User Manual for Multi-parameter Patient Monitor North-vision Tech. Inc.
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Chapter 7 Working Principle
7.1 The Principle of NIBP Measurement
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.
7.2 Points to be noted in NIBP Measurement
7.2.1 Operation instructions
Like common non-invasive blood pressure measurement, improper operation may cause
inaccurate or blank result or misunderstanding of the measuring information when the oscillating
method is used to take the measure of blood pressure. This point needs particular attention of the
operators.
1. Requirements of the cuff:
1) Appropriate cuff should be selected according to the age of the subject.
2) Remember to empty the residual air in the cuff before the measurement is commenced.
3) Locate the cuff in such a way that the “φ” mark is at a location where the clearest pulsation
of brachial artery is observed.
4) The cuff should be tightened to a degree where insertion of one finger is allowed.
5) The lower end of the cuff should be 2cm above the elbow joint.
2. The subject should lie on the back so that the cuff and the heart are in a horizontal position and
the most accurate measure is taken. Other postures may lead to inaccurate measurement.
3. Do not speak or move before or during the measurement. Care should be taken so that the cuff
will not be hit or touched by other objects.
4. With the oscillating method, when blood pressure is measured, the inflation pressure of the
