Comparison of distinctive models for calculating an interlobar emphysema heterogeneity index in patients prior to endoscopic lung volume reduction

Abstract

Background

The degree of interlobar emphysema heterogeneity is thought to play an important role in the outcome of endoscopic lung volume reduction (ELVR) therapy of patients with advanced COPD. There are multiple ways one could possibly define interlobar emphysema heterogeneity, and there is no standardized definition.

Purpose

The aim of this study was to derive a formula for calculating an interlobar emphysema heterogeneity index (HI) when evaluating a patient for ELVR. Furthermore, an attempt was made to identify a threshold for relevant interlobar emphysema heterogeneity with regard to ELVR.

Patients and methods

We retrospectively analyzed 50 patients who had undergone technically successful ELVR with placement of one-way valves at our institution and had received lung function tests and computed tomography scans before and after treatment. Predictive accuracy of the different methods for HI calculation was assessed with receiver-operating characteristic curve analysis, assuming a minimum difference in forced expiratory volume in 1 second of 100 mL to indicate a clinically important change.

Results

The HI defined as emphysema score of the targeted lobe (TL) minus emphysema score of the ipsilateral nontargeted lobe disregarding the middle lobe yielded the best predicative accuracy (AUC =0.73, P=0.008). The HI defined as emphysema score of the TL minus emphysema score of the lung without the TL showed a similarly good predictive accuracy (AUC =0.72, P=0.009). Subgroup analysis suggests that the impact of interlobar emphysema heterogeneity is of greater importance in patients with upper lobe predominant emphysema than in patients with lower lobe predominant emphysema.

Conclusion

This study reveals the most appropriate ways of calculating an interlobar emphysema heterogeneity with regard to ELVR.

Keywords:

• CT-quantitative
• COPD
• emphysema heterogeneity
• endoscopic lung volume reduction

Supplementary materials

Table S1 ROC curve analysis of all patients (n=62) to determine the predictive accuracy of the different volume-weighted HIs (HI * targeted lobe volume) with respect to FEV₁ increased after ELVR assuming an increase in FEV₁ of 100 mL to indicate MCID

Table S2 Definitions of the additional HIs calculated from the TAR

Table S3 ROC curve analysis of all patients (n=62) to determine the predictive accuracy of HIs calculated from the TAR with respect to FEV₁ change after ELVR assuming an increase of FEV₁ of 100 mL to indicate MCID

Table S4 ROC curve analysis of all patients (n=62) to determine the predictive accuracy of the different HIs with respect to FEV₁ improvement after ELVR assuming an increase in FEV₁ of 100 mL to indicate MCID

Table S5 ROC curve analysis of all patients with available 6MWT results (n=44) to determine the predictive accuracy of the different HIs with respect to 6MWT improvement after ELVR, assuming an increase in 6MWT of 26 minutes to indicate MCID

Table S6 ROC curve analysis of all patients with available SGRQ test results (n=47) to determine the predictive accuracy of the different HIs with respect to SGRQ improvement after ELVR, assuming an increase in SGRQ of 4 units to indicate MCID

Table S7 ROC curve analysis of all patients (n=62) to determine the predictive accuracy of the different HIs with respect to RV reduction after ELVR, assuming a decrease in RV of 0.31 L to indicate MCID

References

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Acknowledgments

D Theilig is a participant in the Charité Junior Clinical Scientist Program and V Schreiter is a participant in the Charité Clinical Scientist Program funded by Charité – Universitätsmedizin Berlin and the Berlin Institute of Health. The authors thank Dominik Herzog and Christian Thomsen for data collection and Bettina Herwig for language editing.

Disclosure

Dr Ralf-Harto Hubner has received lecture fees and devices from Pulmonx, the company producing the one-way valves. The authors report no other conflicts of interest in this work.