Increasing density of erythrocytes in blood increases its capacity to carry oxyg
ID: 3481060 • Letter: I
Question
Increasing density of erythrocytes in blood increases its capacity to carry oxygen. However, the viscosity of the blood increases with hematocrit and the blood flows less easily. One might hypothesize that there is an optimum hematocrit for oxygen carriage. Viscosity does not increases linearly with hematocrit. In one study, for hematocrits of 20, 35, 52, and 62%, viscosities were found to be 1.4, 2.0, 3.0, and 4.0 centipoise (a unit for measuring viscosity). Since flow rates vary inversely with viscosities, the relative rates at which erythrocytes (and the oxygen they carry) flow through blood vessels can be found by dividing the hematocrit values by their respective viscosities. What are these ratios for the four hematocrit values? Is there an optimum erythrocyte concentration for blood flow? How well does it correspond to the typical values for men and women (about 45% and 40% respectively)?
Explanation / Answer
The study of flow Dynamics of blood is called Hemorheology.
Hematocrit is the major content of the blood which impacts the flow rate.Blood flow rate is Non-Newtonian. It means as the viscosity increases the flow rate decreases but after a certain point increase in viscosity will increase flow. This happens due to change in shape of erythrocytes, viscosity increases as the density of erythrocytes increases and after a point when there is no space between the erythrocytes for the plasma to flow the erythrocytes stretch and form layers over one another providing space for plasma to flow.This is also called as Viscoelastic nature of blood.
Considering the above values of hematocrit concentration and corresponding viscosities, flow rate can be given by dividing hematocrit concentration by it's Viscosities.
1. 20/1.4 = 100/7 =14.28
2. 35/2.0= 350/2= 175
3. 52/3.0= 520/3= 173
4. 62/4.0= 620/4= 155
As it can be seen the flow rate increases initially from 20% concentration to 52% concentration but than it decreases with increase in viscosity.
That means the optimum hematocrit concentration for optimum blood flow should be around 50% which is true for humans as 45% and 40% in males and females respectively.