Comparison of impedance measured by the forced oscillation technique and pulmonary functions, including static lung compliance, in obstructive and interstitial lung disease

Abstract

Objective: To examine whether the parameters of impedance measured by the broadband frequency forced oscillation technique (FOT) were reflected by changes in lung compliance induced by emphysema and fibrosis, we retrospectively compared the parameters of FOT and pulmonary functions, including static lung compliance (Cst), in obstructive lung disease (OLD) and interstitial lung disease (ILD).

Patients and methods: The data of 18 patients with OLD (16 with COPD, two with asthma COPD overlap), 11 with ILD, and 24 healthy volunteers, whose respiratory impedance was measured using a MostGraph-01 and other pulmonary functions including Cst and lung resistance (R_L) were measured on the same day and were retrospectively collected and compared.

Results: The parameters of resistance, reactance, and resonant frequency showed good correlations with ventilation unevenness (r=0.63, −0.89, 0.77, respectively) and lung elastic resistance (r=0.59, −0.80, 0.73, respectively) in all groups (N=53). These indices were significant determinants of increased respiratory resistance and more negative shift of respiratory reactance (Xrs) at lower frequency (P<0.001). Decreased functional residual capacity was also a determinant of Xrs at 5 Hz (X5) (P<0.05). The differences in mean X5 in the expiratory phase relative to those in the inspiratory phase (within-breath changes in X5) were associated with airflow obstruction (P<0.002) and lung elastic resistance (P<0.001). However, no significant correlations between Cst and any parameters of respiratory impedance were observed.

Conclusions: These findings suggest that the impedance parameters measured by FOT are reflected by airway obstruction, ventilation unevenness, and lung resistance, but hardly reflected by changes in lung compliance due to emphysema or fibrosis in both CLD and ILD.

Keywords:

• forced oscillation technique
• resistance
• reactance
• esophageal balloon method
• chronic obstructive pulmonary disease

Acknowledgment

This work was not supported by any grant or other funding sources.

Summary at a glance

Impedance parameters of forced oscillation technique mainly reflected airway lesions, ventilation unevenness, and lung volume, but not changes in lung parenchyma directly, not only in obstructive lung disease but also in interstitial lung disease, because the oscillating wave may be affected by airways leading to alveoli.

Disclosure

Prof. Dr. Keisaku Fujimoto reports grants from Koganei Corporation, Murata Manufacturing Co., LTD., Seiko Epson Corporation, Denso Corporation, grants and personal fees from Nippon Boehringer Ingelheim Co., Ltd., personal fees from Astellas Pharma Inc., AstraZeneca K.K., Fukuda Denshi Co., Ltd, Fukuda Lifetec Co., Ltd., Japan Association for the Advancement of Medical Equioment, Japan Respiratory Society, Kyorin Pharmaceutical Co., Ltd, Meiji Seika Pharma Co., Ltd., MSD K.K., Novartis Pharma K.K., Teijin Home Healthcare Limited, and Teijin Pharma Limited, outside the submitted work. The authors report no other conflicts of interest in this work.