In congenital heart disease (CHD) with pulmonary hypertension (PH) resulting from high pulmonary flow, we sometimes experience patients whose PH continues even after the normalization of flow following surgery. Preoperative identification of these patients is difficult even using direct hemodynamic measurements at cardiac catheterization. The purpose of this study is to interpret the state of the pulmonary vascular bed more precisely using a new theoretical approach and to present the criteria available for avoiding residual PH.
During preoperative routine catheter examination in CHD patients with PH we applied the Windkessel model to the pulmonary circulation and calculated the diastolic time constant (Td) of the pulmonary circulation. Td of Group 1 (0.50±0.03 sec), 6 patients who manifested residual PH after surgery, was higher than that of group 2 (0.23±0.14 sec), 42 patients with normalized pulmonary artery pressure after surgery. Furthermore, the relationships between Td and pulmonary blood flow (Qp) or pulmonary to systemic flow ratio (Qp/Qs) were very sensitive for distinguishing between these two groups. Group 1 was located in the left-upper quadrant of the graph of Td vs Qp or Td vs Qp/Qs relationships, whereas group 2 was located in the right-lower quadrant.
The relationships between Td and Qp or Qp/Qs were considered to reflect the pathological change in the pulmonary vasculature more precisely. As a consequence, they would be very useful in understanding the state of the pulmonary vascular bed and avoiding residual PH.