Pulmonary edema and pulmonary fibrosis lead to hypoxemia primarily by:

Pulmonary edema and pulmonary fibrosis primarily lead to hypoxemia by impairing the diffusion of gases across the alveolocapillary membrane. In conditions like pulmonary edema, fluid accumulation in the alveoli interferes with gas exchange by increasing the distance between alveolar air and the blood in the capillaries. This fluid can obstruct the normal flow of oxygen from the alveoli into the blood, thus reducing the amount of oxygen available to be transported throughout the body.

Similarly, pulmonary fibrosis involves the thickening and scarring of lung tissue, which also increases the distance for diffusion and can lead to abnormal gas exchange. This thickening alters the permeability of the alveolocapillary membrane, making it less efficient for oxygen to pass into the bloodstream.

By impairing the ability of oxygen to diffuse from the alveoli into the blood, both pulmonary edema and pulmonary fibrosis contribute to hypoxemia, making this the correct choice.