Transfer coefficients better reflect emphysematous changes than carbon monoxide diffusing capacity in obstructive...

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology
• Diagnostic Imaging

Background:

• The overlap between asthma and chronic obstructive pulmonary disease (COPD) presents diagnostic challenges.
• Understanding lung diffusion parameters like carbon monoxide diffusion capacity (DLco) and transfer coefficients (Kco) is crucial for managing obstructive lung diseases.

Purpose of the Study:

• To investigate the behavior of DLco and Kco in patients with asthma and COPD, particularly in relation to emphysematous changes.
• To determine if Kco is a more accurate indicator of emphysematous lung changes than DLco in obstructive lung diseases.

Main Methods:

• Evaluated DLco and Kco in nonsmokers with asthma (As-NS), smokers with asthma (As-Sm), and COPD patients, controlling for airflow limitation (FEV1%).
• Quantified emphysema using computed tomography (CT) by measuring emphysema volumes (lung attenuation volume, %LAV) and small pulmonary vessel area (%CSA<5 mm²).
• Correlated DLco and Kco with %LAV and %CSA<5 mm² across different patient groups.

Main Results:

• %Kco correlated inversely with reduced FEV1% in As-NS but not in As-Sm.
• %Kco differentiated between asthma and COPD groups even when airflow limitation was matched, whereas %DLco was only reduced in COPD.
• %LAV and %CSA<5 mm² showed stronger correlations with %Kco than with %DLco, indicating Kco better reflects emphysematous changes.

Conclusions:

• %Kco is a more sensitive marker of pathophysiology in obstructive lung diseases, including smokers with asthma, compared to %DLco.
• The findings suggest that %Kco provides a better reflection of emphysematous changes, offering valuable insights into disease mechanisms.
• Precise interpretation of %DLco and %Kco may aid in understanding the pathophysiology of obstructive lung diseases.