Expansion
Cardiac output equals oxygen consumption divided by the arteriovenous oxygen difference
Expansion
Cardiac output = oxygen consumption / (arterial oxygen content - mixed venous oxygen content)
Typical values:
- Oxygen consumption about 250 ml per minute
- Arterial oxygen content about 200 ml per litre
- Mixed venous oxygen content about 150 ml per litre
- So output = 250 / 50 = 5 litres per minute
Mixed venous blood must be sampled from the pulmonary artery, since that is the first point at which venous return from the whole body is fully mixed.
The principle generalises to any organ and any substance: uptake equals flow times the concentration difference across the organ. The same logic underlies measurement of renal plasma flow with para-aminohippurate and hepatic blood flow with indocyanine green.