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Effects of oxygen therapy on pulmonary arterial hypertension in chronic obstructive lung disease.

In patients suffering from chronic obstructive lung disease pulmonary arterial hypertension is mainly due to anatomical lesions. For this reason it does not regress following acute administration of oxygen, unlike functional pulmonary arterial hypertension due to vasoconstriction, which superimposes itself on the anatomical lesions during exacerbations of respiratory insufficiency. At present there is convincing proof that protracted treatment with oxygen is able to reduce pulmonary arterial hypertension sustained by anatomical alterations. Two recent studies, one carried out in the U.S. (duration of follow-up: 6 months), the other in Great Britain (duration of follow-up: 5 years), have reached this conclusion. The effects of oxygen on pulmonary arterial hypertension are directly proportional to the number of hours in which oxygen is administered daily; in any case this number should not be below 15 hours/day. The reasons for which treatment with oxygen is not able to arrest the evolution of pulmonary arterial hypertension in some patients and the role of the reduction in blood viscosity due to oxygen therapy remain to be clarified.