Effects of respiration and circulation on central blood temperature of the dog

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Abstract
Blood temperature (T) was measured with thermistor catheters in the heart and great vessels of 58 anesthetized dogs. Thermal gradients were obtained by catheter pullback and from 2,021 paired measurements in the aorta and 9 other intravascular sites. Magnitude, waveform, and time course of T variations at respiratory frequency were analyzed. Their magnitude was augmented or diminished by factors which are known to increase or decrease respiratory variations of venous return. They are attributed to T differences between regional venous beds and respiratory variations of their contribution to mixed venous blood. The aortic (AO)[long dash]pulmonary artery (PA) temperature difference (TAO[long dash]PA) was significantly related to VI. In six dogs TTA-PA was[long dash]0-001 [plus or minus] 0.027[degree]C (N 70) during apnea and spontaneous respiration and[long dash]0.031 [plus or minus] 0.023[degree]C (N 90) during respiratory hyperventilation (V\ > 300 cc/min per kg). TAO, TPA and TPW (pulmonary artery wedge), and T bronchus measurements demonstrated cooling of the lungs with hyperventilation and rewarmlng during apnea. The changes of T^q averaged[long dash]0.11 [plus or minus] 0.044 C, and of TAO[long dash]PA -0.047 [plus or minus] 0.025[degree]C per unit increase of Vj liter/min per kg. The findings suggest heat transfer from the blood during transit through the pulmonary vascular bed. We conclude that heat transfer may take place at the alveolar capillary interface, and that alveolar temperature may vary over narrow limits as a function of ventilation and pulmonary blood flow.