Venturi tube calibration for airflow and volume measurement

Ventilation measurement by Venturi meters (Vm) has not been validated for human ventilation application in basic and applied physiology. This project aimed to demonstrate the feasibility of the Vm as an inexpensive, robust method for inspiratory ventilation measurements used in Indirect Calorimetry. A differential pressure transducer sensitive from 0 to 1000 Pa combined with Vm made from retail PVC tubing (50 mm Inside Diameter (ID) at inlet, 17.5 mm ID throat section) allowed for airflow measurement of 1–8 L s⁻¹. A Turbine (Ti) was used as the criterion method. Variable airflow of atmospheric, temperature, pressure saturated (ATPS) conditions, were produced through manual 3 L_ATPS manoeuvres of a calibration syringe and constant airflow was induced using a commercial air compressor. The Vm produced valid volumetric airflow (V̇) estimates across non-steady state pulsatile flow conditions (± 0.22 L s⁻¹ 95% confidence limits with zero bias for Bland-Altman). The Vm also made valid V̇ measurements for steady-state continuous flow (± 0.065 L s⁻¹ 95% confidence limits with zero bias for Bland-Altman). Column statistics revealed Vm mean estimates of 3 L calibrated syringe manoeuvres at different flow rates (0.1–8 L s⁻¹) to be 2.972 ± 0.020 vs. 3.066 ± 0.022 L for Ti, respectively, with less than half the percentage error (0.9 vs. 2.2%, respectively). The results indicate that air flow measured by a Vm has similar accuracy to a criterion device for simulated human inspiratory airflow conditions. Further instrumentation and validation studies will lead to potential use of the Vm for measurements in human ventilation, such as airflow (L·s⁻¹), tidal volume (V_T) and minute ventilation (L·min⁻¹).