Limitations of thermodilution cardiac output measurements in the rat

Abstract
Heat loss from the vascular system could introduce an error in thermodilution cardiac output determinations. Cardiac output measured in the rat via the thermodilution technique following right atrial injection yielded different values (P < 0.001), depending whether sampling was from the pulmonary artery (460 .+-. 31 ml/min per kg), right ventricle (311 .+-. 19), or thoracic aorta (245 .+-. 15). Recirculation errors could not account for the differences. Heat loss from the vascular system was measured from extravascular thermistors within both the thorax and the abdomen. These dilutions were 22-57% in peak height of aortic curves recorded at approximately the same location. Differences in calculated cardiac output between sampling sites could be attributed to rapid heat conduction directly from the right atrium and inferior vena cava to the thoracic aorta with progressive loss of indicator from both the right ventricle and pulmonary artery.

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