Utility of forced expiratory time as a screening tool for identifying airway obstruction and systematic review of English literature

SETTING: This study was conducted at a pulmonary function laboratory of a tertiary care hospital in North India. OBJECTIVE: The objective was to study the diagnostic characteristics and clinically useful threshold of forced expiratory time (FET, measured by auscultation over trachea) as a screening tool for identifying airway obstruction and to substantiate the diagnostic utility of FET through a systematic review of English literature. METHODS: FET was compared in seventy patients with airway obstruction (Group A) and seventy controls with normal spirometry (Group B). Within-subject reproducibility of FET, and its correlation with spirometric parameters, was assessed. Diagnostic accuracy of FET in detecting airway obstruction was evaluated at various time thresholds. A systematic review of English literature on FET was also carried out. RESULTS: Median FET was significantly longer in Group A (7.04 s [interquartile range (IQR) 6.67–7.70 s] vs. 4.14 s [IQR 3.60–4.68 s], P < 0.001). At a threshold of 5 s, FET had high sensitivity (0.943) and reasonable specificity (0.814) in detecting airway obstruction. FET measurements were reproducible and correlated negatively with forced expiratory volume in first second (FEV1), FEV1/forced vital capacity, and peak expiratory flow. The systematic review yielded 13 publications. At a widely used threshold of 6 s to describe airway obstruction, pooled sensitivity and specificity from five datasets were 0.802 (95% confidence interval [CI] 0.668–0.890) and 0.837 (95% CI 0.570–0.952), respectively. CONCLUSION: FET of 5 s or more, rather than the commonly recommended threshold of 6 s, should be regarded as abnormal.