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.

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.

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.

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.