Guided by - Mrs. Debarati Ganguly Assistant Professor Dept. of ECE

Presented by - S Vivekanand Roll No. 17 S7 EC-B

Wearable Photoplethysmographic

Sensors

OUTLINE

What is Photoplethysmography

Types

Principle

Different modes

Advantages

HOW PHOTOPLETHYSMOGRAPHY ?

Photo Plethysmography

Photoplethysmography

Plethysmography (PG) ?

Plethysmography is a measurement technique that can be used to measure the volume changes in different parts of the body.

A plethysmograph is an instrument for measuring changes in volume within an organ or whole body.

TYPES OF PLETHYSMOGRAPHY

Air-Displacement

Photo

Strain gauge

Impedance

PRINCIPLE OF PPG

Most changes in blood flow occur mainly in the arteries . (but not in the veins).

PPG sensors optically detect changes in the blood flow volume via reflection from or transmission through the tissue.

The changes in light intensity are associated with small variations in blood perfusion.

MODES OF PPG

Two modes : Transmissive mode - fingers / toes / earlobe Reflective - forehead / cheek

TRANSMISSIVE MODE

In transmission mode, the light transmitted through the medium is detected by a photodiode opposite to the LED source.

The measurement site is limited.

It can be placed at fingertips, nasal septum, cheek, tongue, earlobe etc.

AbsorptionReflection at capillary bed

Diffuse Transmission

Specular Reflection

IR - LED

Photodiode

ArterioleVenule

Capillary Bed

SkinFat

Transmissive PPG

REFLECTIVE MODE

In reflective mode, the photodiode detects light that is back-scattered or reflected from the tissues, bone and blood vessels.

It eliminates the problems associated with sensor placement.

A variety of measurement sites can be used.

AbsorptionReflection at capillary bed

Diffuse TransmissionSpecular Reflection

IR - LED Photodiode

ArterioleVenule

Capillary Bed

SkinFat

Reflective PPG

The waveform is represented by two components of current :

Direct current - detected signals from tissues

Alternating current – detected signals from blood volume changes

HOW PPG IS OBTAINED ?

LIGHT WAVELENGTH

The shorter wavelengths of light are strongly absorbed by melanin, however red and near-IR light passes easily.

Light with wavelengths b/w 500-600nm (green yellow region) gave better results shallow tissues.

IR and near IR were better for deep tissue blood flow.

Ear piece PPG sensor

PPG ring sensor Fingertip PPG sensors

ADVANTAGES

PPG is inexpensive and cheap.

Since it consumes very less power, it is an ideal ambulatory device.

does not need special training or guidance.

A range of clinically relevant parameters can be obtained from PPG signal.

CONCLUSION

They offer a simple, reliable, low-cost means of monitoring pulse rate non-invasively.

PPG technology has been used to develop small wearable, pulse rate sensors.

More than ten companies producing these sensors commercially.(MIO alpha-MIO Global and Philips)

THANK YOU

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