Redefining spirometry hesitating start criteria based on the ratio of extrapolated volume to timed FEVs

The primary purpose of this study was to investigate alternative hesitating start criteria for spirometry maneuvers that do not achieve an acceptable plateau. The current hesitating start criterion that has been in use for 30 years is based on clinical opinion from expert users; it was not established based on information from peer-reviewed scientific studies.

A total of 1,719 workers met the eligibility criteria for this study and contributed 24,945 trials. The fitted lines obtained from linear regressions of each dependent variable, volume of air calculated at time zero using the back extrapolation method (extrapolated volume [EV])/FEV(1), EV/FEV in 3 s (FEV(3)), and EV/FEV in 6 s (FEV(6)) on EV/FVC were determined. The 95th percentile of the prediction interval of each dependent variable corresponding to EV/FVC = 5% was calculated.

The values for EV/FEV(1), EV/FEV(3), and EV/FEV(6) corresponding to the 5% EV/FVC value were determined to be 6.62%, 5.59%, and 5.25%, respectively.

A new hesitating start criterion using EV/FEV(6) of 5.25% is recommended for tracings that do not achieve a plateau or when an FEV(6) is performed. An EV/FEV(3) of 5.59% could be incorporated into spirometry software as an early warning signal that could help operators identify trials with potential hesitating starts.