Heart rate

Most involve stimulant-like endorphins and hormones being released in the brain, some of which are those that are 'forced'/'enticed' out by the ingestion and processing of drugs such as cocaine or atropine.

Normally, vagal stimulation predominates as, left unregulated, the SA node would initiate a sinus rhythm of approximately 100 bpm.

Among these receptors are various proprioreceptors, baroreceptors, and chemoreceptors, plus stimuli from the limbic system which normally enable the precise regulation of heart function, via cardiac reflexes.

These chemoreceptors provide feedback to the cardiovascular centers about the need for increased or decreased blood flow, based on the relative levels of these substances.

[16] Using a combination of autorhythmicity and innervation, the cardiovascular center is able to provide relatively precise control over the heart rate, but other factors can impact on this.

Epinephrine and norepinephrine have similar effects: binding to the beta-1 adrenergic receptors, and opening sodium and calcium ion chemical- or ligand-gated channels.

The rate of depolarization is increased by this additional influx of positively charged ions, so the threshold is reached more quickly and the period of repolarization is shortened.

Caffeine works by increasing the rates of depolarization at the SA node, whereas nicotine stimulates the activity of the sympathetic neurons that deliver impulses to the heart.

[19] In a study conducted on 8 female and male student actors ages 18 to 25, their reaction to an unforeseen occurrence (the cause of stress) during a performance was observed in terms of heart rate.

[22] The heart rate can be slowed by altered sodium and potassium levels, hypoxia, acidosis, alkalosis, and hypothermia.

[16] Acidosis is a condition in which excess hydrogen ions are present, and the patient's blood expresses a low pH value.

Enzymes, being the regulators or catalysts of virtually all biochemical reactions – are sensitive to pH and will change shape slightly with values outside their normal range.

This distinct slowing of the heart is one component of the larger diving reflex that diverts blood to essential organs while submerged.

[16] A study shows that bottlenose dolphins can learn – apparently via instrumental conditioning – to rapidly and selectively slow down their heart rate during diving for conserving oxygen depending on external signals.

[27] Other studies have shown all-cause mortality is increased by 1.22 (hazard ratio) when heart rate exceeds 90 beats per minute.

[7] ECG of 46,129 individuals with low risk for cardiovascular disease revealed that 96% had resting heart rates ranging from 48 to 98 beats per minute.

In this test, a person is subjected to controlled physiologic stress (generally by treadmill or bicycle ergometer) while being monitored by an electrocardiogram (ECG).

The intensity of exercise is periodically increased until certain changes in heart function are detected on the ECG monitor, at which point the subject is directed to stop.

[citation needed] Adults who are beginning a new exercise regimen are often advised to perform this test only in the presence of medical staff due to risks associated with high heart rates.

"[45] While this formula is commonly used (and easy to remember and calculate), research has consistently found that it is subject to bias, particularly in older adults.

This theoretical range varies based mostly on age; however, a person's physical condition, sex, and previous training also are used in the calculation.

[56] A greater reduction in heart rate after exercise during the reference period is associated with a higher level of cardiac fitness.

[57] Another study reported a four-fold increase in mortality in subjects with an abnormal HRR defined as ≤12 bpm reduction one minute after the cessation of exercise.

This pulse rate can be found at any point on the body where the artery's pulsation is transmitted to the surface by pressuring it with the index and middle fingers; often it is compressed against an underlying structure like bone.

For example, Miguel Indurain, a Spanish cyclist and five time Tour de France winner, had a resting heart rate of 28 beats per minute,[68] one of the lowest ever recorded in a healthy human.

Daniel Green achieved the world record for the slowest heartbeat in a healthy human with a heart rate of just 26 bpm in 2014.

High heart rate is associated with endothelial dysfunction and increased atheromatous plaque formation leading to atherosclerosis.

[73] Other studies have shown that a high resting heart rate is associated with an increase in cardiovascular and all-cause mortality in the general population and in patients with chronic diseases.

In each case, the authors are actually referring to instantaneous HR, which is the number of times the heart would beat if successive RR intervals were constant.

[84] This is thought to occur because in addition to the direct beneficial effects of legumes, they also displace animal proteins in the diet, which are higher in saturated fat and cholesterol.