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
