Philips HeartStart XL - ECG Monitoring Functions; Patient Impedance Functions

M4735A Service Manual 6-7
System Functional Descriptions
6
ECG Monitoring Functions
There are two separate ECG front ends: one for signals coming in on the
paddles or pads cable, and one for signals coming in on the 3- or 5-lead ECG
cable.
ECG - Paddles/Pads
The ECG signal picked up by the paddles or disposable defibrillation pads is
carried by the cable to the pads/paddles connector, and then to the Power
PCA. There it is amplified, filtered, digitized and passed across a patient
isolation barrier before being passed to the Control PCA via a large ribbon
cable.
The Control PCA then performs digital signal processing on the ECG data,
and is responsible for:
z ECG waveform analysis and Shock Advisory (in AED Mode).
z Formatting and presenting the ECG to the display and to the printer.
z Counting heart rate and generating heart rate alarms.
z Reporting on the status of the patient connection.
ECG - 3- or 5-lead cable
The ECG signal picked up by the ECG monitoring electrodes is carried by the
ECG cable to the ECG connector, and then to the Parameter PCA. There it is
amplified, filtered, and digitized before being passed to the Control PCA via a
large ribbon cable.
The Control PCA then performs digital signal processing on the ECG data,
and is responsible for
z Formatting and presenting the ECG to the display and to the printer.
z Counting heart rate and generating heart rate alarms.
z Reporting on the status of the patient connection, and alerting the user
to measurement problems.
Patient impedance functions
The M4735A measures patient impedance in two ways: an impedance mea-
surement before the shock, and a resistance measurement during the shock.
Before the Shock
The M4735A makes a small-signal AC impedance measurement (at 32 kHz)
in the steady state situation before a shock is delivered. This measurement is
used to detect Pads Off and Paddles Off. It is also used for the Paddle Contact
Indicator (PCI) function, in which the quality of the contact the paddles are
making with the patient is indicated on an LED bar graph on the Sternum
paddle. The unit only displays a numeric value in Diagnostic Mode, as part of
the ECG test.