The Diagnostic Value of Forced Expiratory Time

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Siraj O. Wali


Forced expiratory time, Mid-expiratory flow, Fev1/FVC ratio, Small airway disease


Objective: Airway obstruction can be clinically quantified at the bedside by measuring the time taken for forced expiration. The aim of this study was to examine the accuracy of the forced expiratory time in detecting airflow limitation, and small airway disease when compared with simple spirometry as a gold standard test.

Method: Simple spirometry and forced expiratory time were performed on 201 subjects (age range; 12-81 years), referred to a pulmonary function laboratory at a tertiary care hospital. The diagnostic accuracy of forced expiratory time and its correlation with spirometric parameters were tested. Forced expiratory time > 6 seconds was regarded as abnormal, and the ratio of forced expiratory volume in the first second to forced vital capacity of < 70% was considered indicative of an airflow limitation.

Results: Forced expiratory time was found to correlate weakly with spirometric parameters. Forced expiratory time at a cut-off value of => 6 seconds had a sensitivity of 61% and a specificity of 79% in predicting obstructive airway disease when compared with simple spirometry. On the other hand, the sensitivity and the specificity of forced expiratory time in predicting small airway disease were 47% and 86%, respectively.

Conclusion: Forced expiratory time does not correlate well with all parameters of a simple spirometry. Its sensitivity and specificity for detecting airflow limitation and small airway disease were not high enough to be used as a diagnostic test. However, it may be effective enough to be utilized to confirm the diagnosis of small airway disease.

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