getemed VitaGuard VG2100, Руководство по эксплуатации

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Algorithms and measuring principles 107
TA
(max)
for asystole: ............. set
Asystole delay +
2 s
TA
(max)
for apnea: ................. 2 s
The purpose of these alarm report delays is to prevent alarms from being
reported every time the alarm limits are violated for short times only.
In other words, the maximum alarm report delay corresponds to the
maximum set delay. The monitor outputs measurements e.g. to the
display every second. The technology’s contribution to the total alarm
report delay is specified as maximum two seconds overall.
10.2 Measuring principle for the heart rate monitor
Every heartbeat, i.e. contraction of the cardiac muscle, generates a
myopotential that propagates through the body as an electric signal
and that can be measured by two sensing electrodes attached to the
body. The graphical depiction of the measured signal is called an
electrocardiogram (ECG).
The amplitude and the polarity (positive or negative) of the measured
signal depend on both the arrangement of the sensing electrodes and
the individual location of the heart.
The signal is very weak (typically one millivolt), so it must be ampli-
fied before it can be used to calculate the heart rate.
For this purpose an instrumention amplifier is used in conjunction
with filter circuitry. This amplifies the ECG signal and reduces all
other unwanted secondary signals, e.g. movement-induced artifacts
and electromagnetic interference.
Interference signals can be optimally suppressed, when a third, so-
called reference electrode is used. Without this reference electrode,
the ECG measuring circuitry must suppress interference signals solely
with the aid of filters. When, however, interference signals exceed a
certain limit, suppression is no longer possible and the ECG signal can
no longer be measured; false alarms are the consequence. The use of