A patient monitoring system collects information from several
transducers connected to a patient. The transducers convert
physiologic electromechanical activity into electrical signals
which are routed to a data acquisition module for digitization.
The digitized data is then processed and displayed on the
monitor screen. Additionally, bedside patient information can
be relayed to a central nursing station, a hospital information
system, or a doctor’s office.
Patient monitors must provide reliable data at all times. For this
reason, it is imperative to have an accurate means for
calibration and troubleshooting of patient monitoring
instrumentation. This function can be accomplished by using
a patient simulator which generates electrical signals similar to
those produced by the transducers.
For this application note, a patient simulator was designed and
built. The simulator consisted of a personal computer
peripheral device and had to be capable of producing the static
display of all numerics and graphics associated with the
following three human parameters: a) body temperature,
b) blood oxygen saturation level, c) heart pulse rate. Having
these capabilities greatly enhances the ability to perform fine
calibration and troubleshooting.
Document Number: 70604
DG406 Multiplexer Optimizes Medical Simulator
FIGURE 1. A Typical Medical Information System
The simulator design goals were as follows:
Theory of Operation
The commands to modify the simulated parameters are sent
from a PC over an RS-232 line to the peripheral device. A
microcontroller containing a UART receives these commands
as 8-bit frames and processes the data. After processing, the
microcontroller uses its I/O port bits to send data to the
parameter generation hardware. The parameter’s signal is
modified as specified by the down-loaded command. The
modified signals are then output to the patient monitor to
produce the appropriate visual displays.
Body temperature: from –1 C to 46 C in 0.1 C
increments, with an accuracy of
Blood oxygen saturation level: sixteen independent
values in the range of 60% to 100%.
Heart pulse rate: fifteen independent values in the range
of 30 to 300 pulses/min.
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Central Nursing Station
Doctor’s Office PC