E.V. Bykov
Associate professor, Ph.D. O.I. Kolomiets
Ural State University of Physical Culture, Chelyabinsk

Keywords: regulation, large vessels, microcirculation, athletes, exercise.

Introduction. Available effective diagnostic techniques of the functional state of athletes engaged in different sports help adequately estimate adaptation to exercise, identify mechanisms of regulation of activity of major systems of the body, which significantly improves the training process management abilities. In recent years, considerable attention has been paid to the study of heart rate variability as one of advanced functional diagnostic techniques in sport, used to estimate functioning of different levels of regulation of the body and to detect the earliest signs of maladjustment and the effectiveness of remedial actions. At the same time, researches associated with the assessment of adaptive changes and the features of autonomic regulation of blood pressure and peripheral hemodynamics depending on the nature of the training-competitive activity of athletes are almost lacking.

The purpose of the study was to define the peculiarities of large vessel tone regulation and microcirculation in athletes engaged in physical activity for different purposes.

Materials and methods. We studied the indicators of the central and peripheral hemodynamics - mean dynamic blood pressure (MDBP) and finger plethysmographic wave amplitude (FPWA) using the method of tetrapolar impedance plethysmography (the "Kentavr" technology by "Microlux") in athletes divided into 3 groups: group 1 - athletes involved in cyclic endurance sports (track and field athletics, cycling, skiing, n=35); group 2 - those engaged in acyclic sports (table tennis, n=30); group 3 - athletes engaged in strength sports (weightlifters, n=24). Activity of neurovegetative regulation levels was estimated using spectral analysis with allocation of the spectrum total power (STP) in the band of frequencies: 1) ultra-low-frequency range (ULF waves up to 0.025 Hz, reflects the metabolic regulation activity); 2) very low-frequency range (VLF, 0.025–0.075 Hz, activity of regulation of the higher autonomic centers (suprasegmental level) and humoral factors); 3) low-frequency range (LF, 0.075–0.15 Hz) - activity of the sympathetic division; 4) high-frequency range (HF, 0.15–0.5 Hz) - influence of the parasympathetic division of the autonomic nervous system (ANS).

Results and discussion. The MDBP value was estimated by the aggregate of regulation components including the effects of the suprasegmental structure and humoral-metabolic factors, as well as the sympathetic division of the ANS, represented by VLF and LF waves, that eventually determined the spectrum total power magnitude.

The highest variability of STP was registered in the representatives of cyclic sports; in strength sports, on the contrary, it decreased significantly: the STP values in Gr-1 were higher by almost 30% compared with Gr-3 (р<0.05). There were no significant differences in the STP value between "players" and representatives of other sports (the differences at the level of a downward trend compared to track and field athletes and an upward trend as against weightlifters). The highest wave amplitude in all the groups was registered within the VLF range of the MDBP spectrum (characterizes the activity of humoral-metabolic factors of large vessel tone regulation). We found that at rest (in horizontal position) VLF wave power was significantly higher compared with that of LF waves - by 2-2.5 times (р<0.01–<0.001). There were no statistically significant inter-group differences, by its value the power of VLF waves ranged similarly to STP (the highest values were registered in cyclic athletes, followed by "players" and weightlifters). The representatives of the groups 1 and 2 had similar power of LF waves, significantly higher than those in the group 3.

Special attention should be paid to the impact of various levels of the MDBP regulation (Fig. 1).

Fig. 1. Allocation of spectrum total power of mean dynamic blood pressure in horizontal position in a band of frequencies in different groups of athletes, %

Initially, we observed the highest relative power of VLF waves in the representatives of Gr-3 (67.3%), and LF wave power (reflects the significance of the sympathetic division of the ANS in large vessel tone regulation) - in "players". The VLF%LF% ratio, reflecting the degree of impact of the suprasegmental and segmental structures on the MDBP value, equaled 2.12 c.u. in Gr-3, 1.94 – in Gr-1 and 1.75 – in Gr-2. Therefore, the impact of the sympathetic division of the ANS of tennis players was greater at rest and, accordingly, the degree of tension of the large vessel tone regulation mechanisms was higher compared to athletes from the other two groups.

Changing to vertical position (FOT - functional orthostatic test) was accompanied by the changing dynamics of the STP index - while in Gr-1 and Gr-2 no statistically significant shifts were detected, in Gr-3 its value decreased by more than 30% (р<0.01 compared to the initial values). In this context, the measure of discrepancy in this index was twofold in Gr-1 (р<0.001) compared with Gr-3 and half as much in Gr-2 than in Gr-3 (р<0.01). Almost in all the spectral ranges in athletes from the three groups, the absolute wave power in the spectral range was not statistically significant, except for the power of VLF-fluctuations in weightlifters - its decrease, as our analysis shows, resulted in the low values of STP. We observed a multidirectional dynamics of changes in the activity of humoral-metabolic factors of regulation in athletes from Gr-1 and Gr-2 (a downward trend) and sympathoadrenal effects (an upward trend) - it was typical both for mean group and individual values. At the same time, orthostasis in weightlifters led to a significant decrease in the power of VLF waves with the preserved power of the LF spectral range. As a result, in FOT the absolute indicator values of VLF and LF waves in weightlifters were 1.5-2 times lower than in cyclic athletes and "players''. A decrease in variability of MDBP in weightlifters in the vertical position is assumed to reflect tension of the regulatory mechanisms of large vessel tone as a characteristic of their adaptation to exercises when developing strength.

We detected some specific differences when analyzing the dynamics of the impact of various components of STP of the mean blood pressure both in the experimental groups and while comparing the dynamics of the intra-group indicators of the absolute and relative wave power. Thus, we detected the following redistribution of the MDBP regulation factors in athletes from all the groups: a decrease in the humoral-metabolic effects was observed mostly in weightlifters (variation of the relative power of VLF waves from 67.3 to 50.5%), and least of all - in Gr-1 - due to the significant activation of the baroreflex mechanisms and sympathoadrenal effects (the LF percent increase up to 46.3%) (Fig. 2).

Fig. 2. Allocation of spectrum total power of mean dynamic blood pressure in vertical position in a band of frequencies in different groups of athletes, %

A significant increase of the role of the sympathetic division of ANS in maintenance of MDBP in the vertical position was proved by calculation of the VLF%LF% ratio: it decreased to 1.43 c.u. in Gr-1 (1.94 in the horizontal position) to 1.28 c.u. in Gr-2 (1.75 in the horizontal position) and its maximum effect was registered in Gr-3 - to 1.09 c.u. (fell by half compared with the initial value - 2.12 c.u.). In the vertical position, changes in blood pressure with an increase of vascular tone (increase of systolic and mean dynamic blood pressure) were due to the effects on vascular walls of a number of vasoconstrictive hormones angiotensin-II, vasopressin, adrenalin, as well as due to an increment in activity of the sympathoadrenal system and baroreflex mechanisms of the vascular tone regulation that influence periphery through sympathetic preganglionic neurons of the spinal cord.

The analysis of the slow-wave variability of the FPWA indicator revealed some significant differences in the system of microcirculation in athletes at rest and during the functional orthostatic test depending on the purpose of the training process.

In initial state, the greatest value of STP was registered in Gr-3, the lowest - in Gr-1. High activity was observed in small vessel tone regulation on the part of local metabolic factors introduced by ULF waves. Their power was the highest in the representatives of Gr-3 and the lowest - in Gr-1. The magnitude of power of VLF waves in horizontal position was higher than that of ULF waves (by 20-30%) and did not differ much in athletes depending on sport.

Activity of the segmental structures was insufficient; but we found that it was significantly higher in track and field athletes compared with "players" and weightlifters (p<0.001) and in "players" compared with weightlifters (p<0.01). When analyzing the relative degree of fluctuation of the FPWA index, we did not observe any significant differences in the impact of different factors of regulation within the ULF, VLF and HF range; they were in evidence only within the low-frequency spectral range, but their significance did not exceed 3.1% of STP. It was humoral factors that affected small vessel tone regulation the most (56–57%), the percent of ULF waves (local, metabolic factors) equaled 40% in Gr-1 and Gr-3 and 42.6% in Gr-2 (Fig. 3).

Fig. 3. Distribution of spectrum total power of finger plethysmographic wave amplitude in vertical position in a band of frequencies in different groups of athletes, %

Changing to the vertical position led to a pronounced decrease in the FPWA variability (р<0.001 in Gr-1, р<0.05 in Gr-2 and Gr-3), which was stipulated by the changes in the activity of regulatory factors - primarily, by the increment in sympathoadrenal activity (the percent of LF waves increased manyfold in all the groups and reached 28–29.7%). It is known that diagnostic significance of myogenic waves within the LF range (0.07–0.15 Hz) was in its association with the state of muscle tone of precapillary sphincters that regulate the blood flow to nutrition stream. Besides, in Gr-2 and Gr-3 we detected power ascension of HF waves and increase of their percent from 14.6 to 18.1%. At the level of microcirculation system, G.V. Krasnikov et al. spot an opportunity to form blood flow waves determined by breathing in a wide range of respiratory frequencies - 0.16–0.03 Hz. Yet, the described changes in the amplitude of blood flow oscillations within the range of endothelium-dependent and pulse waves reflected reactive compensatory changes caused by paced rhythm and depth of breathing (high-amplitude breathing vibrations). The authors note that the resulted mechanical pressure of the vascular wall activates endothelium-dependent vasodilatation mechanisms. In our study we registered a significantly higher STP in athletes from Gr-2 and Gr-3.

In addition, it has been established that the redistribution of effects of the factors of small vessel tone regulation was also accompanied by a twofold decrease of the relative power of ULF waves (20.6% in Gr-1, 18.6% in Gr-2 and 19.6% in Gr-3) and a considerable decrease in the percent of VLF waves. However, the degree of decrease in the relative wave power within the VLF spectral range was different: it reached 46% in track and field athletes and dropped to 35.3% in "players" and weightlifters. Such a significant decrease of the role of humoral component during FOT in Gr-2 and Gr-3 was balanced out by the involvement of additional regulatory factors - respiratory undulations: the percent of HF waves equaled 14.6% in weightlifters and 18.1% in "players".

Conclusions. We assume that the detected peculiarities of the spectral characteristics of FPWA of "players" and weightlifters in the orthostatic test testify to tension of the regulation mechanisms of the peripheral blood flow during strength training sessions and acyclic exercises performed by tennis players.

The identified features of the regulation of large and small blood vessels are essential in the long-term adaptation of the vascular bed to comprehensive coordination exercises.

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