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

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 (P̄pa) and total pulmonary resistance (TPR). The increase over base line of P̄pa was 41.3% in animals aged 2-4 wk, 83% 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.