It is not impossible that in
a few years time, following the prohibition of the mercury, this method
will be replaced by another automatic one.
10.2.1 The self-measurement
device using a stethoscope (microphonic method)
After the inflation of the
cuff, the artery of the arm is compressed and the blood is blocked.
Then, the cuff is gradually deflated, at on average 2 to 3 millimetres
of mercury per second. During this phase, the noise emitted by the
artery changes: when the artery is compressed, no noise is audible
to the practitioner or the patient who listens with his stethoscope
or the microphone which " replaces
the ears ".
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
corresponds to the auscultatory method. It is used of course by the
practitioner, but also by the automatic device of the measurement of
the blood pressure. The cuff of the practitioner is connected with
a mercury sphygmomanometer, but mercury is now forbidden for the publics
Thus, cuffs including a membrane
able to measure the blood pressure have been created. These cuffs are
called aneroid and classically require the use of a stethoscope to hear
the noises of the artery.
Sometimes, a microphone has
been integrated into the cuff to obtain an automatic device.
nfortunately, this device is
not always highly reliable because of the dexterity needed in their handling
and the reduction in the precision of the cuff with time.
Nevertheless, this device has
not currently been abandoned.
10.2.2 The oscillometric
During the progressive deflating
of the cuff, 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 the systolic blood pressure.
Progressively as the pressure
decreases in the cuff, the oscillations will become increasingly significant,
until the maximal amplitude of these oscillations defining the mean blood
Then, the oscillations continue
to be audible during the pressure decrease in the cuff, until the time
when they disappear: the pressure then read on the device corresponds
to the minimal blood pressure or the diastolic blood pressure.
This method of measurement of
the blood pressure is the oscillometric method. It is a simple technique,
effective and validated by many medical societies. This technique can
be easily automated, and can be used as a self-measurement device by
a great number of patients with high blood pressure.
Currently, the majority of the
self-measurement devices for blood pressure use this technique and the
devices are generally reliable.
10.2.3 The Photoplethysmographic
This method can obtain the blood
pressure at the level of the arteries of the fingers. A small cuff is
inflated around the finger, and a constant pressure is maintained. Any
variation in the pressure at the level of the finger will involve a modification
of the pressure in the cuff, which thus converts it into blood pressure.