Near-Newtonian Blood Behavior - Is It Good to Be a Camel?

Area of Science:

• Comparative physiology
• Hemodynamics
• Exercise physiology

Background:

• Horses show increased hematocrit with exercise, enhancing oxygen transport.
• Camels, conversely, can experience reduced hematocrit during racing, necessitating supplementation.
• Distinct red blood cell (RBC) mechanical properties in camels raise questions about exercise responses.

Purpose of the Study:

• To investigate the rheological differences between camel and horse blood, particularly concerning red blood cell behavior during exercise.
• To understand how camel erythrocyte properties influence whole blood viscosity and flow dynamics.
• To explore the implications of these unique properties for camel endurance and potential exercise-induced vascular changes.

Main Methods:

• Rheometry was used to analyze the flow behavior of dromedary camel blood.
• Whole blood viscosity (WBV) was measured at varying hematocrit levels (packed cell volume - PCV).
• Comparative analysis of camel blood rheology against horse blood was performed.

Main Results:

• Camel blood exhibited near-Newtonian behavior, a unique characteristic among mammals, with only marginal shear thinning.
• Camel whole blood viscosity exceeded horse WBV at high shear rates, especially with increased PCV.
• Camel blood showed no yielding, indicating low component cohesion and a continuous viscous liquid state even at high PCVs.

Conclusions:

• The unique rheology of camel blood, characterized by low cohesion and subtle pseudoplasticity, facilitates lactate washout and supports sustained performance.
• High PCV in camels can increase cardiac work and endothelial energy input, potentially leading to vascular remodeling.
• Avoiding elevated PCV during strenuous exercise is crucial in camels to mitigate risks of adverse vascular adaptation.