Significances of spirometry and impulse oscillometry for detecting small airway disorders assessed with endobronchial optical coherence tomography in COPD

Abstract

BackgroundSpirometry confers limited value for identifying small-airway disorders (SADs) in early-stage COPD, which can be detected with impulse oscillometry (IOS) and endobronchial optical coherence tomography (EB-OCT). Whether IOS is useful for reflecting small-airway morphological abnormalities in COPD remains unclear.ObjectivesTo compare the diagnostic value of spirometry and IOS for identifying SADs in heavy-smokers and COPD based on the objective assessment with EB-OCT.MethodsWe recruited 59 COPD patients (stage I, n=17; stage II, n=18; stage III–IV, n=24), 26 heavy-smokers and 21 never-smokers. Assessments of clinical characteristics, spirometry, IOS and EB-OCT were performed. Receiver operation characteristic curve was employed to demonstrate the diagnostic value of IOS and spirometric parameters.ResultsMore advanced staging of COPD was associated with greater abnormality of IOS and spirometric parameters. Resonant frequency (Fres) and peripheral airway resistance (R5–R20) conferred greater diagnostic values than forced expiratory volume in one second (FEV1%) and maximal (mid-)expiratory flow (MMEF%) predicted in discriminating SADs in never-smokers from heavy-smokers (area under curve [AUC]: 0.771 and 0.753 vs 0.570 and 0.558, respectively), and heavy-smokers from patients with stage I COPD (AUC: 0.726 and 0.633 vs 0.548 and 0.567, respectively). The combination of IOS (Fres and R5–R20) and spirometric parameters (FEV1% and MMEF% predicted) contributed to a further increase in the diagnostic value for identifying SADs in early-stage COPD. Small airway wall area percentage (Aw% 7–9), an EB-OCT parameter, correlated significantly with Fres and R5–R20 in COPD and heavy-smokers, whereas EB-OCT parameters correlated with FEV1% and MMEF% in advanced, rather than early-stage, COPD.ConclusionsIOS parameters correlated with the degree of morphologic abnormalities of small airways assessed with EB-OCT in COPD and heavy-smokers. Fres and R5–R20 might be sensitive parameters that reliably reflect SADs in heavy-smokers and early-stage COPD.

Feasibility and clinical applications of multiple breath wash-out (MBW) testing using sulphur hexafluoride in adults with bronchial asthma

“…Small airway disease was detected with IOS even in early stages and linked to typical symptoms such as dyspnoea 45 . In early stages, IOS parameters outperformed conventional spirometry when differentiating heavy smokers with normal lung function as well as early-stage COPD 46 20 . Even in absence of spirometric obstruction, LCI was already pathologically altered 22 .…”

<p>Oscillation Mechanics, Integer and Fractional Respiratory Modeling in COPD: Effect of Obstruction Severity</p>

“…42 Recent studies have shown associations between resistance variations and the degree of morphologic abnormalities of small airways assessed with endobronchial optical coherence tomography in COPD and heavy smokers. 43 It should be noted that these parameters are also influenced by the shunt impedance from the upper airway, as well as by the tissue resistance. The changes observed indicate increasing heterogeneity of the respiratory system with the progression of the disease.…”

Impulse oscillometry for detection of small airway dysfunction in subjects with chronic respiratory symptoms and preserved pulmonary function

“…Compared with spirometry, it is independent of the subjects’ efforts because of the externally superimposed oscillation signals [ 8 ]. Furthermore, it may have higher sensitivity in detecting SAD and seems to be better correlated with small airway structures [ 9 – 11 ]. Since IOS could reflect the viscous property of the respiratory system by resistance (Rrs), elastic and inertial property by reactance (Xrs), it might provide deeper information on individuals’ pathology changes when applied coupled with spirometry.…”