Optical Heart Rate Monitoring (OHR)

EESM5600 Term Paper Proposal Topic: Optical heart rate monitoring (OHRM)

Outline of Term Paper Content:
Objectives and Motivations:
Our objectives of the term paper projects are to explore a survey research on recent developments using photonic technology. Optical Heart rate monitoring (OHRM) was chosen to be our project topic. The application of Photoplethysmography (PPG) technology would be discussed.
Introduction
Heart Rate is determined by the number of times beats in one minute. It is difficult to measure accurately and the most important physiological parameters reflecting our body condition. Continuous or routine measurement of heart rate become essential once patients were suffering from any diseases.

The principle of PPG sensors is optical detection of blood volume changes in the neurovascular bed of the tissue. It contains two main optical devices, such as a light source and an optical light detector. In the past, red and Infrared (IR) light-emitting diodes (LEDs) were commonly used as the light source. The main function of the PPG sensor was monitoring the changes in the light intensity via reflection from or transmission through our tissue. This changes in terms of light intensity are associated with small variations in blood perfusion of the tissue and provide information on the cardiovascular system, especially the pulse rate of our body. Light pass though biological tissue can be absorbed by different substances, such as pigments in the skin, bone and venous

Blood would absorb more light than the surrounding tissue. Thus, a reduction in the amount of blood is detected as an increase in detected light intensity. Green light is suitable for the measurement of superficial blood flow in skin. Since light with wavelengths between 500 and 600 nm (the green-yellow region of the visible spectrum) exhibits the largest modulation depth with pulsate blood absorption. IR or near-IR wavelengths are better for measurement of deep-tissue blood flow. Recently, Green-wavelength PPG devices are becoming increasingly popular due to the large intensity variations in modulation observed during the pulse rate for these wavelengths iii. Reflected and Transmitted Signal of PPG sensor Wearable PPG system has two operating mode – transmission and reflectance mode as shown in figure 3, 4.
In transmission mode, the light transmitted through the medium was detected by a Photodector (PD) opposite to light-emitting diode (LED) source; while in reflectance mode, PD detects light which back-scattered or reflected from tissue, bone or blood vessels. Figure 3: Reflection type PPG Figure 4: Transmission type