Which condition is most likely associated with an inability to diffuse O2?

The condition most closely associated with an inability to diffuse oxygen is pneumonia or ARDS (Acute Respiratory Distress Syndrome). Both of these conditions lead to significant impairment in the alveoli, where gas exchange occurs. In pneumonia, lung inflammation and accumulation of fluid and pus in the alveoli hinder the diffusion of oxygen into the blood. Similarly, ARDS is characterized by widespread inflammation in the lungs, leading to increased permeability of the alveolar-capillary membrane, which further complicates oxygen diffusion.

While hypoxic respiratory failure is a consequence of the inability to supply adequate oxygen to the tissues, it is a symptom rather than a specific condition that directly describes a failure of oxygen diffusion. Chronic bronchitis, although it contributes to airway obstruction and can result in lowered oxygenation, primarily affects air flow rather than diffusion in the alveoli. Thus, while all these conditions can lead to reduced oxygen levels in the blood, pneumonia and ARDS specifically highlight the primary issue of impaired diffusion.