IMPEDANCE CARDIOGRAPHY IN THE MEASUREMENT OF CARDIAC-OUTPUT - STUDIESIN RABBITS

A thoracic electric bioimpedance device with improved signal processin g was used to noninvasively measure cardiac output in eight New Zealan d White rabbits (average wt = 4.7 kg). Prospective correlation was per formed between aortic thermodilution and impedance cardiography in a c losed chest model. Aortic thermodilution was compared to the electroma gnetic flowmeter in an open chest model. In four rabbits, the change i n the impedance signal (dZ/dt) was quantified after repeated mechanica l occlusion of the aorta and pulmonary artery. The mean cardiac output as measured by the impedance device was 0.56 +/- 0.01 liter/min (rang e 0.29-1.16 liter/min) compared to 0.53 +/- 0.01 liter/min (range 0.25 -0.83 liter/min) by aortic thermodilution. For the 116 data pairs, reg ression analysis revealed a statistically significant agreement (r = 0 .82, P < 0.001) between the two techniques. The mean difference betwee n the techniques (bias) was -0.03 liter/min and 81% of the impedance v alues were within 0.1 liter/min of the individual thermodilution measu rements. A statistically significant decline in the mean magnitude of the dZ/dt signal tracing (1.16 +/- 0.10 V-pre, 0.31 +/- 0.4 V-post, P < 0.005, n = 21) was observed upon aortic arch occlusion. Conversely, pulmonary artery occlusion did not have a statistical effect on the im pedance signal (1.07 +/- 0.09-pre, 0.95 +/- 0.08-post, P > 0.05, n = 2 0). In conclusion, a significant correlation was observed between impe dance cardiography and aortic thermodilution in measurement of cardiac output in sedated, anesthetized rabbits. This simple technique which involves application of skin electrodes may prove useful in measuremen t of cardiac output in surgical experimental small animal models. Our data support the hypothesis that the impedance signal, dZ/dt, which is an essential component of stroke volume estimation in impedance cardi ography, results in great proportion from aortic outflow during the ca rdiac cycle. (C) 1995 Academic Press, Inc.