Increasing heart rate from 120 to 160 beats/min caused a parallel shift in the pump function graph, with oxygen consumption decreasing as output increased.
The study demonstrates that in the feline left heart, maximum power output and optimum efficiency occur at different levels of mean output, and heart rate changes shift the pump function curve.
Pump function of the feline left heart was determined by measuring the relationship between mean left ventricular pressure and mean left ventricular output, obtained by changing the arterial load on a beat-to-beat basis. The effect of a change in heart rate from 120 to 160 beats . min-1 was studied and a parallel shift of the pump function graph was found. Care was taken to keep left ventricular end-diastolic pressure constant with the change in frequency. If the mean pressure and output values obtained at 160 beats . min-1 were multiplied by the ratio between the two frequencies (0.75), almost complete superposition of the two graphs was obtained. Changes in arterial load also caused changes in oxygen consumption, mean external power and external efficiency of the heart. We plotted these variables, altered them as a function of mean left ventricular output for easy comparison with the pump function graph. It was found that oxygen consumption decreases with increasing output. Mean external power and efficiency attain maxima for different values of mean output. If the left heart in the intact animal is controlled to function at its maximum power output, this can therefore not be achieved at the optimum efficiency level. The results of the present study and those obtained earlier were compared with the behaviour of a time varying compliance model.
Elzinga et al. (Fri,) conducted a other in Feline left heart pump function. Change in heart rate from 120 to 160 beats/min and arterial load vs. 120 beats/min was evaluated on Pump function (relationship between mean left ventricular pressure and mean left ventricular output). Increasing heart rate from 120 to 160 beats/min caused a parallel shift in the pump function graph, with oxygen consumption decreasing as output increased.