What is Fick Principle in Physiotherapy?

What is the Fick Principle?

The Fick principle and Fick equation are named after A. Fick, a cardiovascular physiologist who developed the principle in the 1870s. The amount of oxygen delivered to tissue can be calculated using the Fick principle.

The Fick principle states that the amount of a substance removed from the blood passing through an organ per unit of time can be calculated by multiplying the blood flow through the organ times the arterial concentration minus the venous concentration of that substance. 

The Fick principle can be used to calculate oxygen consumption for the entire body or for a specific tissue or organ. In the case of oxygen consumption for the entire body, the Fick principle results in the following equation:
 VO₂ = Q × a-v O₂ difference 
where Q equals cardiac output and,
a-v O₂ difference equals arterial-mixed venous oxygen difference.


This equation can be used to calculate oxygen consumption at rest, at submaximal workloads, and at maximal workloads. The Fick principle can also be used to calculate the uptake of any substance, such as glucose used in metabolism, by a tissue or organ.

• When a substance’s concentration is greater in arterial than in venous blood, it indicates that tissue is removing that substance from blood (e.g., oxygen).  
• When a substance’s concentration is greater in venous blood compared with arterial blood, it indicates that the tissue is giving off that substance (e.g., carbon dioxide).