Oscillometry (OS) measures lung function with minimal patient effort. Sugiyama et. al (Resp. Med. 2013, 107: 875-82) suggested that intra-breath variations in reactance at 5 Hz (X5) may discern COPD and ILD. We wished to study if intra-breath changes in X5 can further distinguish COPD, ILD and COPD-ILD overlap.
OS measurements (tremoFlo AOS, THORASYS Inc.) were obtained from 40 subjects equally distributed into 5 groups: COPD with Emphysema confirmed by quantitative CT scan (CE); COPD without Emphysema (CX); COPD-ILD overlap (CI), ILD only (IL) and healthy controls (HC). We graphed X5 over volume (X5(V)) and calculated total, inspiratory and expiratory X5 (X5tot, X5in, X5ex, respectively), and X5in – X5ex (ΔX5).
Relative to HC, the CE group showed a strong downward shift and shape change in X5(V), and significant changes to all parameters (p<0.05, Holm–Bonferroni; Figure). CX and CI curves were altered to a lesser degree, and their parameters did not reach significance relative to HC or CE (p=0.08…0.14). For IL, we observed no changes in outcome parameters or X5(V).
Our data confirmed known changes of X5 in COPD but failed to reproduce Sugiyama's increasingly negative ΔX5 in ILD. We also did not observe shape changes in X5(V) that might help detect ILD, with or without overlap with COPD. However, intra-breath changes in X5 may help distinguish emphysematous from non-emphysematous COPD.