Human respiratory input impedance between 32 and 800 hz measured by
interrupter technique and forced oscillations.
Frey, Urs, Bela Suki, Richard Kraemer, Andrew C. Jackson.
Dept. of Biomedical Engineering, Boston University, 44, Cummington
Street, 02215 Boston. MA, and Dept. of Pediatrics, University of
Bern, Inselspital, 3010 Berne, Switzerland.
APStracts 3:0501A, 1996.
Respiratory input impedance (In) over a wide range of frequencies has
been shown to be useful in determining airway (Raw) and tissue
resistance (Rti) in dogs or airway wall properties in human adults.
Zin measurements are non-invasive and therefore potentially useful in
investigation of airway mechanics in infants. However, accurate
measurements of Zin at these frequencies using forced oscillatory
techniques (FOT) in infants are difficult because of their relatively
high airway resistance and large compliance of the face mask. If
pseudo-random noise pressure oscillations generated by a loudspeaker
are applied at the airway opening (FOT), the power of the resulting
flow decreases inversely with frequency because of capacitive
shunting into the volume of the gas in the speaker chamber and in the
face mask. We studied whether high frequency respiratory impedance
can be measured using rapid flow interruption (High speed interrupter
technique (HIT)) in which we expect the flow amplitude in the
respiratory system to be higher than in the FOT. We compared Zin
measured by high speed interrupter technique (HIT) with Zin measured
by the forced oscillation technique (FOT) in a dried dog lung and in
5 healthy adult subjects. The impedance was calculated from two
pressure signals measured between the mouth and the high speed
interruption valve (HIT). The impedance could be assessed from 32 to
800 Hz. Its real part at low frequency as well as the frequency and
amplitude of the first and second acoustic resonance, measured by FOT
and measured by HIT, were not significantly different. The power
spectrum of oscillatory flow using the HIT showed amplitudes which
were at least 100 times greater than those using FOT, increasing at
frequencies > 400 Hz. In conclusion, the high speed
interrupter technique enables the measurement of high frequency Zin
data from 32 to 800 Hz with particularly high flow amplitudes and
therefore possibly better signal to noise ratio. This is particularly
important in systems with high airway resistance e.g. in infants,
when measurements have to be performed through a face mask.
Received 5 November 1995; accepted in final form 28 November
1996.
APS Manuscript Number A1156-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996