METHOD

The method used is based on Boyle's law that the volume of a gas varies in inverse proportion to the pres-sure to which it is subjected. At the beginning of the test, the subject has an unknown volume of gas in his chest; at either end-inspiration or end-expiration, when there is no air flow, the pressure of this alveolar gas is known to be atmospheric. If his airway isthen oc-cluded so that no pulmonary gas can escape, and he com-presses the pulmonary gas by a voluntary expiratory ef-fort, the pulmonary gas now has a new pressureand vol-ume. Thechange in pulmonary gas pressure can be measured readily during airway occlusion since mouth pressure equals alveolar pressure in a closed systems The change in pulmonary gas volume can be measured by utilizing an air-tight body plethysmograph and a sensitive electrical capacitance manometer. From knowl-