INCREASED RESPIRATORY SYSTEM RESISTANCE AND BRONCHIAL SMOOTH-MUSCLE HYPERTROPHY IN CHILDREN WITH ACUTE POSTOPERATIVE PULMONARY-HYPERTENSION

Following surgery for congenital heart disease, there is often an incr eased reactivity of the pulmonary vasculature to stimuli, resulting in rapid increases in pulmonary artery pressure and a clinical impressio n of stiff lungs. Lung mechanics were measured in 30 children, mean ag e 6.7 +/- 4.1 mo, who were ventilated and had pulmonary artery pressur e monitoring following surgery for congenital heart disease. A group o f 15 patients developed postoperative pulmonary hypertension. In these patients, respiratory system resistance was 43% higher (p = 0.001) an d compliance 11% lower (p = 0.004) during acute pulmonary hypertension compared with baseline pulmonary artery pressure. No changes in resis tance or compliance were seen in the 15 patients who did not develop p ulmonary hypertension. The changes in lung mechanics interfered with m echanical ventilation, resulting in a 9.4% rise in Pa-CO2 during pulmo nary hypertension. The bronchial smooth muscle was found to be increas ed by 68%, and the vascular smooth muscle was more than twice normal i n lung biopsies from 9 pulmonary hypertension patients compared with 6 age-matched postmortem control patients who had no cardiac or pulmona ry disease. The bombesin-immunoreactive pulmonary neuroendocrine cells (PNEC) were also increased in the pulmonary hypertension patients. Th ese findings suggest a coconstriction and cohypertrophy of bronchial a nd vascular smooth muscle during pulmonary hypertension. Mediators, su ch as bombesin, endothelin-1, and serotonin, are known to be produced by PNEC and may be involved in the observed vasoconstriction, increase d respiratory system resistance, and smooth muscle hypertrophy.