1. Defintion
The heart rate is defined as the number of times the heart contracts and relaxes per minute. It is an indicator of the heart’s efficiency in pumping blood throughout the body.
Typically, heart rate and pulse frequency are correlated. In rare instances, referred to as a “pulse deficit,” there may be a discrepancy between the two measurements.
2. Classification
- Bradycardia (Low Heart Rate): <60 beats per minute
- Tachycardia (High Heart Rate): 60 – 100 beats per minute
- Normocardia (Normal Heart Rate): >100 beats per minute
3. Factors Affecting Heart Rate
The sympathetic nervous system is responsible for increasing heart rate, particularly during instances of physical or emotional stress (fight and stress reaction), while the parasympathetic nervous system exerts a baseline inhibitory effect, thereby facilitating a reduction in heart rate during periods of rest.
The parasympathetic nervous system exerts its primary influence on the heart through the vagus nerve, which releases acetylcholine to reduce the heart rate by decreasing the rate of depolarization of the sinoatrial (SA) node, the heart’s intrinsic pacemaker. This parasympathetic action establishes a lower resting heart rate, typically between 60 and 100 beats per minute for adults, a state known as parasympathetic tone. In the absence of parasympathetic regulation, the intrinsic heart rate, driven by the SA node, would be considerably higher, around 100 to 110 beats per minute.
Baroreceptors, located in the carotid arteries, aortic arch, and atria, regulate heart rate by detecting alterations in blood pressure and transmitting signals to the autonomic nervous system, prompting adjustments in heart rate in response to changes in blood pressure. When blood pressure is elevated, the baroreceptors signal the autonomic nervous system to reduce heart rate, whereas when blood pressure is low, they prompt an increase in heart rate.
Additionally, hyperthermia at the SA node can result in an increased frequency due to the elevated conduction velocity.
3.1. Reflexes
- Baroreceptor Reflex (Baroreflex)
- Depressor Reflex
- Pressor Reflex
- Carotis Sinus Reflex
- Bainbridge Reflex (Atrial Reflex)
- Chemo Reflex
- Bezold-Jarisch Reflex
- Cushing Reflex
- Oculocardiac Reflex
- Hering-Breuer Reflex (respiration Reflex)
4. Physiological Values
- Resting heart rate (adults): 60–100 beats per minute (BPM)
- Resting heart rate (athletes): 49–60 BPM
- Resting heart rate (children):
- Newborns: 90–170 BPM
- Infants (up to 1 year): 90–150 BPM
- Children (1–10 years): 70–130 BPM
- Children (over 10 years): 60–100 BPM
- Target heart rate during moderate exercise (adults): 50–70% of maximum heart rate
- Target heart rate during vigorous exercise (adults): 70–85% of maximum heart rate
- Maximum heart rate: Approximately 220 minus age (e.g., for a 30-year-old: 220 – 30 = 190 BPM)
These values can vary based on individual fitness, age, and overall health.