A COMPARATIVE STUDY OF INTRAPULMONARY GAS MIXING AND FUNCTIONAL RESIDUAL CAPACITY IN PULMONARY EMPHYSEMA, USING HELIUM AND NITROGEN AS THE TEST GASES12

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Abstract
A comparative study has been made of the measurement of functional residual capacity by the method of Darling, Cournand, and Richards by the open circuit helium washout method in normal subjects and in patients with pulmonary emphysema. In the normal subjects, agreement between the two methods was good, but in the patients with emphysema a significantly larger mean value was obtained by the helium method than by the Darling method. This discrepancy appears to represent adequately the mean intrapulmonary gas concentration in patients with severe defects in intrapulmonary gas mixing. Substitution of nitrogen for helium in the washout procedure made no significant difference in the measurement of functional residual capacity and produced no consistent changes in the apparent characteristics of the slowly ventilated lung spaces of patients with emphysema. The rate of gas diffusion is apparently not a limiting factor in the ventilation of the large, slowly ventilated lung regions of patients with pulmonary emphysema.