It Explains about the Blood pressure measurement by using photoelectric transducers

1. BLOOD PRESSURE MEASUREMENT
BY USING PHOTOELECTRIC
TRANSDUCERS
BY
ARAVINDKUMAR B

2. PHOTOEMISSIVE TUBE
 A photoemissive tube consists of a gas-filled tube
with two electrodes, one cathode, and another
anode.
 Cathode acts as one electrode, and it has a
specially coated material around it.
 When light falls on the cathode, it releases
electrons.
 The release in electron produces a current, which is
proportional to the light intensity.
 Usually, antimony, silver, bismuth is employed as
coating materials.

3. PHOTOVOLTAIC CELL
 A photovoltaic cell has an outer layer of selenium,
coated with a transparent metal film. The metal film
and selenium layer are insulated from each other,
and this forms the barrier layer.
 Light with high intensity illuminates the barrier layer.
 As the light falls on it, it releases electrons, which
causes a potential difference in the barrier layer.
 After the occurrence of potential difference, the
metal film turns into positive, and selenium layer
turns into negative.
 This is an example for the active transducer.

4. BLOOD PRESSURE MEASUREMENT
 We can measure pulsatile blood volume change
with a Photodetector. To detect the pulse, we can
either use Transmittance or Reflectance techniques
as shown in the figure.
 In transmittance technique, pulsating blood flow
modifies the optical density.
 In reflectance technique, blood flow changes the
intensity of reflected light.
 The changes in blood flow are seen immediately
with these methods.