Evaluation of the VMM turbine for spirometry in the applied physiology laboratory

The volume measurement module turbine (VMM) was evaluated in 51 subjects for spirometry in applied physiology against the Stead-Wells spirometer (SW) and Wright peak flow meter (WM). The volume and flow ranges (VMM) were, FEV1 1.32 to 3.94 L (mean 2.62, confidence interval [CI] 2.46 to 2.78); forced vital capacity (FVC) 1.97 to 5.06 L (mean 3.50, CI 3.29 to 3.71); and peak expiratory flow rate (PEFR) 290 to 624 L.min-1 (mean 434, CI 407 to 461). The mean difference for FEV1 was 0.09 L (CI 0.05 to 0.14), FVC 0.04 L (CI -0.02 to 0.10), and PEFR 18.0 L min-1 (CI 8.7 to 27.3) less than SW or WM. Bias with FEV1 and FVC was not significant, though PEFR demonstrated a significant proportional error. The repeatability coefficients for FEV1 and FVC were 0.18 and 0.20, comparable to the SW; but for PEFR they were greater, 58.4 versus 33.8 L.min-1 by WM. The VMM turbine is accurate and reliable for the measurement of FEV1 and FVC over the ranges studied; however, care should be taken when interpreting PEFR.