Evidence is accumulating that blood flow patterns in the cardiovascular system and in cardiovascular devices do, in some instances, depend on blood viscoelasticity. Thus, to better understand the challenges to providing circulatory support and surgical therapies for pediatric and adult patients, viscous and elastic components of complex blood viscoelasticity of 31 pediatric patients were compared to those of 29 adult patients with a Vilastic-3 rheometer. A random effects model with categorical age covariates found statistically significant differences between pediatric and adult patients for log viscosity (p = 0.005). Log strain (p < 0.0001) and hematocrit (p < 0.0001) effects were also significant, as were the hematocrit-by-log-strain (p = 0.0006) and age-by-log strain (p = 0.001) interactions. The hematocrit-by-age interaction was not significant. For log elasticity, age differences were insignificant (p = 0.39). The model for log elasticity had significant log strain (p < 0.0001), log strain squared (p < 0.0001) and hematocrit (p < 0.0001) effects, as well as hematocrit-by-log-strain and hematocrit-by-log-strain-squared interactions (p = 0.014). A model for log viscosity with continuous age was also fit to the data, which can be used to refine cardiovascular device design and operation to the age of the patient. We conclude that there are distinct differences between pediatric and adult blood viscosity, as well as substantial variation within the pediatric population, that may impact the performance of devices and procedures.

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Motivated by questions related to flow in pediatric cardiovascular devices, the purpose of this study was to compare pediatric and adult complex viscoelasticity η* = ηV − iηE, where ηV and ηE are viscous and elastic components, respectively, measured in oscillatory flow in a capillary tube [Thurston 1972]. For normal blood, viscosity is increased at low shear rates by red cell aggregation and reduced at high shear rates due to disaggregation, orientation and deformation of red cells. The elastic part is also normally psuedoplastic, indicative of the deformation of red cell aggregates at high shear and individual cells at low shear, respectively.