Heterogeneity in the respiratory symptoms of patients with mild-to-moderate COPD

Abstract

Kate M Johnson,1 Abdollah Safari,1,2 Wan C Tan,3 Jean Bourbeau,4 J Mark FitzGerald,2 Mohsen Sadatsafavi1,2,5 On behalf of the Canadian Cohort of Obstructive Lung Disease (CanCOLD) study and the Canadian Respiratory Research Network 1Collaboration for Outcomes Research and Evaluation, Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC, Canada; 2Institute for Heart and Lung Health, Department of Medicine, The University of British Columbia, Vancouver, BC, Canada; 3Centre for Heart Lung Innovation (the James Hogg Research Centre), St Paul’s Hospital, Vancouver, BC, Canada; 4Respiratory Epidemiology and Clinical Research Unit, McGill University Health Centre, Montreal, QC, Canada; 5Centre for Clinical Epidemiology and Evaluation, Vancouver Coastal Health Institute, Vancouver, BC, Canada Background: The burden of symptoms varies markedly between patients with COPD and is only weakly correlated with lung function impairment. While heterogeneity in lung function decline and exacerbations have been previously studied, the extent of heterogeneity in symptoms and the factors associated with this heterogeneity are not well understood.Methods: A sample of the general Canadian population ≥40 years with persistent airflow limitation was followed for up to 3 years. Participants reported whether they experienced chronic coughing, phlegm, wheezing, or dyspnea during visits at 18-month intervals. We used mixed-effect logistic regression models (separately for each symptom) to assess overall heterogeneity in the occurrence of symptoms between individuals, and the proportion of variation in symptom burden explained by lung function vs all other clinical characteristics of participants.Results: Four hundred forty-nine participants (53% male, mean age 67 years) contributed 968 visits in total, and 89% of patients reported at least one symptom during follow-up. There was substantial heterogeneity in the individual-specific probabilities for the occurrence of symptoms. This heterogeneity was highest for wheeze and dyspnea (IQR of probabilities: 0.13–0.78 and 0.19–0.81, respectively). FEV1 explained 28% of the variation between individuals in the occurrence of dyspnea, 8% for phlegm, 3% for cough, and 2% for wheeze. All clinical characteristics of participants (including FEV1) explained between 26% of heterogeneity in the occurrence of cough to 49% for dyspnea.Conclusion: There is marked heterogeneity in the burden of respiratory symptoms between COPD patients. The ability of lung function and other commonly measured clinical characteristics to explain this heterogeneity differs between symptoms. Keywords: population, respiratory symptoms, chronic obstructive pulmonary disease, variability, cough, phlegm, wheeze, dyspnea

Keywords

• Population
• Respiratory symptoms
• Chronic Obstructive Pulmonary Disease
• Variability