Effect of hypoxia on adaptation of the pulmonary circulation to extra-uterine life in the pig

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Abstract
Pigs were exposed to hypoxia for 2 to 5 days, at ages ranging from birth to 2 weeks. The effect of hypoxia on structural adaptation of the pulmonary arterial circulation to extra-uterine life was studied by applying quantitative morphometric techniques to the injected autopsy lung specimens. In animals exposed to hypoxia from birth, the reduction in arterial muscularity, and increase in size and number which normally takes place after birth, began to occur, but the process was arrested by exposure to hypoxia which with increase in exposure time caused a secondary increase in muscularity. In animals allowed to adapt fully to extra-uterine life and first exposed at 14 days, increase in muscularity as shown by an increase in wall thickness and extension of muscle into smaller and more peripheral arteries than is normal, was secondary to the hypoxic insult and similar to that reported in adults of other species. Animals exposed at between 2 and 7 days of age showed an intermediate response, failure to adapt normally plus a secondary increase in muscularity. Right ventricular hypertrophy developed in all animals. The studies emphasise the vulnerability of the newborn pulmonary circulation to hypoxia and the rapidity with which structural change occurs.