Photoplethysmography: Types and Applications
1. PHOTOPLETHYSMOGRAPHY
Photoplethysmography (PPG) is a simple and low-cost optical technique that can be used to detect blood volume changes in the microvascular bed of tissue (1).
Pulse Photoplethysmography was introduced to the world by Hertzman in the year 1938.
It is a noninvasive technique that makes use of light source and a detector.
The change in blood volume is synchronous to heart beat and hence this method can indirectly measure heart rate.
PPG has been used to assess skin perfusion since the 1930’s. Since then it has been used in determining the flux of RBCs through a volume of tissue, blood volume fluctuation, blood flow as a response to stress, medicines, and other clinical conditions. Largely it measures blood flow more precisely than blood volume fluctuation (2).
2. TRANSMITTANCE AND REFLECTANCE PPG:
The photoplethysmography may either be transmittance or reflectance type. Any changes in light transmittance or reflectance are attributed to blood flow and beating of heart.
TRANSMITTANCE PPG:
In transmittance type photolethysmograph, the light source falls on the tissue and light from the other side of the tissue is measured by means of the detector.
Transmittance type PPG is restricted to thin tissue such as finger or ear lobe. This method is restricted to outpatients to monitor pulse and heart rate. Transmittance PPG Reflective PPG
REFLECTANCE PPG:
In reflectance type photoplethysmography, the light source and detector are placed on same side of body part as the reflected light only needs to be measured.
It is used in emergencies such as hypothermia, and shock when the peripheral blood flow is compromised and transmittance type PPG is not feasible. They may be used on ear, nasal septum forehead, vagina and esophagus.
Reflectance mode PPG is advantageous as it avoids external venous compression potentially.
3. MECHANISM AND INFERENCE OF PPG:
PPG is an optical measurement changes in blood volume in an
Photoplethysmography (PPG) is a simple and low-cost optical technique that can be used to detect blood volume changes in the microvascular bed of tissue (1).
Pulse Photoplethysmography was introduced to the world by Hertzman in the year 1938.
It is a noninvasive technique that makes use of light source and a detector.
The change in blood volume is synchronous to heart beat and hence this method can indirectly measure heart rate.
PPG has been used to assess skin perfusion since the 1930’s. Since then it has been used in determining the flux of RBCs through a volume of tissue, blood volume fluctuation, blood flow as a response to stress, medicines, and other clinical conditions. Largely it measures blood flow more precisely than blood volume fluctuation (2).
2. TRANSMITTANCE AND REFLECTANCE PPG:
The photoplethysmography may either be transmittance or reflectance type. Any changes in light transmittance or reflectance are attributed to blood flow and beating of heart.
TRANSMITTANCE PPG:
In transmittance type photolethysmograph, the light source falls on the tissue and light from the other side of the tissue is measured by means of the detector.
Transmittance type PPG is restricted to thin tissue such as finger or ear lobe. This method is restricted to outpatients to monitor pulse and heart rate. Transmittance PPG Reflective PPG
REFLECTANCE PPG:
In reflectance type photoplethysmography, the light source and detector are placed on same side of body part as the reflected light only needs to be measured.
It is used in emergencies such as hypothermia, and shock when the peripheral blood flow is compromised and transmittance type PPG is not feasible. They may be used on ear, nasal septum forehead, vagina and esophagus.
Reflectance mode PPG is advantageous as it avoids external venous compression potentially.
3. MECHANISM AND INFERENCE OF PPG:
PPG is an optical measurement changes in blood volume in an