Abstract 15081: The Viscoelastic Yield Stress of Blood is Negatively Associated With Pulmonary Blood Flow in the Fontan Circulation

Introduction: In the Fontan (FN) circulation pulmonary blood flow (Qp) is passive, resulting in severely decreased shear rate and velocity in pulmonary arteries to the point of stasis. Yield stress (YS) is the shear stress required for blood to transition from stasis to a moving fluid. Therefore, YS may be a determinant of Qp in FN. We evaluated YS in patients with FN and Glenn (GLN) circulations and whether increased YS is associated with decreased Qp. Methods: We enrolled 20 patients with biventricular (2V) congenital heart disease (CHD) and 41 patients with single ventricle CHD (19 FN and 22 GLN) who were undergoing a clinically indicated cardiac catheterization. Two patients were excluded due to pulmonary vascular disease. We obtained blood samples at the time of catheterization and measured blood viscosity across shear rates 1 s -1 to 1000 s -1 using a Rheolog viscometer We calculated YS by curve-fitting of the viscosity measurements to a Casson fluid model. Hypothesis: We hypothesize that higher yield stress will be associated with lower pulmonary blood flow in Fontan circulation. Results: The FN group was the oldest and had the largest BSA (FN>2V>GLN; p<0.0001). Hematocrit was highest in GLN (GLN>FN>2V; p<). Blood viscosity was higher across all shear rates in GLN compared to both FN and 2V (p<0.001 for all shear rates) and higher in FN than 2V from 1 s -1 to 150 s -1 (p<0.05 for all shear rates). YS was highest in GLN (GLN>FN>2V; p< ). YS was negatively associated with Qp in both FN (R2 0.33, p=0.02) and GLN (R2 0.2, p=0.038), but not 2V (see Figure). Hematocrit was negatively associated with Qp in 2V (R2 0.34, p=0.028) and trended toward negative association in FN (R2 0.27, p=0.099), but not in GLN. Stepwise regression of Hct and YS vs Qp in FN demonstrated YS as the primary predictor of Qp. Conclusions: Our data demonstrate that the yield stress of blood derived from the Casson fluid model is a significant determinant of pulmonary blood flow in FN circulation.