The effect of colic on oxygen extraction in horses.

Blood oxygen transport and oxygen extraction were assessed in horses with colic. A gravity score (GS) ranging from 1 to 3 was attributed to each colic case with healthy horses used as controls. Jugular venous and carotid arterial blood samples were collected and concentrations of 2,3-diphosphoglycerate, adenosine triphosphate, inorganic phosphate and chloride were determined. pH and partial pressures of carbon dioxide (PCO(2)), and oxygen (PO(2)) were also measured. Oxygen equilibrium curves (OEC) were constructed under standard conditions and oxygen extraction ratios calculated. Haemoglobin oxygen affinity measured under standard conditions (P50(std)) was unchanged in colic horses compared with healthy controls. Horses with the highest GS, i.e. 3 had lower blood pH values than healthy animals. Arterial and venous partial pressures of oxygen at 50% haemoglobin saturation (P50(a) and P50(v)) were significantly higher in horses suffering from colic (GS=3) than in healthy horses. The oxygen extraction ratio was also significantly increased in colic horses with a GS of 3. A rise in the oxygen extraction ratio detected in the most severely affected animals seemed to reflect the compensatory properties of the oxygen transport system where extraction of oxygen from the blood increases when systemic oxygen delivery decreases, as might be anticipated in horses with colic.

Haemoglobin oxygen affinity and regulating factors of the blood oxygen transport in canine and feline blood.

Complete dynamic oxygen equilibrium curves (OEC) on dogs and cats whole blood were measured at 33, 37 and 41 degrees C. OEC were also run at three partial carbon dioxide pressures (20, 40 and 80 mmHg) as well as at five pH levels (7.2, 7.3, 7.4, 7.5 and 7.6). 2,3- diphosphoglycerate (DPG) concentrations were determined. Results were compared to those previously published in humans, using the same experimental method [Comp. Biochem. Physiol. 106 (1993) 687]. In standard conditions (pH 7.4, pCO2 40 mmHg and temperature 37 degrees C), the partial oxygen pressure at half-saturation of haemoglobin (p50) was 30.0+/-1.3 mmHg for dogs and 34.1+/-1.8 mmHg for cats. Cat's OEC was thus rightshifted compared to dog's OEC, itself rightshifted compared to human OEC. 2,3-DPG concentrations were higher in dogs than in men until they were very low in cats. Contrary to that observed in human medicine, no significant correlation was identified between standard p50 and canine 2,3-DPG values. Influence of pH, pCO2 and temperature on the OEC was saturation dependent. In dogs, Delta log p50/Delta pH was equal to -0.370, Delta log p50/Delta log pCO2 was 0.093 and Delta log p50/Delta T was 0.020. In cats, Delta log p50/Delta pH was equal to -0.405, Delta log p50/Delta log pCO2 was 0.080 and Delta log p50/Delta T was 0.016. Practically, temperature and pH variations exert a lesser influence in domestic carnivores than in humans, effect of pCO2 being similar in both.