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Abstract

A method and apparatus for measuring blood pressure by measuring a photoplethysmographic (PPG) signal of a user with the arm in a raised position and in a lowered position and measuring the difference in timing between them, which represents a change in pulse transit time. The PPG signal is measured in the wrist of the user relative to the PPG signal in the finger of the user. A camera built into a mobile telephone may form a first optical sensor for measuring the PPG signal in the finger and an attached accessory camera, such as an infrared camera, or an optical sensor in a wrist-worn device to obtain the PPG signal in the wrist. Alternatively, a head-worn device may be used as a second optical sensor. Signal averaging based on the timing of the finger-originating PPG signal is used to average the waveforms in the wrist-originating PPG signal for arm-up and arm-down, and the timing difference is measured between the arm-up averaged waveform and arm-down averaged waveform. A calibration process is used to derive a relationship between the change in pulse transit time and the subjects blood pressure allowing a display of an estimate of the blood pressure of the subject on the screen of the mobile telephone.

First Claim