The Contraction force of the heart is the force with which the heart contracts and sets blood in motion. It depends on various factors and can be influenced by medication.
What is the force of contraction?
A physiological contraction force of the heart is the prerequisite for the heart being able to pump so much blood into the body's circulation that the entire body is adequately supplied with blood.
At rest, the human heart pumps the entire volume of blood through the circulation about once per minute. With each pumping action, each of the heart chambers transports about 50 to 100 milliliters of blood. The heart contracts about 50 to 80 times per minute.
The higher the force of contraction of the heart, the more blood can be expelled. The force of contraction is controlled, among other things, by the influence of sympathetic nerve fibers. The force of contraction can also be influenced with medication.
Function & task
The heartbeat is triggered by action potentials. These spread through the specialized muscle tissue of the heart. The first thing during a pumping cycle is the atria of the heart to fill. At the same time, the chambers eject blood into the body's circulation. The heart muscles in the chambers then relax again and the blood can flow from the atria into the chambers. This phase is known as ventricular diastole.
The filling of the chambers is supported by a contraction of the atria (atrial systole). When the chambers are sufficiently filled, the ventricular muscles contract. The pocket flaps of the chambers open and blood can flow into the arteries. This phase is called ventricular systole.
How much the chambers contract and how much blood they then expel is influenced by a number of factors. During physical exertion, the heart's action is stimulated by the influence of nerve fibers of the sympathetic nervous system. The neurotransmitter noradrenaline is released from the cells of the heart muscles. Adrenaline also reaches the heart via the blood. The effect of the transmitters and hormones on the heart muscle is mediated via so-called β1 adrenoceptors.
Various mechanisms open up calcium channels in the cells, so that more calcium can flow into the cells. This leads to an increased muscle contraction of the heart. Norepinephrine and adrenaline thus influence the force of contraction of the heart. They have a positive inotropic effect.
The contraction force of the heart usually adapts automatically to the physical demands. Extra blood volume stretches the heart muscle. This also improves the function of the muscle cells. This mechanism is known as the Frank Starling mechanism. It states that there is a connection between the filling and the ejection capacity of the heart. The greater the volume of blood that flows into the heart during diastole, the greater the volume of blood that is ejected during systole. Increasing filling of the atria leads to a stronger contraction of the heart with an increase in stroke volume. So one could say that the force of contraction of the heart depends on the preload.
The Frank Starling mechanism is used to adapt the heart's activity to fluctuations in pressure and volume. The goal is that the right and left chambers always pump the same volume. In the event of faults, complications would arise within a very short time. The result would be pulmonary edema, for example.
Illnesses & ailments
Heart failure is a condition in which the heart does not have the ability to contract. Heart failure is also called heart failure or heart muscle weakness. It can arise from almost any heart disease. Typical causes are coronary artery disease (CHD), heart muscle inflammation (myocarditis), heart valve diseases, heart valve defects or pericarditis (pericarditis).
Chronic lung diseases can also cause heart failure. Risk factors also include increased cholesterol, diabetes mellitus, smoking, alcohol addiction and being very overweight.
In heart failure, the cardiac output is reduced due to a decrease in the stroke volume. The contraction force of the heart is no longer sufficient to supply the body with sufficient blood. The body then reacts with a release of adrenaline and noradrenaline. On the one hand, this constricts the blood vessels and, on the other hand, the contraction force of the heart is increased. However, since the heart muscle is insufficient, the hormones and transmitters no longer work on the heart's receptors. The vessels, however, contract. This increases blood pressure. Despite the reduced force of contraction, the heart now has to pump against high pressure in the vessels. As a result, the condition of the heart worsens increasingly (vicious circle).
Digitalis preparations are often used to treat heart failure. These are cardiac glycosides, which are mostly obtained from the thimble. Digitalis has a positive inotropic effect. The contraction force of the heart is increased, which also increases the stroke volume.
Cardiac tamponade is a life-threatening disease that is associated with a reduced force of the heart to contract. With cardiac tamponade, the heart is compressed. The cause is usually fluid build-up in the pericardium. These can be caused by pericardial inflammation, hemorrhage, aortic aneurysms, and heart attacks.
Due to the compression by the fluid in the pericardium, the heart can no longer relax during diastole. This means that sufficient filling is no longer possible. According to the Frank Starling mechanism, the contraction force of the heart decreases when the atrial filling is reduced. As a result, there is a lower stroke volume. The result is a backlog of blood in front of the heart. In addition, the body is not adequately supplied with arterial blood. Typical symptoms of cardiac tamponade are low blood pressure, fast heartbeat, rapid breathing, and blue skin. Cardiac tamponade is a medical emergency. There is a risk of cardiogenic shock.
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