Variability of pulmonary function tests in stable corticosteroid dependent asthma patients

We studied 24 corticosteroid dependent asthmatic patients over a period of 10 months to establish a baseline for future therapeutic trials with corticosteroid sparing agents. Clinical symptoms, steroid dose, peak expiratory flow rate (PF), forced expiratory volume in 1 second (FEV1), and forced vital capacity (FVC) were recorded at clinic visits. Correlation was sought between PF and FEV1, steroid dose versus PF and symptom severity, and PF versus time and symptoms. There was considerable weekly variability of PF and FEV1. However, when viewed over almost a year, 54% had no significant change in PF. 29% actually worsened and 17% improved. The data suggest that to assess the effect of a steroid-sparing agent accurately, one must first establish a reliable baseline over several months to eliminate weekly variability. The current trend of obtaining a baseline over a 1 to 2 month interval is inadequate in this study population. We also found that neither patient assessment of severity of symptoms nor corticosteroid dosage correlate with objective spirometric measurements.