244. A Patient's Own "Brain Stethoscope" for Measurement of Brain Compliance: Remote Assessment of Control of Hydrocephalus

Authors: Nathan Kostick; Rajkumar Dhar; Richard Sandler; Hansen Mansey, PhD; Kim Manwaring, MD (, )

Introduction:

Suspicion of shunt failure is based on a patient reporting progressive headache, nausea and vomiting.  It is difficult for patients and parents to differentiate normal childhood illness from shunt failure.  Practical and cost-effective, home-based devices have not yet been developed to guide a decision to proceed to the ER.  While a failed shunt is associated with increased ICP, alteration of brain compliance is also typical.  The ICP waveform can be derived from tympanic (TM) waveform pulsation.  Abnormal compliance is associated with faster rise time of the waveform.  A modified stethoscope which "hears" the infrasonic TM movement can be remotely monitored to detect this change.

Methods:

A standard stethoscope was modified for airtight external ear canal fit; the dome was exchanged for an ultrasensitive magnetic reluctance sensor, allowing detection of the ICP pulse.  Previous data has showed waveforms are identical to an implanted ICP sensor.  The analog TM waveforms are analyzed in real time by measuring slope ratio of the pulse.  4 normal subjects (age 22-30) underwent tilt table testing to induce incremental ICP.  Additionally, hyperventilation, Valsalva, and Queckenstedt maneuvers were observed.  One shunted patient used the device at home to show shunt stability with well controlled hydrocephalus.

Results:

The slope method of waveform analysis  showed consistent and stable changes to represent abnormal increased ICP and abnormal brain compliance. 

Conclusion:

1)  A personalized "brain stethoscope" can correctly derive the ICP waveform from TM pulsation
2)  Analysis of the TM waveform by slope ratio can indicate normal vs abnormal brain compliance, the latter indicating shunt failure.
3)  Simple maneuvers show expected physiologic change.
4)  The "brain stethoscope" is a practical, inexpensive tool to objectify and facilitate correct diagnosis