The Relationship between Closing Volume of the Lung and Transpulmonary Pressure,

Closing volumes of the lung were measured in six healthy male subjects by the argon-bolus washout method. At the same time transpulmonary pressure lung volume loops were plotted, and best-fit exponential regressions subsequently fitted to the inflation and deflation limbs. Closing volumes matched the lung volumes at which the recorded pressures departed from the exponential fits during deflation, and it was concluded that this inflexion represented the onset of airway closure. Residual volume, closing volume, closing capacity and closing capacity expressed as a percentage of total lung capacity, were all linearly related to age. These relations allowed the construction of ideal pressure-volume curves for lungs aged 30 to 50 which typify the effect of age on the mechanical properties of the human lung.