Change in Forced Expiratory Time and Spirometric Performance During a Single Pulmonary Function Testing Session

BACKGROUND: Among patients with obstructive lung disease, the correlation between clinical improvement and bronchodilator response is poor. Forced expiratory time (FET) may explain some discrepancy, but FET has received little attention.

METHODS: We analyzed change in FET during the 3 initial satisfactory flow-volume loops in 102 consecutive patients, 37 with normal spirometry and 65 with airflow obstruction referred to a Veterans Administration pulmonary function testing (PFT) laboratory over 5 months. Patients included both PFT-naïve and PFT-experienced individuals. We also evaluated the relationship between FET and spirometric performance (sum of forced expiratory volume in the first second and forced vital capacity) and the effect of inhaled bronchodilator on FET among patients with airflow obstruction.

RESULTS: Normals and patients with airflow obstruction showed significant increments in FET and in spirometric performance during the 3 initial successive pre-bronchodilator attempts (p < 0.001 for both groups). This was true for PFT-naïve and PFT-experienced individuals. There were significant associations between increments in FET and improvements in spirometric performance in all subgroups. After inhaled bronchodilator there was a further FET increment among patients with airflow obstruction (p = 0.009), but there was no significant difference between bronchodilator responders and nonresponders.

CONCLUSIONS: Patients with normal pulmonary function and those with obstruction develop longer FET during the initial phases of spirometric testing, regardless of previous PFT experience. Longer FET is associated with better spirometric performance. Bronchodilator administration is associated with modest prolongation of FET, but change in FET did not help identify bronchodilator responders.