A simple dichromatic densitometer for repeated measurements of cardiac output in small animals

Measurement of cardiac output in anesthetized rats by dye dilution using a fiberoptic catheter

A method is described for the measurement of cardiac output and oxygen saturation in closed-chest rats using a small (2.4 F) commercially available fiberoptic catheter and a reflection-spectral-photometer. Positioned in the aortic arch, the catheter functions as an oxymeter for oxygen saturation and as a densitometer for measurement of indocyanine green, obviating the need for blood removal and passage through a densitometer. The sensitivity and reproducibility of this method were characterized in 90 rats by thermodilution, radiolabeled microspheres, and electromagnetic flow methods as standard references. Basal cardiac output as well as changes in cardiac output during isoproterenol infusion and blood removal and replacement were measured. In addition, multiple measurements of cardiac output over 1 min were used to document the method's suitability in constructing a ventricular function curve. With the fiberoptic catheter, cardiac output varied predictably with anesthesia, with rats on dial-urethane (n = 23) having values of 150 +/- 39 (SD) ml/min/kg and 2 and 1% enflurane (18-35 rats per group) yielding cardiac outputs of 190 +/- 60 and 236 +/- 77 ml/min/kg, respectively. Pentobarbital produced the least cardiovascular depression (n = 15) with an average cardiac output of 322 +/- 22 ml/min/kg. The average cardiac output with this method in 90 rats (regardless of anesthesia) was 214 +/- 91 (SD). This value was comparable to cardiac output values determined in paired experiments from radiolabeled microspheres (9 rats) 220 +/- 43, electromagnetic flow (11 rats) 177 +/- 33, and a subset of rats with thermodilution (231 +/- 45 ml/min/kg). The within measurement (repeat measurements) variability with the fiberoptic method was consistently less than the rat-to-rat variability when compared to the thermal and radiolabeled microsphere methods, but it was comparable to electromagnetic flow. The method can be used when rapid measurements (4 measurements within 60 s) of cardiac output are required, as in constructing a ventricular function curve, and can readily detect small changes in cardiac output during controlled hemorrhage and isoproterenol infusion. In summary, this method gives measurement of oxygen saturation and cardiac output by dye dilution without blood removal. There is less surgical preparation than required for electromagnetic cardiac output, and it is an alternative to the thermodilution method.

Cardiac output by dye dilution using a left carotid loop in conscious rats

By a modified dye dilution method using a simple dichromatic densitometer, cardiac output (CO) in conscious rats was determined. Under anesthesia, a carotid loop was made in the left carotid artery with a polyethylene tube (PE50) and exteriorized. A sensor of the densitometer was set at the center of the carotid loop. Indocyanine green dye solution was injected into the right atrium via the jugular vein. CO was calculated from the dye dilution curve obtained. In the conscious state (6 hours after ether anesthesia),CO in normotensive, spontaneously and DOC/saline hypertensive rats was determined without affecting blood pressure and heart rate. However, CO in the pentobarbital or urethane anesthetized rats was decreased with other hemodynamic changes. The validity of this method was confirmed with a hydraulic model system and in anesthetized open-chest cats using an electromagnetic flowmetry. From these studies, it was concluded that the modifed dye dilution method for measuring CO in conscious rats was reliable and useful for hemodynamic studies in hypertensive rats.