Feline left ventricle does not always operate at optimum power output

In a previous study we showed that under a variety of conditions the feline left ventricle operates at optimum external power. This condition was defined as matching. In the present study matching of left ventricle and systemic arterial tree has been further investigated in the open-thorax cat during control, after volume loading (n = 8), and during norepinephrine infusion (n = 8). The pump-function graph relating mean left ventricular pressure and mean flow was fitted with a parabola characterized by two parameters, the pressure axis and the flow axis intercepts (Pmax and Fmax, respectively). After volume loading, as well as during norepinephrine infusion, the pump-function graph showed an outward shift plus a clockwise rotation. Pmax and Fmax increased 27 and 8% during volume loading and 37 and 8% during norepinephrine. In the steady states the mean flows at the working point and at the point of optimum external power were determined. During control and volume loading these flow values could not be shown to differ. However, during norepinephrine infusion, flow at the working point was found to be smaller than at optimal external power. This finding implies that during norepinephrine, the left heart does not operate at optimum external power; so a mismatch of heart and periphery is obtained.