Tools for Non-Invasively Measuring Brain Compliance By Mark L. Manwaring

What is Engineering? To contrive or plan out usually with more or less subtle skill and craft; to guide the course. S ystematic 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.

Normal fetal brain

A Ventriculoperitioneal (VP) Shunt

Over drainage and slit ventricles – a statistical “setup” for repeat surgery

Detection of shunt failure Standard practice rests on history, clinical exam, and CT scan changes—unreliable on initial assessment ¼ of time ICP measurement is definitive, but invasive and impractical prior to ER

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 removal—the cure?

The Ear is a Speaker -- a recent discovery 1.Internal carotid artery and its distral tributary is the generator of the ICP pulse inside the cranium. 2.Pulse travels through CSF and brain. 3.Tissues change the ICP waveform morphology dependent on brain compliance—increased amplitude and risetime. 4.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).

General Ear Anatomy Middle & Inner Ear— CSF pulse travels into endolymph

Measuring the Output of the Ear: Our Prototype Head band with “microphone” for detection of low frequency ICP pulse.

Ear microphone allows tracings from both ears simultaneously.

Unfiltered signals: Piezo sensor tympanic membrane and ICP sensor

The “brain stethoscope”: an apparatus and method for outpatient and home ICP monitoring

ICP vs earlobe pulse – standing upright

Vertical Position Coray Jotham

Horizontal Position CorayJotham

Minus 45 degrees—intracranial pressure exceeds 27 cm H2O (20 mm Hg)

Completely inverted—ICP greater than +45 cm (31 mmHg); CPP <50 mm Hg; cerebral congestion; retinal petichiae after prolonged period

Blue – signal from external ear canal; Green – pulse oximeter

Phase relationship between TMD and pulse oximeter at +45°

Phase relationship in horizontal position Note increased amplitude but no phase shift

Inversion to -45° Marked phase shift

Complete inversion = -90° Further phase shift seen

27 males, age Five positions: +45°, 0°, -15°, -30°, -45°

27 males, the average and +/- 1 SD

Hysteresis of phase shift in a subject moved from horizontal to -45° and back, pausing 30sec in each position

Patients with VP shunts showed three patterns: Poor compliance, normal range, and overdrainage

A Prototype Hardware/Software System to Capture and Display Compliance Information

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 ?