Relationship between peripheral blood flow and blood temperatures in lambs during hypoxemia and hemorrhage

The relationships between the peripheral blood flow and arterial and venous blood temperatures were examined in 5 lambs (mean weight 10.5 kg, 4-12 weeks old) during hypoxemia and hemorrhage. Blood flow to one hind limb was measured continuously with an electromagnetic flow transducer around the femoral artery. Aortic and venous blood temperatures were monitored by means of thermistor catheters in the descending aorta and iliac vein. The intravascular catheters and flow transducer were implanted chronically and all studies were performed in conscious lambs, resting quietly. Skin temperatures were recorded at the hip and at the foot. The total heat in the hind limb (Htot), the net heat transported by circulating blood (Hbl), and the metabolic heat produced in the hind limb were calculated. The arterial and venous blood temperature were related to peripheral blood flow. When the flow was constant over a control period, blood temperatures remained constant. Hypoxemia, produced by administering a low oxygen gas mixture to the lamb, did not alter femoral blood flow, nor did it affect vascular temperatures. During hemorrhage, femoral blood flow fell, arterial temperature rose by 0.46 degrees C and venous temperature by 0.85 degrees C; arteriovenous temperature difference decreased from 0.85 to 0.44 degrees C. There was an inverse relationship between femoral blood flow and venous temperature in each individual lamb subjected to hemorrhage, with a correlation of 0.91. For each 10-ml/min decrease in peripheral blood flow the venous temperature rose an average of 0.33 degrees C. Changes in peripheral blood flow were immediately reflected by changes in the venous temperature.