Which of the following is NOT a factor that influences the diffusion rate across respiratory membranes of the lungs?

The diffusion rate of gases across respiratory membranes is influenced primarily by factors that affect how gases move from areas of higher concentration to areas of lower concentration. These factors include the thickness of the membrane, the surface area available for diffusion, and the diffusion coefficient of the gas itself.

The thickness of the respiratory membrane plays a significant role in the ease with which gases can diffuse; a thicker membrane decreases the rate of diffusion. Similarly, a larger surface area facilitates a higher rate of diffusion as there is a greater area for gas exchange to occur.

Additionally, the diffusion coefficient of a gas indicates how easily a particular gas can move through the membrane. This is affected by factors such as the gas's molecular weight and solubility.

In contrast, oncotic pressure disparities relate to the movement of fluids and solutes rather than gases. Oncotic pressure, often influenced by protein concentrations in blood and interstitial fluid, does not directly impact the diffusion of gases across the alveolar-capillary membrane. Therefore, it is not considered a factor in the diffusion rate of respiratory gases. This understanding clarifies why the chosen answer is correct; oncotic pressure differences do not play a role in the mechanics of gas diffusion in the lungs.