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A Small, High-Fidelity Reflectance Pulse Oximeter David Thompson, B.S. and Steve Warren, Ph.D. Department of Electrical & Computer Engineering Kansas State University, Manhattan, KS, 66506, USA

Abstract Pulse oximeters have become standard equipment in both biomedical education and clinical settings. Since the operational principles of a pulse oximeter are straightforward, and since the analysis of these sensor data require basic computational and mathematical toolsets, this type of device is well suited to hands-on experiences geared toward both undergraduate and graduate students. However, this seemingly simple type of biomedical device offers challenges in the areas of motion artifact reduction, light excitation/collection, signal fidelity, and parameter extraction that provide rich material for undergraduate and graduate education and research. This paper addresses a new design for a silver-dollar-sized reflectance pulse oximeter that is easy for students to use and incorporates multiple design enhancements that result in high-quality photo-plethysmograms. The pulse oximeter communicates with a LabVIEW virtual instrument via a serial USB interface. The double sided pulse oximeter board contains surface mount circuitry on one side and a reflectance sensor on the other side, where large area photodiodes are arranged radially around a central, dual red & near-infrared LED excitation source. The pulse oximeter is unique in that it is entirely digitally controlled and adjusts signal baselines depending on existing light levels. Additionally, it provides high fidelity red and near-infrared plethysmograms that demonstrate hundreds of analog-to-digital converter levels from peak to valley. Because the plethysmograms are unfiltered, they are good candidates for education and research projects that address signal filtering, blood oxygen saturation calculation algorithms, physiological parameter extraction from photo-plethysmographic signals, light/tissue interaction modeling, and the use of photo-plethysmograms in applications such as biometric authentication. These new devices have been employed in (a) a Fall 2006 lecture/laboratory pair within a biomedical instrumentation course sequence taken by undergraduate and graduate students, (b) undergraduate honors research experiences, and (c) graduate signal processing research.

I. Introduction Blood oxygen saturation, often referred to as the sixth vital sign, can be obtained via a well known, empirically discovered technique referred to as pulse oximetry.1, 2 In recent decades, pulse oximeters have become a staple in clinical environments and are therefore an expected element of any biomedical engineering curriculum. At a conceptual level, the operational principles of pulse oximetry are straightforward and easily conveyed in the classroom; pulse oximeters are therefore attractive for undergraduate hands-on laboratories. However, pulse oximeters intended for practical monitoring environments offer design challenges in the areas of motion artifact reduction, light excitation/collection geometries, wearability, power management, and physiological parameter extraction. This makes them ideal targets for educational design projects and independent research efforts at both the undergraduate and graduate levels.3, 4

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Thompson, D., & Warren, S. (2007, June), A Small, High Fidelity Reflectance Pulse Oximeter Paper presented at 2007 Annual Conference & Exposition, Honolulu, Hawaii. 10.18260/1-2--2793