A method to measure cardiac output (CO) based on ultrasound velocity dilution during hemodialysis was validated in an animal model against direct measurement using a transit time technique and a calibrated pump. In two anesthetized pigs, a 20 mm transit time ultrasound flow probe was placed on the ascending aorta to measure CO, and the right femoral artery and vein were cannulated for hemodialysis access. The dual sensor HD01 Hemodialysis Monitor was positioned on the arterial and venous tubing lines for measurement of cardiac output by ultrasound velocity dilution (COUD) by intravenous injections of 10-20 ml isotonic saline at 37 degrees C. COUD (n = 29) was compared with CO from the transit time flow probe (COT). During the second part of the experiment, the animal was placed on right atrial to left atrial bypass using a calibrated roller pump. The COUD (n = 9) was compared with cardiac output as measured by pump flow (COp). A linear relationship was observed between COUD and COT (COUD = 0. 948 X COT + 0.086 L/min, r = 0.95), and between COUD and COp (COUD = 1.06 X COp - 0.327 L/min, r = 0.99). Thus, cardiac output measured by ultrasound velocity dilution during hemodialysis is in good agreement with well established, but invasive, transit time and pump standards.
