Journal of Applied Physiology, Vol 43, Issue 5 911-915, Copyright © 1977 by American Physiological Society
Acoustic helium analyzer for closing volume measurement
L. H. Hamilton, N. T. Christman and D. A. Rickaby
An acoustic gas analyzer was developed to measure helium during the closing
volume (CV) test. It is based on the principle that altering the
composition of a gas mixture will change the velocity at which sound is
transmitted through the gas. The change in transit time for an acoustic
burst across an in-line (breathe-through) cell is measured as a function of
He concentration in the expired air during the CV test. Although CO2 and
H2O vapor affect the signal, so it is not specific for He, the system
provides good records of CV. A comparison of measurements in 21 normal
subjects demonstrated no differences for CV measured in the same breath by
the bolus technique using the acoustic gas analyzer and by the resident gas
method using a nitrogen analyzer. Differences in closing volumes measured
by the He bolus technique and the resident gas method might exist in
patients with some kinds of pulmonary disease, and the suggestion is made
that CV measurements by the two methods might assist in describing
pulmonary alterations in patients with bronchopulmonary disease.
