The Dynamics and Fluid Mechanics of the Intra-Aortic Balloon Heart Assist Device

摘要

The technique of intra-aortic balloon pumping for assistance to the failing human circulation requires that a limp, gas-filled bag be introduced into the aorta. The bag is caused to inflate and deflate under the action of a pressure source outside the body via a small-bore tube. The volume displacements of blood achieved in this manner are designed to reduce the effort of the failing heart. A mathematical model of the arterial system, called the 'tapered elastic tube model', is developed consistant with physiologic input impedance measurements. In conjunction with a simple model of the balloon, the 'pressure-node, flow-source' model, any two of the four variables heart pressure, heart flow, balloon pressure and balloon displacement flow may be predicted, given the remaining two. A principal conclusion is that the balloon should be both inflated and deflated during diastole, the period when the heart is not pumping, for maximum benefit to the heart. In experiments in a lumped-element hydraulic model of the arterial system, both the conventional 'limp balloon' and a balloon design including longitudinal mechanical constraints were tested. Experiments simulated trials in both humans and dogs, for both liquid and gas inflation. The 'beamed balloon' was found in every case to overcome a serious problem of limp balloon operation, which is that the balloon inflates to full extent locally and occludes the aorta before it reaches its full displacement volume, causing high heart pressures and poor performance of the device. (Author)