Author(s)

Matthew Miller¹, Mark Slootsky¹, Ravi A. Patel¹, Melissa Mert², Ahmet Baydur^3*

¹Divisions of Geriatric, Hospital, Palliative and General Internal Medicine, University of Southern California, Los Angeles, California, USA.
²Department of Biostatistics, School of Preventive Medicine, University of Southern California, Los Angeles, California, USA.
³Pulmonary, Critical Care and Sleep Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.

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.

Chronic Obstructive Pulmonary Disease, Dyspnea, Expiratory Flow Limitation, Hyperinflation, Inspiratory Capacity

Miller, M. , Slootsky, M. , Patel, R. , Mert, M. and Baydur, A. (2019) Relation of Indices of Lung Hyperinflation to Dyspnea in Patients with Chronic Obstructive Pulmonary Disease: A Physiologic Assessment and Discussion. Open Journal of Respiratory Diseases, 9, 75-88. doi: 10.4236/ojrd.2019.93007.