A pilot study of hot-wire, ultrasonic and wedge-bellows spirometer inter- and intra-variability

The aim of this pilot study was to compare spirometric values obtained with different types of spirometers, spirometers of same type, and repeated measurements with the same spirometer in a pulmonary function laboratory setting. 12 healthy volunteers performed spirometry on four hot-wire (SensorMedics), two ultrasonic (Spirare) and one wedge-bellows (Vitalograph S) spirometers, according to ATS/ERS (American Thoracic Society/European Respiratory Society) guidelines. Spirometric values were compared using linear mixed models analysis with a random intercept for subjects and a fixed effect for type of spirometer used. Confidence intervals and p values were adjusted for multiple comparisons. Mean ± SD (L) values for hot-wire, ultrasonic and wedge-bellows spirometers for FVC (forced vital capacity) were 4.02 ± 0.66, 3.69 ± 0.61 and 3.93 ± 0.69, and for FEV1 (forced expiratory volume in one second) 3.06 ± 0.44, 2.95 ± 0.44 and 3.10 ± 0.49. Significant differences were found between hot-wire and ultrasonic and between wedge-bellows and ultrasonic spirometers for FVC and FEV1, and between hot-wire and wedge-bellows spirometers for FVC but not for FEV1. There were no significant differences between spirometers of same type, and low mean differences in repeated measurements for all spirometers included. In conclusion, the pilot study shows systematically higher values for FVC and FEV1 for hot-wire and wedge-bellows compared to ultrasonic spirometers.