text: The Fick principle states that blood flow to an organ can be calculated using a marker substance if the following information is known:
  * Amount of marker substance taken up by the organ per unit time
  * Concentration of marker substance in arterial blood supplying the organ
  * Concentration of marker substance in venous blood leaving the organ
  Developed by Adolf Eugen Fick (1829–1901), the Fick principle has been applied to the measurement of cardiac output. Its underlying principles may also be applied in a variety of clinical situations.
  In Ficks original method, the "organ" was the entire human body and the marker substance was oxygen. The first published mention was in conference proceedings from July 9, 1870 from a lecture he gave at that conference; it is this publishing that is most often used by articles to cite Ficks contribution.The principle may be applied in different ways. For example, if the blood flow to an organ is known, together with the arterial and venous concentrations of the marker substance, the uptake of marker substance by the organ may then be calculated.