Technical and Functional Assessment of 10 Office Spirometers: Discussion

The tests done with the computer-controlled mechanical syringe indicate that the spirometers working under ideal laboratory conditions, at least at ambient conditions, are reliable, but they do not guarantee that the same performances will be obtained in real-life conditions, as patients are tested throughout the day, as it was the case in our study. Therefore, we and other groups propose that the spirometers should be tested both with waveform generators (on a bench) and with real patients.
The precision of FEV1 measured by the office spirometers was comparable to that of the standard spirometers. Only one device showed unacceptable limits of precision (> 200 mL) for FEV1 (± 0.295 L for the Simplicity).
All the office spirometers were less reproducible for the measurement of FVC when compared to the standard spirometers. FVC appears more difficult to measure by the small spirometers (Table 2). Three office spirometers measured FVC with a precision worse than 200 mL (Table 2).
Although statistically significant in some office spirometers, the biases observed for FEV1 or FVC are probably not clinically relevant. Even if we consider the accuracy criteria of the ATS for diagnostic devices as the limits of acceptable bias, all the office spirometers tested for FEV1 and for FVC met this criteria. However, the SpiroStar had a bias of- 4.9 for FEV1/FVC (Table 4). This device underestimated FVC and consequently overestimated FEV1/FVC ratio as compared to the diagnostic spirometers. Some stage 1 COPD patients could therefore be misclassified as stage 0 in that way.
The present data also show that the limits of agreements were generally larger for FVC than for FEV1. We fixed the acceptable limits of agreement by analogy with the short-term coefficients of repeatability of FEV1 (320 mL) and FVC (450 mL) measured in COPD patients. These coefficients corresponded to the maximum absolute limit of agreement times 0.9 as computed using the Bland and Altman analysis with our data. Hence, the limits we chose were 350 mL (FEV1) and 500 mL (FVC). Relatively wide limits of agreement were found with some office spirometers for FVC.
Underestimation of low FEV1 and overestimation of high FEV1 were also found with some office spirometers. This proportional difference may also result in an underestimation of the FEV1/FVC ratio and COPD misclassification.

This entry was posted in Spirometers and tagged comparative study, COPD detection, pulmonary function tests, spirometer, spirometry.