Total inspiratory and expiratory impedance in patients with severe chronic obstructive pulmonary disease

Abstract

OBJECTIVES:Several studies have confirmed the high potential of the forced oscillation technique for the assessment of respiratory modifications related to chronic obstructive pulmonary disease. However, most of these studies did not employ within-breath analyses of the respiratory system. The aim of this study is to analyze respiratory impedance alterations in different phases of the respiratory cycle of chronic obstructive pulmonary disease patients and to evaluate their clinical use.METHODS:39 individuals were evaluated, including 20 controls and 19 individuals with chronic obstructive pulmonary disease who experienced severe airway obstruction. We evaluated the mean respiratory impedance (Zm) as well as values for inspiration (Zi) and expiration cycles (Ze), at the beginning of inspiration (Zbi) and expiration (Zbe). The peak-to-peak impedance (Zpp), and the impedance change (ΔZrs) were also analyzed. The clinical usefulness was evaluated by investigating the sensibility, specificity and the area under the receiver operating characteristic curve.RESULTS:The respiratory impedance increased in individuals with chronic obstructive pulmonary disease in all of the studied parameters (Zm, Zi, Ze, Zbi, Zbe, ΔZrs and Zpp). These changes were inversely associated with spirometric parameters. Higher impedances were observed in the expiratory phase of individuals with chronic obstructive pulmonary disease. All of the studied parameters, except for ΔZrs (area under the receiver operating characteristic <0.8), exhibited high accuracy for clinical use (area under the receiver operating characteristic >0.90; Sensibility ≥ 0.85; Sp ≥ 0.85).CONCLUSIONS:The respiratory alterations in severe chronic obstructive pulmonary disease may be identified by the increase in respiratory system impedance, which is more evident in the expiratory phase. These results confirm the potential of within-breath analysis of respiratory impedance for the assessment of respiratory modifications related to chronic obstructive pulmonary disease.

Forced Oscillation Technique in the Detection of Smoking-Induced Respiratory Changes

“…Note the smaller difference between inspiration and expiration in the normal subject ( Figure 5A) and the higher values of expiratory impedance in the COPD patient ( Figure 5B). The parameters used to interpret raw single-frequency FOT data depend slightly on the research group (Dellacà et al 2004;Johnson et al 2005;Dellacà et al 2010;Silva et al, 2011). In general, Zrs and its components (Rrs, Xrs) are considered as the mean values during inspiration (Zi, Ri, Xi) and expiration (Ze, Re, Xe), the difference between Xi and the mean Xe (Xrs) has been used as an index of expiratory flow limitation (Dellacà et al 2004).…”

“…In general, Zrs and its components (Rrs, Xrs) are considered as the mean values during inspiration (Zi, Ri, Xi) and expiration (Ze, Re, Xe), the difference between Xi and the mean Xe (Xrs) has been used as an index of expiratory flow limitation (Dellacà et al 2004). In previous studies from our group (Silva et al, 2011), the mechanical alterations during different phases of the respiratory cycle were characterized using the following parameters:…”

“…The authors concluded that the identified model values are sensitive to variations between healthy and COPD lungs. In a recent work from our group, Silva et al (2011) used the parameters described in section 3.4.2 to evaluate the diagnostic potential of mono-frequency FOT in patients with severe COPD. The respiratory impedances were always significantly higher in COPD patients than in the control group (Figure 7; Zm, Zbi, Zi, Zbe and Ze; p<0.001).…”

“…Another important advantage, particularly in pathophysiological research, is that FOT can be used to provide information on the mechanical characteristics of the respiratory system that is complementary to the information provided by spirometry Macleod and Birch, 2001;Oostveen et al, 2003;Bates et al, 2011;Kaczka and Dellacà 2011). This technique has the potential to greatly increase our knowledge regarding the pathophysiology of smoking, as well as to help in the clinical diagnosis of early smoking-induced respiratory alterations and COPD (Faria et al, 2009;Faria et al, 2010;Silva et al, 2011;Postma et al, 2012;Amaral et al, 2012).…”

Pesquisas em pneumologia recentemente publicadas em revistas brasileiras

“…Silva et al (55) found that, in patients with severe COPD, respiratory alterations can be identified by increased respiratory system impedance, which is more evident in the expiratory phase. Their results seem to confirm the potential of within-breath analysis of respiratory impedance for the assessment of COPD-related respiratory alterations.…”