The Concavity of the Maximal Expiratory Flow\u2013Volume Curve Reflects the Extent of Emphysema in Obstructive Lung Diseases

Fumi Mochizuki,Hiroichi Ishikawa,Azusa Watanabe,Hironori Masuko,Keiji Fujiwara,Naoya Tanabe,Takafumi Shimada,Susumu Sato,Nobuyuki Hizawa,Hiroaki Iijima,Yohei Yatagai,Jun Kanazawa,Shigeo Muro,Masanari Shiigai,Tohru Sakamoto

doi:10.1038/s41598-019-49591-2

Abstract

A concave-shaped maximal expiratory flow-volume (MEFV) curve is a spirometric feature in chronic obstructive pulmonary disease (COPD). The MEFV curve is characterized by an increase in the Obstructive Index, which is defined as a ratio of forced vital capacity to the volume-difference between two points of half of the peak expiratory flow on the MEFV curve. We hypothesized that the Obstructive Index would reflect the severity of emphysema in patients with COPD and asthma-COPD overlap (ACO). Thus, the aim of this retrospective study was to evaluate whether the Obstructive Index on spirometry is associated with the extent of emphysema on computed tomography (CT) in patients with COPD, ACO, and asthma (N = 65, 15, and 53, respectively). The percentage of low-attenuation volume (LAV%) and wall area (WA%) were measured on CT. The Obstructive Index was higher in patients with COPD and ACO than in those with asthma. Spearman correlation showed that a greater Obstructive Index was associated with a higher LAV%, but not WA%. Multivariate analysis showed that Obstructive Index was associated with LAV% (standardized β = 0.43, P < 0.0001) independent of other spirometric indices. The Obstructive Index is a useful spirometric index that reflects the extent of emphysema.

Highlights

Chronic obstructive pulmonary disease (COPD) is a major concern worldwide, as its prevalence and mortality rate continue to increase, imposing a huge economic burden[1,2]
This study investigated whether the Obstructive Index, measured spirometrically, could be used to predict the extent of emphysema, as measured on computed tomography (CT), using cross-sectional data of patients with COPD, asthma– COPD overlap (ACO), or bronchial asthma (BA); this has not been reported previously
Previous physiological studies showed that concave maximal expiratory flow-volume (MEFV) curves on spirometry are common in patients with COPD and that this shape reflects the loss of elastic recoil; no report to date has investigated its association with the severity of emphysema

Summary

Introduction

Chronic obstructive pulmonary disease (COPD) is a major concern worldwide, as its prevalence and mortality rate continue to increase, imposing a huge economic burden[1,2]. Numerous CT studies have shown that the emphysema phenotype is associated with a rapid decline in forced expiratory volume in 1 second (FEV1)[4], frequency of exacerbations[5], a poor prognosis[6], osteoporosis[7], occurrence of lung cancer[8], loss of skeletal muscle mass[9], and reduction in body mass index (BMI)[10]. Spirometry is widely used for low-cost management of COPD and non-invasively measures lung function parameters, such as FEV1 and forced vital capacity (FVC) It allows for the visualization of the maximal expiratory flow-volume (MEFV) curve. We explored the usefulness of the Obstructive Index by comparing quantitative CT (QCT) of lung emphysema with visual assessment of MEFV curves in patients with chronic obstructive lung diseases

Methods

Results

Conclusion