Quad Rat Vitals Monitor Robert Bjerregaard

1

, Matthew Bollom

1

, Caitlyn Collins

1

, Derek Klavas

1

Advisor:

Paul Thompson

1

, PhD.

Client:

Alex Converse

2

, PhD.

1

Department of Biomedical Engineering,

2

Department of Medical Physics; University of Wisconsin - Madison Final Design Abstract

The design and construction of a rat vitals-monitoring system is essential for simultaneously monitoring multiple anesthetized rats. Our client currently runs PET scans on four rats concurrently, and the scans can last up to two hours. During the two hour scans, the rats are under anesthesia and doses of the anesthesia medications must be adjusted based on the rats’ vitals. The client desires to have an accurate, reliable, and easy to use rat vital monitoring device to aid in this process. The current design for this monitoring device includes force-sensing resistors for monitoring breathing rate, thermistors to monitor rectal temperatures, and pulse oximeters to monitor SpO 2 levels and heart rates. The design also includes an easy to read graphical user interface (GUI) that displays running averages of the four vitals, histories graphs of the four vitals, and live traces of heart rate and breathing rate. All information is presented on a single screen, and data from each trial is stored for further analysis.

Project Motivation

Our client’s research requires him to monitor four vitals of each rat individually. The laboratory assistants must be informed in a timely manner if any of the four vitals enter critical ranges so adjustments to the anesthesia can be made.

Our client’s current setup. Picture taken in spring 2009.

Existing Devices

• MouseOx, produced by Starr Life Science™ and the Nellcor N-100 • Monitor SpO 2 levels, heart rate, and MouseOx monitors breathing rate • Not capable of monitoring multiple rats • Four separate units not cost effective MouseOx: Image taken from http://www.starrlifesciences.com/images/products/ mouse_analog.png

Design Criteria

•

SpO

2

(

±

2%)

•

Heart rate (up to 500 beats/min)

•

Rectal temperature ( 33



C - 38



C )

•

Respiration rate (20-30 breaths/min)

Breathing Rate

• Force sensing resistor (Figure 1) wired in series with 5V voltage divider • Velcro™ respiration belt (Figure 1) fabricated with ABS plastic plate to help direct force from the thoracic cavity onto FSR • Testing results yielded similar waveforms with and without the Figure 1. Respiration belt (left) used in tandem with FSR (right) respiration belt (Figure 2) Figure 2. Comparison of voltage data obtained by two different breath detection methods. Top: FSR placed on top of rat with respiration belt. Bottom: FSR placed underneath rat without respiration belt

Temperature

Figure 3. Circuit consists of a voltage divider and a non-inverting operational amplifier.

Figure 4. Digital thermometers purchased from local store modified to measure rectal temperatures.

•

Thermistor resistance varies linearly with temperature in desired temperature range (~33



C - 38



C)

Pulse Oximeter

• Circuit currently under construction by graduate student • Photodiode & LED were excised from an existing Nellcor pulse oximeter probe and mounted with heat shrink on a plastic clothespin with a compromised spring (Figure 5).

• Testing was conducted on an anesthetized rat and data was collected for processing as seen in Figure 6.

• More data is required to verify the accuracy of the pulse oximeter probe Figure 5. Modified pulse oximeter probe with mounted LED’s and photodiode Figure 6. Photodiode voltage versus time after filtering in MATLAB

Graphical User Interface

Figure 7. Screenshot of actual LabVIEW GUI • Data autosaves every 15 seconds • Live traces of breathing and heart rate displayed • Contains scalable history graphs of heart rate, breaths per minute, temperature, and SpO 2 • Displays current vital values • Chart marker allows for easy follow-up analysis

Acknowledgements

We would especially like to thank Liz Ahlers, Tim Balgemann, Dr. Alex Converse, Peter Klomberg, Amit Nimunkar, Professor Paul Thompson, Ph.D., and Professor John Webster, Ph.D., Nate Werbeckes

References

Webster, J. G., Design of Pulse Oximeters. IOP Publishing Ltd 1997.

Starr Life Sciences™ Corp. © 2009 Nellcor Puritan Bennett LLC. © 2009 Jack Ho, Joseph Yuen, Nate Werbeckes (Last semester’s team) accessed at http://homepages.cae.wisc.edu/~bme300/rat_monitor_s09/ Picture demonstrates use of thermistor and force plate. Pictures taken November 30, 2009.

Picture demonstrates use of respiration belt.

Future Work

• Integrate new pulse oximeter circuit • Fabricate three additional pulse oximeter circuits and probes • Prepare new computer for integration into final design • Fabricate circuitry housing and print circuit boards • Test device on rats during PET scans