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Pump function of the feline left heart: changes with heart rate and its bearing on the energy balance
Insights
This study reveals that feline left heart pump function shifts parallelly with increased heart rate. Maximum power output does not coincide with optimal efficiency, impacting cardiac performance.
Area of Science:
- Cardiovascular Physiology
- Cardiac Mechanics
Background:
- Understanding left heart pump function is crucial for diagnosing and treating cardiac conditions.
- Previous models have not fully captured the dynamic interplay between heart rate, arterial load, and cardiac efficiency.
Purpose of the Study:
- To quantitatively assess feline left heart pump function under varying arterial loads and heart rates.
- To investigate the relationship between cardiac output, pressure, oxygen consumption, power, and efficiency.
- To compare experimental findings with a time-varying compliance model.
Main Methods:
- Determined left heart pump function by measuring the relationship between mean left ventricular pressure and output.
- Manipulated arterial load beat-by-beat while maintaining constant left ventricular end-diastolic pressure.
- Analyzed changes in heart rate (120 to 160 beats/min) and their effect on pump function graphs.
- Quantified oxygen consumption, mean external power, and external efficiency as functions of mean left ventricular output.
Main Results:
- A parallel shift in the left heart pump function graph was observed with increased heart rate.
- Scaling pressure and output values at 160 beats/min by 0.75 resulted in near-complete graph superposition.
- Oxygen consumption decreased with increasing left ventricular output.
- Mean external power and efficiency reached their maxima at different mean output values.
Conclusions:
- Feline left heart pump function exhibits predictable shifts with changes in heart rate.
- Operating the left heart at maximum power output does not align with achieving optimal efficiency.
- The findings provide valuable data for refining cardiac models and understanding cardiac energetics.
Abstract:
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.