Varicose veins.

Pulmonary hypertension due to chronic hypoxia Treat the lung not the pressure Pulmonary vasoconstriction in response to hypoxia is a basic reflex that occurs in all mammals studied. It has long been thought to have two main physiological functions. In the fetus it is responsible for closing off the pulmonary circulation to prevent blood from shunting through the unventilated lung. After birth it ensures that perfusion is constantly matched to ventilation. The problem comes when the lung is faced with global hypoxia due either to high altitude or to chronic hypoxic lung disease. Then the reflex seems malign and causes pulmonary hypertension. Not surprisingly, hypoxic vasconstriction is virtually absent in those animals that live constantly at high altitude. Bar headed geese, for example, fly over the Himalayas to nest in Tibet. These birds and also mammals that live at high altitude seem to suffer very little from their inability to control the flow of blood to the underventilated lung-so is the reflex of any benefit to adult animals or man?