Oscillometry (OS) measures lung mechanics with minimal patient effort, com plements traditional physiology, yet is infrequently used. OS estimates small airways function in part, by measuring frequency dependence of resistance.
We wished to explore OS resistance for meaningful small airways phenotypes and relate them to clinical, physiologic and imaging metrics.
Subjects from community respirology practice with COPD, a 10 pack-year smoking history, and either a post bronchodilator FEV 1/FVC<0.70 (GOLD) or MMEF<65% predicted or RV>130% predicted (at risk) underwent 3-5 measurements of forced OS (tremoFlo C-100. 5-37Hz. Thorasys, Montreal QC. Canada). From 3 tracings with a 5 Hz coherence (COHs) of >0.6, 5 & 19 Hz resistance (11511191, frequency dependence of resistance (R5.191, 5 Hz reactance (X5(, resonance frequency (Fres), reactance area (Ax) and inspiratory-expiratory Xs (6X5) were calculated. Lung function, CAT & mMRC questionnaires, and acute exacerbations rates (AER), were abstracted from charts. Ainvoylopeaor (ainvavinsoector.acil-bwh.org) was used to measure LAA‹.950,, and lung density from CT scans obtained within 24 months of OS. Emphysema was defined as LAA,.950siu >10%. Subjects were divided into low, medium and high overall resistance by approximate tertiles of R19 <3 (LowR), 3.4 (MedR) and >4 (Hill) cmH2O/L/sec and subgroups of small airways predominant (SA+) or small airways non-predominant (SA-) phenotype by 9 >1 or <1 cmCH20/Usec respectively. Differences were determined with ANOVA for continuous and Ma rascuillo chi square for binomial variables. Kolmogorov-Smirnov (KS) was used for post hoc SA+ vs. SA- differences. Significance was set at p<0.05, Holms adjusted for multiple measures. The study had IRB approval.
139 subjects were grouped as in Fig. 1. Groups did not significantly differ in age, sex, BMI, smoking history, CAT, mMRC, chronic bronchitis, AER or Due but did for X5, Fres, A, 6Xs, F EV1, FVC, FEV /FVC, MMEF, TLC, SVC, FRC, RV, RV/TLC, VA, VARLC, and R„ (ANOVA, p< 2.47X10- I 3-7.92X10-3).FEVs, FEV1/FVC, MMEF, TLC, FRC, RV and RV/TLC always differed between SA- and SA+ subgroups (KS, p<0.0001-0.049). Proportions of subjects in GOLD 1,11, III and IV, and A, B, C, D, (Fig. 1), and with emphysema differed significantly between groups (chi square a<0.0001).
OS resistance data may be used to characterize phenotypes of COPD by means of the RS_ 19 to identify those subjects with greater airflow limitation, more hyperinflation and gas trapping, a greater likelihood of emphysema and more advanced GOLD classification of COPD and support the notion that small airways disease is important in COPD.