Calculating the optimal hematocrit under the constraint of constant cardiac power

Michal Sitina,Heiko Stark,Stefan Schuster

doi:10.1038/s41598-021-83427-2

Michal Sitina, Heiko Stark + Show 1 more

Open Access

https://doi.org/10.1038/s41598-021-83427-2

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Abstract

In humans and higher animals, a trade-off between sufficiently high erythrocyte concentrations to bind oxygen and sufficiently low blood viscosity to allow rapid blood flow has been achieved during evolution. Optimal hematocrit theory has been successful in predicting hematocrit (HCT) values of about 0.3–0.5, in very good agreement with the normal values observed for humans and many animal species. However, according to those calculations, the optimal value should be independent of the mechanical load of the body. This is in contradiction to the exertional increase in HCT observed in some animals called natural blood dopers and to the illegal practice of blood boosting in high-performance sports. Here, we present a novel calculation to predict the optimal HCT value under the constraint of constant cardiac power and compare it to the optimal value obtained for constant driving pressure. We show that the optimal HCT under constant power ranges from 0.5 to 0.7, in agreement with observed values in natural blood dopers at exertion. We use this result to explain the tendency to better exertional performance at an increased HCT.

Highlights

In the blood flow of humans and higher animals, a trade-off between sufficiently high erythrocyte concentration to transport oxygen and sufficiently low blood viscosity to allow rapid flow has been achieved during evolution
We have presented two models of global oxygen supply, which differ in their constraints—notably constant driving pressure and constant cardiac power
We have shown by a novel calculation that the oxygen supply in the latter case achieves maximum at higher hematocrit values

Summary

Introduction

In the blood flow of humans and higher animals, a trade-off between sufficiently high erythrocyte concentration (known as hematocrit or HCT for short) to transport oxygen and sufficiently low blood viscosity to allow rapid flow has been achieved during evolution. According to the c alculations[1,2,3,4], the optimal value should be independent of the level of exertion This is in contradiction with the observation in endurance runner animals like dogs or horses, which are called natural blood d opers[6] because they increase their hematocrit at exertion via expulsion of concentrated blood from the spleen. Another contradiction comes from the prohibited practice of blood boosting in high-performance sports. Before performing the calculation of the optimal hematocrit under the constraint of constant cardiac power, we recapitulate the calculation under constant perfusion pressure We discuss both optimization approaches in a broader context of cardiovascular physiology. We explain the tendency to better exertional physical performance at an increased hematocrit, at least over shorter periods

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