Fick Principle+

Adolf Eugen Fick was a German physiologist. He earned his doctorate in medicine at Marburg. In 1855 he introduced Fick’s law of diffusion, which governs the diffusion of a gas across a fluid membrane. In 1870 he was the first to devise a technique for measuring cardiac output, called the Fick principle.

The idea behind the the Fick principle is that perfusion through an organ (or entire being for that matter) can be determined by measuring the difference in oxygen concentration between arterial and venous blood (this would explain why atmospheric air contains 21% oxygen and expired air contains 16% oxygen).   What’s important to note is Dr. Fick was using oxygen to measure cardiac output (he could have used another gas).   The work of understanding this equation is comes from analyzing the variables that affect the oxygen gradients.  Physicians, physiologists, scientists have toyed with this equation for many years and what can be inferred from Fick’s equations is that the movement of oxygen in the body depends on the following:

1.  Adequate concentration of inspired oxygen
2.  Appropriate movement of oxygen across the alveolar-capillary membrane into the arterial bloodstream.
3.  Adequate number of red blood cells to carry the oxygen
4.  Proper tissue perfusion
5.  Efficient off-loading of oxygen at the tissue level.