Factors Affecting Cardiac Output
Cardiac output also known as CO is defined in unit equations measurements or in words. In other terms, it refers to the capacity of blood pumped from the ventricles going to the aorta in a minute. Stroke volume and heart rate are the determinants of stroke volume. Though the heart rate is primarily influenced by nervous input, there are a couple of factors that change the stroke volume and consequently, influence cardiac output. Some of these factors affect the output indirectly by affecting the stroke volume and heart rate. Determination of cardiac output is expressed through the equation: CO=HR x SV.
Heart rate
When the heart is at rest, the rate is somewhere between sixty and one hundred beats a minute on average. When the heart rate increases as a result of stimulation or excitement caused by medication, drugs or some other source, the resulting effect is an increase of cardiac output. Heart rate decrease that is as a result of medication or electrical abnormality results to a decrease in cardiac output. Whenever the heart rate changes and becomes fast, the heart lacks enough time required to fill with adequate blood between heart beats and this results to a decrease in cardiac output.
Stroke volume
This is measurement of blood volume pumped from left ventricle in a single cardiac contraction. It is determined through measurement of blood volume in the left ventricle right before a contraction takes place.
Factors that indirectly affect cardiac output
Catecholamine’s is a chemical produced during excitement like work, activity or even work. Such episodes lead to an increase in the stroke volume and heart rate consequently rising the cardiac output. In some cases, cardiac output can decrease to a critically low level as a result of certain poisons or medications.
During a heart attack or myocardial infarction, there is also a major variation in the cardiac output. During the starting phase of a heart attack cardiac output variation is very significant and the response of the body is increased production of catecholamine which also leads to increased cardiac output. This leads to increase in the pressure the heart used in order to pump blood and can lead to increased pressure and also increase the hearts workload as it already experienced tissue death as a result of artery blockage.
Age, gender, physical fitness and body temperature are also other factors that might affect the cardiac output and these aspects vary from one individual to another. For instance, females are known to have a high heart resting rate as compared to makes while the heart rate of infants is higher compared to that of adults.
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Sources:
http://www.livestrong.com/article/109347-factors-affect-cardiac-output/
https://www.inkling.com/read/medical-sciences-naish-revest-syndercombe-1st/chapter-11/factors-affecting-cardiac-output
http://healthmad.com/health/factors-affecting-cardiac-output/