Value of the peak expiratory flow in bronchodynamic tests.

OBJECTIVE: To determine the accuracy of the peak expiratory flow (PEF) as an alternative parameter to the forced expiratory volume at first second (FEV1) in the bronchodynamic tests.

METHODOLOGY: We studied 84 patients, 53 males and 31 females, with average age 46 +/- 13 years, as clinic suspects of bronchial asthma. PEF was determined with a "mini-Wright peak flow meter" and a spirometry was obtained. Based on the results, 44 subjects were classified under group 1 (FEV1/FVC < 70% and FEV1 < 80% of theoretic value) and subjected to a bronchodilator test. While in group 2 subjects (normal spirometry), a methacholine challenge was performed. During each procedure, PEF readings were obtained before FEV1 determination. The usefulness of the PEF for the diagnosis of reversibility or bronchial obstruction with respect to the FEV1 was assessed in both groups.

RESULTS: In the bronchodilator tests, a cut-off point was found for the increase in the PEF > 18%, which showed a sensitivity of 85%, specificity of 79%, positive predictive value of 77% and negative predictive value of 86%, with respect to an increase in the FEV1 > 15%. In the methacholine challenge, a decrease in the PEF > 12% only achieved a sensitivity of 74% and specificity of 71%.

CONCLUSION: Peak expiratory flow may be an useful parameter in bronchodilator tests. However, it should not be used in methacholine challenge.