Fick Principle

According to Jonathan

Cardiac Output

The volume of blood being pumped by the heart in one minute.

CO = SV x HR

Adolf Fick (1829-1901)

Cardiac Output can be determined by the difference in concentration of a substance in the blood as it enters and exits an organ

Allen Thicke

In order to apply the Fick Principle, the following must be 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

Therefore: Cardiac Output can be determined from the difference in oxygen concentration in blood before it enters and after it leaves the lungs

Blood flow to an organ can be calculated using a

marker substance.

organ= lungs

marker substance= oxygen

Step 1: Determine Volume of O2 consumed in one minute

Using a spirometer with attached CO2 absorber

A commonly used value for O2 consumption at rest is 125ml O2 per minute

VO2=125ml

Step 2:Determine O2 content in blood

O2 content in arterial blood Let’s assume oxygen concentration of arterial blood is

approximately 200ml of O2 per litre CA=200 ml O2 / l blood O2 content in venous blood Let’s assume oxygen concentration of mixed venous

blood is approximately 150ml of O2 per litre

CV=150 ml O2 / l blood

Step 3:Do the math!

CO = (VO2/[CA - CV])*100

so: CO = (125/[200 - 150])*100

When do we use the Fick Principle?

We don’t. Sometimes used in renal physiology to determine blood

flow in the kidneys Marker substance is not oxygen, but Aminohippuric acid

The End

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