Relation of Indices of Lung Hyperinflation to Dyspnea in Patients with Chronic Obstructive Pulmonary Disease: A Physiologic Assessment and Discussion

Matthew Miller,Melissa Mert,Ahmet Baydur,Ravi A Patel,Mark Slootsky

doi:10.4236/ojrd.2019.93007

Matthew Miller, Melissa Mert + Show 3 more

Open Access

https://doi.org/10.4236/ojrd.2019.93007

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Abstract

Background: The severity of COPD is commonly assessed by the reduction in forced expiratory volume at one second (FEV1), although more recently prognostic factors influencing survival have also incorporated functional capacity, degree of breathlessness on exertion, and body mass index. Increasingly, the reliability of physiological parameters such as FEV1 to predict patient-centered outcomes has been brought into question. Objectives: To evaluate the relationship between dyspnea as assessed by the Modified Medical Council Dyspnea (MMRC) scale, the Global Initiative for Chronic Obstructive Lung Disease (GOLD 2014) staging and indices of lung hyperinflation and spirometry. Methods: Data were retrospectively analyzed at a 600-bed tertiary care center including spirometry, plethysmographic lung volumes, single breath carbon monoxide diffusion capacity and dyspnea graded according to MMRC, and GOLD staging. Results: Data for 331 patients were analyzed. Differences amongst FEV1, IC, IC/TLC, FRC and RV/TLC were significant between GOLD I/II and GOLD III/IV groups. The closest relationship to GOLD staging was seen with FEV1, FVC and slow vital capacity (SVC). FEV1/FVC, IC, and IC/TLC were inversely associated with MMRC score, while RV/TLC exhibited a positive relation with MMRC score. Conclusions: Indices of lung hyperinflation are closely associated, with dyspnea as assessed by MMRC grading with TLC, RV/TLC and IC exhibiting the closest relations, more so than FEV1. GOLD staging also shows strong correlations with lung volume subdivisions (weakly with TLC), more so than with FEV1. That TLC changed little between GOLD stages can be explained by the presence of collateral interalveolar channels and population characteristics different from those of other studies. These findings further support the concept that more than a reduction in FEV1, lung hyperinflation contributes to the sensation of dyspnea in airflow limitation.

Highlights

Chronic obstructive pulmonary disease (COPD) is a heterogeneous group of disorders characterized by incompletely reversible expiratory flow limitation [1]
forced expiratory volume in 1 second FRC (FEV1)/forced vital capacity (FVC), inspiratory capacity (IC), and IC/total lung capacity (TLC) were inversely associated with MMRC score, while RV/TLC exhibited a positive relation with MMRC score
Of note was that while the proportion of males tended to decrease as severity of dyspnea increased, the opposite trend was seen with Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage: the majority of patients in the GOLD IV group was male

Summary

Introduction

Chronic obstructive pulmonary disease (COPD) is a heterogeneous group of disorders characterized by incompletely reversible expiratory flow limitation [1]. Its severity is usually characterized by a decrease in forced expiratory volume at one second (FEV1) [1], more recently prognostic factors influencing survival have incorporated functional capacity, degree of breathlessness on exertion, and body mass index [2] [3]. The severity of COPD is commonly assessed by the reduction in forced expiratory volume at one second (FEV1), more recently prognostic factors influencing survival have incorporated functional capacity, degree of breathlessness on exertion, and body mass index. Conclusions: Indices of lung hyperinflation are closely associated, with dyspnea as assessed by MMRC grading with TLC, RV/TLC and IC exhibiting the closest relations, more so than FEV1. GOLD staging shows strong correlations with lung volume subdivisions (weakly with TLC), more so than with FEV1

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