Graduate Thesis Or Dissertation
 

A method of controlling the left ventricular wall stress of the human heart

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  • In this thesis a method is presented for maintaining the left ventricular wall stress of the human heart at a constant level during the systole (active portion of the heart's cycle). This constant stress level makes it possible to take isotonic measurements on the heart muscles. The left ventricle of the human heart is modeled on a hybrid computer. To accomplish this task certain assumptions as to the shape and muscle characteristics of the left ventricle are made; then the relations for stress and pressure are obtained. The simulating force for this active left ventricle is a curve, simulated by a Diode Function Generator, representing the muscle characteristics of the left ventricle as a function of time. This model substitutes for the portion of an active heart needed to design the control device. With this model of the left ventricle, a control device is developed, using an analog computer, which acts as a pump controlling the amount of fluid in the left ventricle during the systole. This pump extracts the fluid from the cavity when the stress rises above the desired level and reinjects the fluid into the cavity when the stress falls below this level. The control device consists of a piston and cylinder assembly with a preloaded spring behind the piston. An electromagnetic feedback control may be used to maintain the stress level. It is not essential, however, since this control system accomplishes the same purpose as a passive device by adjusting the system parameters. The parameter values are given in Chapter III of this thesis. This control device is applicable to any left ventricle within the range of 60 to 150 ml. Another possible future application of this control device is its use as an auxiliary pump to control the pressure in the left ventricle of a failing human heart. This device could be connected to the aorta. This use of the control device is theoretical and has not yet been tested.
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