Laura Ellwein Fix, PhD

Applied Dynamics in Cardiorespiratory Physiology

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Modeling of regulation in cardiovascular and pulmonary systems
Differential equations and dynamical systems
Data-driven patient-specific parameterization
Numerical methods and optimization in physiological systems
Algorithm development for biomedical applications
Computational fluid dynamics


Evaluation of factors in compromised breathing in preterm infants using pulmonary dynamics modeling
Henry Rozycki MD; Joseph E. Khoury, MD; Russell Moore, MD; Matthew Brandes, PhD (MCV).
Students: Lauren Linkous, Jeffrey Evans, Richard Foster

  • A foundational model parameterized for an idealized preterm infant has been created and the first manuscript of this project was published in 2018.  Preliminary results have been presented at mathematics, engineering, and clinical conferences since 2016.  Collaborators have received IRB approval for clinical data collection in the NICU at CHoR for use in future model fitting and parameter estimation and began collecting in fall 2017. This effort was adopted by VCU’s Engineering Capstone and two teams of four students have developed device prototypes for preterm infant wall stiffening. We recently developed a submodel of ribcage / abdominal mechanics to model thoracoabdominal asynchrony (“chest retractions”).
    Current opportunities for investigation include:

    • Parameter estimation with pseudodata and NICU data
    • Incorporation of neural control as driver of model
    • Addition of gas transport and chemoreflex response to breathing alterations
    • Model effects of high frequency oscillation ventilation and/or high flow nasal cannula
    • Addition of stochastic components

Evaluation of Wall Shear Stress for Investigation of Restenosis in Stented Coronary Arteries Reconstructed Using Optical Coherence.
John F. LaDisa, Jr., Marquette University; Hiromasa Otake MD, Kobe University Graduate School.
Students: Ali Aleiou, Joshua Hughey

  • The success of drug eluting stents is limited by restenosis and late stent thrombosis. Stenting as a common intervention alters artery geometry, exposing an artery to adverse wall shear stress (WSS). For DES it is not conclusively known if optimizing WSS leads to clinical benefits. The objective of this study is to determine the relationship between DES-induced WSS indices and two markers of poor outcomes, change in lumen area and category of stent malapposition.

Modeling Cerebrovascular Reactivity in a Computer Model of Cardiorespiratory Dynamics
Student: Mariana Fernandes Gragnani

  • Cardiovascular disease is often associated with impaired regulatory processes but their interaction is not well understood. The goal of this project was to create a computer model of blood vessel resistance in the brain (cerebrovascular resistance, or CVR) that functionally depends on blood gas levels and blood pressure. This is an extension of work from 2013 in which an empirical piecewise model of CVR was created within an existing closed-loop compartment model of the whole body circulation system.  Current efforts focus on combining proposed open-loop models from earlier literature dependent on blood pressure and gas levels, with a framework that we have recently implemented in the closed-loop whole body circulation model.

Collaborative Research: A National Consortium for Synergistic Undergraduate Mathematics via Multi-Institutional Interdisciplinary Teaching Partnerships.
Multiple institutions. Rebecca Segal, Vennie Filippas, Hilary Clark (VCU).

Designing a Novel Hypothalamic-Pituitary-Adrenal Axis Sensor System and Mathematical Modeling for Clinical Applications.
Benjamin Nicholson, David Chan, Vamsi Yadavalli (VCU)


Fluid dynamics analysis of pulmonary vasculature for understanding pulmonary arterial hypertension.
Mette Olufsen, NCSU; Umar Qureshi (postdoc), NCSU; Naomi Chesler, UW-Madison; Nick Hill, University of Glasgow.
Student: Mitchel Colebank

Translating Near Infrared Spectrocopy Oxygen Saturation Data for the Noninvasive Prediction of Spatial and Temporal Hemodynamics during Exercise.
John F. LaDisa, Jr., Sheila Schindler-Ivens, and Michael Danduran, Marquette University; Margaret Samyn, Children’s Hospital of Wisconsin.

Image-based Quantification Workflow for Coronary Morphology.
John F. LaDisa, Jr., Marquette University; Raymond Migrino, VA Health Care System (Phoenix); David Marks, Medical College of Wisconsin.

Modeling Autoregulation in the Kidney.
Anita Layton, Duke; Julia Arciero, IUPUI; Ashlee Ford Versypt,

Cardiovascular and Respiratory Regulation, Modeling and Parameter Estimation. PhD Thesis.
Advisor: Mette Olufsen, NCSU.