Designing a chest pulse oximeter to measure blood oxygen level

Nowadays, the biomedical devices hold a prominent position within medicine. Pulse oximeter has become a significant tool to detect oxygen level in blood. This measurement can be performed from different sites of human body such as fingertip, forehead, earlobe and nose. However, medical doctors agree that any SpO2 measurement should be better performed from sites closer to the heart in order to detect some diseases in their early stages. In this study, a reflective sensor was designed and SpO2 estimations were carried out from right index fingertip and intercostal artery in center of left chest and then, the results were compared. In this device, the sensor capture red and infra-red light that comes from related area from human body and produces an analog signal. The captured signal was amplified, filtered, digitized and sent to Personal Computer to process by using several digital windows namely Hamming, Blackman, Bartlett, Digital Prolate Spheroidal Sequence, Kaiser and Parzen-Rosenblatt. SpO2 estimations were obtained from related calibration equation for each window output. These equations were obtained from measurements of eight healthy volunteers. Another group of twenty-one healthy volunteers are included into the study while obtaining SPO2 estimations from right index fingertip and from the intercostal artery in the center of the left chest. The average SpO2 estimated from chest photoplethysmograms are 95.87±0.26, 95.88±0.26, 95.93±0.64, 95.75±0.36, 95.84±0.32 and 95.78±0.28 for Digital Prolate Spheroidal Sequence, Hamming, Kaiser, Blackman, Bartlett and Parzen-Rosenblatt windows, respectively. The average SpO2 estimated from fingertip photoplethysmograms are 96.15±0.29, 96.15±0.25, 95.70±0.40, 96.07±0.35, 96.12±0.41 and 96.13±0.31 for DPSS, Hamming, Kaiser, Blackman, Bartlett and Parzen-Rosenblatt windows, respectively. The results show that, there is no systematic difference between SpO2 estimations from chest and fingertip (P<0.5).