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BACKGROUND:
Spirometry is used to physiologically assess patients with central airway obstruction (CAO) before and after interventional bronchoscopy, but is not always feasible in these patients, does not localize the anatomic site of obstruction, and may not correlate with the patient’s functional impairment. Impulse oscillometry may overcome these limitations. We assessed the correlations between impulse oscillometry measurements, symptoms, and type of airway narrowing,
before and after interventional bronchoscopy, and whether impulse oscillometry parameters can discriminate between fixed and dynamic CAO. METHODS: Twenty consecutive patients with CAO underwent spirometry, impulse oscillometry, computed tomography, dyspnea assessment, and bronchoscopy, before and after interventional bronchoscopy. The collapsibility index (the percent difference in airway lumen diameter during expiration versus during inspiration) was calculated using morphometric bronchoscopic images during quiet breathing. Variable CAO was defined as a collapsibility index of > 50%. Fixed CAO was defined as a collapsibility index of < 50%. The degree of obstruction was analyzed with computed tomography measurements. RESULTS: After interventional bronchoscopy, all impulse oscillometry measurements significantly improved, especially resistance at 5 Hz, which decreased from 0.67 _ 0.29kPa/L/s to 0.38 _ 0.17kPa/L/s (P < .001), and reactance at 20 Hz, which increased from –0.09 _ 0.11 to 0.03 _ 0.08 (P < .001). Changes in dyspnea score correlated with resistance at 5 Hz, the difference between the resistance at 5 Hz and the resistance at 20 Hz, and the reactance at 5 Hz, but not with spirometry measurements. The type of obstruction also correlated with dyspnea score, and showed distinct impulse oscillometry measurements.
Methods
The ethics committee of St Marianna University School of Medicine approved this study, and all subjects gave informed consent.
Conclusions
Our study adds to the body of evidence supporting the use of impulse oscillometry for physiologic assessment of patients withCAO.15-18 Although impulse oscillometrymay not be the ultimate test to distinguish between small and large airway processes, or the solution to anatomically localize flow-limiting bronchial segments in patients with CAO, it is noninvasive, effort-independent, can usually differentiate fixed from variable obstruction, and is useful for assessing CAO before and after interventional bronchoscopy. Larger scale studies should clarify whether impulse oscillometry is more sensitive than spirometry for differentiating fixed from variable obstruction, and more sensitive than spirometry for detecting CAO.
