Which value is most helpful in determining the presence of pulmonary emphysema in a patient with moderate obstructive pulmonary impairment?

In the assessment of pulmonary emphysema, the most useful value is the diffusing capacity for carbon monoxide (DLCO). Emphysema is characterized by the destruction of alveolar walls and a subsequent reduction in surface area available for gas exchange. This destruction leads to a decrease in the lung's ability to transfer gas from the alveoli to the blood, which is reflected by a reduced DLCO.

Additionally, patients with emphysema typically present with an obstructive pattern on spirometry, showing decreased FEV1/FVC, but the DLCO specifically helps in differentiating emphysema from other forms of obstructive disease such as chronic bronchitis, where the DLCO may be normal or only slightly reduced.

While the FEV1/FVC% ratio and peak flows like FEF25-75 can indicate the presence of obstructive lung disease, they do not provide specific information about the integrity of the alveolar-capillary membrane or the extent of emphysema. Similarly, the nitrogen washout test primarily evaluates lung volume and distribution, rather than the specific gas exchange characteristics that are compromised in emphysema. Thus, DLCO is the most critical parameter in confirming the presence of pulmonary emphysema in cases of moderate obstruct