Chronic vascular pulmonary dysplasia associated with neonatal hyperoxia exposure in the rat

Chronic sequelae of neonatal hyperoxia was studied in male rats exposed to 0.96-1.0 FiO2 for the first 8 days of life. At 58 days of age functional and morphologic cardiopulmonary changes were compared with controls. Right ventricular systolic pressure was measured percutaneously under anesthesia and was increased in the O2 group (29.5 mm Hg +/- 3.1 versus 23.2 mm Hg +/- 3.5, p less than 0.001). Lung and heart weights were similar between groups. Right ventricular weights however were increased in the O2 group (0.197 g +/- 0.023 versus 0.175 g +/- 0.020, p less than 0.001). Air pressure-volume curves were similar but in the O2 rats saline deflation curves were shifted left and maximal fluid lung volumes were greater (14.1 +/- 1.2 versus 12.0 +/- 0.7 ml, p less than 0.001). Pulmonary arteries were perfused at 100 cm H2O with a barium-gel mixture and lungs were fixed at 25 cm H2O with formalin. Microscopic examination of lungs revealed dysplastic changes of alveolar architecture which included irregularly enlarged alveoli and incomplete alveolar septation. Morphometric studies of the lungs showed that the O2 rats had an increased volume proportion of parenchyma (0.865 +/- 0.020 versus 0.850 +/- 0.019, p less than 0.05), increased mean linear intercept (72.3 microns +/- 9.5 versus 53.6 microns +/- 5.0, p less than 0.001), decreased number of alveoli per mm2 (207 +/- 34 versus 319 +/- 39, p less than 0.001) and fewer small arteries (20-200 microns) per mm2 (8.7 +/- 1.3 versus 14.9 +/- 2.4, p less than 0.001). The number of small arteries/100 alveoli was similar.(ABSTRACT TRUNCATED AT 250 WORDS)