Pulmonary vascular-bronchial interactions: acute reduction in pulmonary blood flow alters lung mechanics

Background-Postoperative pulmonary hypertension in children after congenita l heart surgery is a risk factor for death and is associated with severe ac ute changes in bath pulmonary vascular resistance and lung mechanics. Objective-To examine the impact of changes in pulmonary blood flow on lung mechanics in preoperative children with congenital heart disease, in order to assess the cause-effect relation of pulmonary vascular-bronchial interac tions. Design-Prospective, cross sectional study. Setting-Cardiac catheterisation laboratory, general anaesthesia with mechan ical ventilation. Interventions-variation of pulmonary blood flow (QF) by either balloon occl usion of an atrial septal defect before interventional closure, or by compl ete occlusion of the pulmonary artery during balloon pulmonary valvuloplast y for pulmonary valve stenosis. Main outcome measures-Ventilatory tidal volume (Vt), dynamic respiratory sy stem compliance (Cdyn), respiratory system resistance (Rrs). Results-28 occlusions were examined in nine patients with atrial septal def ect (median age 9.5 years) and 22 in eight patients with pulmonary stenosis (median age 1.2 Sears). Normalisation of Qp during balloon occlusion of at rial septal defect caused no significant change in airway pressures and Rrs , but there was a small decrease in Vt (mean (SD): 9.61 (0.85) to 9.52 (0.9 7) ml/kg; p < 0.05) and Cdyn (0.64 (0.11) to 0.59 (0.10) ml/cm H2O*kg; p < 0.01). These changes were more pronounced when there was complete cessation of Qp during balloon valvuloplasty in pulmonary stenosis, with a fall in V t (9.71 (2.95) to 9.32 (2.84) ml/kg; p < 0.05) and Cdyn (0.72 (0.29) to 0.6 4 (0.26) ml/cm H2O*kg; p < 0.001), and there was also an increase in Rrs (2 5.1 (1.7) to 28.8 (1.6) cm H2O/litre*s; p < 0.01). All these changes exceed ed the variability of the baseline measurements more than threefold. Conclusions-Acute changes in pulmonary blood flow are associated with simul taneous changes in lung mechanics. While these changes are small they may r epresent a valid model to explain the pathophysiological impact of spontane ous changes in pulmonary blood flow in clinically more critical situations in children with congenital heart disease.