Cardiac output is a measurement of how well the heart works, calculated by multiplying heart rate and stroke volume. A range of 4-8 liters is considered normal, with variations based on fitness level. Exercise increases cardiac output, but a lack of increase could indicate heart problems.
There are a number of measurements of how well a heart works and one of them is determining the volume of blood the heart pumps in one minute. This is called cardiac output, and its measurement is a common feature of several family heart tests. It can be measured when people have an echocardiogram and is often calculated even more accurately if a person has an angiogram or heart catheterization.
To understand cardiac output, which is often referred to as Q, it is helpful to understand a few other key terms. One of them is stroke volume or SV. SV would be the most accurate measurement possible of the amount of blood leaving the heart with each stroke. Equally important is heart rate or HR; this is the number of beats per minute.
Assuming people know or can guess stroke volume, it becomes fairly easy to calculate cardiac output. It is simply the product of heart rate and stroke volume in just one minute. This amount may vary from person to person. Those with heart problems may have reduced output and very well trained athletes may have higher volume output. Interestingly, people with significant athletic training don’t usually have higher heart rates, but they do tend to have higher stroke volumes, meaning their hearts pump slower but pump more blood with each beat.
There can be variety in what is considered normal cardiac output. Many people say that the volume of 5 liters is normal, which is like saying that the body circulates its entire blood supply in one minute. This measurement is not always the “normal” one for people, and many suggest that a cardiac output range of 4-8 L is a more appropriate statistic, or that any number received is best interpreted by a physician. It should be understood that some accounts for the variation are based on things like fitness level, and production is generally expected to be greater in those with greater heart health.
As might be expected, in the healthy heart, cardiac output increases with exercise. The heart beats faster and circulates blood faster, in theory. When the blood being pumped doesn’t increase as you would expect, this could be a significant health outcome. It could suggest an inability of the heart to respond adequately to exercise, and this could cause the heart to become overwhelmed or be more at risk with exercise. A stress echocardiogram could be a means of measuring the heart at work and determining that output is healthy and appropriate. People who have had heart problems in the past often have them periodically to determine what forms of exercise they can safely perform.
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