C108-05 The FEV1 From Spirometry Efforts Demonstrating Submaximal Inhalation Error (SIE) Can Be Corrected to Produce an Accurate Estimate of the FEV1 Generated From Full Inflation

Abstract Background Submaximal inhalation error (SIE) is a common spirometry error caused by starting the forced exhalation before the patient reaches full inflation and is a major cause of excessive variability of spirometry results in clinical trials. Attempts to correct the spirometry operator technique have been only partially successful. We have previously shown the utility of the FIVCmax/FVC to identify SIE when end of forced exhalation conditions are comparable in the effort providing FIVCmax and the effort being evaluated. Objective We hypothesized that FEV1s compromised by emergence from efforts with SIE could be mathematically corrected to produce an accurate estimate of the FEV1, comparable to those from efforts that started from full inflation. Methods A total of 2525 efforts from 478 anonymized forced spirometry measurement sessions showing FVCs 2.0L obtained from a clinical trial for asthma were reviewed. The reported FEV1s in these measurements came from efforts showing good SOFE and a rapidly inhaled FIVC/FVC, suggesting full inflation. SIE was evaluated using FIVCmax/FVC in 1065 efforts showing good SOFE, FIVC/FVC suggesting full inflation and with EOFE comparable to the effort providing the largest FIVC (FIVCmax).156 efforts with acceptable SOFE and EOFE conditions comparable to that showing the largest FIVC also revealed FIVCmax/FVC 1.05, suggesting SIE. A correction factor was applied to the FEV1 from these SIE efforts. FEV1corrected = measured FEV1 + ((FIVCmax - FVC) x FEV1/FVC reported for the measurement). The corrected FEV1 was compared to the reference (reported) FEV1. Results The mean difference between the FEV1 reported and the FEV1 adjusted was -0.037 L (t-test p 0.001, SD 0.072L, range -0.237 to 0.176L). 148 of the 156 adjusted FEV1s (94.9%) were within the repeatability tolerance of +0.150 L of reference FEV1. The volume below full inflation by this assessment was 0.255L (+ 0.178L, max 1.18L). Figure 1 shows the difference between the corrected FEV1 from efforts with SIE plotted against the magnitude of the SIE, the difference between the FIVCmax and the FVC of the corrected effort. The green shaded area contains all corrected FEV1s that are within the repeatability tolerance of + 0.150 L of the reported FEV1. Conclusions A simple mathematical correction appears to produce an accurate estimate of FEV1 when applied to FEV1s from SIE efforts in an asthma cohort. Results are promising but further work is required to validate this adjustment in this and other cohorts. This abstract is funded by: None