Background Fractal dimension (D) characterises the size distribution of low attenuation clusters on CT and assesses the spatial heterogeneity of emphysema that per cent low attenuation volume (%LAV) cannot detect. This study tested the hypothesis that %LAV and D have different roles in predicting decline in FEV1, exacerbation and mortality in patients with COPD.
Methods Chest inspiratory CT scans in the baseline and longitudinal follow-up records for FEV1, exacerbation and mortality prospectively collected over 10 years in the Hokkaido COPD Cohort Study were examined (n=96). The associations between CT measures and long-term outcomes were replicated in the Kyoto University cohort (n=130).
Results In the Hokkaido COPD cohort, higher %LAV, but not D, was associated with a greater decline in FEV1 and 10-year mortality, whereas lower D, but not %LAV, was associated with shorter time to first exacerbation. Multivariable analysis for the Kyoto University cohort confirmed that lower D at baseline was independently associated with shorter time to first exacerbation and that higher LAV% was independently associated with increased mortality after adjusting for age, height, weight, FEV1 and smoking status.
Conclusion These well-established cohorts clarify the different prognostic roles of %LAV and D, whereby lower D is associated with a higher risk of exacerbation and higher %LAV is associated with a rapid decline in lung function and long-term mortality. Combination of %LAV and fractal D may identify COPD subgroups at high risk of a poor clinical outcome more sensitively.
- COPD ÀÜ mechanisms
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KS and NT contributed equally.
Contributors KS: study concept and design, statistical analysis, interpretation of data and drafting the manuscript; NT: acquisition of data, statistical analysis, interpretation of data and editing the manuscript; NVT: CT analysis and interpretation of data; MS: interpretation of data and critical revision of the manuscript; HM: acquisition of data and interpretation of data; SS: acquisition of data and interpretation of data and editing the manuscript; SM: acquisition of data and interpretation of data; MM: interpretation of data; TH: interpretation of data; EO, YN: interpretation of data; SK, MN: interpretation of data and finalising of the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests The Hokkaido COPD Cohort Study is 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 a grant to the Respiratory Failure Research Group from the Ministry of Health, Labour and Welfare, Japan. MS reports grants from GlaxoSmithKline, grants from Novartis and grants from AstraZeneca outside the current work. None of these companies had a role in the design or analysis of the study or in the writing of the manuscript. The Kyoto University Cohort Study was supported by the Japan Society for the Promotion of Science (JSPS) (No 16390234, No 21590964 and No 17H06807) and a grant to the Respiratory Failure Research Group from the Ministry of Health, Labour and Welfare, Japan. NT, SS and TH report a grant from Fujifilm Medical outside the current work.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available on reasonable request.