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11CHANGEABILITY OF HEART PUMPING FUNCTION AT DIFFERENT MOTOR MODES
N.I. Abzalov, Ph.D.
R.A. Abzalov, professor, Dr.Biol.
R.R. Abzalov, Ph.D.
Institute of physical culture, sport and regenerative medicine of Kazan federal university, Kazan
Key words: heart pumping function, heart rate, stroke volume, cardiac output, changeability of indicators of heart pumping function, enhanced motor activity, unrestricted motor activity.
Introduction. The core indicators of heart pumping function: heart rate, stroke volume, and derived from them cardiac output are developed differently during muscle exercise. The most thoroughly studied indicator of heart pumping function - heart rate, responds quickly to the slightest change in the environment [2, 6, 8, 10]. At the same time, stroke volume as a more inert indicator of heart pumping function provides mainly cardiac output and changes relatively slowly [1, 3, 5, 9, 10]. Reserve capabilities of the core indicators of heart pumping function have not been studied well enough, particularly stroke volume and cardiac output. I.A. Arshavsky (1982) believes, heart rate changeability, determined by the difference between the data at maximum muscle tension, as well as those at rest, namely the functional reserve, is enhanced mainly due to an increase in heart rate when performing maximum muscular loads and to a lesser extent owing to resting heart rate data. However, the indicators of heart rate during maximum muscular load have been studied insufficiently. Changeability of stroke volume and cardiac output are assumed to be less studied, especially at muscle exercise and physical activity [3, 7, 9]. The purpose of the study was to examine changeability of the indicators of heart pumping function at different modes of motor activity.
Materials and methods. The research was conducted in the Exercise Physiology Laboratory at the Department of Theory of Physical Culture of Institute of Physical Culture, Sport and Regenerative medicine, Kazan Federal University. 337 students (168 boys and 169 girls) of different age were involved in the experiment. The probands were divided into two groups: group 1 was made of students who were under the conditions of unrestricted motor activity, i.e. their motor activity was presented mainly by two or three physical education lessons a week; group 2 - students who were under the conditions of enhanced motor activity. The probands in this group were engaged in various school sports clubs and children's sports schools and had mass degrees (advanced, senior). First-class athletes, candidates for master of sports and more skilled ones were not examined, since their narrow sports specialization is developed during training.
The probands performed physical exercise on the Kettler Ergoracer exercise bike, where the power of exercise was set and regulated using a special software ERGO-KONZEPT, developed specifically for
these models of exercise bikes. Cadence was 65-75 rpm. The physical stress test was performed to failure. At the beginning pedaling power was 50 W, and then it gradually increased. Heart rate measured using the automated measuring device OMRON RX-3 (HEM-640-E) was recorded all the time. This device is fully compliant with the Directive EU93/42/EEC (Medical Device Directive). The resulting indicators of heart rate were fixed in a specific record for each proband. In addition, we registered heart rate per second during exercise on the KETTLER ERGO RACER exercise bike with the software ERGO-CONZEPT (Germany).
We used point disk electrodes for rheogram registration. They were attached to the neck and chest on an elastic band. Electrodes used allowed freedom of movement and were well fixed on the body during bicycle exercise. When registering, we used the analog-to-digital converter (ADC) of the Maclab/ 4e system, designed by ADInstruments (Australia). This device is used to save various analog signals on Power Mac 8200/120 and acts as a signal amplifier. These measurement data were recorded, presented and processed with high accuracy and resolution using the Chart software. Amplifier setup procedures, signal filtering and calibration are fully automated. The results of measurements and analysis can be easily transferred to spreadsheets and text editors of other applications, such as Claris Works and IGOR Pro.
Rheographic signals were obtained using the device rheoplethysmograph 4RG-2M, produced in the
experimental workshops of Russian Academy of Medical Sciences.
The indicators of heart pumping function were registered under the following conditions:
- before a workout in an upright position "sitting on a chair";
- during a workout "sitting on a bicycle".
In order to study changes in the indicators of stroke volume and cardiac output we calculated the figures of these parameters in exactly the same conditions as during heart rate check. The value of stroke volume (SV) was calculated using the Kubicek' formula (1974) modified by R.A. Abzalov (1987) [4]. Results and discussion. Heart rate changeability was determined by the difference between the data during maximum exercise, as well by the resting values. The indicators of resting heart rate sitting decline with age, meaning the developing age-related bradycardia. The heart rate indicators of 6-7-year-olds were 95,51 ± 2,16 bpm. By the age of 17-18 heart rate fell and reached 72,61 ± 2,17 bpm. The girls' indicators of heart rate in each age group are slightly higher than those of boys. When performing maximum muscle exercise, the indicators of heart rate for boys and girls increase slightly from one age group to another, but these differences do not reach reliable values. This suggests that the maximum indicators of heart rate change significantly with age. Therefore, a reliably marked increase of heart rate changeability among both boys and girls is due to the heart rate fall at rest sitting. It was the first thing we established. Heart rate falls in each age group under the influence of systematic muscular exercise. This fall is statistically significant. However, the indicators of heart rate during maximum muscular exercise performed by
schoolchildren engaged in systematic muscular training do not differ from those of schoolchildren having unrestricted motor activity. Hence, higher indicators of their heart rate changeability are obtained mainly by reduced indicators of resting heart rate.
The indicators of resting stroke volume in school boys and girls increase as they move from one age group to another. The increase of stroke volume is more pronounced at systematic muscle training. This is due to the fact that when performing muscle load, stroke volume increases and the changeability indicators of stroke volume change due to unidirectional changes of stroke volume both during exercise and at rest, but the difference between the data of schoolchildren aged 17-18 years and 6-7 years becomes reliable. The changeability indicators of stroke volume in schoolchildren, subject to enhanced motor activity (both in boys and girls), are significantly more pronounced than in children with unrestricted motor activity.
The integrative indicator of heart pumping function, cardiac output, depends on stroke volume to a greater extent and on heart rate to a lesser one. As seen from Table 1, the indicators of cardiac output in schoolchildren who were under the conditions of enhanced motor activity, particularly in 6-7-year-olds at rest, were 2,80 ± 0,26 l/min. The value of cardiac output increases from one age group to another and reaches 6,09 ± 0,27 l/min by the age of 17-18. The girls' indicators of resting cardiac output do not differ significantly from those of boys. The indicators of cardiac output increase sharply and significantly during muscular exercise. The indicators of cardiac output of 6-7-year-old boys and girls reached the level of 26,7-26,8 l/min. There was an increase in cardiac output by the age of 17-18 compared with the data at rest. Changeability of cardiac output in 6-7-year-old males and females who were under conditions of enhanced motor activity was in the range of 24 l/min. By the age of 17-18 cardiac output reached 29,68 ± 1,43 l/min and 27,67 ± 1,73 l/min for boys and girls respectively compared with the data at rest. Significant differences in the changeability indicators of cardiac output of 17-18-year-olds were not detected. Thus, the changeability indicators of cardiac output of both boys and girls increase in the course of individual development, and it indicates increased functional reserve capacity of heart. Conclusion.
According to the findings of our research, HR changeability increases with age and at muscular training. As opposed to the literature data (I.A. Arshavsky, 1980) the HR changeability index is provided by HR changes at rest and HR indicators remain at approximately the same level when performing maximum muscular load, regardless of age and activity in training. The changeability indices of stroke volume and cardiac output grow with age and under conditions of muscular exercises. These changes are significantly less notable than heart rate, for the changes in changeability of stroke volume and cardiac output are unidirectional, that is increasing both at rest and when performing muscular load. The more pronounced increase in stroke volume and cardiac output provokes increased changeability of these indicators [1, 3, 6, 7, 8, 9]. Changes in heart rate indices at rest and at muscular exercise are multidirectional: heart rate falls
at rest and increases sharply during exercise. This ensures the high level of development of HR changeability. The study of the HR, stroke volume and cardiac output changeability indicators, together with the theoretical value, seems to be of practical value too. They determine the reserve capabilities of heart pumping function, which ensures the high level of body's physical working capacity.
References
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