Design of a Cranial Vascular Mechanics Model

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Design of a Cranial Vascular Mechanics Model

• Sean S. Kohles, PhD
• Director, Kohles Bioengineering, Portland, OR
• Adjunct Associate Professor,
• Mechanical Engineering, PSU OSU,
• and Surgery, OHSU

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Purpose of this Seminar

• Introduce myself as potential project advisor
• Describe design objectives and motivation for the
  proposed project
• Medical issues
• Biologic and biomimetic materials
• End users
• Performance specifications

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Kohles Training

• University of Wisconsin
• Engineering Mechanics (BS, MS)
• Bioengineering (PhD)
• Orthopedic Surgery (Postdoc)
• University of Oregon
• Exercise Science (Visiting Assistant Professor)

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Previous PositionWorcester Polytechnic
Institute,Massachusetts

• Tenure-track faculty in
• Biomedical Engineering
• Biomechanics, biomaterials, biotransport, and
  design courses
• Mechanical Engineering
• Biology Biotechnology
• Adjunct appointments
• Clinical Science (Tufts Univ School of Vet Med)
• Physiology Orthopedics (Univ of Mass Med School)

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Kohles Research Foci

• Biomechanics and biotransport
• Tissue and implant mechanics
• Biomaterials and tissue engineering
• Surgical device design
• Orthopedic, dental, minimally invasive
• Biostatistics and mathematical modeling

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Current Vascular Mechanics Project

• Collaboration with Biomedical Signal Processing
  (PSU) and Complex Systems (OHSU) Laboratories
• James McNames, PhD ECE-PSU
• Brahm Goldstein, MD Pediatrics-OHSU
• Wayne W. Wakeland, PhD Systems Science-PSU
• Mark Weislogel, PhD ME-PSU

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Design Objectives

• Create a proof-of-concept mechanical model of
  cranial vascular mechanics
• Flow system with variable control of
• Fluid pressure and volume
• Fluid pathways (vessel tubes vs porous media)
• Head analog which simulates key tissues
  (biomimetics)
• Hard and soft tissues, fluids
• Synthetic composite arrangement

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Brain and CardiovascularBiomechanics

• The head or cranium is a natural thick-walled
  pressure vessel
• Cranial tissues contained within the bony
  calvarium
• Brain and connective tissues (1200 mL), static
• Cerebral spinal fluid, CSF (150 mL), dynamic
• Blood (150 mL), dynamic
• Hydrostatic (buoyancy forces in CSF) and
  hydrodynamic (blood flow) states

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Brain and Cardiovascular Biomechanics

• Pulsatile flow driven by the heart
• Volumetric flow to the brain
• 750 ml/min
• Vessel pathway controls mass transport
• Arteries to arterioles to capillaries to venules
  to veins
• Normal arterial pressure range
• 60 to 160 mmHg or 8 to 21.3 kPa
• fainting to edema
• Autoregulatory system
• Heart rate, vessel dilation/constriction, etc.

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Medical Significance

• Traumatic brain injury (TBI) due to an external
  physical force such as acquired during an auto
  accident.
• Leading cause of death and disability in children
  and adolescents in the United States
• The brain swells as a consequence of the injury,
  the pressure within the calvarium increases
  causing regional or global ischemia
• Decreased blood supply due to constriction or
  obstruction of the blood vessels.
• This secondary injury, in turn, causes cell death
  and potentially permanent impairment or brain
  death.

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Medical Device State of the Art

• Few technologies other than medical images exist
  to monitor brain, post injury
• Current devices tap into cranium and vessels to
  measure static/dynamic pressures
• New devices measure volume change (DV) associated
  with pressure change (DP)
• Compliance, S DV/DP
• Combined measure of flow resistance
• in vessels and compressibility
• or distensibility of cranial tissues

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Medical Needs

• No physical models exist to
• Judge accuracy of current devices
• Complement mathematical models which attempt to
  predict autoregulatory system
• Educate physicians and researchers on the unique
  mechanical dependence of brain function

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Proposed Project Team

• 2 or 3 ME students with interests in biomechanics
  and biomaterials
• Advised by Dr. Kohles and ME Design Faculty
• 2 ECE students with interests in biosensors and
  controls
• Advised by Dr. McNames and BSP Lab Faculty
• Resources Bench space in the Microgravity and
  Surface Tension Lab, 449-SB2, thanks to Dr.
  Weislogel

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Design Loop Creativity with a Purpose
Practical Problem (Need)
Helps to Solve
Motivates

• Contributions/Constraints
• Clients Users
• Design Performance Specifications

Design Question
Design Solution
Defines
Finds
Design Problem/Goal
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Nuclear Magnetic Resonance and Computed
Tomographic Images
Thank you for your attention!