Phasic left ventricular volume in the isolated heart

The study was undertaken to assess cardiac performance with phasic left ventricular (LV) volume as an additional variable. Since little is known about this variable, an isolated heart was chosen as experimental preparation. Hearts of mongrel dogs were used in which the circulations through right and left heart were separated; also the entire coronary system was perfused isolated from the aortic pressure. Thus, LV performance may be studied in a preparation in which many parameters can be controlled independently: filling- and arterial pressures, coronary bloodflow and oxygen delivery rate, and frequency. LV volume is obtained by making the LV blood slightly ferromagnetic by dilution with a ferromagnetic fluid. The LV contents thereby act as a varying size 'core' of an induction coil placed around the heart. A homogeneous magnetic field induces a voltage in the coil linearly proportional to instantaneous LV volume. The continuous volume registration exhibits the typical characteristics of isovolumic periods, ejection- and filling phases, and atrial contribution to filling. In a previous study using the method in situ the authors showed the accuracy of the measurement to be better than 93%. Since the method is independent of geometry it may, in principle, be used for the right ventricle as well. The authors conclude that both the volume method and the preparation used are ideally suited to expand the study of cardiac performance.