We modified the pressure gauge of a Bourns BP200 infant ventilator to allow it to display either mean airway pressure (P̅aw) or conventional airway pressure fluctuations. The modification consists of a pneumatic toggle switch and a needle valve connected in-line to the pressure gauge. When the switch is activated, the resistance of the needle valve and the compliance of the pressure gauge combine to form a pneumatic low-pass filter, whose output is read as P̅aw on the pressure gauge.
Chatburn et al. (Mon,) studied this question.