Within-breath respiratory impedance and airway obstruction in patients with chronic obstructive pulmonary disease

Abstract

OBJECTIVE:Recent work has suggested that within-breath respiratory impedance measurements performed using the forced oscillation technique may help to noninvasively evaluate respiratory mechanics. We investigated the influence of airway obstruction on the within-breath forced oscillation technique in smokers and chronic obstructive pulmonary disease patients and evaluated the contribution of this analysis to the diagnosis of chronic obstructive pulmonary disease.METHODS:Twenty healthy individuals and 20 smokers were assessed. The study also included 74 patients with stable chronic obstructive pulmonary disease. We evaluated the mean respiratory impedance (Zm) as well as values for the inspiration (Zi) and expiration cycles (Ze) at the beginning of inspiration (Zbi) and expiration (Zbe), respectively. The peak-to-peak impedance (Zpp=Zbe-Zbi) and the respiratory cycle dependence (ΔZrs=Ze-Zi) were also analyzed. The diagnostic utility was evaluated by investigating the sensitivity, the specificity and the area under the receiver operating characteristic curve. ClinicalTrials.gov: NCT01888705.RESULTS:Airway obstruction increased the within-breath respiratory impedance parameters that were significantly correlated with the spirometric indices of airway obstruction (R=−0.65, p<0.0001). In contrast to the control subjects and the smokers, the chronic obstructive pulmonary disease patients presented significant expiratory-inspiratory differences (p<0.002). The adverse effects of moderate airway obstruction were detected based on the Zpp with an accuracy of 83%. Additionally, abnormal effects in severe and very severe patients were detected based on the Zm, Zi, Ze, Zbe, Zpp and ΔZrs with a high degree of accuracy (>90%).CONCLUSIONS:We conclude the following: (1) chronic obstructive pulmonary disease introduces higher respiratory cycle dependence, (2) this increase is proportional to airway obstruction, and (3) the within-breath forced oscillation technique may provide novel parameters that facilitate the diagnosis of respiratory abnormalities in chronic obstructive pulmonary disease.

Respiratory impedance is correlated with morphological changes in the lungs on three-dimensional CT in patients with COPD

“…The correlations between WT and impedance were independent of Ai, and vice versa, according to the partial correlation analysis. Peribronchial fibrosis and consequent remodeling of airway tissue associated with COPD progression reduces airway compliance, which may result in a decrease in respiratory reactance 30 31 . The correlation between thickening of airways walls and respiratory reactance observed in the present study was compatible with this hypothesis.…”

“…Third, static CT images obtained at full-inspiration could not account fully for dynamic changes in the lungs during tidal breathing. Airway caliber collapses in the expiratory phase because of low elastic recoil pressure due to parenchymal destruction (emphysema) 32 33 , which is thought to be associated with within-breath difference in respiratory impedance 17 31 34 . Time-series analyses of airways could provide further insights into respiratory impedance.…”

Brazilian studies on pulmonary function in COPD patients: what are the gaps?

“…In recent work from our group, Silva et al 62 , 63 evaluated the diagnostic accuracy of monofrequency oscillometric pulmonary function in smokers and patients with COPD. These studies evaluated mean within-breath respiratory impedance ( Z rs ) during inspiration ( Z i ), expiration ( Z e ), and respiratory cycle dependence (∆ Z rs = Z e – Z i ).…”

“…These results indicate that COPD induces respiratory cycle dependence, which is proportional to the degree of airflow obstruction. Another important finding of these studies 62 , 63 is that the Z rs observed in different phases of the respiratory cycle may be useful in the detection of COPD.…”

Histologic and biochemical alterations predict pulmonary mechanical dysfunction in aging mice with chronic lung inflammation

“…Respiratory impedance, as measured at airway opening is widely regarded as a sensitive indicator of pulmonary pathology in lung disease [ 4 , 11 – 15 ]. Impedance measurements are typically analyzed using inverse modeling, where spectral data are fit to simple mechanical models with a small number of free parameters.…”