Respiratory input impedance up to 256 Hz in healthy humans breathing foreign gases

307-320, 1993.-Currently available data concerning respira-tory input impedance (Zrs) at frequencies up to 300 Hz indicate that Zrs is determined mainly by the airways and, in particular, the gas compressibility in the airways and the airway wall com-pliance, Hence, measurements of Zrs when breathing gases with different physical properties would be useful in investigat-ing airway mechanics and the role of acoustic propagation. Zrs measured with a standard generator (Zst) and corrected for the upper airway shunt (Zrs*) were measured in nine healthy sub-jects breathing air or a gas mixture consisting of 20 % 0, and 80 % He or SF,. The frequency band was extended up to 256 Hz for air and He-O, and up to 128 Hz for SF,-0,. Zrs exhibited a similar pattern for the three gases, with a shift toward low fre-quencies as the gas density increased. Moreover, the resonance peaks tended to be narrower and higher as the gas density in