Studies on the Nature of the Arterial Blood Oxygen Unsaturation in Chronic Pulmonary Disease

¹ The Cardio-Respiratory Laboratory, University of Southern California School of Medicine.

1. Our studies indicate that shunting producing arterial blood oxygen unsaturation is one of varying magnitude whether it be due to an arteriovenous fistula of the lung, intracardiac shunting from right to left or at the alveolar level in chronic pulmonary diseases such as: pulmonary fibrosis, collagen diseases, sarcoidosis, pneumoconiosis and emphysema. The decrease noted in the arterial blood oxygen saturation with exercise on air breathing was not restored to a normal level on a high oxygen breathing mixture (such as 32.0 per cent oxygen) as one would expect if the major difficulty were alveolar capillary-membrane block.

2. The use of (1) graded levels of oxygen breathing, especially 32.0 per cent oxygen and 40.0 per cent oxygen, and (2) the use of intermittent positive pressure breathing on compressed air only constitute simple tests indicating the nature of the arterial blood oxygen unsaturation.

3. The use of 100 per cent oxygen breathing at rest in an inadequate test to rule out shunting, as this not only obscures shunting at the alveolar level, but in some cases if measured with exercise a decreased saturation results in the presence of a normal resting saturation (100 per cent).

4. These studies indicate that in chronic pulmonary disease in general (except beryllosis) that the primary cause of the arterial blood oxygen unsaturation is due to the presence of poorly ventilated alveoli or to the perfusion of blood through nonventilated or poorly ventilated areas and that an alveolar-capillary membrane block is not a significant factor producing the hypoxia.