Tools for Non-Invasively Measuring

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Tools for Non-Invasively Measuring Brain
Compliance By Mark L. Manwaring
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• What is Engineering?
• To contrive or plan out usually with more or less
  subtle skill and craft to guide the course.
• Systematic study of algorithmic processes that
  describe and transform information their theory,
  analysis, design, efficiency, implementation, and
  application.
• Encompasses many areas of specialization.
  Software development, systems development and
  hardware selection, studies of compatibility
  between hardware and software, language
  development and modification, or perhaps a
  combination of these and any number of other
  diverse applications and concepts.
• Must be familiar with the language of the
  physical sciences, mathematics, and English.

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Normal fetal brain
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A Ventriculoperitioneal (VP) Shunt
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Over drainage and slit ventricles a statistical
setup for repeat surgery
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Detection of shunt failure

• Standard practice rests on history, clinical
  exam, and CT scan changesunreliable on initial
  assessment ¼ of time
• ICP measurement is definitive, but invasive and
  impractical prior to ER

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Optimizing outcome of hydrocephalus

• Avoidance of complications at surgery
  malposition and infection
• Avoidance of longterm complications of
  obstruction and overdrainage
• Simplify and eliminate shunts where possible
  (evolving role of third ventriculostomy and
  related surgeries)
• Optimize hydrocephalus control for cognitive
  outcome
• Wean shunts to ligation and removalthe cure?

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The Ear is a Speaker -- a recent discovery

• Internal carotid artery and its distral tributary
  is the generator of the ICP pulse inside the
  cranium.
• Pulse travels through CSF and brain.
• Tissues change the ICP waveform morphology
  dependent on brain complianceincreased amplitude
  and risetime.
• CSF waveform transmitted backwards across hearing
  apparatus
• (cochlear endolymph?ossicles?tympanic membrane).
• 5. ICP pulsation not perceived due to
  frequency below hearing threshold (20 Hz to 20
  kHz).

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General Ear Anatomy
Middle Inner Ear CSF pulse travels into
endolymph
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Measuring the Output of the EarOur Prototype

• Head band with microphone for detection of low
  frequency ICP pulse.

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Ear microphone allows tracings from both ears
simultaneously.
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Unfiltered signals Piezo sensor tympanic
membrane and ICP sensor
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The brain stethoscope an apparatus and method
for outpatient and home ICP monitoring
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ICP vs earlobe pulse standing upright
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Vertical Position

• Coray

Jotham
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Horizontal Position

• Coray

• Jotham

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Minus 45 degreesintracranial pressure exceeds 27
cm H2O (20 mm Hg)
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Completely invertedICP greater than 45 cm (31
mmHg) CPP lt50 mm Hg cerebral congestion
retinal petichiae after prolonged period
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Blue signal from external ear canal Green
pulse oximeter
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Phase relationship between TMD and pulse oximeter
at 45
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Phase relationship in horizontal positionNote
increased amplitude but no phase shift
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Inversion to -45Marked phase shift
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Complete inversion -90 Further phase shift
seen
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27 males, age 18-25. Five positions 45, 0,
-15, -30, -45
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27 males, the average and /- 1 SD
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Hysteresis of phase shift in a subject moved from
horizontal to -45 and back, pausing 30sec in
each position
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Patients with VP shunts showed three patterns
Poor compliance, normal range, and overdrainage
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A Prototype Hardware/Software System to Capture
and Display Compliance Information
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Issues to be worked on --

1. A better method than using the FFT for
   determining phase angles
2. Measuring ICP with pulse oximeters
3. A long-term, implantable measuring device
   associated with the shunts.
4. Theory the head is resonant chamber. Can the
   problem of hydrocephalus be cured by fixing the
   resonance problem?