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Diffusion capacity in the lungs is primarily influenced by the integrity of the alveolar membrane. The alveolar membrane serves as the interface where gas exchange occurs, and its structure and function are critical for the effective diffusion of oxygen and carbon dioxide between the air in the alveoli and the blood in the pulmonary capillaries.

When the alveolar membrane is intact and functioning properly, it allows for optimal transfer of gases due to its large surface area and the thinness of the membrane, which facilitates diffusion. Factors that can compromise this membrane—such as inflammation, fibrosis, or edema—can significantly impair diffusion capacity and lead to decreased gas exchange efficiency.

In contrast, while airway resistance, alveolar surface tension, and lung compliance are important factors in overall lung function, they do not directly affect the diffusion capacity as significantly as the integrity of the alveolar membrane. High airway resistance may obstruct airflow but does not inherently alter the ability of gases to diffuse through the alveolar membrane. Similarly, changes in alveolar surface tension and lung compliance influence respiratory mechanics but are secondary when considering the direct process of gas diffusion.