Four-year calibration stability of the EasyOne portable spirometer.

BACKGROUND Clinical practice guidelines recommend daily spirometer calibration checks and weekly linearity checks. The long-term stability of the volume and flow accuracy of a specific model of spirometer should be carefully characterized before modification of the frequency of calibration checks is considered for that model of spirometer. METHODS The EasyOne ultrasonic flow-sensing spirometer was chosen for use by the clinical centers at the 2002 inception of the World Trade Center Worker and Volunteer Medical Screening Program. The screening program quality-control procedure required that the expiratory and inspiratory volume accuracy of each spirometer be checked every day of testing, and the flow accuracy (linearity) checked every week. The calibration check results were transferred to a central database for summary. RESULTS Over 5,000 calibration-check results (4,109 single-speed and 1,189 three-speed) were accumulated from a total of 34 spirometers during the period February 2003 through March 2007. The mean single-speed calibration errors (and 5th-95th percentiles) were -2 mL (-80 to 70 mL) for exhalation and -10 mL (-80 to 60 mL) for inhalation. 98% of the exhalation and 97% of the inhalation calibration checks were accurate within 3.0%. There was no evidence of significant non-linearity according to the results of the 3-speed calibration checks (mean errors of -3, -5, and -6 mL at each speed). CONCLUSIONS The EasyOne retained inhalation and exhalation volume accuracy of better than 3% for at least 4 years. Routine multiple-speed volume calibration checks may not be necessary with the EasyOne. The acceptability and repeatability of patient efforts should be the primary focus of quality-assurance programs with spirometers that have been demonstrated to remain accurate for long periods.