Seeking the optimal hematocrit: May hemorheological modelling provide a solution?

Area of Science:

• Exercise Physiology
• Hemodynamics
• Sports Science

Background:

• Hematocrit influences oxygen supply and blood viscosity, with complex effects on blood flow.
• The hematocrit/viscosity ratio (h/η) is proposed to optimize tissue oxygenation.
• Understanding hematocrit's role in athletes requires analyzing its relationship with viscosity during exercise and training.

Purpose of the Study:

• To analyze exercise-related hematocrit alterations using a theoretical model based on the hematocrit/viscosity ratio.
• To investigate the influence of red blood cell rigidity on discrepancies between actual and predicted hematocrit.
• To examine how endurance training affects the hematocrit/viscosity ratio and hematocrit levels in athletes.

Main Methods:

• Reconstructed blood viscosity at high shear rate using Quemada's equation.
• Calculated theoretical and actual hematocrit/viscosity ratios in athletes.
• Correlated discrepancies with red blood cell rigidity and training parameters.

Main Results:

• Actual hematocrit deviates from theoretical optimal values in athletes, influenced by red blood cell rigidity.
• Submaximal exercise acutely decreases the h/η ratio, a change well-predicted by the model.
• Endurance training increases h/η and reduces hematocrit discrepancies, with training volume correlating to hematocrit reduction.

Conclusions:

• Athletes exhibit 'viscoregulation' through fine-tuning of the h/η ratio.
• Hematocrit alterations during exercise and training are adaptive mechanisms for optimizing blood flow and oxygen transport.
• The hematocrit/viscosity ratio serves as a key indicator of hemorheological adaptation in trained individuals.