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The next modeling technique we considered was a pulsatile, beat-to-beat method. This model is based upon time-varying, ventricular compliances which lead to a pulsatile nature. Using an electrical analog of resistors, capacitors, and diodes, the model represents blood flow through a compartmentalized CV system of eight quadrants: systemic arterial and venous, pulmonary arterial and venous, left and right atria and ventricles. A set of eight equations, solved simultaneously, yields pressure changes for each of the eight compartments over time.
As a body experiences hemorrhage, it responds in phases, depending on how much blood has been lost. For loss of 10-15%, the baroreflex controls physiologic response and maintains mean systemic arterial blood pressure by regulating vascular resistance and compliance, and heart rate. For loss of 15- 30%, the vagovagal effect dominates, reversing the above trend by decreasing heart rate and resistance, and increasing compliance. For loss exceeding 30%, the vagovagal effect subsides, and once again, trends reverse. Heart rate and resistance increase, and compliance decreases.
The acute hemorrhage model performs well for losses up to 30% of initial blood volume. Since experimental data is sparce for losses greater than that, more research on physiologic response at that level of hemorrhage is required before the model can be designed to accomodate such extreme hypovolemia.
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TrauMAP models some immediate consequences of penetrating trauma (gunshot and stab wounds). The system ties together the spatial (geometric) properties of an anatomical object with the object's role as part of the appropriate physiological system. By associating the physical presence of a substance or object with its functional role, TrauMAP can infer simple effects of a structural change on physiology, and vice versa. This can be useful for detecting situations where independent physiological systems become dependent because they are physically adjacent to one another. TrauMAP ultimately will use knowledge of the physical dependencies of physiological processes to infer when more detailed physiological models are necessary (those that incorporate knowledge about spatial concerns).
We represent anatomical parts with volumetric, viscoelastic elements (physics-based, deformable body dynamics). We model the significant physiological systems with conventional models expressed in ordinary differential equations (cardiopulmonary mechanics), coupling the anatomical and physiological modeling to produce an interactive simulation.
The user can change parameters such as individual lung, ribcage, diaphragm, or mediastinum compliances or resistances during the simulation. As well, the user can introduce topological changes such as a chest wall breach (right or left), which produces a pneumothorax (which can be further qualified as simple, open, or tension). Our models consist of descriptions of the physical components and the laws that govern their interaction (such as volume balance), making them amenable to serve as a foundation for a wide variety of physiological and pathophysiological behaviors. Our work is unique, to our knowledge, because of our multi-degree-of-freedom chest wall. We model individual contributions of the ribcage, diaphragm, abdomen, two lungs, play among ribs, and the mediastinum. With this model, we can model a wide range of physiological and pathophysiological behavior, including pneumothoraces and paradoxical breathing.
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