Effects of phlebotomy on haemodynamic characteristics during exercise in standardbred trotters with red cell hypervolaemia.

This research article describes a study that looked into how removing a portion of blood (phlebotomy) could affect the heart and blood flow characteristics during exercise in specifically bred horses with an excessive amount of red blood cells.

Objective and Methodology

• The main purpose of the research was to understand the effects of phlebotomy on the hemodynamic responses, changes in blood flow, and oxygen transport during exercise in Standardbred trotters with red cell hypervolaemia (RCHV)—a condition characterized by an abnormally high concentration of red blood cells.
• The study was conducted on five Standardbred trotters. Approximately 22% of the total blood volume was removed from each horse, and detailed observations were recorded.
• Measurements were taken during different speeds of exercise on a treadmill and continued until fatigue. Metrics such as oxygen uptake, pulmonary artery pressure, systemic artery pressure, heart rate, hematocrit, and hemoglobin concentrations were carefully monitored.
• Further data was extrapolated and calculations were performed to determine parameters like arteriovenous O2 content difference, pulmonary vascular resistance, total systemic resistance, blood and plasma viscosity, and erythrocyte (red blood cell) aggregation tendency.
• An endoscopy was conducted post-exercise, and statistical analysis of gathered data was done using ANOVA (Analysis of Variance) method.

Results & Observations

• The study found that removing blood (phlebotomy) led to a decrease in hematocrit and hemoglobin during the exercise. Blood and plasma viscosity were also found to be lower post-phlebotomy, while erythrocyte aggregation tendency was higher.
• Along the course of the exercise, pulmonary artery pressure, systemic artery pressure, pulmonary vascular resistance, total systemic resistance, and arteriovenous O2 content difference were lower after phlebotomy.
• Heart rate was found to be higher post-phlebotomy during submaximal exercise. Oxygen delivery and oxygen uptake was lower after blood removal, from the phase of submaximal exercise to fatigue.
• Phlebotomy also affected the tolerance levels of these horses, as run time to fatigue was shorter after blood removal.
• Four out of five horses showed signs of exercise-induced pulmonary hemorrhage (EIPH) before blood removal, and the degree of bleeding decreased but wasn’t completely eliminated after phlebotomy.

Conclusion

• The findings of the research concluded that, despite the 22% reduction in blood volume improving the hemodynamic and haemorheological parameters and the degree of EIPH, the RCHV Standardbred trotters highly depend on the oxygen delivery to the working muscles for maintaining maximum performance.
• The reductions in vascular resistance and pressure post-phlebotomy were likely due to the lowered blood viscosity.