The Use of Computational Modeling and Simulation to Create Virtual Patients: Application to Cardiac Pacing and Defibrillation Systems

Abstract

Computational models have long been used in engineering applications and are increasingly being used in medical device design. Physics-based equations describe simple structures and field problems such as the bending of a beam or the electrical field gradient across conducting material. For more complex problems, techniques such as finite element analysis (FEA) are used to discretize a structure of interest into smaller domains that are coupled together to solve the entire problem. Statistical Monte Carlo simulation methods can be used to solve similar problems many times with the addition of random variability. It is straightforward to imagine parallels between medical devices and engineering applications. For example, consider the flexing of a stent graft and the flexing of a reinforced gasoline hose. Another example is the similarity between a suspension link in an automobile and an artificial implanted joint. Continuing the automotive theme, compare the electronic cables on a steering wheel to an implanted pacemaker lead. Despite differences in physical environment between biomedical and industrial applications, the fundamental engineering principles behind performance and reliability are the same.Although there are applications for computational modeling across all parts of the biomedical industry, there are often aspects of medical device design that make them ideal for the use of computational models. For example, devices typically act in a specific physical and local manner (e.g., structural support, electrical stimulation, measurement for diagnostic purposes). In contrast, drugs often act in a systemic fashion with complex pharmacological interactions [1]. The local action of a device enables a much simpler path for simulating the engineering mechanisms required for successful operation, as compared to the systemic mechanism of action for drugs. For example, placement of a stent will not affect hair growth. Another distinguishing feature of medical devices is that they are often evolutionary in nature, with successive models differing only slightly from a predecessor. This enables the validation of engineering simulations on the predecessor device, providing confidence for predicting the performance of a new device.When clinical outcomes can be directly simulated in a computational model, the result can be thought of as a virtual patient [2]. If sufficiently credible, virtual patient models can inform or even replace human clinical evaluation in some applications. The entire anatomy and physiology of a patient does not need to be included in the simulation, but rather only those aspects which are needed for the clinical outcome of interest. For example, a simulation that predicts the structural integrity of the femoral stem of a hip prosthesis would incorporate the kinetic activities of daily living and force transmission through the hip joint, and would not use a parameter such as blood pressure. A virtual patient model of closed-loop blood glucose control systems for diabetes would focus on metabolic ...

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