Study: Forced Oscillation Technique May be Useful for Assessing COPD

According to a new study, airway function measurements evaluated with the forced oscillation technique (FOT) provide useful information complementary to spirometry in patients with chronic obstructive pulmonary disease (COPD).

“The association between respiratory impedance and imaging changes in the lungs could aid understanding of COPD pathology,” the researchers wrote.
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In order to evaluate potential correlations between respiratory impedance, as measured by FOT, and airway structures in patients with COPD, the researchers conducted a study including 98 participants with COPD, and 49 reference subjects without COPD, 14 of whom were never smokers. Patients with COPD had a history of smoking, a median age of 73 years, and 92.9% were men.

Researchers measured the wall thickness and airway intraluminal area (Ai) of the 3rd and 6th generation bronchi, and the percentage low-attenuation area with less than -950 HU (%LAA) of the lungs using a 3-dimensional computerized tomography (CT) scan. Respiratory impendence was measured by FOT, and spirometry data were obtained.

Overall, the researchers’ results showed that COPD patients had higher respiratory impendence, decreased Ai, and increased %LAA compared to participants without COPD.

“Indices of respiratory resistance and reactance and forced expiratory volume in 1 second (FEV1) were correlated with Ai, and the association between percent predicted FEV1 and Ai was predominant in distal bronchi,” the researchers stated.  

In addition, wall thickness was correlated with differences in respiratory resistance between R5-R20 and the FEV1/forced vital capacity (FVC) ratio. The FEV1/FVC ratio and respiratory reactance were correlated with %LAA in patients with COPD.

“The respiratory impedance as well as spirometric data may reflect different components of pathogenic changes in COPD, and could be used as complementary approaches for COPD assessment,” the researchers concluded.

—Melissa Weiss


Karayama M, Inui N, Mori K, et al. Respiratory impedence is correlated with morphological changes in the lungs on three-dimensional CT in patients with COPD [published online February 8, 2017]. Nature. doi:10.1038/srep41709.