Diffusion gradient for oxygen between the alveoli and pulmonary capillaries?

Alveoli

* Partial pressure of oxygen (PO2) = 100 mmHg

* Concentration of oxygen = 13.4 mM

Pulmonary capillaries

* Partial pressure of oxygen (PO2) = 40 mmHg

* Concentration of oxygen = 5.3 mM

The diffusion gradient for oxygen from the alveoli to the pulmonary capillaries is therefore:

100 mmHg - 40 mmHg = 60 mmHg or

13.4 mM - 5.3 mM = 8.1 mM

This gradient drives the diffusion of oxygen across the alveoli-capillary membrane.