# How many cells can our blood tolerate?

## Albert Einstein's equation helps to calculate the optimal hematocrit value

Read out"Blood is thicker than water, " says the vernacular and is thus literally right: Because the vital juice consists of almost half of solid ingredients. Humans and many animals all have about 40 percent red blood cells - that this is the optimal proportion, German researchers have now confirmed with the help of a formula of none other than Albert Einstein.

The largest proportion of human blood - about 40 percent in total - have the red blood cells. They contain the red dye hemoglobin and are responsible for the transport of oxygen. "It is amazing that this proportion is not only approximately the same for all humans, but also for many other vertebrates, " says Stefan Schuster from the Friedrich Schiller University Jena. The assumption therefore suggests that this value represents an optimum proven in evolution. "With a lower volume fraction of red blood cells, less oxygen is transported, " explains the researcher. "With a higher proportion, the oxygen transport would indeed be increased. But as the blood would be thicker, the transport speed would decrease at the same time. "

### Einstein also calculated viscosities of liquids

As Schuster and his colleague Heiko Stark have now found out, the optimal hematocrit value - which indicates the volume fraction of the red blood cells - can be calculated with an equation that goes back to none other than Albert Einstein. In addition to relativity theory and quantum physics, the ingenious researcher also dealt with the viscosity of liquids. "There are already several theoretical approaches in the literature for calculating the optimal hematocrit value, " says Schuster. The bioinformaticians of the University of Jena have now investigated which of these equations is best suited to express the dependence of the viscosity of the liquid (blood) on the volume fraction of the particles (blood cells) and were found in Einstein.

Accordingly, the viscosity of a liquid depends on the viscosity of the solvent and the volume fraction of its solid constituents. In addition, Einstein's equation still contains the factor 2.5. "Using a modification of this equation proposed by Arrhenius in the equation for the flow velocity and determining the maximum, one obtains an optimum of exactly 40 percent, " Stark says and calculates: 1 divided by 2.5 equals 0.4 or just 40 percent. The normal hematocrit of humans thus seems to be optimal from a fluid physics point of view. This also explains why the same value can be found in many animal species, such as lions, antelopes, goats, elephants and rabbits.

### Diving marine mammals have more blood cells

In their article, the bioinformaticians have listed the experimentally determined hematocrit values of a total of 57 vertebrate species from the literature. "But there are also some deviations from the optimum", Stark explains. For example, the hematocrit in seals is significantly higher at 63 percent. There are probably additional criteria. For example, sea creatures need a larger storage capacity for oxygen because of the long dive times. display

Incidentally, the results of the Jena researchers also question the illegal practice of blood doping in sport. An attempt is made to increase the concentration of the oxygen-carrying hemoglobin in the blood and thus the athlete's ability to perform. As a result, the hematocrit value rises artificially. "But this is not just criminal, but it is, as our calculations have it, more than questionable in terms of its physiological effect, " adds Schuster. (Journal of Applied Physiology, 2012, DOI: 10.1152 / japplphysiol.00369.2012)

(Friedrich-Schiller-University Jena, 15.06.2012 - NPO)