Microprocessor control of intra-aortic balloon pumping

Abstract

An automatic control scheme for the control of intra-aortic balloon pumping has been implemented on a Digital Equipment Corporation LSI-11 micro-processor system and tested in experiments conducted on a mock circulatory loop as well as in a series of acute animal experiments. The control algorithm employed by the digital controller (LSI-11) is identical in form to that employed by Clark et al. (3), and consists of [1] the beat-by-beat evaluation of a performance index that reflects the objectives of balloon pumping, and [2] the adjustment of balloon inflation and deflation times within the diastolic period so as to maximize this performance index according to a steepest ascent algorithm. In order to reduce convergence time and minimize disturbances around the optimum operating point, a scheme that reduces search step size as the search proceeds from initial values is also incorporated in the algorithm. Importantly, this system obeys a bedside measurement constraint in that it requires only readily available physiologic signals for its operation; the ECG for timing purposes, and the central aortic pressure for evaluation of the system performance index. A number of conventional safety features are also implemented in the controller to, for example, guard against untimely balloon inflation in the occurrence of aberrant heart beats.

Finally, the ability of this digital controller to reach an optimum independent of the dynamics of the particular pneumatic pumping system utilized, coupled with the flexibility in design capability and relatively low cost of implementation via the microprocessor system, provide a significant advance in the area of the automatic control of intra-aortic balloon pumping.