Long term performance of a hand held spirometer

Background - A study was undertaken to test the long term performance of a small hand held spirometer for self-administered serial spirometric testing. Methods - Thirty turbine pocket spirometers (MicroMedical DiaryCard) were used in a clinical trial on 22 emphysematous patients with severe alpha(1)-antitrypsin deficiency. The spirometers were able to store the date, time, forced expiratory volume in one second (FEV(1)), forced vital capacity (FVC), peak expiratory flow (PEF), and flow-volume loop for each blow. Every four weeks when the patients came for alpha(1)-antitrypsin infusions the performance of their spirometer was checked before and after retrieval of the data from the spirometer. Calibration checks were threefold and included volume calibration with a 1.0 litre and 3.0 litre syringe, and flow calibration with a decompression calibrator. Results - After two years of study the mean number of spirometric recordings performed per spirometer was 693 (range 237-1178), and the mean number of calibration checks was 33 (range 2-57). The coefficient of variation of the calibration signal was 1-2% for syringes and 0.5-1% for the decompression calibrator. The bearings of one turbine exhibited excessive friction after 17 months. None of the other 29 instruments showed drift, and a general drift of all spirometers towards larger or smaller readings could not be shown. However, unforeseen problems in the stability of the calibrating devices were observed. Conclusions - The small hand held turbine spirometers are suitable for long term patient-administered serial spirometric testing. The two year durability is acceptable and the long term reproducibility excellent.