Fick principle

The Fick principle describes developed by Adolf Fick classical method of physiology to determine cardiac output. The term is not identical to the ( also formulated by Adolf Fick ) Fick's laws of diffusion ( Fick's law ). The method relies on the principle of the indicator dilution method:

The river is one of an organ absorbed or released by him indicator corresponds to the difference of the indicator rivers in the inflow tract and outflow tract. The indicator used here is oxygen, it yields the following formula:

Wherein HMV is the cardiac output, the absorbed amount of oxygen per unit time and the arteriovenous oxygen difference avDO2. Therefore, there arises the need to measure the respiratory gases and make a determination of oxygen concentrations in arterialized and mixed venous blood.


For the determination of cardiac output is required the absorbed in the lungs per time quantity of oxygen (), which can be determined via a spirometric measurements of the respiratory gases and the oxygen concentration in the arterial () and mixed venous () blood, which can each have a can determine blood gas analysis. The pulmonary blood flow per unit of time () is the amount of oxygen absorbed in the lungs

Since virtually all the blood that flows through the lungs, also flows through the heart, you can take the equate HMV. By rearranging the formula thus obtained for cardiac output

Being referred to as arteriovenous oxygen difference ( avDO2 ).