Gas compression artefacts when testing peak expiratory flow meters with mechanically-driven syringes

Area of Science:

• Pulmonary Function Testing
• Metrology
• Biomedical Engineering

Background:

• Mechanical syringes are used to calibrate peak expiratory flow (PEF) meters, requiring adherence to American Thoracic Society (ATS) standards for 2% accuracy.
• Gas compression within syringes can introduce significant inaccuracies, particularly with high-resistance PEF meters.

Purpose of the Study:

• To investigate the gas compression artifact in a mechanical syringe during PEF meter testing.
• To quantify the impact of syringe volume on PEF measurement accuracy.

Main Methods:

• A 13.6 L mechanical syringe (PWG) was connected to a mini-Wright PEF meter.
• Scaled ATS standard waveforms (750 and 450 L/min) were discharged at varying syringe volumes (Vsyr).
• PEF readings were recorded and compared to target flows derived from piston displacement.

Main Results:

• PEF readings decreased linearly with increasing syringe volume (Vsyr).
• PEF decreased by 0.31% and 0.27% per liter for 750 and 450 L/min waveforms, respectively.
• Gas compression caused overreading of actual PEF by approximately 4% at 13.6 L Vsyr, reducing to 1% at 3.62 L Vsyr.

Conclusions:

• Gas compression errors in large mechanical syringes can exceed the 2% inaccuracy limit for high-resistance PEF meters.
• Measurements can be corrected for gas compression by linearly extrapolating PEF recordings to zero volume.
• Accurate calibration of PEF meters requires accounting for gas compression effects, especially at larger syringe volumes.