Evaluation of respiratory impedance in patients with chronic obstructive pulmonary disease by an impulse oscillation system

Abstract

An impulse oscillometry system (IOS) assesses pulmonary resistance and reactance. The present study investigated which IOS measurement is correlated with airflow obstruction, airway conductance and lung volume in chronic obstructive pulmonary disease (COPD). A total of 180 patients with COPD were selected and 95 agreed to follow‑up 1 year after the initial tests. IOS measurements [R5, R20, X5 and resonant frequency (Fres)], body plethysmography [forced end‑expiratory flow (FEF)75, total lung capacity, residual volume (RV) and total inspiratory resistance (Rtot)] and spirometry [forced expiratory volume in 1 sec (FEV1)] were performed. Pearson's or Spearman's correlation tests were used to determine the correlation between the IOS and other measurements. R5, X5 and Fres were all significantly associated (P<0.05) with FEV1, FEF75, RV and Rtot. However, R20 was not correlated with these measurements except from FEF75 and Rtot (r values were all<0.25). The strongest associations were observed with FEV1 and the reactance measurements X5 (r=0.635), Fres (r=‑0.721) and R5 (r=‑0.496); FEF75 with X5 (r=0.505), Fres (r=‑0.629) and R5 (r=‑0.468); RV with X5 (r=‑0.485), Fres (r=0.570) and R5 (r=0.326); and Rtot with X5 (r=‑0.691), Fres (r=0.632) and R5 (r=0.570). There was a significant increase in FEV1 and X5 after one year as compared with the RV. The other measurements did not change over the year. The changes in X5, Fres and R5 were significantly correlated with the changes in FEV1 and the correlation coefficients were 0.355, ‑0.364 and ‑0.381, respectively. Similarly, the changes in X5, Fres and R5 were significantly correlated with the changes in RV and the correlation coefficients were ‑0.264, 0.287 and 0.318, respectively. In the COPD patients, the IOS reactance measurements were more closely correlated with other pulmonary function measurements rather than with resistance measurements. The IOS reactance measurements, particularly X5, appear to indicate changes in pulmonary compliance caused by airflow obstruction.

Clinical application value of impulse oscillometry in geriatric patients with COPD

“…The compliance of COPD patients decreased overall, and a previous study has reported results consistent with ours 17. Furthermore, Gong et al20 demonstrated that X5, R5, and Fres are the IOS measurements most closely associated with more traditional measurements of pulmonary function in COPD patients. The associations between FEV 1 and the IOS measurements were as follows: X5 ( r =0.635), Fres ( r =−0.721), and R5 ( r =−0.496); these results were consistent with our results.…”

Expiratory reactance abnormalities in patients with expiratory dynamic airway collapse: a new application of impulse oscillometry

“…Similarly, D ellacà et al showed the greater potential of reactance ( X ) data compared to resistance ( R ) data to demonstrate airflow limitation: the R time course, unlike that for X , did not present clear differences between inspiration and expiration. Two articles have studied IOS in COPD [ 18 , 30 ]. Both found that reactance rather than resistance correlated most with FEV 1 , RV and TLC.…”

Acoustic Methods for Pulmonary Diagnosis

“…Advantages of FOT/IOS include higher sensitivity in detecting peripheral airway obstruction, short duration, and a requirement for little patient cooperation compared to spirometry, which is difficult for children, the elderly, and physically or cognitively impaired patients [94; 96]. For these reasons, FOT/IOS have proven useful in human studies for diagnosing asthma and COPD [53; 95; 98; 99; 100]. Current challenges to FOT/IOS come from its relatively recent introduction to the clinical setting, making it difficult to compare results due to the lack of standardized, healthy values.…”