Forced oscillation technique (FOT) provides a non-invasive direct measure of respiratory system resistance requiringminimal patient effort, yet is infrequently used in the office setting.
We wished to assess 1) the feasibility of using FOT in community practice, 2) FOT parameters by GOLD classification, and 3) the relationship of FOT parameters with PFTs, COPD assessment test (CAT) and mMRC dyspnea scale (mMRC).
Subjects from a community respirology practice with COPD, ≥10 pack-year smoking history, and either a post bronchodilator FEV1/FVC<0.70 (GOLD), MMEF<65% predicted or RV>130% predicted (non-GOLD), and healthy controls (HC) recruited from clinic staff,
underwent 3-5 measurements of FOT (tremoFlo C-100, 5-37Hz, Thorasys, Montreal, QC, Canada) when well. From 3 tracings with a 5 Hz coherence (COH5) of >0.6, 5 Hz resistance (R5), frequency dependence of resistance (R5-19), 5 Hz reactance (X5), resonance frequency (Fres), reactance area (AX) and inspiratory-expiratory X5 (ΔX5) were calculated for each subject. Annual spirometry, lung volumes (255 plethysmographic, 45 N2 washout), Raw, DLco, CAT and mMRC were abstracted from charts. Subjects were divided into GOLD
classifications I-IV and A-D, and compared with non-GOLD COPD and HC. Differences for biometrics, PFTs and ln transformed FOT parameters were determined with ANOVA and post hoc Student t-tests, or χ2 as appropriate, Bonferroni corrected, and excluding HC.
Pearson correlations were determined for FOT parameters vs. PFTs, CAT and mMRC.
Time between FOT and PFTs was 4±5 months (mean±SD). ΔX5 could be calculated in 297/300 COPD subjects (99%) and 20/21 HC (95%). Age, sex distribution, smoking history and BMI were similar between non-GOLD, GOLD I-IV and A-D. There were significant.
differences between all FOT parameters by increasing GOLD I-IV and A-D but more so for GOLD I-IV than A-D (Table 1). Strong correlations were present between R5 vs. FEV1 (-0.64, p<0.0001), X5 vs. FEV1, FEV1/TLC and Raw (r=0.68, 0.62, -0.66, p<0.0001), Fres vs. FEV1 (-0.64, p<0.0001) and AX vs. FEV1, MMEF, FEV1/TLC and Raw (r=-0.72, -0.64, -0.62, 0.65, p<0.0001). CAT and mMRC correlated weakly with both AX and FEV1 (CAT: r=0.32, -0.29, p<0.0001, mMRC: r=0.29, -0.32, p<0.0001).
FOT is feasible in community practice. In this small COPD population, FOT parameters worsen more with increasing GOLD I-IV than A-D, demonstrate strong correlations with PFTs, and correlate with CAT and mMRC as well as spirometry.
FOT offers a quicker and easier measure of lung function than spirometry and is feasible in the office setting.