Investigating the relationships among lung function variables in chronic obstructive pulmonary disease in men.

Ming-Lung Chuang,I-Feng Lin

doi:10.7717/peerj.7829

Abstract

BackgroundIn patients with chronic obstructive pulmonary disease (COPD), the independent contributions of individual lung function variables to outcomes may be lower when they are modelled together if they are collinear. In addition, lung volume measurements may not be necessary after spirometry data have been obtained. However, these hypotheses depend on whether forced vital capacity (FVC) can predict total lung capacity (TLC). Moreover, the definitions of hyperinflation and air trapping according to lung function variables overlap and need be clarified. Therefore, the aim of this study was to evaluate the relationships among various lung function parameters to elucidate these issues.MethodsDemographic data and 26 parameters of full lung function were measured in 94 men with COPD and analyzed using factor and correlation analyses.ResultsFactor analysis revealed five latent factors. Inspiratory capacity (IC)/TLC and residual volume (RV)/TLC were most strongly correlated with all other lung volumes. IC/TLC, RV/TLC, and functional residual capacity (FRC)/TLC were collinear and were potential markers of air trapping, whereas TLC%, FRC%, and RV% were collinear and were potential markers of hyperinflation. RV/TLC >0.4 (or IC/TLC <0.4) was comparable with the ratio of forced expiratory volume in one second (FEV1) and FVC <0.7. FVC% and FEV1% were poorly correlated with TLC%. The correlation study showed that TLC%, RV/TLC, and FEV1% could be used to represent individual latent factors for hyperinflation, air trapping, inspiration, expiration, and obstruction. Combined with diffusion capacity%, these four factors could be used to represent comprehensive lung function.ConclusionsThis study identified collinear relationships among individual lung function variables and thus selecting variables with close relationships for correlation studies should be performed with caution. This study also differentiated variables for air trapping and lung hyperinflation. Lung volume measurements are still required even when spirometry data are available. Four out of 26 lung function variables from individual latent factors could be used to concisely represent lung function.

Highlights

A total of 94 male participants with chronic obstructive pulmonary disease (COPD) were enrolled after excluding 10 participants (Table 1 and Fig. 1). Five of these 10 participants who were excluded were diagnosed with bronchial asthma including three females and another five had spirometry data that did not meet the inclusion criteria
Up to 26 lung function parameters were presented in absolute values, %predicted, and as the ratio of lung volume or capacity and total lung capacity (TLC) or forced vital capacity (FVC) for each patient
Lung volume in liters was closely related to body height, sex, and age and it was usually presented with %predicted

Summary

Introduction

Lung function variables including residual volume (RV)/total lung capacity (TLC), inspiratory capacity (IC)/TLC, RV% predicted and forced expiratory volume in one second percentage predicted (FEV1%) have been reported to be well correlated with the outcomes of patients with chronic obstructive pulmonary disease (COPD) including physiological deterioration, dyspnea, exercise intolerance, acute exacerbations, and mortality (O’Donnell, Revill & Webb, 2001; Nishimura et al, 2002; Casanova et al, 2005; Tantucci et al, 2008; Vassaux et al, 2008; Zhang et al, 2013; Chuang, Huang & Su, 2015; Shin et al, 2015). Hyperinflation and air trapping are defined using lung volumes in percentages (%) combined with ratios of functional residual capacity (FRC), IC or RV and TLC (Ruppel, 1991; Gagnon et al, 2014; Cohen, 2017; Vaz Fragoso et al, 2017). These definitions are unclear and arbitrary and understanding the relationships among these variables may improve the definitions. The correlation study showed that TLC%, RV/TLC, and FEV1% could be used to represent individual latent factors for hyperinflation, air trapping, inspiration, expiration, and obstruction. Four out of 26 lung function variables from individual latent factors could be used to concisely represent lung function

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