IMPLEMENTATION OF A DYNAMIC AND EXTENSIBLE MECHANICAL VENTILATOR MODEL FOR REAL-TIME PHYSIOLOGICAL SIMULATION.

We have designed and implemented a generic virtual mechanical ventilator model into the open-source Pulse Physiology Engine for real-time medical simulation. The universal data model is uniquely designed to apply all modes of ventilation and allow for modification of the fluid mechanics circuit parameters. The ventilator methodology provides a connection to the existing Pulse respiratory system for spontaneous breathing and gas/aerosol substance transport. The existing Pulse Explorer application was extended to include a new ventilator monitor screen with variable modes and settings and a dynamic output display. Proper functionality was validated by simulating the same patient pathophysiology and ventilator settings virtually in Pulse as a physical lung simulator and ventilator setup.

Computational simulation to assess patient safety of uncompensated COVID-19 two-patient ventilator sharing using the Pulse Physiology Engine.

BACKGROUND: The COVID-19 pandemic is stretching medical resources internationally, sometimes creating ventilator shortages that complicate clinical and ethical situations. The possibility of needing to ventilate multiple patients with a single ventilator raises patient health and safety concerns in addition to clinical conditions needing treatment. Wherever ventilators are employed, additional tubing and splitting adaptors may be available. Adjustable flow-compensating resistance for differences in lung compliance on individual limbs may not be readily implementable. By exploring a number and range of possible contributing factors using computational simulation without risk of patient harm, this paper attempts to define useful bounds for ventilation parameters when compensatory resistance in limbs of a shared breathing circuit is not possible. This desperate approach to shared ventilation support would be a last resort when alternatives have been exhausted. METHODS: A whole-body computational physiology model (using lumped parameters) was used to simulate each patient being ventilated. The primary model of a single patient with a dedicated ventilator was augmented to model two patients sharing a single ventilator. In addition to lung mechanics or estimation of CO2 and pH expected for set ventilation parameters (considerations of lung physiology alone), full physiological simulation provides estimates of additional values for oxyhemoglobin saturation, arterial oxygen tension, and other patient parameters. A range of ventilator settings and patient characteristics were simulated for paired patients. FINDINGS: To be useful for clinicians, attention has been directed to clinically available parameters. These simulations show patient outcome during multi-patient ventilation is most closely correlated to lung compliance, oxygenation index, oxygen saturation index, and end-tidal carbon dioxide of individual patients. The simulated patient outcome metrics were satisfactory when the lung compliance difference between two patients was less than 12 mL/cmH2O, and the oxygen saturation index difference was less than 2 mmHg. INTERPRETATION: In resource-limited regions of the world, the COVID-19 pandemic will result in equipment shortages. While single-patient ventilation is preferable, if that option is unavailable and ventilator sharing using limbs without flow resistance compensation is the only available alternative, these simulations provide a conceptual framework and guidelines for clinical patient selection.

Parameterization of Respiratory Physiology and Pathophysiology for Real-Time Simulation.

We have refactored the Pulse Physiology Engine respiratory software with enhanced parameterization for improved simulation functionality and results. Realistic patient variability can be applied using discretized lumped-parameters that define lung volumes, compliances, and resistances. A new sigmoid compliance waveform helps meet validation of compartment pressures, flows, volumes, and substance values. Further parameterization and enhanced logic for the application of pathophysiology allows for more accurate modeling of both restrictive and obstructive diseases for mild, moderate, and severe cases.Clinical Relevance- This free and open model provides a well-validated respiratory system for integration with medical simulations and research. It improves the Pulse modeling software and allows for new, low-cost training and in silico testing use-cases. Applications include virtual/augmented environments, manikin-based simulations, and clinical explorations.

An Interactive, Patient-Specific Virtual Surgical Planning System for Upper Airway Obstruction Treatments.

Upper airway obstructions leading todifficulty breathing are significant problems that often require surgery to improve patient quality of life. However, these surgeries often have poor outcomes with little symptom improvement. This paper outlines the design of an interactive, patient-specific virtual surgical planning system that uses patient CT scans to generate three-dimensional representations of the airways and incorporates computational fluid dynamics (CFD) as a part of the surgical planning process. Individualized virtual surgeries can be performed by editing these models, which are then analyzed using CFD to compare pre- and post- surgery flow characteristics to assess patient symptom improvement. The prototype system shows significant promise by being intuitive, interactive, with a potential fast flow solver that provides near real-time feedback to the clinician.

Pharmacokinetic and pharmacodynamic modeling in BioGears.

Pharmacokinetics/pharmacodynamics models were designed and integrated into the BioGears® physiology engine to address the need for real time drug effects for varying patients and injury profiles. Ten drugs were validated using experimental and subject matter expert data. The plasma concentration curves had a good fit with experimental data and 48 of 50 physiologic parameters displayed a less than 10% error compared to the validation data.

Impedance boundary conditions for the pulmonary vasculature including the effects of geometry, compliance, and respiration.

With few exceptions, previous models of the pulmonary vascular system have neglected the effects of respiration. This practice is acceptable for normal cardiac function; however, for compromised function, respiration may be critical. Therefore, we have initiated the steps to develop boundary conditions that incorporate the effects of respiration through the use of an impedance boundary condition derived from a bifurcating structured tree geometry. The benefit to using the geometry based method lies in that strategic changes can be made to the geometry to mimic physiologic changes in vascular impedance. In this paper, a scaling factor was used to modify the radius of resistance vessels of the structured tree to capture the maximum change in impedance caused by respiration. A large vessel geometry was established from a lung cast, the structured trees were applied at the outlets, and an experimental flow waveform was applied at the inlet. Finite-element analysis was used to compute the resulting inlet pressure waveform. An optimization minimizing the difference between measured and computed pressure waveforms was performed for two respiratory states, maximal expiration and inspiration, to determine best-fit models for the pulmonary vasculature, resulting in pressure waveforms with an rms error of 0.4224 and 0.7270 mmHg, respectively.