P3.13 Friday, Jan. 6 Ontogeny of viscosity in the chick embryo, Gallus gallus: Cheating the hematocrit dependence of blood viscosity KOHL, Z.F.*; HEDRICK, M.S.; CROSSLEY, D.A.; Univ. of N. Texas; Univ. of N. Texas; Univ. of N. Texas email@example.com
Peripheral resistance in the cardiovascular system is dictated by two variables, vessel geometry and blood viscosity (ηbl). While many studies have emphasized the vascular contribution, fewer studies have addressed the potential variance in resistance attributed to ηbl. Hematocrit (Hct) is the primary determinant of ηbl and rises during development, requiring embryonic animals to deal with increasing viscosity over the same time period. We measured ηbl of chick embryonic blood in the latter 50% of development and compared it to previous adult data at 38°C. We hypothesized that ηbl would increase as a function of Hct during development and would be comparable to adult blood over a similar range of Hct values. The equation for ηbl is ηbl=ηpl(k*Hct), where ηbl is plasma viscosity and k is a constant. Embryonic ηbl showed remarkably little variance at 1.67 ± 0.03 centipoise (n=27; ±SEM) at 60%, 70%, 80%, and 90% of incubation (days 13, 15, 17, and 19) with a range of measured Hcts of 18-35%. Embryo ηbl was also invariant when Hct was set to 20-40% at 1.72 ± 0.04 centipoise (n=29) and began to increase exponentially when Hct exceeded 40%. Blood viscosity as a function of Hct is described in embryos by ηbl=0.57(0.036*Hct) and in adults by ηbl=0.96(0.039*Hct). Overall, embryonic chickens had 55 ± 1.4% (n=39) lower ηbl than adults from 0-70% Hct, and this lower viscosity cannot be attributed only to differences in plasma viscosity. The unique viscous properties of chick embryo blood allow systemic O2 transport capacity to increase during development while minimizing resistance to blood flow due to ηbl. Supported by NSF CAREER IBN IOS-0845741 to DAC.