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The human heart is an involuntarily contracting muscle responsible for the distribution of blood throughout the body. The heart's sequence of motions can be categorized as contraction, which is known as systole, and diastole, which is a term used to describe relaxation. The end systolic volume is simply the volume of blood that remains in the heart after the completion of a contraction.
Blood is the nutrient-rich fluid that fills the body's veins and arteries, enabling the organs and other structures it reaches to perform their functions. Without the oxygen, clotting factors, vitamins, and minerals in blood, the organs that rely on these life-sustaining particles could not function. The heart is the motor behind the blood transfer mechanism, and without its contractions and relaxations, blood would have no way of moving throughout the body.
End systolic volume can be thought of as the blood left over in the heart. When the heart relaxes, its chambers expand, causing a decrease in chamber pressure that makes blood enter. When enough blood enters the chambers, the pressure equalizes, at which point, in a healthy heart, contraction initiates. Not all of the blood that was once in the chambers exits with each beat, leaving a specific end systolic volume remaining.
The more blood circulated generally means the more abundant nutrients are to the body, making healthy physiological function more likely. There is a direct relationship too between the blood available for ejection from the heart and the volume actually ejected. This principle is known as the Frank Starling law after the physiologist who first recognized it. Basically, the higher the preload, or volume of blood in the heart before contraction, the higher the stroke volume, which is the amount of blood sent throughout the body with a single contraction.
The heart, blood, and end systolic volume are not directly visible without medical intervention, so using specific measurements can help to illustrate what actually happens in the heart. End systolic volume, for example, is typically between 16 and 143 milliliters, with the mean usually in the range of 50 milliliters. Stroke volume is about 70 milliliters on average, and end diastolic volume, the amount of blood after the relaxation phase, ranges from 65 to 240 milliliters.
The significance of measuring many of these values is to better assess any aspects of the heart that may not be functioning correctly. It is therefore much easier to identify and treat potential ailments. These values, of course, are subject to change and slightly dependent upon the tools used to measure them.