DESIGN OF A NEURAL IMPLANT MONITORING SYSTEM

MONITORING SYSTEM

Jessie Qian and Lacey Cirinelli

Spring 2005 Senior Design Project

Dept. of Bioengineering-The Pennsylvania State University, University Park, PA 16802

Sponsor: Dr. Ryan S. Clement, Neurotechnology Lab
THREE COMPONENT DESIGNS
Electrocardiograph

Design Criteria

  • The basic circuit (consisting of a voltage-current converter) will be integrated into the EKG breadboard and project box; the design will be mobile and sturdy enough for repeated lab use

  • •Operates over normal rat respiration rate (63-126.5 breaths/min) and body temperature (90o-110oF)

  • •Viewable on a multi-channel oscilloscope

  • ¡Compatible with DataWave software (DataWave Tech., Wausau, WI) 
Alternative Designs [4]

A) Capnograph

A medical instrument normally used in hospitals and doctors' offices; it measures the amount of CO2 in exhaled air.  The microbridge sensor detects a sample size for the instrument which then determines the percent of carbon dioxide in the patients' breath sample.  The microbridge can then determine an accurate sample size. 

 

The reason that this design was not implemented was due to the fact that it was overly detailed and our sponsor just wanted something that would allow him to view the intake and output of breaths in the rat body.  Also the cost for each capnograph ranged in price from $2000-$3000 which was far too expensive.

 

B) Total Body Plethysmography [2, 5, 6]

 

Body plethysmography measures the total amount of air the lungs can hold (total lung volume).  In order for this to work, the rat must sit inside an airtight booth called a plethysmograph and breathe through a mouthpiece while pressure and airflow measurements are collected. 

 

This design could not be used as it is not feasible for the rat to be breathing in an airtight box while surgery is being done. 

 

C) Strain Gages [2, 7-10]

 

Two elastic bands (across the abdomen and the stomach) with a strain gage attached to each are placed on the rat.  Each band is composed of a tube filled with mercury and then sealed shut on either end.  When the rat inhales, the strain in the gage increases and this is then measured by a wheatstone bridge.

 

This design wasn't chosen due to the fact that mercury was going to be filled in each of the tubes.  As it is a toxic material, the sponsor felt that it would be best to not implement this design.

 

D) Magnetometer [2, 9-30]

 

Two elastic bands (across the abdomen and the stomach) measure the body surface by calibrating the strength of the magnetic field generated at the opposite surface through the attachments of ferrite coils. 

 

After talking to experts in the field of magnetometers at Harvard University, it was determined that building a magnetometer would require someone with a more complete and thorough electrical engineering background; this design was consequently abandoned.

 

 

Current Design: Voltage-Current Converter

 

 

Figure 11: Schematic of a voltage to current circuit [31]
 

From this circuit, it is possible to measure the output current and correlate it to the known voltage input.  This will indirectly measure the resistance of the system.  Increase of the lung volume of the rat during breathing also means that there will be an increase in resistance shown in the circuit.  Measurements from the rat may be done through the same microelectrodes that were used in the electrocardiograph.

 

 

 

 

 

 

 

Figure 12: Hand made microelectrodes used for both the EKG and for the respiration circuit

 

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References:
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 http://www.edn.com/article/CA233726.html?text=voltage+and+to+and+current+and+circuit&

 

 

 

 

 

 

webpage design by Jessie Qian, 2005