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App Makes Cell Phone an Oxygen Saturation Monitor for Heart and Lung Patients

Device predicts cardiopulmonary status with 100% accuracy

Patients with chronic cardiopulmonary diseases could soon have a method to help them accurately monitor their health and warn doctors at the first sign of trouble, according to researchers at the University of Illinois at Urbana-Champaign.

By carrying their cell phones, equipped with a health-tracking app developed by the university team, patients’ oxygen saturation levels can be passively monitored with medical accuracy.

Oxygen saturation is a standard measure of health status, the single most important clinical measure. Unlike other methods of measuring oxygen saturation levels, which detect sharp drops causing desaturation, the MoveSense app continuously monitors saturation, making the resultant patterns possible to model accurately — and the patient is required only to carry a smart phone while walking.

The team published its findings in Telemedicine and e-Health.

“The ability to accurately measure oxygen saturation without the use of a pulse oximeter is something that has never been achieved until now,” said lead investigator Dr. Bruce Satz. “The oximeter, a noninvasive medical device usually placed on the patient’s finger, measures the proportion of oxygen in the blood, combining the status of the two major circulatory systems, the heart and the lung. The saturation level is an overall measure of the patient’s cardiopulmonary fitness.”

The new app was developed with the aid of findings from one of Schatz’s previous investigations, in which he found that phone sensors can accurately measure a subject’s walking patterns (gait).

Doctors often use the 6-minute walk test for patients with heart and lung disease, such as congestive heart failure, chronic obstructive pulmonary disease, and asthma. The test provides information regarding a patient’s functional capacity and response to therapy for a wide range of chronic cardiopulmonary conditions.

The investigators used the MoveSense app, in conjunction with their existing gait model, to administer 6-minute walk tests to 20 patients with cardiopulmonary disease.

The patients wore pulse oximeters (so that the readings could be compared with the MoveSense data) and carried smart phones running MoveSense software, which continuously recorded oxygen saturation and gait. Continuous saturation defined categories corresponding to status levels, including transitions. Continuous motion was used to compute eight gait parameters from the sensor data. The researcher’s existing gait model was then trained with these data points and used to predict transitions in oxygen saturation.

The researchers discovered that their oxygen saturation readings divided patients into three pulmonary-function categories: one with consistently high saturation; one with consistently low saturation; and a third in which saturation varied and the patients were clinically unstable. In addition, the team discovered that an analysis of the saturation, combined with the gait data, could predict a patient’s saturation category with 100% accuracy.

The ability to predict the saturation category of a patient from his or her gait will allow medical professionals to monitor patients’ vital signs, predict their clinical stability, and act quickly should their condition decline, the researchers say. Patients need only carry their personal phones during daily living, as testing has shown that periodic samples are sufficient and that even inexpensive smart phones are powerful enough to record the necessary data.

“Given our previous success with predictive modeling of gait with chronic lung disease patients, and our knowledge of the correlation between gait speed and oxygen desaturation in walk tests, we knew that if we could passively and continuously record oxygen saturation using a smart phone, we could predict cardiopulmonary status in a medically accurate and economical way,” Schatz said.

Source: Medical Xpress; July 22, 2015.

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