Heart rate is the number of heartbeat cycles per minute, and a heartbeat cycle, also called cardiac action, includes the beating phases of systole and diastole. Systole refers to the contraction of the ventricles including blood ejection phase and diastole refers to the resting phase of the ventricles with simultaneous contraction of the atria and filling of the ventricles. The change in heart rate is one of several regulatory mechanisms by which the body can adjust the delivery rate of the heart in the short term to meet momentary demand.
What is heart rate?
Heart rate is the number of heartbeat cycles per minute, and a heartbeat cycle, also called a cardiac action, includes the beating phases of systole and diastole. Heart rate, is used to refer to the number of heartbeats per minute. A heartbeat comprises a complete stroke cycle, consisting essentially of the phases systole and diastole. During systole, which lasts approximately 300 milliseconds, the ventricles contract and force blood into the aorta (left ventricle) and pulmonary artery (right ventricle). During this phase, the relaxed atria fill with blood again. In the subsequent phase called diastole, the relaxation phase of the chambers (ventricles), the atria contract. They release their blood to the ventricles through the opened leaflet valves. The heart rate can be measured by simple means as a pulse. Its frequency can be palpated at various points on the body where arteries run close to the surface and determined by stopwatch or second hand. Varying the heart rate is one of several ways for the body to adjust the heart’s pumping capacity to meet short-term needs. The resting heart rate in a healthy adult is about 60 to 80 beats per minute. It can rise to its individual maximum rate during extraordinary physical exertion, which depends on age and fitness and can exceed 200 beats per minute.
Function and task
The ongoing demand for energy and oxygen by body tissues, especially skeletal muscle and the brain, is highly dependent on the power being called upon. During high athletic performance, the energy requirements and oxygen hunger of the affected muscle areas increase sharply. The body’s first, immediately effective measure is then to increase the heart rate. This significantly increases the blood flow per unit of time. The achievable individual maximum heart rate depends mainly on physical fitness and age. As a rough guide for the maximum pulse, the formula 220 minus age applies. This means that a healthy 40-year-old man with average fitness has a maximum pulse of about 220 – 40 = 180 beats per minute. Women of the same age reach a maximum pulse that is about 6 beats per minute higher. The individual maximum heart rate is therefore about three times the value of the resting heart rate. The heart rate can be used specifically to achieve certain training goals during fitness or running training. The most favorable range for building cardiovascular fitness is only 65-75% of the maximum frequency. In this frequency band, fat metabolism is activated, i.e. fat reserves are increasingly “burned” to produce energy for the muscles and carbohydrate reserves tend to be spared. The body is optimally stimulated to strengthen the cardiovascular system. Checking the heart rate during training can be done, for example, using inexpensive pulse watches that react acoustically when the pulse exceeds the previously set maximum value. In the frequency range above 85%, the anaerobic phase already begins; the heart can no longer supply the muscles with sufficient oxygen, so they have to resort to an additional alternative supply for a short time. The range above 85% of the maximum frequency should be reserved for experienced competitive athletes for targeted competition preparation. In general, it can be observed that the heart rate decreases with increasing training success, i.e. with increasing fitness at the same performance.
Diseases and ailments
An abnormal heart rate can have many causes. A pulse that is too fast or too slow, as well as arrhythmias in which the normal interaction between the atria and ventricles is disturbed, can be assigned to various complexes of causes.In many cases, there is a disturbance in the generation of beats in the so-called sinus node in the right atrium or a disturbance in the transmission of impulses to the atrioventricular node (AV node), which collects the electrical impulses from the atria and transmits them to the muscle cells of the ventricles, but can also generate its own, slower “reserve beat” if the sinus node fails. Relatively common is the so-called atrial fibrillation, which manifests itself in a high heart rate of usually more than 140 beats per minute and is often associated with a loss of performance, since despite a high heart rate, the volume of blood pumped may be reduced. While atrial fibrillation is not immediately life-threatening, other arrhythmias such as ventricular fibrillation and ventricular flutter are acutely life-threatening and require immediate emergency action. Ventricular fibrillation is characterized by contraction frequencies of more than 300 beats per minute, while the pumping volume drops to almost zero and can quickly express itself in cardiovascular collapse. Arrhythmias of this kind can be caused, for example, by acquired heart diseases such as valvular defects (valvular insufficiency), myocardial infarction, inflammation of the heart muscle and pericardium, or after surgical interventions on the heart. Other causes may lie outside the heart, such as hyperthyroidism, disturbances of the electrolyte balance (potassium, magnesium), side effects of certain drugs, psychovegetative disorders (stress, anxiety) or even poisoning with neurotoxins. The heart rate or rhythm disorders can also be caused by congenital anomalies. Congenital abnormalities include supernumerary (accessory) conduction pathways and some possible cardiac and valvular defects. A condition called cardiomyopathy, which is associated with impaired function of the heart muscles (electrical or mechanical), may also be congenital and lead to cardiac problems with arrhythmias.
