ARTERIAL OXYGEN UNSATURATION IN SICKLE CELL DISEASE

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Abstract
In vitro studies of the blood O2 dissociation curve, as well as of ventilatory function and pulmonary gas exchange, were performed in 10 patients with sickle cell disease. Mean vital capacity was significantly reduced whereas maximal breathing capacity was normal. Arterial O2 unsaturation was present in most subjects and could generally be quantitatively accounted for on the basis of lowered arterial O2 tension and blood O2 affinity. Most of the subjects had a widened alveolar-arterial O2 tension difference whose magnitude correlated inversely with the hemoglobin level. In some subjects, venoarterial shunting accounted for the bulk of the AaPo2 [alveolar-arterial oxygen tension] difference. In others, an abnormal degree of inequality of ventilation-perfusion relations was presumably responsible. Arterial O2 unsaturation favors lower venous O2 saturations, which predispose to in vivo sideling and its consequences.