The number of times the heart beats or completes a cardiac cycle in one minute.
The number of cardiac cycles per minute.
The number of times per minute that the heart fills with blood and then pumps the blood into the vascular system.
The number of times the heart beats per minute.
Number of heart contractions (beats) per minute. A normal adult heart rate is about 60-80 beats per minute; an abnormally rapid heart rate (over 100 beats per minute in an adult) is tachycardia; an abnormally slow rate (below 60 beats per minute in an adult) is bradycardia. A child normally has a heart rate faster than an adult.
The number of heartbeats per unit of time, usually expressed or written as number per minute.
Heart rate refers to the speed at which the heart contracts to circulate blood throughout the body. For most individuals, the resting heart rate falls within the range of 60 to 100 beats per minute. In childhood, heart rate tends to be higher and gradually decreases with age. Highly physically fit individuals may exhibit a resting heart rate below 60 beats per minute.
The heart rate and the amount of blood ejected with each contraction can vary significantly based on the body’s need for oxygenated blood. At rest, the heart typically contracts at a rate of 60 to 80 beats per minute, with each ventricle pumping about 80 ml of blood per beat (approximately six liters per minute). During intense physical activity, the heart rate can increase to around 200 contractions per minute, and the output may rise to nearly 250 ml per beat, resulting in a total output of 50 liters per minute. These adjustments in heart rate and output are controlled by the heart muscle and the autonomic nervous system, which is responsible for regulating automatic body functions.
Initially, the heart muscle reacts automatically to any rise in activity by enhancing its output. This response happens due to the contraction of active muscles, which compress the veins passing through them, thus propelling the blood back towards the heart. As the ventricles fill with more blood during the diastole phase (the filling phase of the heart’s cycle), they contract more forcefully during ventricular systole to efficiently eject the blood.
Next, the heart rate is regulated by the autonomic nervous system. The components of this system responsible for heart function include the cardiac center, a cluster of nerve cells located in the brainstem, and two sets of nerves known as parasympathetic and sympathetic nerves. These nerves, under the control of the cardiac center, exert contrasting effects on the heart, allowing for the regulation of heart rate.
During periods of rest, the parasympathetic nerves, particularly the vagus nerve, are active. These nerves transmit signals to the sinoatrial node, resulting in a slowdown of the heart rate from its intrinsic rate of approximately 140 impulses per minute to around 70 impulses per minute (known as vagal inhibition). However, during or in anticipation of physical activity, vagal inhibition reduces, causing the heart rate to accelerate. Furthermore, the sympathetic nerves come into action, releasing the hormone noradrenaline, which further increases heart rate and the strength of contractions. Additionally, the adrenal glands release adrenaline and noradrenaline, contributing to an elevation in heart rate.
The transition from parasympathetic to sympathetic activity is prompted by any signal to the cardiac center indicating a demand for increased blood output from the heart. These signals may arise from factors like fear or anger, low blood pressure, or a decrease in oxygen levels in the blood.
Doctors can assess the heart’s rate and rhythm by either feeling the pulse or listening to the heart using a stethoscope. For a more precise measurement, an electrocardiogram (ECG) is conducted to measure the heart’s electrical activity. A resting heart rate surpassing 100 beats per minute is referred to as tachycardia, while a rate below 60 beats per minute is termed bradycardia.