ABSTRACT
Under static conditions, the pressure exerted by the passive respiratory system depends on elastic, surface, and gravitational forces operating on the lung and the chest wall (i.e., rib cage and diaphragm-abdomen). The pressure exerted by the respiratory system is given by the difference between alveolar pressure and body surface pressure. To determine the static relation between the lung volume and the relaxation pressure of the respiratory system (Rohrer, 1916; Rahn et al., 1946), the subject inspires or expires a volume of air and then relaxes against an obstructed airway, and the pressure across the obstruction is measured. Since there is no flow, the pressure in the mouth or in a nostril equals alveolar pressure. Then the subject breathes in or out maximally from a spirometer so that the volume at which the pressure was measured can be related to one extreme of the vital capacity. This volume must be corrected for the compression or expansion of the gas in the respiratory system caused by the change of pressure during relaxation. When these
458 D'Angelo and Agostoni
measurements are made at several volumes, the volume-pressure curve during relaxation is obtained. This method may not be applied to all subjects and some training is necessary.
