Impact of bronchial wall thickness on airflow obstruction in bronchiectasis
Introduction
Bronchiectasis is a chronic disease with permanent dilation of the bronchi (Barker, 2002; Reid, 1950). This generally occurs in the context of host-mediated inflammatory responses and tissue damage due to foreign materials and bacteria (Cole, 1986; McShane et al., 2013). The impairment of lung function in bronchiectasis is characterized by airflow obstruction (Pande et al., 1971), which is evaluated using spirometry. Notably, forced expiration volume in 1 s (FEV1) decreases as the disease progresses and is a major physiological index of disease severity (Evans et al., 1996; Martinez-García et al., 2020). In contrast with healthy subjects, FEV1 decreases and airflow obstruction progresses as large airways are dilated abnormally in patients with bronchiectasis (Kaminsky, 2012; Lynch et al., 1999). However, the decrease in FEV1 does not reflect the impairment of large airways; small and middle airway constriction has been identified as one of the causes of airflow obstruction in bronchiectasis (King, 2009; Roberts et al., 2000).
In addition to studies for airway diameter, abnormality in respiratory impedance, which is measured noninvasively using oscillometry, has been reported in bronchiectasis (Guan et al., 2016, 2015). Oscillometry provides respiratory impedance with broadband frequency by analyzing the mechanical waves superimposed on respiratory maneuvers on spontaneous breathing (Oostveen et al., 2013). Respiratory impedance represents the mechanical properties of the respiratory system and is comprised of respiratory resistance (Rrs) and respiratory reactance (Xrs) (Oostveen et al., 2003). Rrs represents the sum of the airway resistance and viscous resistance of lung and thoracic tissue (Oostveen et al., 2003), whereas Xrs reflects the dynamic elastance and inertia of the respiratory system (King et al., 2020). In bronchiectasis, Xrs at 5 Hz (X5) and the difference between Rrs at 5 and 20 Hz (R5-R20) are reportedly associated with FEV1 and the degree of airflow obstruction (Guan et al., 2015). However, the mechanism by which abnormal mechanical properties of airways affect airflow obstruction has not been thoroughly investigated in bronchiectasis. Since bronchial wall thickness is associated with the decline in FEV1 and the development of airflow obstruction in chronic obstructive pulmonary disease (COPD) (Mohamed Hoesein et al., 2015), impaired mechanical properties due to bronchial wall thickening were also hypothesized to affect airflow obstruction in bronchiectasis, independent of airway diameter.
The present study aimed to investigate the correlation of respiratory impedance with spirometric parameters and high-resolution computed tomography (HRCT) findings presenting with bronchial wall thickness and to assess the underlying mechanism of airflow obstruction in bronchiectasis.
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Patients and study design
This retrospective observational study was conducted at the National Hospital Organization Osaka Toneyama Medical Center (a 410-bed referral hospital for respiratory diseases in Osaka, Japan). Screened were all adult patients (age ≥ 20 years old) who were diagnosed with bronchiectasis at the National Hospital Organization Osaka Toneyama Medical Center between January 1st, 2015 and December 31st, 2017. Patients who underwent spirometry, oscillometry, and HRCT at the time of diagnosis were
Baseline characteristics
A total of 98 adult patients with bronchiectasis who underwent spirometry, oscillometry, and HRCT qualified for this study and were evaluated (Fig. 2). The patients’ baseline characteristics are shown in Table S1. The median age (interquartile range) was 73 (66–78) years. Mycobacterium avium complex and other non-tuberculous mycobacterial pulmonary diseases were the major underlying causes of bronchiectasis (43/98 patients, 43.9 %), and most patients received macrolides as antimicrobial therapy
Discussion
This is the first comprehensive study of airflow obstruction in bronchiectasis evaluated using oscillometry. This study implies the mechanism underlying airflow obstruction in bronchiectasis; increased airway elastance due to abnormal bronchial wall thickening might deteriorate the degree of airflow obstruction.
To date, studies have been conducted to investigate the mechanism underlying airflow obstruction in bronchiectasis using HRCT (Lynch et al., 1999; Roberts et al., 2000). A previous
Author contributions
Conceptualization and design: Y.Y.; methodology, Y.Y.; data collection; Y.Y., T.K. (Tomoki Kuge), K.T., T.M., T.K. (Takahiro Kawasaki); analysis and interpretation of data: M.M. (Mari Miki), K.M., M.M. (Masahide Mori); writing the original draft: Y.Y.; supervision: H.K. All of the authors reviewed and approved the submission of the final manuscript.
Funding
The authors received no specific funding for the present study.
Data availability
All data generated or analyzed during this study are included in this published article and its supplementary information files.
Transparency document
Declaration of Competing Interest
The authors declare no conflicts of interest in association with the present study.
Acknowledgements
The authors would like to thank Ms. S. Ito, Ms. S. Sakaguchi, and Mr. T. Uenishi (Laboratory for Clinical Investigation, National Hospital Organization Osaka Toneyama Medical Center, Toyonaka, Japan) for their help with spirometry and oscillometry measurements.
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