In diffusion limited gas exchange, which factor is primarily maintained?

• A. Gas solubility
• B. Partial pressure difference
• C. Blood flow rate
• D. Alveolar volume

Answer: (B)

In diffusion limited gas exchange, the factor that is primarily maintained is the partial pressure difference across the alveolar-capillary membrane. In this scenario, the rate of gas exchange is controlled by how much of the gas can diffuse across the membrane, which is directly influenced by the difference in partial pressures of the gases involved.

When gases diffuse, they do so from an area of higher partial pressure to an area of lower partial pressure. For diffusion to occur effectively, a stable and significant gradient must be maintained. If the partial pressure of the gas in the alveoli is higher than that in the blood, diffusion will occur until equilibrium approaches. In pathology or under certain conditions, if the blood flow is limited or if there is a constraint in how gases can diffuse, maintaining this difference becomes crucial to ensure that adequate gas exchange occurs.

Gas solubility is important in determining how much of a gas can be dissolved in the blood and may influence the overall exchange, but it is not the primary factor being maintained within the context of diffusion limitation. Similarly, while blood flow rate and alveolar volume are factors that impact gas exchange, they are not the primary determinants in diffusion limitation scenarios. The key takeaway is that in diffusion limited gas exchange, sustaining a substantial partial pressure