Background There is considerable heterogeneity among patients with emphysematous chronic obstructive pulmonary disease (COPD). We hypothesised that in addition to emphysema severity, ventilation distribution in emphysematous regions would be associated with clinical-physiological impairments in these patients.
Objective To evaluate whether the discordance between respiratory volume change distributions (from expiration to inspiration) in emphysematous and non-emphysematous regions affects COPD outcomes using two cohorts.
Methods Emphysema was quantified using a low attenuation volume percentage on inspiratory CT (iLAV%). Local respiratory volume changes were calculated using non-rigidly registered expiratory/inspiratory CT. The Ventilation Discordance Index (VDI) represented the log-transformed Wasserstein distance quantifying discordance between respiratory volume change distributions in emphysematous and non-emphysematous regions.
Results Patients with COPD in the first cohort (n=221) were classified into minimal emphysema (iLAV% <10%; n=113) and established emphysema with high VDI and low VDI groups (n=46 and 62, respectively). Forced expiratory volume in 1 s (FEV1) was lower in the low VDI group than in the other groups, with no difference between the high VDI and minimal emphysema groups. Higher iLAV%, more severe airway disease and hyperventilated emphysematous regions in the upper-middle lobes were independently associated with lower VDI. The second cohort analyses (n=93) confirmed these findings and showed greater annual FEV1 decline and higher mortality in the low VDI group than in the high VDI group independent of iLAV% and airway disease on CT.
Conclusion Lower VDI is associated with severe airflow limitation and higher mortality independent of emphysema severity and airway morphological changes in patients with emphysematous COPD.
Data are available on reasonable request.
http://dx.doi.org/10.1136/thoraxjnl-2021-218288
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Data are available on reasonable request.
Contributors HS: Concept and design of the study, data acquisition, statistical analysis, data interpretation and drafting of the manuscript; NT: concept and design of the study, data acquisition, data interpretation, manuscript editing, the guarantor of the paper; AO: analyses of CT data and data interpretation; KS: data interpretation; SK: data interpretation; KT: data acquisition and interpretation; TO: data interpretation and creating software to analyse the airway structure; TK: data interpretation; MS: data interpretation; HM: data acquisition and interpretation; AS: data acquisition and interpretation; MN: data acquisition, data interpretation, and critical revision of the manuscript; SS: data acquisition and interpretation; SK: data interpretation and revision of the manuscript; TH: data interpretation and revision of the manuscript for important intellectual content.
Funding The Kyoto-Himeji cohort was partially supported by a grant from the Fujifilm Corporation and Japan Society for the Promotion of Science (JSPS) (Grants-in Aid for scientific research 19K08624). The Hokkaido COPD Cohort Study was supported by a scientific research grant to the Hokkaido COPD Cohort Study from the Ministry of Education, Science, Culture and Sports of Japan (17390239 and 2139053 to MN), Nippon Boehringer Ingelheim, Pfizer, and the Respiratory Failure Research Group received a grant from the Ministry of Health, Labour, and Welfare, Japan for the Hokkaido COPD cohort.
Provenance and peer review Not commissioned; externally peer reviewed.
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