3.10 Continuous Non-Invasive Blood Pressure Measurement
164
After each calibration measurement of BP, the reference value
PWTT
ref
corresponding to that
measurement is calculated. The difference between the current PWTT
i
and the reference value
PWTT
ref
is taken as an informative parameter of the cNIBP channel:
dPWTT = PWTT
i
- PWTT
ref
dPWTT
is measured in milliseconds. In a healthy person at rest, fluctuations in dPWTT usually
do not exceed 10 ms.
In most clinical situations, fluctuations in dPWTT correspond to fluctuations
of blood pressure, therefore, significant deviations in dPWTT may indicate
significant changes in blood pressure. If the dPWTT value is positive, then the
blood pressure value decreased in comparison with the calibration value, and
if it is negative, then it increased.
When the absolute value of dPWTT increases above the specified threshold, the cNIBP channel
triggers an additional measurement of blood pressure in the cuff.
dPWTT
threshold can be defined in two ways:
set manually by the operator - fixed threshold;
calculated automatically by the cNIBP channel - adaptive threshold.
When calculating the adaptive threshold
dPWTT
, the following parameters are taken into ac-
count:
the need to ensure patient comfort;
natural instability of
PWTT
;
the need for regular measurements even with a stable
PWTT
value.
Figure 3-19 shows the typical behavior of the adaptive threshold after a BP measurement by the
cuff. The threshold is displayed as two curves, symmetrical about the horizontal axis, because
the same threshold is compared with both positive and negative dPWTT values. Noise curve
along the horizontal axis (zero line) - current dPWTT value.
Figure 3-19. A particular case of PWTT dependence from on systolic blood pressure
The features of the behavior of the adaptive threshold dPWTT are following:
Immediately after measuring blood pressure, the threshold is big, and then decreases rapid-
ly. This reduces the probability of repeated blood pressure measurements in the first
minutes of the interval and increases patient comfort.
After some time (about 10 minutes), the threshold value stabilizes and is determined mainly
by the absolute value and the degree of PWTT instability. This is the standard threshold val-
ue that is held most of the time between measurements. With an increase in instability or a
rapid change in dPWTT, the threshold value increases, which helps to avoid false and inef-
fective starts of blood pressure measurement. Once dPWTT has stabilized, the threshold
decreases again. Thus, if the patient's blood pressure changes suddenly, then the meas-
urement will start not in the transient period, when the pressure is constantly changing, but
in the stabilization period, when the measurement result is much more reliable and accurate.
Summary of Contents for MPR6-03
Page 1: ...Patient Monitor MPR6 03 User Manual RM 501 01 000 01 01 UM Version 7 05 2020 ...
Page 2: ...2 ...
Page 193: ...193 ...