Chest
Volume 125, Issue 5, May 2004, Pages 1902-1909
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Special Reports
Is My Lung Function Really That Good?: Flow-Type Spirometer Problems That Elevate Test Results

https://doi.org/10.1378/chest.125.5.1902Get rights and content

Most spirometry errors reduce test results, and it is widely assumed that measurement accuracy is guaranteed by frequent spirometer calibrations or calibration checks. However, zero errors and changes in flow-type spirometer sensors may occur during testing that significantly elevate test results, even though the spirometer was calibrated recently. To draw attention to these often-unrecognized problems, this report presents anomalous spirograms and test results obtained from occupational medicine clinics and hospital pulmonary function laboratories during quality assurance spirogram reviews. The spurious results appear to have been caused by inaccurate zeroing of the flow sensor, or by condensation, mucus deposition, or unstable calibration of various flow-type spirometers. These errors elevated some FVCs to 144 to 204% of predicted and probably caused 40% of 121 middle-aged working men in respirator medical clearance programs to record both FVC and FEV1 > 120% of predicted. Since spirometers report the largest values from a test, these errors must be recognized and deleted to avoid false-negative interpretations. Flow-type spirometer users at all levels, from the technician to the interpreter of test results, should be aware of the potential for and the appearance of these errors in spirograms.

Section snippets

Spirogram Reviews

Spirograms were submitted for quality assurance (QA) review on a consulting basis or by National Institute for Occupational Safety and Health-approved spirometry course participants from industrial medical departments, occupational medicine clinics, and hospital pulmonary function laboratories. The reviews found elevated test results and anomalous graph shapes recorded by several different flow-type spirometers. All problem graphs were recorded on calibrated spirometers, indicating that changes

Effects of Errors on Respiratory Screening Programs

Complete sets of spirometry results were obtained from three small respirator medical clearance programs: one from an industrial facility that manufactured pet food, and two from mobile testing programs for employees of household waste and sewage management facilities. Since the programs had comparable spirometers and appeared to have similar problems with zero errors and sensor contamination, the three groups were combined for this report. There were 121 men in the three programs (age range,

Recommendations

The prevalence of these zero and sensor obstruction errors cannot be documented from the examples presented here, but in the authors' experience, they are not rare: approximately 5 to 10% of the participants in the lead author's National Institute for Occupational Safety and Health-approved spirometry courses submit graphs with problems like these. A survey including spirogram QA reviews of occupational medicine clinics and pulmonary function testing laboratories would permit the prevalence of

Conclusion

Unlike poor testing technique, which often reduces spirometry test results, errors due to faulty zeroing or partial blockage of flow-type spirometer sensors can seriously elevate test results, potentially leading to false-negative interpretations rather than false-positives.15 The existence of these errors and their appearance should become widely recognized among spirometry users so that falsely elevated test results can be avoided or deleted. QA programs should scrutinize spirograms for these

ACKNOWLEDGMENT

Dr. Townsend acknowledges the important role played by her students and clients in improving teaching about spirometry, as they continue to bring real-life spirometry problems to her attention.

References (15)

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This work was performed at the office of M.C. Townsend Associates, Pittsburgh, PA.

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