Definition
The cardiac output per minute (HMV) is defined as the volume of blood pumped per minute from the heart into the body’s circulation. Alternatively, the term body time volume is also used, but the term cardiac output per minute is more common. The cardiac output per minute is used as a measure of the pumping function of the heart, i.e. it describes the ejection rate of the heart or, in short, the cardiac output. A similar term for cardiac output is cardiac output during the cardiac cycle, but it has no relation to a specific time unit.
How can I calculate or measure my cardiac output?
The heart minute volume is the product of the heart rate (HF), which can be determined by the pulse, and the stroke volume. The cardiac output per minute is therefore equal to the heart rate times the stroke volume (HMV = HF x stroke volume). In simple terms, the stroke volume is the volume ejected by the left ventricle during a heartbeat.
To determine the heart minute volume, it is therefore necessary to determine the stroke volume. However, this is complicated and time-consuming, yet there are several methods to determine the stroke volume. One can calculate the stroke volume with the so-called thermodilution method.
In this method, a Swan-Ganz catheter is inserted through a vein in the neck over the right half of the heart into the pulmonary arteries. Cold fluid is then injected into the right atrium and the catheter measures the temperature change. In the course of the procedure, the catheter’s measurement data on the temperature loss and the further course of temperature can be used to measure the cardiac output per minute.
A simpler, but also less accurate method is echocardiography, i.e. heart ultrasound. Here, the stroke volume can be calculated by measuring the diameter of the outflow tract of the left ventricle, which is calculated into a three-dimensional surface using the circular surface formula. In addition, the cardiac output can be calculated from the oxygen concentration in venous blood, arterial blood and the oxygen uptake from the lungs.
The cardiac output is the volume of oxygen absorbed per unit of time from the lungs divided by the oxygen concentration in the arterial blood, which must be subtracted from the oxygen concentration in the mixed venous blood. This ultimately corresponds to the blood flow through the lungs, which can be equated with the cardiac output per minute. In addition, there are several other methods that can be used to determine the stroke volume.
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