A patient presents with a DLCO below the normal range. What might this suggest?

• A. Bronchial obstruction
• B. Alveolar damage
• C. Increased respiratory rate
• D. Normal diffusion

Answer: (B)

A reduced diffusion capacity of the lungs for carbon monoxide (DLCO) indicates a potential issue with how well gas exchanges occur in the alveoli. Normally, DLCO testing assesses the ability of the lungs to transfer gas from inhaled air to the bloodstream. If a patient has a DLCO below the normal range, it is often indicative of alveolar damage or dysfunction.

Alveolar damage can arise from various conditions, such as pulmonary fibrosis, emphysema, or alveolar hemorrhage. These conditions result in either a reduced surface area for gas exchange or compromised alveolar integrity, leading to impaired oxygen transfer efficiency. Thus, a low DLCO is suggestive of pathological changes at the alveolar level rather than issues related to airflow obstruction, respiratory rate changes, or normal diffusion characteristics.

In contrast to alveolar damage, bronchial obstruction typically affects airflow but may not directly impact the diffusion capacity unless it significantly alters lung volumes and surface area for gas exchange. An increased respiratory rate does not inherently diminish DLCO, and normal diffusion would not present with a DLCO reduction at all. Therefore, the identification of alveolar damage as the cause of a reduced DLCO is fundamental in understanding pulmonary function and in diagnosing underlying lung conditions.