A novel approach to defining the relationship between lung function and symptom status in asthma

We present a novel approach to estimating functional relationships between forced expiratory volume in 1 second (FEV₁) and asthma-related symptoms on a population-wide basis. We used asthma-related clinical trials that reported estimates of mean lung function (measured as FEV₁ percent predicted) and symptoms (symptom score or percentage of symptom days or nighttime awakenings). Using average baseline values from each study in weighted linear regression analyses, we found a negative association between lung function and symptom score (P < 0.001) and the percentage of nighttime awakenings (P = 0.18), but no association between lung function and symptom days. We also found consistent relationships between the mean changes in lung function and symptoms at follow-up within the studies. Functional relationships between FEV₁ percent predicted and asthma-related symptoms can be useful for inferring the effect on the symptoms of a population associated with overall improvements in lung function.