Systematic-to-pulmonary collaterals: a source of flow energy loss in Fontan physiology.

Patients with Fontan-modified, single-ventricle heart frequently have systemic collaterals that increase pulmonary blood flow. Competitive flow from these auxiliary vessels can also elevate pulmonary artery pressure, a process leading to erosion of flow's mechanical energy. An analogous analytical description of mixing fluid streams was used to provide insight into flow energetics associated with systemic-to-pulmonary collaterals in Fontan-type circulation. We find that theoretical pressure increases and flow energy losses due to mixing vary quadratically as the velocity differences of the interacting fluid streams. Moreover, the predicted flow energy loss is shown to depend directly on the resultant pressure increase. Based on studies of aortopulmonary collaterals in patients with Fontan anatomy, we provide an estimate of pulmonary artery pressure elevation and flow energy loss, factors that are of considerable clinical importance.