Performance of the isolated, ejecting heart: effects of aortic impedance and exogenous substrates

The workload of the isolated, left-ventricular ejecting heart (i.e. working heart) is determined by the left atrial filling pressure and the afterload imposed on the left ventricular outflow tract. In addition to the level of end-diastolic aortic pressure, afterload is highly determined by the aortic impedance. For the isolated, ejecting heart optimum matching of the left ventricle to its afterload requires the highest possible similarity between the impedance of the artificial aortic conduit and the natural aortic impedance. The present study shows that the haemodynamic performance of the ejecting rat heart preparation can be affected by the impedance of the aortic conduit. A proper choice of substrates in the perfusion fluid further improves the performance of the heart in the artificial set-up. The present paper also provides guidelines with respect to the design of the aortic cannula and compliance chamber. The occurrence of turbulence, which is related to the Bernoulli pressure drop, is a major determinant of the impedance of the aortic conduit. This effect is used to simulate the natural resistance component of the aortic impedance. Further, the applicability of the perfusion model can be extended by the so-called assisted-mode perfusion, which allows automatic adjustment from antegrade to retrograde perfusion if the heart is not able to generate sufficient pumping power to provide its own coronary perfusion.