User Manual for Vital Signs Monitor
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8.1.2 Factors affecting ECG signal
Interference from Electrosurgical Unit;
Doesn’t filter the interference waveform;
Poor grounding;
Electrodes are not placed properly;
Use expired electrode or use disposable electrode repeatedly;
The skin placed electrode is unclean or poor contract caused by scurf and hair;
Electrode long-time used.
8.2 NIBP Monitoring
8.2.1 Measuring Principle
Blood pressure may be measured in an invasive way (whereby the sensor will be inserted into blood vessel
directly) or a non-invasive way. The non-invasive way includes several methodologies, such as the Korotkoff
Sound Method and oscillating method. The Korotkoff Sound Method is used as a conventional way, whereby
stethoscope is used to measure the blood pressure. By the oscillating method, an inflation pump will fill the
air, and release it slowly. A computer will record change of the cuff pressure when the air is released. With
this record, the blood pressure value will be determined. First of all, make sure the signal quality judgment
by computer meets the requirements of accurate calculation (such as sudden limb movement or cuff being hit
during the measurement). If the answer is negative, give up the calculation. If the answer is positive, proceed
with calculation of the blood pressure value.
As change of the blood pressure is recorded by electric sensor, which sensitivity is much higher than that of
human ears, the oscillating method uses different definitions for measurement of diastolic pressure, mean
arterial pressure and systolic pressure from the Korotkoff Sound Method. When the oscillating method is
used, the circuit in the measuring apparatus will separate the amplitude of the cuff pressure from its change
with pulsation. With the oscillating method, the blood pressure at the maximum amplitude of cuff pressure is
defined as the mean arterial pressure. The blood pressure at amplitude of cuff pressure forward reduced
according to proper proportion is defined as systolic pressure, while the blood pressure at amplitude of cuff
pressure backward reduced according to proper proportion is defined as diastolic pressure. The maximum
change of pulse pressure occurs at these two points. They are equivalent to the point with pulse sound and
the point without pulse sound respectively in the Korotkoff Sound Method.
When the risk of invasive monitoring method outweighs its advantage of accuracy, non-invasive monitoring
method shall be used.
Comparison between blood pressure measuring methods
To overcome the effect of human hearing variation and air release speed on measurement accuracy when the
conventional Korotkoff Sound Method is used to take measure of blood pressure, people have been
dedicated to study of automatic measurement of blood pressure. By now, automatic blood pressure
measuring system based on the principle of oscillating method is mature. In practice, however, various
problems are encountered, such as why the measures taken by the oscillating method is lower or higher than
