Response of the pulmonary circulation to acute hypoxia in the growing pig

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Abstract
In a previous article we have analyzed the structure of the growing pig lung and correlated the findings with cardiorespiratory function studies on the same animals (J. Appl. Physiol: Respirat. Environ. Exercise Physiol. 45: 806–817, 1978). The present study analyzes the pulmonary and systemic vascular responses to acute hypoxia in some of those animals at three ages, 2–4, 5–8, and 9–12 wk, the lung of the 12-wk-old pig being structurally similar to that of the adult. In all anesthetized animals, acute hypoxia (5 min 10% fractional inspired oxygen concentration) increased mean pulmonary arterial pressure (Ppa) and total pulmonary resistance (TPR). The increase over base line of Ppa was 41.3% in animals aged 2–4 wk; 83.0% in those aged 5–8 wk, and 136.9% in those aged 9–12 wk; for TPR the increase in the three age groups was 66.4, 92.4, and 138.9%, respectively. This difference in vasoactivity with age is associated with the progressive extension of smooth muscle into the intra-acinar arterial tree, which we have previously shown is an important feature of the structural remodeling that occurs during postnatal lung development in both man and swine.