Author Topic: Online Graphical Display of Blood Oxygen Saturation and Pulse Rate  (Read 1597 times)

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Author : Dilpreet Kaur, Sukhwinder Kumar, Shashi Sharma
International Journal of Scientific & Engineering Research Volume 2, Issue 6, June-2011
ISSN 2229-5518
Download Full Paper : PDF

Abstract—This paper will design a non-invasive pulse oximeter using the ADuC842 microcontroller. A pulse oximeter is a medical device that indirectly monitors the oxygen saturation of a patient's blood and heart rate. The hardware has been developed for the pulse oximeter and programming/coding has been done for calculating blood oxygen saturation and pulse rate of a patient. The results are displayed on the OLED or transported to PC. The software used is ASPIRE (Advanced Systems Programming Integrating Real-time Emulation) verion 1.05. Assessing a patient’s need for oxygen is the most essential element to life; no human life thrives in the absence of oxygen.
Index Terms— Heart rate, microcontroller, oxygen saturation, pulse oximeter.

1 Introduction
In the earlier days, the common method used to measure blood oxygen saturation was arterial blood gas measurement. An Arterial Blood Gas (ABG) is a blood test that is performed using blood from an ar-tery. It involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. This method was invasive, expensive, difficult, painful and potentially risky.
The pulse oximeter [1] [5] was introduced in the early 1980s. It is particularly a convenient, non-invasive measurement instrument. Pulse oximeter is less expensive compared to the old health monitoring devices, simple to use as it needs no user calibration, small enough to be wearable and accurate enough for clinical use. For these reasons, in almost every hospital, critical care units and surgical theatres; the pulse oximeter is acknowledged as a standard monitoring device.
Pulse oximeter is recommended for the monitoring of patients during anesthesia or those with conditions such as asthma. It is used to assess the viability of limbs after plastic and orthopaedic surgery. It is recommended as an important care tool for new born infants and patients during surgery. Pulse oximeters are also useful for pilots operating in a non-pressurized aircraft above 10,000 feet where supplemental oxygen is required. It is also useful for mountain climbers and athletes whose oxygen levels may decrease at high altitudes or with exercise.

2 Overview
The principle [6] of pulse oximetry is based on the red and infrared light absorption characteristics of oxygenated and deoxygenated haemoglobin. Oxyge-nated haemoglobin absorbs more infrared light and allows more red light to pass through whereas deox-ygenated (or reduced) haemoglobin absorbs more red light and allows more infrared light to pass through.  Red light is in the 600-750 nm wavelength light band whereas infrared light is in the 850-1000 nm wave-length light band. The absorption relationship of oxy-gen levels in the blood for the red and infrared wave-lengths is shown in figure 1.
Figure 1: Absorption relationship of oxygen levels in the blood for the red and infrared wavelengths
There are two methods [2] of sending light through the measuring site, transmission and the reflectance. In the transmission method, the emitter and the photo detector are opposite of each other with the measuring site in-between. The light can then pass through the site. In the reflectance method, the emitter and photo detector are next to each other on top of the measuring site. The light bounces from the emitter to the detector across the site.
With each heart beat, the heart contracts and there is a surge of arterial blood, which momentarily increases arterial blood volume across the measuring site. This results in more light absorption during the surge. If light signals received at the photodiode are looked at 'as a waveform', there should be peaks with each heartbeat and troughs between heartbeats.
A newborn’s heart rate [4] [7] is typically around 120 beats per minute (bpm). A heart rate in the vicinity of 70 beats per minute (bpm) is considered normal for an adult. When a person enters his golden years, the heart rate slows to approximately 50 bpm. When exercising, the heart rate may double. Accounting for all of this data, to say, 50 to 200 bpm are considered good readings for the heart rate.

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