V - How
to measure high blood pressure?
Principles
5.1 - The
most reliable method: to place a probe measuring the pressure directly
in the artery
5.2 - The most
useful method: The measure of the blood pressure using a sphygmomanometer
with a cuff
Measurement
of the blood pressure
5.3 - At rest
at the doctors
5.4 - At rest
at home, using a self-measurement device
5.5 - During
a physical exercise
5.6 - Measurement
by an ambulatory monitoring of the blood pressure during 24 hours
Description of the device
5.7 - The cuff
5.8 - Method for the measurement of the blood pressure
5.9 - The sphygmomanometer
5.8 -
Method for the measurement of the blood pressure: listening (microphonic),
oscillometric or much more rarely photoplethysmographic.
Once the cuff is inflated,
the artery of the arm is compressed and the passage of the blood
is stopped. Then, the cuff is gradually deflated, at on average 2
to 3 millimetres of mercury per second.
During this phase, two phenomena
occur:
- Auscultatory
method
The noise emitted by the artery changes: when the artery
is compressed, the physician listening with his stethoscope or the microphone
which «replaces
the ears» hears no noise. Then, when the pressure decreases in the
cuff, the artery starts to emit a noise: the pressure then measured on the
device defines the maximal blood pressure or systolic blood pressure.
Then, the noise continues
to be heard during the decrease of the pressure in the cuff, until
the noise disappears: the pressure then read on the device defines
the minimal blood pressure or diastolic blood pressure.
This method of measurement
of the blood pressure is the auscultatory method. It is used by the
physician, but also by an automatic measurement of the blood pressure
device.
Auscultatory method
- Oscillometric
method
The pulsations induced
by the artery are different: when the artery is compressed, no pulsation
is perceived by the device, then when the pressure decreases in the
cuff, the artery starts to emit pulsations: the pressure then measured
on the device defines the maximal blood pressure or systolic blood
pressure.
During the pressure decrease
in the cuff, the oscillations will become increasingly significant,
until a maximum amplitude of these oscillations defines the average
blood pressure.
Then, the oscillations
can still be seen during the decrease of the pressure in the cuff,
until they disappear: the pressure then read on the device defines
the minimal blood pressure or diastolic blood pressure.
This method of measurement
of the blood pressure is the oscillometric method. It is very often
used in the automatic device for the measurement of the blood pressure
because of its excellent reliability. On the other hand, it is less
precise than the microphonic or auscultatory method. Many devices
and in particular the automatic devices measuring the blood pressure
during 24 hours, use the two measurement techniques.
Oscillometric method
- Photoplethysmographic
method
This technique measures
the blood pressure at the level of the arteries of the fingers. A
small cuff is inflated around the finger, and the pressure is maintained
constant in the small cuff. Any variation of pressure on the level
of the finger will involve a modification of the pressure in the
cuff, which thus translates it into blood pressure.
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last reviewed on : 18 dec 2011 |
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