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 (FEV(1)) and asthma-related symptoms on a population-wide basis. We used asthma-related clinical trials that reported estimates of mean lung function (measured as FEV(1) 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 FEV(1) 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.