Use of the Emerson Adult Ventilator for Helium Flow-Volume Calibration

We describe a method for routine calibration of a pneumotachograph integrator system used for the measurement of maximum expiratory flow-volume (MEFV) curves. This calibration permits the sequential measurement of MEFV curves with the patient breathing air and subsequently a helium-oxygen (80%-20%) mixture (He-O2). An Emerson 3-PV adult volume ventilator is used to deliver a constant volume and reproducible flow pattern with either air or He-O2. Tracings are recorded on an X-Y recorder, and two sets of variable gains on the integrator system permit superimposition of curves of equal volume and flow pattern. Loss of correspondence between curves measured on successive days without recalibration is less than 5%. This method offers a simple, reproducible way of adapting a pneumotachograph integrator system to the measurement of helium flow-volume curves.