Lung volume, compliance, and arterial oxygen tensions during controlled ventilation

The relationship between total dynamic compliance (lung plus chest wall), functional residual capacity, and alveolar-arterial oxygen gradients (A-a DO2) was studied in paralyzed dogs during constant-volume ventilation with pure oxygen. Rapid changes in functional residual capacity (FRC), produced by forced deflation of the lungs, were associated with a rapid fall in total compliance and rise in A-a DO2. Subsequent hyperinflations (deep breaths) restored compliance to control levels more readily than A-a DO2. Changes in the FRC, measured with a whole-body plethysmograph, were related directly to total compliance and inversely to A-a DO2. Collapse of the terminal regions of the lungs produced by forced deflations was associated with a decrease in total compliance of 36%, and a decrease in FRC of 26% with a simultenaous rise in A-a DO2 to a mean of 547 mm Hg. It is concluded that intermittent deep breaths administered during constant-volume ventilation will not necessarily restore control levels of compliance and A-a DO2 equally well. This difference is probably dependent on altered alveolar surface characteristics or mechanics, or both, secondary to the collapse process, which prevent restoration of structural integrity by a deep breath. total dynamic compliance; functional residual capacity; alveolar-arterial oxygen tension difference; atelectasis; deep breath Submitted on October 31, 1963