Correlation of spirometry and symptom scores in childhood asthma and the usefulness of curvature assessment in expiratory flow-volume curves.

BACKGROUND Spirometry, and in particular forced expiratory volume in the first second (FEV(1)), are standard tools for objective evaluation of asthma. However, FEV(1) does not correlate with symptom scores, and hence its value in the assessment of childhood asthma may be limited. Therefore, some clinicians subjectively assess the presence of curvature in the maximum expiratory flow-volume (MEFV) curves obtained from spirometry, where concave patterns are observable despite normal FEV(1) values. OBJECTIVE To evaluate the usefulness of subjective and objective measures of the curvature in the descending phase of the MEFV curve for the assessment of asthma. METHODS We obtained symptom scores and performed spirometry in 48 patients with asthma (21 females, mean +/- SD age 10.8 +/- 2.4 y). We measured FEV(1), the ratio of FEV(1) to forced vital capacity (FEV(1)/FVC), maximum expiratory flow at one quarter of the way, and at halfway, through the forced expiratory maneuver (MEF(25) and MEF(50), respectively), and maximum expiratory flow in the middle half of the forced expiratory maneuver (MEF(25-75)). Expiratory obstruction was ranked independently by 3 pediatric pulmonologists, by subjective assessment of the MEFV curve. In addition, the curvature of the descending limb of the MEFV curve was quantitatively estimated by introducing an "average curvature index." RESULTS No significant correlations were found between FEV(1), MEF(50), MEF(25), and MEF(25-75,) respectively, and symptom score (r = -0.22, p = 0.14; r = -0.23, p = 0.11; r = -0.28, p = 0.057; r = -0.27, p = 0.06). A weak correlation was found for FEV(1)/FVC and symptom score (r = -0.33, p = 0.021). However, quantitatively determined average curvature index (ACI) correlated significantly better with measured symptom scores (r = 0.53, p < 0.001) and were in good agreement with the assessment of expiratory obstruction from subjective curvature assessment. CONCLUSIONS Our general findings show that individual lung function variables do not correlate well with symptoms, whereas subjective curvature assessment is thought to be helpful. With the average curvature index we have illustrated a potential clinical usefulness of quantifying the curvatures of MEFV curves.