Modeling the dynamic interaction between left ventricle and intra-aortic balloon pump.

An analog model is developed to characterize how alterations of some intra-aortic balloon pump (IABP) parameters affect the coupling between left ventricle (LV) and aorta. The time-varying elastance concept is applied to modeling both active components (LV and IABP) in the assisted circulation. Pressure and flow waveforms in the system are determined by numerically integrating five simultaneous state equations that represent the system dynamics. Validity of the model is supported by good agreement between model predictions and published data on LV pressure-volume (P-V) loops, end-systolic P-V relations, and hemodynamic consequences of adjusting IABP timing and speed. The model also predicts that increasing balloon volume increases the diastolic aortic pressure augmentation but has a negative effect of increasing LV load. Increasing balloon diameter over length ratio and holding a constant volume increases the diastolic augmentation and decreases the LV demand. Positioning the balloon closer to the heart improves systolic unloading but affects neither diastolic augmentation nor cardiac output. These results suggest that occlusivity is a major determinant of IABP effectiveness and plays a more important role than balloon volume and position.