The relationship of Forced Expiratory Volume in one second (FEV1) and Maximum Mid-expiratory Flow Rate (MMEF) in the diagnosis of exercise-induced asthma (EIA) was analyzed in this study. Specifically, the percent decrease in MMEF and FEV1 was correlated and the sensitivity of MMEF in the diagnosis of EIA was determined.
This is a cross-sectional study of 91 asthmatic patients, 7-18 years old, classified as either intermittent or newly diagnosed mild persistent. They underwent exercise challenge test (ECT) using the treadmill protocol and the FEV1 and MMEF responses were recorded as the greatest fall expressed as a percentage of the baseline. Other statistical tools used were the pearson correlation and the linear regression analysis.
Based on a ≥ 15% fall in FEV1, there were 60 patients in the positive exercise induced bronchoconstriction (EIB) group and 31 patients in the negative EIB group. The prevalence of exercise-induced asthma was 65.9%. Baseline spirometry was within normal limits for both groups. There was a significant correlation between the percent decrease in FEV1 and MMEF after an ECT. A fall of ≥ 25% in MMEF approximated a ≥ 15% fall in FEV1 with a sensitivity of 90%. The percent decrease in MMEF that could approximate the percent decrease in FEV1 of 10% or 13% was also computed using the equation derived from the linear regression analysis as follows: (Estimated) MMEF % fall = 10.017 + 1.031 x (FEV1 %fall).
This study demonstrated that a ≥ 25% fall in MMEF showed good correlation with a ≥ 15% fall in FEV1, with a sensitivity of 90%.
The significant correlation between the percent decrease in FEV1 and MMEF confirms that changes occur in both large and small airways. MMEF may serve as an additional parameter or may be a useful alternative in the diagnosis of EIA, especially in patients with a < 15% fall in FEV1 or those with a submaximal effort during a forced expiratory maneuver.
Agnes Angela Sanchez, None.