ESTIMATION OF HEMOGLOBIN USING OPTICAL SENSOR
Hemoglobin (Hb) is the most vital component in human blood, and is responsible for transporting oxygen from the lungs to the rest of our body. It is composed of a protein, called globin, and an iron containing compound called heme. Hemoglobin level is an important clinical parameter for assessing anemia in both chronic and acute conditions, If Hb concentration falls below normal, this is called anemia. Anemia is to be one of the most serious problem in the world.
A non-invasive method allows pain free continuous on-line patient monitoring with minimum risk of infection and facilitates real time data monitoring allowing immediate clinical reaction to the measured data. It is well known that pulsatile changes of blood volume in tissue can be observed by measuring the transmission or reflection of light through the blood volume. This diagnostic method is known as photoplethysmography (PPG). This non-invasive optical measurement method is based on radiation of red and near infrared light, emitted by Light Emitting Diodes (LED) in the range of 600nm to 1400nm. The detector detects the light transmitted through the finger. Then it will give the result in real time.
Fig 1 shows the block diagram of the entire system.
The device consists of two LEDs of different wavelengths- 650nm and 940nm. These wave lengths are selected in particular because it is at these wavelengths that the spectral absorptivity of hemoglobin and oxy-hemoglobin is considerable. The LEDs are derived with transistor driver circuit. The light form the LED made to pass through the finger. The light that gets partially transmitted through blood is received on a photo diode. The output of the photodiode is sent to PIC microcontroller. PIC microcontroller controls the output of photodetector and ADC converter converts the value of the hemoglobin in digital form. The output of ADC is given to microcontroller for processing. The out is displayed through LCD display.
• Finger will be put on the Red LED , IR LED and Photodetector.
• Red and infrared light is then emitted sequentially through the body tissue.
• The transmitted light is sensed by photodiode.
• Out-put voltage of photodiode increases linearly with light intensity.
Figure 2 Circuit diagram
It is with LED and matched Photo detector devices working at the red and near infrared wavelengths. The averaged intensity of the LED should be constant and preferably be sufficiently low to minimize excessive local tissue heating and also reduce the risk of a non-ionizing radiation hazard. The choice of photodetector is also important. Its spectral characteristics are chosen to match that of the light source. A photodetector converts light energy into an electrical current. Near infrared devices can be encased with daylight filters. The photodetector connects to low noise electronic circuitry that includes a trans-impedance amplifier and filtering circuitry. There are two main PPG operational configurations: transmission mode operation where the tissue sample (e.g. finger) is placed between the source and detector, and reflection mode operation where the LED and detector are placed side-by-side. Three channel PPG research systems many of the studies reported in the PPG literature are for a single site, often the ear, finger or toe, where pulses can easily be detected. Multiple finger site pulse data have also been reported by us. PPG systems are also available commercially. This is illustrated with finger ring-based PPG sensors for monitoring beat-to-beat pulsations and the need formation artefact reduction, optimal sensor placement and minimizing battery power consumption. Innovative LED and photodetector array technology has been incorporated into a PPG finger sensor oxygen saturation and respiration to be measured along with hematocrit derived from optical characteristics at five different wavelengths (569, 660, 805, 904 and 975 nm). Respiratory information was extracted using digital filtering techniques and blood oxygen saturation (SpO2) predicted using the standard ratio for the red and near infrared wavelengths.
Data from 5 volunteers of different ages and with varying Hb levels is acquired using the optical sensor built.
Table1: Result Comparision
Members Clinically report Device report
1. 15.4gm/dl 15gm/dl
2. 14.2gm/dl 14gm/dl
3. 13.6gm/dl 11.9gm/dl
4. 12gm/dl 12.9gm/dl
5. 9.6gm/dl 9gm/dl
An optical non contact type sensor for hemoglobin measurement is developed. With the help of developed technique it is possible to measure hemoglobin with two wavelengths 660nm and 940nm. This developed device is tested on some subjects and the results are promising.
Hb sensor developed of our project is fully integrated into a wearable fingerclip.