Ecg Processing - Mallinckrodt NELLCOR NPB-4000 Service Manual

10.2.11 Recorder

10.3 ECG PROCESSING

10.4 RESPIRATION PROCESSING
The optional recorder (printer) module is installed in the right panel of the
monitor. Refer to the NPB-4000/C monitor operator' s manual for printing
procedures. It provides users with the capability to obtain hard-copy records of
selected vital signs information. Basic control of the recorder is implemented by
two push-switch controls on the recorder front panel. One of these is used to
obtain continuous recordings of the real-time waveforms displayed in the top two
graphic frames. Along with the waveforms, the recorder prints the values of the
vital signs being displayed. The printing continues until the user presses either
recorder switch a second time.
The other control switch initiates a printout for 20 seconds of the same
information recorded by the continuous control.
If scrolling is enabled in a display frame containing trend data when the
continuous recording switch is operated, then the trend record for that vital sign
is printed. If the snapshot recording switch is operated, then only the trend data
on the display is printed.
The recorder may be programmed via the monitor menu display to print a
snapshot recording when an alarm condition occurs.
Printing is accomplished on 50-mm wide thermal paper at printer speeds
programmable up to 50 mm/sec.
The technique used in ECG senses the varying potential difference between two
points at the skin surface which respond to the chemical actions of the muscular
activity of the heart.
Three electrodes are attached to the patient' s right arm (RA), left arm (LA) and
left leg (LL). The varying potentials at these locations are cable-connected to
the ECG circuit inputs where they are conditioned, and the difference of
potential between two selected leads is digitized before transmitting through
opto-isolators to the processor. The processor-installed algorithms operate on
the signals to develop drivers for the graphic display and to compute the heart
rate in beats per minute (bpm).
In addition to the acquisition of the QRS waveform complex, the ECG input and
subsequent signal processing computing circuitry perform a number of other
functions:
• They detect a "lead-off" condition if one of the electrode connections is
disrupted.
• They detect the presence of pacemaker signals within the QRS waveform
complex of the ECG.
• They generate a synchronization pulse for external use with defibrillators .
The Defib Synch Pulse output is available at a connector in the rear panel.
Section 10: Introduction and System Description
10-5