Effects of cardiac contractility and vascular load on heart rate in athletes
Фотографии:
Associate Professor, PhD V.R. Orel^{1}
Dr.Biol., Professor R.V. Tambovtseva^{1}
^{1}Russian State University of Physical Education, Sport, Youth and Tourism (GTSOLIFK), Moscow
Keywords: elastic and peripheral resistance, heart rate, power output, pressure, left ventricle.
Introduction. Heart rate (HR) is the most easily measurable parameter. In order to monitor individual responses to physical exercise loading, HR is measured in athletes during muscular work of different types: while exercising on weight machines, under different types of training and competitive loads. By the HR values and its dynamics during muscular work and recovery we can make an objective estimation of the functional status of the cardiovascular system of an athlete, his level of individual physical working capacity [1, 5, 8, 9] and adaptive response to a particular physical load.
However, HR is not an independent determinant of the athlete’s physical condition. HR values are affected by the interaction of the basic physiological mechanisms that determine the cardiac output hemodynamic mode. On the one hand, heart rate depends on cardiac contractility, venous return, cardiac ventricular and atrial volume, and on the other hand  on vascular load, with the elastic and peripheral resistance of the arterial system being its components [1, 7, 8, 9] that depend on the power of muscular work and its performance time.
Further on we will analyze joint variations of heart rate and factors of systemic hemodynamics and vascular load of the left ventricle at rest and under dosed muscular work forming the heart rate.
Objective of the study was to detect the peculiarities of the influence of cardiac contractility and vascular load on heart rate in athletes.
Methods and structure of the study. The data provided below were obtained while examining athletes (n=143) of different specializations and skill levels aged 1834 years. At rest and during muscular work on the cycle ergometer with the power of 500 and 1000 kgm/min systolic and diastolic blood pressure was measured using the auscultatory method, and minute blood volume and phases of the cardiac cycle were recorded by means of the tetrapolar rheography using RHEODYNE504 softhardware measuring complex [1, 3, 8, 9].
Moreover, blood pressure and cardiac hemodynamic indices were measured both at rest and during pedaling the cycle ergometer by analogy with the performance measurements [10].
The test indices were calculated using the softhardware measuring complex according to the previously obtained formulas [7, 8, 9], based on the well known models [4, 7, 8]. We also made the statistical processing of the research results [2] and calculated the HR sensitivity coefficients [11] based on the values of their formative factors. In general terms, [1, 11] the man value of the coefficient of sensitivity h (%) of Y with respect to the value of X, by which it is actually determined, is rated by the percentage changes d_{Х} in X and is expressed in the formula:
(1)
where – partial derivative of Y with respect to X at ; – mean values of the indicators and ; from here on d_{Х} = 1%.
During the statistical processing of a large amount of data, the angular coefficient a_{X} in the linear regression equation Y = a_{X}·X + b_{X} can be used [1, 9] as a partial derivative in .
The sensitivity coefficient (h) indicates the percentage of change in Y, by which it varies from its mean value, when X changes by d_{Х} percent of its mean value. Below we will analyze joint variations of heart rate and factors of systemic hemodynamics and vascular load of the left ventricle at rest and under dosed muscular work forming the heart rate.
Results and discussion. Table 1 represents the values of HR, elastic (Ea) and peripheral (R) resistance of the arterial system and one of the indicators of the left ventricular contractility  left ventricular contractile force (LVCF) [8, 9].
All indices change significantly in passing from rest to muscular work on the cycle ergometer performed with the power of 500 and 1000 kgm/min. The obtained values increased no less than 2fold compared to those obtained at rest, and the cardiac contractile force increased on the average 8fold. The submitted data are in good agreement with the results received earlier [7, 9].
The selective impacts of the vascular resistance and LV contractility on HR under different conditions, presented in Table 1, were detected by means of the correlation and regression analyses of the data [2, 8]. Using the formula (1) we evaluated the coefficients of HR sensitivity (h) to the changes affecting its indicator values (Table 1).
Table 1. Heart rate, vascular resistance and LV contractility at rest and during muscular work
Indicators 
Rest 
Power of muscular work, kgm/min 

500 
1000 

Heart rate, bpm (HR) 
66.3 ± 6.1 
112 ± 7.8 
147 ± 11 
Elastic resistance, dyn·cm^{5} (Еа) 
1102 ± 216 
1454 ± 216 
2107 ± 379 
Peripheral resistance, dyn·s·cm^{5} (R) 
1720 ± 241 
818 ± 62 
612 ± 43 
LV power output, mW 
1217 ± 251 
3897 ± 611 
9812 ± 2283 
The correlation and sensitivity coefficients for HR in terms of Ea, R and LV contractile force are presented in Table 2.
Table 2. Coefficients of sensitivity (h) and correlation (C) of HR with vascular resistance and LV contractility at rest and during muscular work.
Indicators 
Rest 
Power of muscular work, kgm/min 

500 
1000 

Elastic resistance 
C 
0.483 
0.724 
0.838 
h 
0.23 
0.233 
0.349 

Peripheral resistance 
C 
0.108* 
0.321 
0.736 
h 
0.067 
0.237 
0.847 

LV power output 
C 
0.07* 
0.517 
0.612 
h 
0.009 
0.053 
0.255 

Note: the * mark means [2] that there is no significant correlation – p>0.1. 
The correlation relationships between HR and Ea are statistically significant indeed, both at rest and during muscular work. Moreover, the correlation coefficient increases strictly with the growth of the muscular work intensity, which is due to the fact that the elastic resistance of the arterial system increases significantly in these conditions.
The coefficients of HR sensitivity to the changes in the elastic resistance increase, passing to a certain extent from rest to more intensive muscular work, rising from 0.23% to 0.35% in terms of a one percent (1%) change of Ea towards its corresponding mean values (Table 1). These data suggest that in all cases the increase of elastic resistance leads to a significant increment in HR, which ranges from 0.23·d_{Х} to 0.35·d_{Х}_{,} where d_{Х} is a percent increase of Ea towards its mean value ( Table 1).
Under rest conditions, neither the peripheral resistance nor the LV contractile force has any statistically significant effect on HR (Table 2). In the meantime, the percentage changes in HR are extremely minor compared to the possible changes (·d_{Х}) in the peripheral resistance and LVCF.
At the same time, during muscular work, the HR correlations with LVCF and peripheral resistance are statistically significant (Table 2). The percentage coefficients of HR sensitivity to the changes in the peripheral resistance turned out to be higher on the average compared with the elastic resistance, increasing during muscular work from 0.237·d_{Х} to 0.847·d_{Х}.
Conversely, the coefficient of HR sensitivity to the cardiac contractile force equaled 0.053·d_{Х}% under load of 500 kgm/min, and under load of 1000 kgm/min, the h value was totally comparable to that of the HR sensitivity to Ea and R  h 0.255·d_{Х}%.
Let us remark here that changes in the peripheral resistance at rest have, on the average, rather a slight effect (Table 2) on HR in these conditions. Most probably, this is due to the relatively low elastic resistance (Table 1) at rest, owing to which the left ventricle function has almost no direct relation to the peripheral resistance.
The increase of Ea with the increasing power of muscular work improves the LV and periphery interaction due to increased arterial wall stiffness (Table 1), providing transmission of noticeable efforts of LV to the peripheral stream through a tenser branching column of the arterial blood. In terms of muscular work, the coefficients of HR sensitivity to the peripheral resistance (Table 2) were even higher than in case of Ea.
As the elastic resistance (Ea) increases during muscular work (Table 1), the HR sensitivity to the LV contractility increases too (1000 kgm/min) (Table 2). This fact is directly associated with the Anrep effect [6, 8] in the intact body of athletes, when the LV contractile force increases in response to the increasing LV vascular load, which leads to the increment in the LV power output.
Conclusion:
 The correlation relationships between the heart rate and elastic resistance of the arterial system are positive and statistically significant both at rest and while performing muscular work on the cycle ergometer.
 During muscular work on the cycle ergometer performed with the power of 500 and 1000 kgm/min, the correlation relationships between the heart rate and peripheral resistance of the arterial system are positive, and HR increases statistically significantly with the increment of the peripheral resistance indices.
 While performing muscular work on the cycle ergometer with the power of 500 and 1000 kgm/min, the correlation relationships between the heart rate and average power of the left ventricular myocardium are positive, and HR increases statistically significantly with the increasing cardiac contractility.
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Corresponding author: ritta7@mail.ru
Abstract. Objective of the study was to analyze the effects of cardiac contractility and vascular load on the heart rate in athletes of different specializations and skill levels at the age of 1834 years. The following parameters were measured: systolic and diastolic blood pressure, minute blood volume and phases of the cardiac cycle (the latter two being recorded by means of the tetrapolar rheography using RHEODYNE504 softhardware measuring complex). Blood pressure and cardiac hemodynamic indices were measured both at rest and while pedaling a cycle ergometer, in a similar way to the performance measurements.
It is shown that, when performing muscular work on the cycle ergometer with the power of 500 and 1000 kgm/min, the correlation relationships of the heart rate with peripheral resistance of the arterial system and average power of the left ventricular myocardium are positive, and HR increases statistically significantly with an increase of the peripheral resistance, as well as with an increase of the cardiac contractility.