My Projects
The Body Monitor PX
Summary
While living in Detroit, I befriended
a couple who had, among other ventures, owned and operated a medical
service provider business. A specialty of that business included
house calls, a now unheard-of service that is of vital importance
to those who aren't mobile anymore.
Decubitus ulcers, or bedsores, represented
a scourge that their doctors saw with alarming frequency. Bedsores
are the degeneration of tissue caused by the prolonged application
of pressure due to a person's own body weight. If a patient is unconscious,
paralyzed, or very feeble, he or she does not have the ability to move
about as you and I would, and bedsores are the result.
The severity of bedsores ranges from redness
and irritation to full necrosis. What this means is that the flesh
dies and decays, leaving festering holes that can reach all the
way to the bone. Treatment involves the surgical removal of dead
and dying flesh, and the application of absorbent materials and
antibiotics. In any event, the associated pain and suffering is
significant.
The only prevention for bedsores, at least
as of the time this project was conceived, is regular movement and
reorientation of the patient's body in order to distribute pressure
loads on the body. The literature we studied at
the time suggested that if a patient spent no more than 2 hours
in a given position at a time, and was rotated with regularity,
they might be spared the curse of bedsores.
Given the number of patients suffering this
affliction, it was evident that they were not receiving proper care.
The question was, how could the quality of their care be measured?
My friends suggested that an electronic "gizmo"
attached to the body or clothing of the patient might be able to
collect this data, but they left it to me to work out the details.
Over the course of several months, I developed the prototype for
an instrument that could do precisely what they had envisioned.
The Body Monitor PX was based on a PIC processor,
programmed in Microchip assembler. Attached to the processor was
a pair of mercury tilt-switches, which could detect body "roll"
in 90-degree quadrants. The system featured an extra crystal used
by the firmware to keep track of real-time, and the compressed results
of attitude measurements were stored in a Xicor flash chip.
The processor was set up to spend the majority
of its time in sleep mode, which meant that the quarter-sized lithium
cells used to power the device would last for weeks. Rudimentary
tamper detection was provided in the form of a microswitch which
activated if the device was removed from the patient.
Data could be downloaded out of the instrument
and into an IBM PC for analysis. The communication was done via
RS-232 through 3.5 mm stereo audio cable. I wrote demonstration
application code that could plot the data extracted from the Body
Monitor, as well as analyze the data. The analysis portion of the
application code looked for violations of the 2-hour rule, tamper
events, and proper distribution of weight over all four quadrants.
Through-hole components and Vectorboard were
used in the prototype instrument, although parts were carefully
selected on the basis of the availability of surface-mount equivalents.
The finished commercial version of the instrument would have used
mercury-free tilt sensors, and would have probably been the size
of a pack of matches.
Regrettably, my prototype was more robust
than my partners' marriage. By the time they emerged from the ruins
of their relationship and the Body Monitor concept was revisited,
we found that somebody else had secured a patent on the idea.
None the less, I still consider the project
a useful exercise in assembly language, SPI bit-banging, and real-time
tracking through firmware.

(revised
08/04/06)
(revised 04/29/09)
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