Use of Impulse Oscillometry in Patients with Chronic Obstructive Pulmonary Disease

Although spirometry is a standard diagnostic tool for obstructive lung diseases, it is rarely performed, and the quality of basic spirometry is low in many countries. The impulse oscillometry system (IOS) is a non-invasive method that requires minimal patient cooperation and, therefore, can be performed even in the pediatric population. It has been also suggested that IOS may help to clarify the relationship between small airway disease and the underlying mechanisms of chronic obstructive pulmonary disease (COPD). The primary objective of the study was to compare IOS parameters in COPD patients with those in healthy individuals. Our secondary objective was to determine the relationship between IOS parameters and standard pulmonary function tests (PFTs). Our hypothesis was that airway resistance detected by IOS would be higher in COPD patients than in controls. Hence, IOS would provide findings comparable to and correlated with those of standardized PFTs for small airway obstruction.

A total of 104 subjects (62 patients with COPD and 42 healthy non-smoking individuals) were included in the study. All subjects underwent spirometry, diffusing capacity for carbon monoxide (DLCO), lung-volume measurements, and IOS.

COPD patients showed significant decreases in forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), FEV₁/FVC, FEF 25-75, and DLCOadj, and significant increases in residual volume (RV) and total lung capacity (TLC) compared with the control group. In terms of IOS parameters, R5%, Z5%, Fres, and R5-R20/R5% values were significantly higher in the COPD group (P = 0.029, P = 0.022, P = 0.009, P = 0.004, respectively). The reactance area (AX) value, defined as the AX, was also significantly increased in the COPD group (P = 0.004). The correlation between FEF 25-75% (L/s) and R5-R20 was moderate and negative (r = -0.491, P < 0.001). A weak correlation (r = 0.240, P = 0.017) was also found between the RV/TLC ratio and R5-R20.

This study showed that airway resistance was increased in the COPD group and that IOS parameters were associated with measures of small-airway function in standard PFTs. IOS can be used as a non-invasive, patient-friendly method that complements PFTs by providing a comprehensive assessment of COPD pathology and pathophysiological changes and detecting changes in symptomatic patients.