Effects of phlebotomy on haemodynamic characteristics during exercise in standardbred trotters with red cell hypervolaemia.
Authors: Funkquist P, Sandhagen B, Persson S G, Hedenstierna G, Essén-Gustavsson B, Nyman G
Journal: Equine veterinary journal
Summary
# Editorial Summary: Phlebotomy and Performance in Standardbred Trotters with Red Cell Hypervolaemia Five Standardbred trotters with red cell hypervolaemia underwent controlled phlebotomy (removal of approximately 22% blood volume) to examine whether the commonly elevated haematocrit in these horses compromises exercise haemodynamics and oxygen delivery. The researchers measured cardiovascular pressures, oxygen uptake, blood viscosity and rheological properties during incremental treadmill exercise to fatigue, before and after bleeding. Although phlebotomy successfully reduced blood and plasma viscosity, lowered pulmonary and systemic vascular resistance, and diminished exercise-induced pulmonary haemorrhage severity, these improvements came at a metabolic cost: oxygen delivery to working muscles decreased, fatigue occurred sooner, and heart rate rose to compensate during submaximal efforts. The findings suggest that whilst red cell hypervolaemia does impose haemodynamic strain through increased viscosity, these horses have adapted their physiology to depend on this elevated oxygen-carrying capacity for maximal performance, making routine phlebotomy counterproductive for athletic function. This work challenges the assumption that reducing haematocrit uniformly benefits performance and indicates that individual assessment of whether elevated red cells represent pathological overload versus beneficial adaptation is essential before recommending blood removal in competition Standardbreds.
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Practical Takeaways
- •Phlebotomy to treat RCHV in trotters may reduce pulmonary bleeding and improve some cardiovascular parameters, but does not enhance exercise performance and actually reduces time to fatigue
- •RCHV in high-performance trotters appears to be a compensatory mechanism for oxygen delivery; reducing blood volume compromises the oxygen supply needed for maximal effort
- •While phlebotomy improves blood rheology and vascular pressures, these benefits do not translate to improved athletic performance in RCHV horses
Key Findings
- •Phlebotomy removing 22% of blood volume reduced blood and plasma viscosity while increasing erythrocyte aggregation tendency in Standardbred trotters with RCHV
- •Pulmonary artery pressure, systemic artery pressure, pulmonary vascular resistance and total systemic resistance all decreased following phlebotomy during exercise
- •Despite haemodynamic improvements, phlebotomy shortened run time to fatigue and reduced oxygen delivery and oxygen uptake in the period from submaximal exercise to fatigue
- •Four of five horses showed exercise-induced pulmonary haemorrhage before phlebotomy; bleeding was diminished but not abolished after phlebotomy