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Figure 2 Schematic representation of the experimental setup used. A Venturi system is placed in series with a pneumotachograph and a mouthpiece, allowing measurement of flow, volume and mouth pressure (Pm), respectively. When compressed air is fed through the Venturi via a computer-driven valve, a negative pressure is generated at the mouth. Its value can be adjusted using a potentiometer. Signals are conditioned, monitored and stored on a personal computer. Volume is obtained by numerical integration of the flow signal. Pm = mouth pressure.
