Research ArticleCARDIOVASCULAR HEALTH

Smartphone-based blood pressure monitoring via the oscillometric finger-pressing method

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Science Translational Medicine  07 Mar 2018:
Vol. 10, Issue 431, eaap8674
DOI: 10.1126/scitranslmed.aap8674
  • Fig. 1 From conventional cuff-based blood pressure measurement to cuff-less BP monitoring using a smartphone.

    (A) Image of a conventional cuff-based oscillometric device and diagram of representative blood pressure (BP) measurement. (B) Schematic diagrams of the proposed oscillometric finger-pressing method for cuff-less BP monitoring using a smartphone, in which the user serves as the actuator instead of the cuff, to vary the external pressure of the transverse palmar arch artery by finger pressing, whereas the phone serves as the sensor to measure blood volume oscillations and applied pressure similar to a cuff, provides a visual display of the applied finger pressure over time to guide the actuation (C), and computes BP similar to a cuff (D). Image of finger anatomy adapted from (35).

  • Fig. 2 Smartphone-based device for real-time monitoring of BP via the oscillometric finger-pressing method.

    (A) Photograph of the smartphone-based device. A three-dimensional (3D)–printed case was affixed to the back of a smartphone. The case includes visual line indicators to guide finger placement and houses photoplethysmography (PPG) and force sensors along with other circuitry to acquire and transmit the finger blood volume oscillation and applied finger pressure measurements to the phone. (B) Photograph of an application running on the phone to provide visual guidance for the finger actuation and display the finger measurements. Photographs illustrating that a user places her/his finger on the sensor according to the line indicators (C), rests the same finger on the surface of the case to apply force in the normal direction with respect to the case (D), and holds the device at the same height as the heart (E).

  • Fig. 3 Device usability results (n = 30 new users).

    Histograms of the (A) number of practice trials needed to learn the requisite finger actuation for all users; (B) percentage of BP measurements versus try again messages outputted by the device over all users; (C) number of try again messages per user; and (D) reasons for the try again messages.

  • Fig. 4 Device accuracy results (n = 32 users).

    Correlation and Bland-Altman plots comparing the brachial BP measurements from the smartphone-based device [oscillometric finger-pressing method (A to D)] and the brachial BP measurements from a finger cuff device [volume-clamp method (E to H)], with each relative to a standard arm cuff device. The filled circles are data points from new users holding both finger devices at the same height as the heart, whereas the unfilled circles are data points from experienced users holding both finger devices below the heart to raise the BP. r, correlation coefficient; μ, bias error (mean of the errors); σ, precision error (SD of the errors); solid line in Bland-Altman plots, bias error; dashed lines in Bland-Altman plots, limits of agreement.

  • Fig. 5 Smartphone-based device hardware.

    Schematic diagram of the PPG and force sensor unit and photograph of this unit, data acquisition and transmission circuitry, and power supply housed within the 3D-printed case affixed to the back of the phone. IR, infrared; LED, light-emitting diode; PD, photodetector; ADC, analog-to-digital converter; BLE, Bluetooth low energy.

  • Fig. 6 Smartphone-based device software.

    Flowchart of the smartphone application and important equations for computing BP running on the phone wherein the input is the measured blood volume waveform and applied pressure and the output is brachial BP values or a try again message. The blue box indicates the beginning of the flowchart, whereas the red boxes indicate the two possible ends of the flowchart. The plot illustrates a parametric model of the oscillogram [blood volume oscillation amplitude (y) as a function of the applied finger pressure (x)] from which BP is computed. BP computation details are provided in the “Software” subsection of Materials and Methods.

  • Fig. 7 Human study design for device testing.

    Photographs of the three BP measurement devices for study: (A) the smartphone-based device, (B) a standard automatic arm cuff device (the reference device), and (C) a finger cuff device (a competing device). (D) Diagram of the experimental protocol for BP measurement using the devices shown in (A) to (C). The protocol included a learning phase for new users to become familiar with the smartphone-based device and a data collection phase involving a measurement with the reference device, two to four measurements with the smartphone-based device, 1 min of measurement with the finger cuff device, and a final measurement with the reference device. Study details are provided in the “Device testing: Formal human study” subsection of Materials and Methods.

Supplementary Materials

  • Supplementary Material for:

    Smartphone-based blood pressure monitoring via the oscillometric finger-pressing method

    Anand Chandrasekhar, Chang-Sei Kim, Mohammed Naji, Keerthana Natarajan, Jin-Oh Hahn, Ramakrishna Mukkamala*

    *Corresponding author. Email: rama{at}egr.msu.edu

    Published 7 March 2018, Sci. Transl. Med. 10, eaap8674 (2018)
    DOI: 10.1126/scitranslmed.aap8674

    This PDF file includes:

    • Table S1. Anthropomorphic information, number of practice trials, and all BP measurements per subject.
    • Legend for movie S1

    [Download PDF]

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Video demonstration of the smartphone-based BP monitoring device.

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