A METHOD FOR THE DETERMINATION OF THE VOLUME OF AIR IN THE LUNGS: MEASUREMENTS IN CHRONIC PULMONARY EMPHYSEMA*

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Abstract
The method is an extension and development of the conventional open circuit method (Cournand, A., et al. J. Clin. Invest. 1941, 20, 681). Mixed expired air was collected for periods of 30 seconds alternately in 2 balloons. The quantity of N2 washed out of the lungs during 15 minutes or more of the O2 breathing was determined from the gas volume and N2 concentration in each balloon collection. The quantity of N2 which would have been eliminated in more prolonged studies was estimated by extrapolating the N2 washout curve. The functional residual capacity (FRC) so determined exceeded that obtained by conventional FRC measurements by between 0.804 and 2.025 1. The magnitude of this discrepancy agrees well with that seen when body plethysmographic estimates are compared with conventional measurements of the FRC. It is suggested that this new method measures the volume of the same intrapulmonary spaces as does the body plethysmograph. It is shown that forced expiratory gas samples after 7 minutes of O2 breathing contain too little N2 for them to be representative of the N2 concentration within the lung in such patients.