ALVEOLAR AND DEAD SPACE VOLUME MEASURED BY OSCILLATIONS OF INSPIRED OXYGEN IN AWAKE ADULTS

Forced sinusoidal oscillations in the inspired concentration of a low- solubility inert gas can be used to measure airways dead space and alv eolar volume. When inspired oxygen is oscillated about its mean value in the same way, the ratio between the amplitudes of the resulting end -expired and inspired oxygen oscillations is the same as that of an in ert gas such as argon. Thus, oxygen forcing oscillations can be used t o measure lung volume. In nine healthy spontaneously breathing adults, the F-IO2 (mean F-IO2 = 0.26, mean minute volume = 8.5 L/min) was for ced to sinusoidally oscillate with an amplitude of +/- 0.04. The mean airways dead space measured using F-IO2 oscillations with a forcing pe riod of 3 min was 0.17 +/- 0.04 L, and the airways dead space measured by a single-breath CO2 technique was no different at 0.19 +/- 0.03 L. An oxygen oscillation of the same period measured the mean end-expire d alveolar volume at 3.1 +/- 0.7 L. Adding together the airways dead s pace and end-expired alveolar volume, obtained by the oxygen oscillati on technique, provided a measure of FRC that at 3.3 +/- 0.7 L matched the FRC of 3.3 +/- 0.8 L measured by whole-body plethysmography. A thi rd measure of FRC using a multiple-breath nitrogen washout technique g ave a smaller volume of 3.00 +/- 0.85 L. The advantage of using F-IO2 oscillations is that accurate FRC measurements can be made continuousl y, without interfering with the subject's natural breathing rhythm.