Heart Rate: Optimal Levels and Health Implications - Family Medicine

Dr. Xiao Yongxun reply Family Medicine

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Dear Mr.
Jfkdjk:
1.
The factors affecting heart rate are quite complex, with autonomic nervous system control being the most significant.
The autonomic nervous system regulates heart rate primarily through the "cardioacceleratory center (CAC)" and the "cardioinhibitory center (CIC)" located in the medulla oblongata.
The cardioacceleratory center transmits stimulation via sympathetic nerve fibers and secretes epinephrine, which increases heart rate and enhances ventricular contractility.
In contrast, the cardioinhibitory center transmits signals via the vagus nerve (parasympathetic fibers) and secretes acetylcholine (Ach), which acts on the sinoatrial node (S-A node) to slow the heart rate or affects the atrioventricular node (A-V node) to delay conduction.
2.
When venous return increases, venous pressure rises, causing baroreceptors in the atrial walls to detect the pressure and send signals to the cardioacceleratory center.
This stimulates the sympathetic nervous system to increase output, leading to an accelerated heart rate and enhanced myocardial contractility, preventing blood from remaining in the heart.
3.
As the heart rate accelerates, the volume of blood ejected from the left ventricle increases.
Baroreceptors located in the walls of the carotid sinus detect the increased pressure against the vessel walls and transmit information via the glossopharyngeal nerve to the cardioinhibitory center, which sends more signals to inhibit the S-A node, slowing the heart rate and ultimately reducing cardiac output and blood pressure.
Conversely, when baroreceptors sense a decrease in pressure against the vessel walls, this leads to an increased heart rate and higher cardiac output.
This mechanism helps maintain a constant blood supply throughout the body.
4.
Additionally, there are pressure receptors located in the walls of the aortic arch.
When these receptors detect increased pressure against the vessel walls, they transmit signals via the vagus nerve to the cardioinhibitory center, which sends more signals to inhibit the S-A node, slowing the heart rate and ultimately reducing cardiac output and blood pressure.
This mechanism is similar to the carotid sinus reflex and helps maintain peripheral blood pressure stability.
5.
The coronary circulation system primarily supplies the heart with the necessary nutrients and oxygen, accounting for about 4-5% of total cardiac output (200-250 ml/min).
This system consists of the left and right coronary arteries.
Coronary blood flow perfusion mainly occurs during diastole, when the aortic valve closes, allowing blood returning from the aorta to perfuse the coronary artery system, providing the oxygen and nutrients required for cardiac contraction.
6.
If the heart contracts too rapidly or too frequently, the duration of diastole will inevitably shorten, leading to reduced coronary blood flow perfusion and resulting in hypoxia.
Therefore, in patients with myocardial hypoxia or heart failure, medications to lower heart rate are often used to allow the heart to rest and achieve greater coronary blood flow perfusion.
This may be one reason some people believe that a faster heart rate is associated with a shorter lifespan.
7.
During embryonic development, a regular heartbeat of about 65 beats per minute appears around the 4th to 5th week, increasing to about 140 beats per minute at 4 months.
After birth, the heart rate is approximately 90-110 beats per minute until the age of 3.
In adulthood, due to vagal control, the heart rate gradually decreases to 70-80 beats per minute; blood pressure rises with left ventricular development, with systolic pressure ranging from 94-112 mmHg and diastolic pressure from 56-60 mmHg.
8.
Clinically, a heart rate of 60-100 beats per minute is generally considered acceptable.
However, if there are symptoms such as palpitations, myocardial hypoxia, or other discomforts, clinicians may use medications to lower the heart rate to alleviate symptoms.
9.
Regular exercise, practicing deep breathing techniques, avoiding anxiety or stress, reducing tea or coffee intake, relaxing, and ensuring adequate sleep can all lower sympathetic nervous system activity and reduce heart rate.
10.
If you have further questions, it is advisable to discuss them with your family physician.

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Reply Date: 2020/08/07