Novel App Measures BP without Accessories

Developed at Michigan State University (MSU; East Lansing, USA), the new application, designed for the iPhone X, visually guides fingertip placement and actuation on both the front camera and screen in order to artificially increase the external pressure of the underlying transverse palmer arch artery. The app then measures both variable-amplitude blood volume oscillations via the camera, and applied pressure via the strain gauge array under the screen to compute BP from the measurements, similar to automatic cuff devices.

In a proof of concept test conducted in 18 volunteers, against both a finger cuff BP and a standard cuff device, the app yielded bias and precision errors of -4.0 and 11.4 mmHg for systolic BP, and -9.4 and 9.7 mmHg for diastolic BP, respectively; the errors were closer to the finger cuff device errors. According to the researchers, the study indicates that cuff-less and calibration-free BP monitoring may be feasible with many existing and forthcoming smartphones. The study was published on September 3, 2018, in Scientific Reports.

“By leveraging optical and force sensors already in smartphones for taking selfies and employing ‘peek and pop’, we've invented a practical tool to keep tabs on blood pressure,” said lead author Professor Ramakrishna Mukkamala, PhD, of the MSU electrical and computer engineering department. “Such ubiquitous blood pressure monitoring may improve hypertension awareness and control rates, and thereby help reduce the incidence of cardiovascular disease and mortality.”

The oscillometric method of measuring blood pressure involves occluding a major artery, typically the brachial artery in the arm with an external pneumatic cuff. When the pressure in the cuff is higher than the blood pressure inside the artery, the artery collapses. As the pressure in the external cuff is slowly decreased, blood begins to spurt through the artery, causing the famous Korotkoff sounds. The pressure measured in the cuff region when blood first passes through is an estimate of systolic pressure. The pressure measured when blood first starts to flow continuously is an estimate of diastolic pressure.

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