In biological clocks, along with circadian rhythms, heart rhythm and heart rate (HR) are among the most important. They are referred to the functional parameters of the heart, and at first glance it is correct. Not the heart, however, controls heart rhythm and HR, but neurohumoral regulation under the umbrella of the central nervous system.
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The heart rhythm and HR are determined by sex, constitution, age, metabolism, functional type, and change in diseases. Their violation is always associated with deterioration in health, and the more they are, the health is worse.
Previously counted that in a healthy person the HR is always correct, and all its violations are an iron certificate of heart disease. Today we know that this is not the case, and many of the detected so-called rhythm disturbances are of diagnostic significance only if they concern a person with a sick heart. Extra cuts (extrasystoles) are found in every second healthy person. In the elderly and senile ages, they occur in almost 100% of cases. With age, the frequency of complicated ventricular arrhythmias increases, making up to 15% of cases in the general population. Short-term supraventricular tachycardias are observed in every fifth, and at HR of up to 120 beats/min, their seizures remain unnoticed or easily transferred. Short-term ventricular tachycardia with a frequency of up to 180 beats/min in 5% of cases can be found in all age groups. They arise, mainly at night. Not only extrasystoles and tachycardias but blockades, including atrioventricular I, II degree, also occur in healthy individuals. Their frequency in childhood is about 10%, and in adolescence decreases to 3%. Most often they arise during rest, night sleep and are associated with an increased parasympathetic activity.
For resting physiological HR range is 50-90 beats per minute.
The HR is subject to daily periodicals: the lowest at night and the greatest at 15-16 hours of the day. The amplitude of diurnal HR fluctuations in healthy young people is 30%. At HR of more than 90 beats/min, the risk of fatal cardiac arrhythmias increases dramatically.
Nikolay Amosov offers more stringent criteria for the upper limit of the resting heart rate as a measure of the level of health:
• up to 50 beats/min in men and 55 beats/min in women and boys – excellent;
• 50-65 beats/min for men and 55-70 beats/min for women and boys – good;
• 66-75 beats/min for men and 71-80 beats/min for women and boys – satisfactory;
• above 75 beats/min in men and 80 beats/min in women and boys – bad.
When the physical load increases, the maximum allowable increase in HR is determined by age and is calculated using the simple formula HRmax = (220 – number of years) beats/min.
Depending on the degree of increase in HR, the following 4 zones of intensity of physical activity are distinguished:
1 (up to 75% HRmax) – physical activity of low intensity;
2 (75-85% of HR) – exercise in aerobic mode (oxygen oxidation of glucose);
3 (85-92% HRMSax) – an anaerobic threshold zone, when the biochemical and energy systems of the body begin to function under conditions of oxygen starvation (anoxic glucose cleavage);
4 (more than 92% of HR) – an anaerobic zone, when the physical load has the maximum intensity and occurs in conditions of oxygen starvation with the formation and accumulation of lactic acid in the muscles.
The third and fourth zones of an intensity of physical activity are recommended only to athletes and require control.
Increasing the resting HR, prolonging the recovery time and decreasing the anaerobic threshold are important signs of physical overexertion or overtraining. In such cases, it is necessary to reduce the volume and intensity of physical activity under the careful control of HR.
The more the resting HR, the tighter and shorter life in the astronomical dimension. The HR accelerates, life becomes heavier and shortens with most diseases. The increase in HR especially affects the life expectancy of patients with arterial hypertension and ischemic heart disease.
The simplest methods are the examination of the pulse on the ray (most often) and other arteries and auscultation of the heart. The examination of the pulse is sufficient, if only it concerns persons with a healthy heart. With a sick heart, its auscultation (listening) is necessary.
In recent years to monitor the heart rhythm and HR use heart rate monitors, from the simplest to use in everyday life to multifunctional for athletes and coaches. In the simplest monitors, the heart rhythm and HR are monitored by recording and analyzing the pulse wave on the radial artery and in multifunctional ones, according to the electrocardiogram (ECG) registration data in one or several channels.
The latest models of monitors have significant volumes of electronic memory and a wireless connection to the computer, which allows you to obtain graphical information about the change in rhythm and HR in various study conditions – rest, physical and mental stress, etc.