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.

The Pulse Physiology Platform is an open-source software application designed to enable accurate and consistent, real-time physiologic simulations for improved medical training and clinical decision-making tools. The platform includes a physiology engine comprised of well-validated lumped-parameter models, differential equations representing feedback mechanisms, and a pharmacokinetic/pharmacodynamic model. The platform also includes a common data model for standard model and data definitions and a common software interface for engine control and robust physics-based circuit and transport solvers. The Pulse Platform has been incorporated into a number of commercial, research, and academic tools for medical simulation. Significance: The Pulse Platform is an innovative, well-validated, open-source tool for medical modeling and simulation in the training and clinical decision-making field.

Detection and monitoring of patients with pulmonary hypertension, defined as a mean blood pressure in the main pulmonary artery above 25 mmHg, requires a combination of imaging and hemodynamic measurements. This study demonstrates how to combine imaging data from microcomputed tomography images with hemodynamic pressure and flow waveforms from control and hypertensive mice. Specific attention is devoted to developing a tool that processes computed tomography images, generating subject-specific arterial networks in which one-dimensional fluid dynamics modeling is used to predict blood pressure and flow. Each arterial network is modeled as a directed graph representing vessels along the principal pathway to ensure perfusion of all lobes. The one-dimensional model couples these networks with structured tree boundary conditions representing the small arteries and arterioles. Fluid dynamics equations are solved in this network and compared to measurements of pressure in the main pulmonary artery. Analysis of microcomputed tomography images reveals that the branching ratio is the same in the control and hypertensive animals, but that the vessel length-to-radius ratio is significantly lower in the hypertensive animals. Fluid dynamics predictions show that in addition to changed network geometry, vessel stiffness is higher in the hypertensive animal models than in the control models.

When modeling the cardiovascular system, the use of boundary conditions that closely represent the interaction between the region of interest and the surrounding vessels and organs will result in more accurate predictions. An often overlooked feature of outlet boundary conditions is the dynamics associated with regulation of the distribution of pressure and flow. This study implements a dynamic impedance outlet boundary condition in a one-dimensional fluid dynamics model using the pulmonary vasculature and respiration (feedback mechanism) as an example of a dynamic system. The dynamic boundary condition was successfully implemented and the pressure and flow were predicted for an entire respiration cycle. The cardiac cycles at maximal expiration and inspiration were predicted with a root mean square error of 0.61 and 0.59 mm Hg, respectively.

Background: The COVID-19 pandemic is stretching medical resources internationally, including 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. This simulation study explores patient compatibility and ventilator settings during multi-patient ventilation without the use of flow compensating resistances. Methods: A whole-body computational physiology model was used to simulate each patient on a ventilator. The primary model of a single patient with a dedicated ventilator was augmented to model two patients sharing a single ventilator. A range of ventilator settings and patient characteristics were simulated for paired patients. In addition to mechanical ventilation parameters, the full physiological simulation provides estimates of additional values for oxyhemoglobin saturation, arterial oxygen tension, and other patient parameters. Findings: These simulations show patient outcome during multi-patient ventilation is most closely correlated to lung compliance, oxygenation index, oxygen saturation index, and endtidal carbon dioxide of individual patients. The simulated patient outcome metrics were satisfactory when the lung compliance difference between two patients was less than 12 cmH2O/mL, 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 unavailable, these simulations provide a conceptual framework for clinical patient selection guidelines if ventilator sharing is the only available alternative.