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Photoplethysmography Biosensors in Smartphones Could Support Remote Pulse Oximetry

Photoplethysmography (PPG) is an easy optical method for detecting volumetric variations in peripheral blood circulation.

Many smartphones are already embedded with the technology to use pulse oximetry, an optical tool able to measure oxygen levels in the blood and heart rate.
Many smartphones are already embedded with the technology to use pulse oximetry, an optical tool able to measure oxygen levels in the blood and heart rate. Image Credit: Pixabay.

It is used in smartwatches, for instance, to track heart and pulse rate. However, PPG biosensors are also included in millions of smartphones, which do not have any clinical applications at present.

A new study has found that PPG already equipped in smartphones can be used in combination with application software for remote clinical pulse oximetry to manage chronic cardiopulmonary disease and probably initial treatment and tracking of persons affected in respiratory viral pandemics, like COVID-19.

The study, published online in the February 2021 issue of the journal Chest, was performed by scientists from the University of California San Diego (UC San Diego) School of Medicine, together with collaborators from the industry.

Pulse oximetry monitoring plays an important role in managing pulmonary diseases, especially during pandemics or epidemics of respiratory viral infections, such as COVID-19 and influenza.

Sara H. Browne, MD, Study First Author and Associate Professor, School of Medicine, University of California San Diego

Browne is also a specialist in infectious diseases.

Oxygen saturation is a useful component of the clinical assessment for finding those patients who need close monitoring. Under home quarantine, remote clinical pulse oximetry helps patients to substantively report heart rate and oxygen saturation besides other symptoms.

Smartphone sensors together with apps could streamline the access to these measurements, but to make use of it, clinicians should know that these measurements are reliable and precise.

Moreover, Browne added that there are aspects of health equity in remote monitoring.

Smartphones with sensors and apps could significantly enhance remote monitoring due to their ubiquity, and don’t require patients to have additional expensive gadgets.

Sara H. Browne, MD, Study First Author and Associate Professor, School of Medicine, University of California San Diego

PPG sensors quantify enlargement or distention of arteries and other vessels found under the skin as blood pulses via them by detecting variations in light that is either absorbed or reflected to a pair of light-emitting diodes present in the device.

The pain-free and non-invasive technology is known as pulse oximetry and is generally employed in clinics and hospitals, mostly to assess oxygen levels in the blood of patients.

As part of the study, scientists hired 10 volunteers (four Asian, three Black, and three Caucasian), where each volunteer positioned an index finger over a smartphone sensor system with an app developed to clinically interpret the consequent optical data.

Then, the volunteers breathed a combination of gases with decreased levels of oxygen, successively decreasing to achieve stable arterial oxygen saturations between 70% and 100%.

They discovered that the smartphone measurements of blood-oxygen levels matched with other Food and Drug Administration-approved clinical tools employed for this purpose.

The researchers then used the same smartphone to examine over 2,200 readings taken concurrently from smartphone pulse oximetry and in-hospital Welch-Allyn instruments in 320 study participants, aged from 18 to 89 years, and constituting a wide range of ethnic and racial backgrounds.

They discovered that the smartphone readings had measurement precision and accuracy analogous to the high-cost FDA-approved hospital instruments.

According to the researchers, wider usage data related to at-home oxygen saturation levels, anonymized and widely disseminated, might also be useful for public health officials to evaluate disease prevalence in a community, and assist direct clinical resources, like the availability of hospital beds.

The researchers encourage more studies on a huge scale, with ultimate consideration of smartphone-based pulse oximetry turning out to be a new health care tool in the clinic and other places.

The co-authors of the study are senior author Florin Vaida, Samuel C. Pan, and Jonathan Gonzalez Garcia from UC San Diego; Mike Bernstein, Physio Monitor, LLC; and Craig A. Easson and Chung-Che Huang from Maxim Integrated.

The study was partially funded by the National Institutes of Health (grant R01MH110057-04S), Maxim Integrated, and Specialists in Global Health.

Journal Reference

Browne, S. H., et al. (2021) Smartphone Biosensor With App Meets FDA/ISO Standards for Clinical Pulse Oximetry and Can Be Reliably Used by a Wide Range of Patients. Chest.

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