A Comparison of Blood Viscosity between the Adult Sheep and Newborn Lamb. The Role of Plasma and Red Blood Cell Type

Abstract

SummaryAdult sheep and newborn lamb blood viscosity (Vc) have been compared by taking into account not only the hematocrit, but also the type of the red cells (adult or fetal) in the circulation and the plasma Vc. At all shear rates studied the whole blood Vc of the adult was higher than that of the newborn. Plasma Vc was 1.58 +-0.18 centipoises in the adult compared to 1.21 +-0.19 in the newborn group (P < 0.001). The mean relative apparent viscosity (whole blood Vc/plasma Vc) was higher in the newborn although the difference was not significant. Abbreviations CP, centipoise Ht, hematocrit Vc, viscosityIn a recent study, blood viscosity of adults and human newborns was compared to determine the part played by the presence of fetal red cell and the plasma viscosity. This work showed that for the same hematocrit adult blood had a higher viscosity than that of the newborn. This was due to a higher viscosity of adult plasma (10).Because the newborn lamb is frequently used as an experimental model for fetal and neonatal circulatory (5) as well as metabolic studies (8) and the results are extrapolated to humans, it was considered of utmost importance to obtain data on rheologic properties of adult and newborn blood in this species. MATERIALS AND METHODSnewborn blood in presence of change in Ht was studied by plotting the logarithm of Vc against Ht. The statistical analysis of the regression lines were performed according to the methods outlined in Snedecor and Cochran (1 I). A preliminary test of the residual variances about the regression lines was done when these tests were not significant, it was then possible to assess the equality of the two slopes. If these tests were not significant the common values of the slopes were estimated, and the intercepts were calculated. The equality of the two intercepts could then be assessed. The Vc of adult and newborn blood in relation to the shear rate was also compared at three Ht ranges: 30-40, 50-60, and 60-70%). The Vc found for each sample was divided by the Vc of its plasma to obtain the relative apparent Vc (2). This ratio reflects the rheologic properties of the erythrocyte suspension. Unpaired Student's t test was used for statistical analyses unless specified otherwise. RESULTSThe influence of Ht changes on the apparent Vc of neonatal and adult blood at four different shear rates is shown in Figure 1. In all instances Vc increases with a rise of Ht, and at a given Ht the Vc decreases with increasing shear rates. Absolute values of adult blood appear to be higher than those of the newborn lamb. The comparison of the rate of change of the Vc of adult and newborn blood in presence of change in Ht is shown in Figure 2. The tests for the equality of variances were not significant at the 0.05 level. The tests of the equality of the slopes were also not significant at 0.05 level. All the tests of the equality of the intercepts were highly significant ( P < 0.001) for all shear rates studied. Figure 3 A, B, and C show the quantitative comparison between the two types of bloo...

Rheology of Fetal and Maternal Blood

“…(3 1) that, under normal conditions, blood viscosity is lower in the neonatal period because of a lower plasma viscosity. This has now been confirmed also for the newborn lamb and adult sheep (32). Earlier reports described an increased whole blood viscosity in normal newborns (3,11,21).…”

Cerebral Vascular Response to Hemorrhagic Hypotension in Newborn Lambs: The Influence of Developing Anemia

“…Our data indicate that a decrease in hematocrit and presumably the decrease in viscosity which accompanies it (10,24) is not critical to the maintenance of CBF or cerebral O2 consumption in newborn animals in the pressure range studied. Therefore, with the rigid definition, constant CBF over a range of CPPs, CBF autoregulation was unaltered by the concomitant development of anemia.…”

“…Several investigations have demonstrated the dependency of CBF on CaO2 (12)(13)(14) and viscosity (10,24). Thus, we attempted to examine the effect of anemia on the hypotensive pressure flow relationship.…”

“…Thus, we attempted to examine the effect of anemia on the hypotensive pressure flow relationship. Independent of vasodilation, viscosity changes due to anemia should reduce vascular resistance (1 1,24), provided Poiseuille's relationship is applicable. This relationship incorporates the effects both of changes in Ca,, and changes in red blood cell concentration on CBF.…”

Colloidal tubular microrobots for cargo transport and compression

“…The viscosity was measured in the range of 0.05 to 300 s −1 . Because of the lack of plates with proper sizes in our rheometer, the viscosity profile of sheep whole blood cannot be measured and was withdrawn from Riopel et al ( 51 ).…”