Nellcor OxiMax N 5500, Руководство по обслуживанию

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System Processing Description
N5500 Service Manual 87
Technical
Information, N5500
10.3 ECG Processing
The measurement of the skin surfaces electrocardiogram is based on the electrical
signals on the skin surface, produced as the heart muscle contracts and relaxes. The
signals are detected by electrodes placed on the patient body. The information on heart
activity carried by these signals varies with the placing of the electrodes.
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:
l
They detect a lead-off condition if one of the electrode connections is
disrupted.
l
They detect the presence of pacemaker signals within the QRS waveform
complex of the ECG.
10.4 NIBP Processing
Overview
The oscillometric technique does not use Korotkoff sounds to determine blood pressure.
The oscillometric technique monitors the changes in cuff pressure caused by the flow of
blood through the artery. The monitor inflates the cuff to a pressure that occludes the
artery. Even when the artery is occluded, the pumping of the heart against the artery can
cause small pressure pulses in the cuff baseline pressure. The monitor lowers cuff
pressure at a controlled rate. As the cuff pressure goes down, blood starts to flow
through the artery. The increasing blood flow causes the amplitude of the pressure
pulses in the cuff to increase. These pressure pulses continue to increase in amplitude
with decreasing cuff pressure until they reach a maximum amplitude at which point
they begin to decrease with decreasing cuff pressure. The cuff pressure at which the
pulse amplitude is the greatest is known as Mean Arterial Pressure(MAP). The manner
in which the pulse amplitudes vary is often referred to as the pulse envelope. The
envelope is an imaginary line that connects the peak of each pressure pulse and forms
an outline. The shape of the envelope is observed by the monitor using a variety of
techniques to determine the diastolic and systolic blood pressure.