User Manual for Vital Signs Monitor
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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
2
waveforms may disappear suddenly? ...and so on. The
following explanations are devised to give the 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 the Korotkoff Sound Method in less error, higher reliability and stability. Their differences may be
reflected in the following aspects.
1.The measures by the Korotkoff Sound Method are liable to effect of human factors. For example,
different people may have different sound judging ability, or different reactivity when listening to heart
sound and reading mercury meter. The air release speed and subjectivity may also affect the judgment.
By the oscillating method, the computation is accomplished by the computer, thus relieving the
possibility of effect due to human factor.
2.With the Korotkoff Sound Method, the measure is taken on the basis of appearance and disappearance
of heart sound. The air release speed and heart rate may have direct effect on the measurement accuracy.
It also has the disadvantages of rapid air release and poor accuracy. In the contrast, with the oscillating
method, the determination is calculated on the basis of cuff pressure oscillatory waveform envelope,
and the air release speed and heart rate has little effect on the measurement accuracy.
3.Statistics show that, when measuring the hypertension, the measure taken by the oscillating method is
likely to be lower than that taken by the Korotkoff Sound Method. When measuring the hypotension,
the measure taken by the oscillating method is likely to be higher than that by the Korotkoff Sound
Method. But, it doesn’t mean the advantages or disadvantages between the oscillating method and the
Korotkoff Sound Method. Comparison with the results taken by more accurate method, let’s say
comparison of the invasive pressure result with the output value by the blood pressure measuring
simulator, will show which method has more accurate results. In addition, higher or lower value should
be a statistical concept. It is recommended those used to adopt the Korotkoff Sound Method use
different physiological calibration for values determined by the oscillating method.
4.The studies have shown that the Korotkoff Sound Method has the worst accuracy when it comes to
measurement of hypotension, while the oscillating method has worse accuracy when it comes to
measurement of controlled hypertension relief.
8.2.2 Factors affecting NIBP measuring
Select a cuff of appropriate size according to the age of the subject.
Its width should be 2/3 of the length of the upper arm. The cuff inflation part should be long
enough to permit wrapping 50-80% of the limb concerned.
Prior to use of the cuff, empty the cuff until there is no residual air inside it to ensure accurate
measurement.
Make the cuff mark
φ
in the position where artery pulsates obviously, the effect will be best.
The lower part of cuff shall 2cm above the elbow joint.
Do not wrap the cuff on too thick clothes(especially for cotton-padded clothes and sweater ) to
take measurement;
The testee shall lie in bed or sit in chair, make the cuff and heart at the same level, the result will
be most accurate, other postures may have inaccurate result;
