Subtyping emphysematous COPD by respiratory volume change distributions on CT

Area of Science:

• Pulmonary Medicine
• Radiology
• Medical Imaging

Background:

• Chronic obstructive pulmonary disease (COPD) exhibits significant patient heterogeneity.
• Emphysema severity and ventilation distribution in emphysematous regions may influence clinical-physiological impairments.

Purpose of the Study:

• To investigate the impact of ventilation discordance between emphysematous and non-emphysematous regions on COPD outcomes.
• To assess the relationship between respiratory volume changes and clinical-physiological impairments in COPD patients.

Main Methods:

• Quantified emphysema using inspiratory CT low attenuation volume percentage (iLAV%).
• Calculated local respiratory volume changes via non-rigidly registered expiratory/inspiratory CT.
• Defined Ventilation Discordance Index (VDI) as log-transformed Wasserstein distance between regional volume change distributions.

Main Results:

• In cohort 1 (n=221), lower FEV1 was observed in the low VDI group compared to high VDI and minimal emphysema groups.
• Higher iLAV%, airway disease, and hyperventilated emphysematous regions were associated with lower VDI.
• Cohort 2 (n=93) confirmed that lower VDI correlated with greater annual FEV1 decline and higher mortality, independent of emphysema severity and airway disease.

Conclusions:

• Lower VDI is a significant predictor of severe airflow limitation in emphysematous COPD.
• Reduced ventilation discordance is associated with increased mortality, independent of emphysema severity and airway morphology.