What is a heart index
The Cardiac output (HMV) or Cardiac output (CO) is the volume of blood that the heart pumps through the bloodstream in one minute. The cardiac output is therefore a Measure for the pump function of the heart.
The cardiac output can be calculated by multiplying the heart rate by the heart rate.
Usually the cardiac output of the right heart is almost the same as the cardiac output of the left heart. The term cardiac output is somewhat more general. In principle, however, it means the same thing, only that the time unit is not specified here. It is abbreviated as HZV. In English and as a technical term also in German, the term cardiac output (abbreviated CO) is used for this.
For practical reasons, the value of the ejection fraction or ejection fraction (EF) has become more common for assessing the pump function, since it can be read directly from the echocardiography. The cardiac output, on the other hand, is determined in more complex cardiac catheter examinations.
If the cardiac output is related to the body surface, the result is called Cardiac Index or. Heart index :
- CI = HMV / body surface area
- At rest, the cardiac output in healthy adults is around 4.5-5 liters / minute. The lower normal value for the heart index is 2.5 l / min / m².
- Under load, the HMV can be increased up to four times and is then up to 20 liters / minute.
The HMV can only be measured indirectly in clinical practice. There are various methods of doing this:
- It can easily be calculated from the stroke volume and heart rate. HMV = heart rate × stroke volume. The stroke volume and heart rate can be estimated from echocardiography.
- Thermodilution is somewhat more complex. A defined amount of cold liquid is injected and the temperature profile of the blood is then recorded using a thermal probe. The HMV can be calculated using the speed of the temperature normalization. One way of putting this into practice is the Swan-Ganz catheter. This is a catheter that is pushed through a large vein in the neck (usually internal jugular vein or subclavian vein) into the pulmonary artery. E.g. with the help of an integrated heating coil, the CO can be determined continuously (i.e. without liquid being injected in the meantime).
- Dye dilution processes work similarly.
- After calibration by another method (e.g. thermodilution), model-based methods continuously calculate the HMV from the arterial blood pressure curve measured by an arterial catheter. An example of this is the PiCCO (Pulscontour Continuous Cardiac Output) system from Pulsion (R), which, in comparison to the Swan-Ganz catheter, offers the advantage of being a significantly less invasive procedure (since there is no catheter through the heart to the inside the pulmonary artery needs to be advanced).
- The HMV can also be calculated using the central venous oxygen saturation and the arterial oxygen saturation if the oxygen consumption is known at the same time (e.g. from partial pressure measurement in inhaled and exhaled air).
- The HMV can also be determined with the help of nuclear cardiology and the magnetic resonance examination.
A decreased cardiac output is found with decreased pumping capacity of the left or right ventricle. Heart valve diseases can also reduce cardiac output, as can hypothyroidism.
An increased cardiac output is found in fever, hyperthyroidism and anemia. Even in hyperdynamic shock states, such as septic shock, the HMV can be increased, although there may be an underperfusion of organs, which is due to a lowering of the peripheral resistance.
Categories: Cardiovascular Physiology | cardiology
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