Patterns of changes and diagnostic values of FEF50%, FEF25%-75% and FEF50%/FEF25%-75% ratio in patients with varying control of bronchial asthma

Background: The pattern of change in FEF50%, FEF25%-75% and FEF50%/FEF25%-75% ratio depends on mechanics of forceful expiration, provided that non-homogenous lung emptying is faithfully recorded in the expiratory flow-volume loops. Objective: To assess the potential clinical value of FEF50%, FEF25%-75% and FEF50%/FEF25%-75% ratio as an indicator of bronchial asthma (BA) control. Methodology: The study involved 75 patients with BA matched for age and gender with 45 non-asthmatic subjects. Based on asthma control test (ACT) and spirometry, asthmatic patients were subdivided into controlled and poorly controlled/uncontrolled. The relationship between FEF50% and FEF25%-75% as well as FEF50%/FEF25%-75% ratio and ACT score were assessed using linear regression. ROC curves were used to assess reliability of FEF25%-75% and FEF50% to diagnose BA in patients with different degree of asthma control. Results: FEF50% correlated strongly with FEF25%-75% (r = 0.989, P 0.001) and the relationship between the two indices is governed by the formula FEF50% = 1.132* FEF25%-75% – 0.003. There was no significant correlation (r = - 0.159, P = 0.083) between FEF50%/FEF25-75% ratio and ACT score. The diagnostic capability of FEF25%-75% for spirometric diagnosis of BA is only marginally better compared to FEF50% (area under ROC curves were 0.88 and 0.89 respectively, P 0.001); however, diagnostic power of both spirometric indices deceased with poor BA control. Conclusion: FEF50%/FEF25%-75% has no clinical value as an indicator for BA control. Role of FEF25%-75% in evaluation of BA is marginally better than FEF50%; however, efficiency of both indices declined substantially as BA control worsened.