Measurement of Cardiac Output in Rats: Using Extracorporeal AV Loop with Ultrasound Dilution Technology – A Validation Study

Novel method to measure cardiac output (CO) in rats using an extracorporeal AV loop with ultrasound dilution (CO D ) technique is proposed and the results are validated with the established Transonic transit time (CO TT ) technology. Male Sprague‐Dawley rats (n=6; 200–500gms) were instrumented with a 2.5SL transit time ascending aorta flow probe (Transonic Systems Inc.) for direct CO TT . Following recovery, subjects were anesthetized with isoflurane and an extracorporeal loop was placed between the artery and jugular vein. Peristaltic pump (Instech Laboratories, Inc) was used to circulate blood (5–8ml/m) through the AV loop, during the procedure. CO D was determined by injecting 30–50μl of isotonic saline into the venous side of the loop. An algorithm to automatically calculate CO D (Transonic Systems, Inc.) was used to obtain CO D in less than a minute after performing the injection. CO of the animal was varied by infusing drugs (dobutamine) & altering isoflurane level and the dynamic range was measured by both methods. CO D and simultaneous CO TT measurements were determined at least twice over the range of injected volumes. An acceptable correlation (r 2 = 0.86) was observed between the two methods over a range of CO TT from 50 to 130ml/m. Results obtained clearly indicate: CO D provides reasonable estimate of CO in rats and can be used for measurements of drug‐induced cardiovascular effects. (Support: NIH SBIR # R44 HL61994)