Automatic control of intra-aortic balloon pumping
Kane, Gerald Randolph
Clark, John W., Jr.
Master of Science
One of several devices proposed to provide circulatory assistance to victims of cardiogenic shock is the intra-aortic balloon pumping technique which utilizes a polyurethane balloon that is inserted through a femoral artery and advanced to a predetermined position in the descending aorta. The balloon is pneumatically driven and typically controlled so as to raise systemic pressure immediately after left ventricular ejection and aortic valve closure. The pressure remains elevated throughout diastole and is lowered via balloon deflation prior to the succeeding ventricular ejection. This form of ventricular assist device has as its goals (1) reduction of the work required of the failing myocardium via reduction of pressure load on the left ventricle and (2) partial replacement of the circulatory role played by the heart by increased mean central aortic pressure and effective cardiac output. As a result, blood flow to the coronary and cerebral circulations is enhanced and increased oxygen supply to hypoxic myocardial tissue is effected. The problem of the choice of balloon inflation and deflation times subject to satisfaction of the stated purposes of balloon pumping is a difficult one. Most devices presently being used to control balloon inflation and deflation utilize the EKG as as information signal regarding events occurring in the cardiac cycle. Upon detection of an R-wave, the balloon is usually inflated after a preset delay and deflated upon receipt of a signal indicating the succeeding R-wave has occurred. The limitations of balloon pumping performed in such an open loop fashion are obvious in the case of the patient with an EKG sufficiently complex as to deceive the R-wave detection scheme. Another severe drawback is the inflexibility of the control policy as open loop methods do not attempt to evaluate the circulatory performance of the balloon on either a cycle-by-cycle or an average basis and, therefore, are insensitive to possible changes in the cardiac or circulatory parameters of the patient. A method is proposed and demonstrated using a hydraulic circulatory system model to demonstrate the feasibility of closed loop computer control of balloon pumping. Circulatory variables such as aortic pressures and flows are continuously monitored, a clinically significant performance index is evaluated, and a control algorithm, which is developed herein, is applied utilizing a small digital computer. Simplifications to enhance clinical desirability, of the method are suggested.