Journal of Applied Physiology, Vol 72, Issue 1 321-331, Copyright © 1992 by American Physiological Society
Gas dispersion in volume-cycled tube flow. II. Tracer bolus experiments
D. P. Gaver 3rd, J. Solway, N. Punjabi, D. Elad, J. B. Grotberg and N. Gavriely
Department of Biomedical Engineering, Tulane University, Louisiana, New Orleans 70130.
We present a new method for rapid measurement of local gas dispersion in
volume-cycled tube flow. After a small bolus of tracer gas (argon) was
injected into the oscillating flow, the time-averaged effective diffusion
coefficient (mean value of Deff/D) for axial transport of a tracer gas is
evaluated from local argon concentration measurements taken by a mass
spectrometer. Two methods are presented for the evaluation of mean value of
Deff/D from the concentration measurements: one uses all the sampled data,
and the other uses only the local peaks of the concentration. Experiments
were conducted in two tubes (radius = 0.85 or 1.0 cm) over a range of
frequencies (0.42 less than or equal to f less than or equal to 8.5 Hz) and
tidal volumes (7 less than or equal to VT less than or equal to 48 ml). The
experimental results show very good agreement with the theoretical
predictions of Elad et al. (J. Appl. Physiol. 72: 312-320, 1992). In the
absence of oscillations (static fluid), the resulting mean value of Deff/D
converges to that of molecular diffusion. We also show that concentration
data may be acquired at any radial or axial position, not necessarily at
the tracer gas injection point, and the resulting mean value of Deff/D is
independent of the spatial position of the sampling catheter. This method
is of similar accuracy and is substantially faster than previous methods
for measuring gas dispersion in oscillatory flows. The rapidity of these
measurements may permit this method to be used for the in vivo assessment
of gas transport properties within the pulmonary system.
