Chapter 8 Monitoring Parameter; Nibp Monitoring; Measuring Principle - Gima 35132 Manuel De L'utilisateur

8.1 NIBP Monitoring

8.1.1 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 those taken by Korotkoff Sound
Method? Why the measures are inclined to decline? Why, in some cases, no result is obtained in spite of the
inflation actions? Why the measure values have big discreteness and even abnormal data in some cases? Why
the SpO
waveforms may disappear suddenly? ...and so on. The following explanations are devised to give the
2
answers.
The Oscillating method vs. the Korotkoff Sound Method
Blood pressure measurement by the oscillating method and Korotkoff Sound Method has good correlation with
the invasive measurement. Notwithstanding, any of the non-invasive blood pressure measurements has its
one-sidedness when it is compared to the invasive measurement. The oscillating method has its advantages over
User Manual for Vital Signs Monitor

Chapter 8 Monitoring Parameter

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