Fick Principle & Cardiac Output
We can use the Fick principle to calculate cardiac output by measuring oxygen consumption.
The Fick principle is based on the understanding that in a steady state, the rate of oxygen consumption must be equal to the difference in oxygen leaving and entering the lungs.
We can arrange the equation to solve for cardiac output as follows:
Total oxygen consumption divided by (O2 content of the pulmonary vein) - (O2 content of the pulmonary artery).
Let's do an example problem to solve for cardiac output:
A patient's total body oxygen consumption is 250 ml of oxygen per minute;
The oxygen content of the pulmonary vein is 0.20 ml oxygen per ml blood;
The oxygen content of the pulmonary artery is 0.15 oxygen per ml blood.
This gives us a cardiac output of 5000 ml, or 5 liters, per minute, which is within the normal cardiac output range for adults.
