This model illustrates the variation in blood hematocrit seen in narrow tubes from the blood hematocrit at the tube outlet.
Model number: 0138
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This model shows the variation of tube hematocrit as a function of
discharge hematocrit and inside diameter of the tube based on the
observations of Fahraeus and the empirical formulation by Pries et al.
It has been noted and confirmed that in small tubes the ratio of red
blood cell velocity and the plasma velocity differ resulting in a
difference in the hematocrit inside the tube from that of the discharge
To illustrate this point take an extreme case where the cells go
twice as fast as the plasma through the tube. The supply and the
discharge hemtocrit must be equal so in order to have the same hematocrit
leaving the tube outlet we must have half the hematocrit in the tube
at any given time as is in the supply or discharge.
The following expression was developed by Pries et al in 1990 (see
reference below) to represent tube hematocrit as a function of discharge
hematocrit and tube diameter the for the compilation of data from
literature at the time documenting the Fahraeus effect.
---- = Hd + (1 + Hd) * (1 + 1.7*exp(-0.415D) - 0.6*exp(-0.011D)