Kate M Johnson 1 , Abdollah Safari 1 , 2 , Wan C Tan 3 , Jean Bourbeau 4 , J Mark FitzGerald 2 , Mohsen Sadatsafavi 1 , 2 , 5 , On behalf of the Canadian Cohort of Obstructive Lung Disease (CanCOLD) study , the Canadian Respiratory Research Network
13 December 2018
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.
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.
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). FEV 1 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 FEV 1) explained between 26% of heterogeneity in the occurrence of cough to 49% for dyspnea.