6
| BT17i
Blood Pressure Sensor User’s Guide
point below the mean pressure where the differences start to get small corresponds to
the diastolic pressure.
Figure 2
. A typical measurement with the Blood Pressure sensor.
1.
Identify the largest pressure “pulse”. This is an estimation of the MAP.
2.
Identify when the data begins forming rapid “pulses”. This is an estimation of the
systolic pressure.
3.
Identify when the data stops forming smaller “pulses”. This is an estimation of the
diastolic pressure.
2. Determining the blood pressure using oscillometric method
A more precise but laborious method to determine the blood pressure is the
oscillometric method. The pressure pulses, when extracted from the cuff pressure, form
an oscillating waveform. The peak-to-peak amplitudes of this waveform vs. pressure
create a bell shaped “envelope curve” (see figure 5). Within the envelope, the pressure
pulse amplitudes increase until maximum amplitude is reached (this point corresponds
to the MAP). After that the pulse amplitudes decrease further until hardly noticeable.
Generally, the systolic blood pressure is found by determining the point along this bell-
shaped envelope for pressure above MAP and for which the value of the pressure
amplitude is 50% of the maximum amplitude value. The diastolic blood pressure is
found using the same method for pressure below MAP and having an amplitude value
of 75% of the maximum amplitude value. These percentage values are obtained from
empirical research.
1
When this method is applied to the measured pressure graph, the bell shaped
“envelope curve” is extracted from the measurement graph as the difference graph of
the pulse pressure graph (the maximal values of the pressure pulses) and the cuff
deflection trend pressure graph. This procedure is described below in details for the
Coach program starting from version 7.3
2
, in 4 steps:
I.
Determining the cuff (trend) pressure
II.
Determining the pulse pressure
III.
Determining the envelope curve
IV.
Determining the blood pressure
1
Mehlsen J et al (1999). Vejledende retnigslinier for hjemmeblodtryksmåling. Ugesk Læ Klaringsrapport nr. 8, 1999.
2
If you use an older version of the Coach program consult the CMA Blood Pressure Sensor 0377i User’s Guide.
Systolic pressure around 115 mmHg
Diastolic pressure around 65 mmHg
