We’ve shown FOT staged COPD correlates better with patient reported outcomes (PROs) than spirometry (SP) staged COPD. We hypothesized non-obstructed subjects (non-OB, FEV1/FVC≥0.7) with either MMEF<65% predicted or RV>130% predicted would be more similar to obstructed subjects (OB, FEV1/FVC<0.7) in the presence of ventilator inhomogeneity (VI, A<X>9 cmH2O/L/s) by FOT. 300 COPD subjects (>10 pack-year smoking and either FEV1/FVC<0.7, MMEF<65%predicted or RV>130%predicted) had PROs (mMRC, COPD Assessment Tests, chronic bronchitis questionnaires and AERs), PFTs (Jaeger or Vmax22, Carefusion, Germany), FOT (tremoFlo C-100, Thorasys, Canada) and in a subset, quantitative CT scan lung density (LD) abstracted from charts. Subjects were assigned to 1 of 4 groups based on FEV1/FVC≥/<0.7 and A<X>/≤9. Differences between continuous variables were determined with ANOVA and dichotomous with χ2. Significance was set at p<0.05 after Bonferroni correction. Subjects were more similar when partitioned by FOT than by SP in terms of CAT, mMRC, chronic bronchitis and emphysema (LD<55g/L) but not AER (Table 1).
While concordant phenotypes of non-VI/non-OB and VI/OB had a clear separation of disease burden in terms of PROs and emphysema, the discordant phenotypes of VI/non-OB and non-VI/OB resembled more their VI status than their OB status. Our data suggests that up to 19% of COPD subjects may be misclassified using SP.