[Determination of the standard oxyhemoglobin dissociation curve in horses. Effects of temperature, pH and diphosphoglycerate].

This study analyses the standard oxyhemoglobin dissociation curve in horses with an emphasis on the impact of temperature, pH, and the concentration of 2,3-diphosphoglycerate. The research indicates a higher affinity for oxygen in equine hemoglobin compared to human, and tracks changes in certain conditions which can influence the way blood gases data are interpreted for horses.

Equine vs Human Oxyhemoglobin Dissociation Curve

• The research primarily focuses on the oxyhemoglobin dissociation curve of horse blood under standard conditions.
• This curve demonstrates the degree of oxygen saturation as a function of varied oxygen tensions and helps in understanding how readily oxyhemoglobin releases its oxygen.
• Against human blood’s dissociation curve, the equine curve shows a higher oxygen affinity – the measure of how tightly the oxygen is bound to hemoglobin.
• For humans, the affinity is noted at 26.6 mm Hg, while it is 23.8 +/- 0.8 mm Hg for horses – signifying that hemoglobin in horse blood binds oxygen more tightly.

Effects of pH and Temperature

• The effect of pH on the P50 (partial pressure of oxygen when hemoglobin is 50% saturated) showed identical results in humans and horses, represented by d log P50/dpH equating to -0.47.
• However, the temperature impact differed as horses showed lesser P50 temperature dependence than humans. The value for horses stood at 0.016 as compared to 0.024 in humans, indicating that the ability of hemoglobin to carry oxygen in horses wouldn’t change as much with fluctuations in body temperature.

2,3-Diphosphoglycerate (DPG) influence

• The study also examined the impact of changes in 2,3-diphosphoglycerate levels on P50 in equine blood.
• DPG is an organophosphate that influences oxygen affinity in hemoglobin, meaning any change in DPG levels can affect how readily hemoglobin binds and releases oxygen.
• The P50 increased by 1 mm Hg every time there was a rise of 4 mumol/gHb in DPG levels in horse blood. This suggests DPG has a critical role to play in regulating oxygen delivery in the equine system.

Study Significance

• The findings provide a better understanding of blood gases’ data interpretation for equine blood, challenging the adequacy of human blood related values in such readings.
• The research underscores the need to take the unique properties of equine blood into account when tracking and analyzing blood gases in horses, potentially leading to more accurate medical diagnoses and interventions.