Fick principle

1. Fick Principle
According to Jonathan

2. Cardiac Output
The volume of blood being pumped
by the heart in one minute.
CO = SV x HR

3. 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

4. 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

5. Step 1:
Determine Volume of O
2
consumed in one minute
Using a spirometer with attached CO
2 absorber
A commonly used value for O
2
consumption at rest is
125ml O
2
per minute
VO
2
=125ml

6. Step 2:
Determine O2 content in blood
O
2 content in arterial blood
Let’s assume oxygen concentration of arterial blood is
approximately 200ml of O
2
per litre
C
A
=200 ml O
2
/ l blood
O
2
content in venous blood
Let’s assume oxygen concentration of mixed venous
blood is approximately 150ml of O
2
per litre

C
V
=150 ml O
2
/ l blood

7. Step 3:
Do the math!
CO = (VO
2
/[C
A
- C
V
])*100
so:
CO = (125/[200 - 150])*100

8. 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

9. The End
Class is not over. Do not leave yet.
Cash donations accepted.