Free Essay: Factors Affecting Cardiac Output
Cardiac output refers to the amount or volume of the blood that the heart pumps through the right or left ventricle in an interval of a single minute. Cardiac output can be measured in different ways including dm3/min. During a systole phase, cardiac output refers to the combined amount of output of both the left ventricle and the right ventricle. There are several factors affecting cardiac output.
Two major factors affect cardiac output. These are the heart rate and stroke volume. Heart rate refers to the number of beats that a heart makes per minute. It can also be defined as the number of the heart-loads of the blood that the heart ejects per minute. Stroke volume on the other hand is the total blood’s volume that a heart can have or fill with. This blood volume is ejected once the heart contracts.
Cardiac output increases when the heart rate increases. This happens in terms of cardiac volumes that measure the blood that the heart releases into the other parts of the body. Once the heart has sufficient resting phase or diastole, the output volume increases.
There are three major factors that can increase stroke volume. These are the after-load, the myocardial contractility and the preload. High preload or venous pressure may increase stroke volume because it causes more filling of the heart during diastole. Increase in blood pressure causes a flow of more blood to the heart which downs pressure gradient.
Decreased after-load or the arterial blood pressure may also cause an increase in the cardiac output because it reduces the input resistance that the heart has to overcome while pumping blood to the vasculature. The heart is required to work harder against the pressure gradient when there is higher arterial pressure in order to pump blood into the body system.
When there is low arterial pressure, the heart has to work hard also and more blood volume is ejected to the vasculature. Efficient pumping of the heart is affected by myocardial contractility. The heart pumps more blood during the systole phase when there is higher contractility. This is because the cardiac muscle increases the ejection force of the heart. Cardiac output increases because the heart is allowed to pump out more blood volume.
Catecholamine also affects cardiac output. Catecholamines are the chemicals that are produced during excitement periods. These chemicals are released while working, exercising or engaging in any other activity. These increases both stroke volume and heart rate which in turn affect cardiac output.
Poisons and some medications also affect cardiac output. This is because they decrease heart rate and the ability of the heart to forcibly contract. This decreases cardiac output to even critical levels.
Assessing cardiac output is vital because it determines the actual performance of the heart regarding the entire cardiovascular system.
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