An alternative thermodilution method to measure cardiac output in a rat model of stagnant hypoxia

Rats are often used to study hemodynamics in animal research. We have estab lished an alternative method to measure cardiac output in a conscious rat u sing a thermodilution technique via a left ventricular injection. The valid ity of this method was evaluated in conscious rats and compared with the re sults obtained using the radiolabeled microspheres (reference sample method ). Using 20 male Sprague-Dawley rats, a baseline cardiac index was measured by thermodilution to determine the baseline cardiac index and to evaluate between animal variability. The baseline cardiac index was compared to the reference sample method with 6 rats. Following baseline measurements, an in tra-atrial balloon was inflated in a stepwise manner to create 2 to 3 diffe rent cardiac outputs, and the cardiac index was computed. For each measurem ent, the cardiac index was first measured by thermodilution and immediately followed by the reference sample method. A total of 21 measurements were o btained, and the results were analyzed by a Bland-Altman plot and the corre lation coefficient was calculated. Although the agreement between the two m ethods was poor, both methods had a good correlation (r(2) = 0.59), With th e thermodilution technique, we demonstrated a small coefficient of variatio n in each measurement, with a low intra-animal and inter-animal variability . As there is no gold standard method to measure cardiac output in rats, we believe that left ventricular thermodilution is a reliable method, and ove rcomes several technical difficulties such as heat loss, one of the signifi cant limitations of the conventional thermodilution method (via right atria l injection). This new thermodilution technique (via the left ventricle) is therefore an attractive alternative method to measure cardiac output in ra ts.