A calibrator for measurements of respiratory impedance

We describe a simple device that may be employed as a compact and quick calibrator for measurements of respiratory impedance. The real and imaginary parts of the complex impedance of the calibrator are computed as a function of frequency from the theory of sound propagation along a cylindrical duct; a table is set up for the usual operational range 0-50 Hz. Theoretical predictions have been tested experimentally by forcing almost sinusoidal waves through the device by a mechanical piston. The calibrator has been used to confirm that experimental results based on the forced oscillation technique may significantly depend on the type and model of the commercial pressure sensor employed.