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System Functional Descriptions
6-8
Patient impedance functions
The M3500B/M5500B measures patient impedance in 2 ways: an impedance
measurement before the shock, and a resistance measurement during the
shock.
Before the Shock
The M3500B/M5500B makes a small-signal AC impedance measurement (at
32 kHz) in the steady state situation before a shock is delivered. This mea-
surement (called PCI) is used to determine whether the pads are connected to
the patient, or not. The unit only displays this value in Diagnostic Mode, as
part of the ECG test.
During the Shock
The M3500B/M5500B also makes a resistance measurement during shock
delivery. This resistance is derived from measurements of voltage and cur-
rent, and is reported on the printed event summary. The unit uses this value to
determine whether to abort the shock, or to allow it to complete.
Since one is a small signal AC measurement of impedance and the other is a
high voltage/high current measurement of resistance, it is normal and
expected for them to produce slightly different numerical results.
SpO
Monitoring Functions
2
The SpO
signal from the sensor is carried by the external SpO
2
SpO
connector, and then to the SpO
2
amplified, filtered, and digitized before being passed to the Interface PCA via
another flex circuit. (Power for the SpO
Interface PCA via this same flex circuit.) The Interface PCA provides on/off
logic, patient isolation, and the power supply for SpO
to the Control PCA via a large ribbon cable.
The Control PCA is then responsible for:
Formatting and presenting the O
bar to the display.
Counting pulse rate, generating O
Reporting on the status of the sensor and its connections, and alerting
the user to measurement problems.
PCA via a flex circuit. There it is
2
PCA and sensor is provided by the
2
. It then sends the data
2
saturation level, pulse rate and pleth
2
saturation level alarms.
2
Theory of Operation
cable to the
2
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