There was no relationship with methacholine responsiveness.
FET was inversely related to FEV 1/FVC in all groups, negatively related to FEV 1 in the obstructed patients, and positively related to FVC in both the normal and restricted patients. Mean FET was 9.6 ± 2.2 s in the normal group, 12.3 ± 3.0 s in those with obstruction, and 8.8 ± 1.9 s in those with restriction. We retrospectively determined FET pre- and postmethacholine challenge in 1,241 patients (818 had normal lung function, 137 were obstructed, and 229 were restricted) and examined its relationships to spirometric and demographic variables in both hyperresponsive and normoresponsive individuals. FET is predicted to correlate negatively with both FEV 1 and FVC if variations in the rate of lung emptying (relative to normal) among individuals in a population exceed variations in the amount of lung emptying. We developed a mathematical theory of FET assuming a linear forced expiratory flow-volume profile that terminates when expiratory flow falls below a defined detection threshold. Forced expiratory time (FET) is a spirometrically derived variable thought to reflect lung function, but its physiological basis remains poorly understood.
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