Cell phone-based pulse oximeter performs measurements at the point-of-care

Pulse oximetry, a noninvasive technique that measures blood oxygen saturation (SpO₂) and heart rate using a photo sensor to track the amount of absorbed light emitted by a red and infrared LED, enables fast diagnosis of hypoxemia (low blood oxygen levels). Difficult to identify clinically until the blood turns blue, the technique can spare a patient from the permanent effects of lack of oxygen (brain damage or even death).

In efforts to boost assessment and management of respiratory disease from the hospital into non-hospital settings, such as those in the developing world, engineers at the University of British Columbia (Vancouver, BC, Canada) are pairing a pulse oximeter with a mobile device. A cell phone's inherent computing power, peripheral resources, and wide availability make it easy to create a low-cost, standalone device that can even be used by patients at home. The real-time wireless communication of results (no delay in interpretation, or response to critical events) offers a distinct advantage over traditional pulse oximeters.

Dubbed the Phone Oximeter, the device combines an FDA-approved pulse oximeter probe and electronics module (Nonin Medical; Plymouth, MA) with an iPod Touch. The software implementation is designed to allow the majority of development to be performed outside of the proprietary software development kit (SDK) frameworks. This maximizes portability across the most common cell phone platforms currently available.

Novel algorithms have been developed for the computation of respiratory rate, previously not available on pulse oximeters. This relatively low-cost, robust prototype pulse oximeter device conveys the quality and trend of physiological data (oxygen saturation, heart rate, respiratory rate) over time through its intuitive user interface. The ease of use, presentation of warning signals generated by the decision support engine, and reliance on symbols mean that it can aid any clinician, regardless of language, in detecting clinical events and making clinical decisions. This prototype has undergone usability evaluation of the graphical interface in Vancouver, BC, Canada, and Kampala, Uganda.

The next generation of the Phone Oximeter will reduce costs further by eliminating third-party hardware and incorporating all signal processing onboard the cell phone. The current decision support engine will be extended to include the integration of clinical expertise and will allow non-specialist healthcare workers to monitor with confidence.

For more in-depth information, please visit www.phoneoximeter.org.

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