ADPD4100 Respiration Rate Monitoring

The ADPD4100 is listed as a featured product for Respiration Rate Monitoring on the following Analog Devices website:

https://www.analog.com/en/applications/markets/healthcare-pavilion-home/vital-signs-measurement/respiration-measurement.html

However, I cannot find much other information about how to perform respiration monitoring with the ADPD4100 on the Analog Devices website or elsewhere. 

Can I please get some guidance?

Are components besides the ADPD4100 needed for respiration rate monitoring? Is the AD5933 (which is also listed as a featured product) needed?

Are there any examples or figures for the circuits / programming needed available?

-Brian

Parents
  • +1
    •  Analog Employees 
    on Jun 18, 2021 12:31 PM

    Hi Brian,

    The ADPD4100 respiration measurement is based on impedance change of the chest during the respiration cycles.  A reference circuit can be found in Figure 5(a) in this article Multiparameter Vital Signs Monitoring Is Easier Than Ever Before | Analog Devices. In this circuit, the excitation is from GPIO2 and excitation current is applied to the body through the RC circuit (GPIO2-10k-1nF-electrodes/body-1nF-10k-GND). IN7 and IN8 form a differential pair to measure the voltage across the two electrodes (body). 

    The components needed for this design are the resistors and capacitors to form a path from the GPIO to ground for applying the excitation to the body.

    Regards,

    Glen B.

  • Thanks for the information, Glen!

    Follow up question - there are many options to select from for GPIO pin output (snippet of options for GPIOOUT1, ADPD4100 datasheet pg 87, shown below). Which of them would be used for respiration rate?

  • 0
    •  Analog Employees 
    on Jun 28, 2021 6:11 PM in reply to MX_bwuerstle

    Hi Brian,

    Subcutaneous fat is typically modeled as a capacitor (or a capacitor in parallel with a big resistor). Depending of the electrodes of choice, the skin-electrode interface has both resistive and capacitive components. To be able to stimulate the deep tissue, pulse as excitation waveform is easy to implement. For the impedance spectroscopy technology, the FFT analysis gives complete information -  the amplitude and the phase information of the data. Hence you can separate the resistive component and capacitive component. For FFT analysis, you would need an ASIC with the FFT engine (such as the AD5940 from ADI) or run the FFT as data processing.

    The example we provided doesn't require FFT. It can achieve decent respiration measurement though.

    Regards,

    Glen B.

  • Hi Glen,

    Hope you're doing well. Thanks for the sample config you posted. We tried out the sample config and reference circuit you've posted above for respiration rate (side note: we didn't include the circuit for ECG since you mentioned we can keep it or remove it). We tried this on EVAL-ADPD4100Z-PPG and EVAL-ADPDUCZ, but are facing issues and wanted your help.

    When we use the above config, nothing shows up on the graph on the Wavetool application and we also get an error when we press the stop sign (screenshots attached).

    After some debugging, we found that when we changed the 0x0107 register for pulse to a value below 64, a straight line appears on the graph. However, no changes show up on the line - it's just a straight line.

    What can the issue be? How can we get the correct respiratory rate?

    Thanks!

  • 0
    •  Analog Employees 
    on Jul 12, 2021 2:51 PM in reply to adpdcoder

    Hello -

    The EVAL-ADPD4100Z-PPG does not have the circuit for the respiration measurement. How did you modify your board to implement the respiration circuit? In the refer circuit and the example config, the IN7/IN8 pair are for bioimpedance-based respiration. If you use different input pair, the config needs to be changed as well.

    The register 0x0107 is for number of pulses as the SNR of the measurement is proportional to the square root of the number of pulses. The number of pulses should not be the source of the error you have.

    Regards,

    Glen B.

  • Hello Glen,

    Thank you for your quick response. I used the following circuit for sensing bioimpedance-based respiration. The passive components - R1, R2, R3, R4, C1, and C2 - and the electrodes are external to the EVAL-ADPD4100Z board.

    What kind of changes will I have to make to the config you provided above for the correct respiration sensing? My understanding is that, with the external circuitry and the appropriate config, bioimpedance-based respiration sensing should work with EVAL-ADPD4100Z. Is my understanding wrong?

    Thank you again!

  • 0
    •  Analog Employees 
    on Jul 12, 2021 5:51 PM in reply to adpdcoder

    Hello - 

    Some of the test points on the EVAL-ADPD4100Z-PPG board are not the pins of the ADPD4100 part. Please check Figure 11 on page. 8 of the EVAL-ADPD4100Z-PPG user guide

    EVAL-ADPD4100Z-PPG (Rev. 0) (analog.com)

    The test points IN7 and IN8 on the EVAL-ADPD4100Z-PPG is for connecting ECG electrodes with ECG circuit is already populated on the board. In addition, GPIO2 on the board is for control of ADXL362. Test point GPIO3 is the only one from the ADPD4100 pin. You would need to modify the board accordingly.

    Regards,

    Glen B. 

Reply
  • 0
    •  Analog Employees 
    on Jul 12, 2021 5:51 PM in reply to adpdcoder

    Hello - 

    Some of the test points on the EVAL-ADPD4100Z-PPG board are not the pins of the ADPD4100 part. Please check Figure 11 on page. 8 of the EVAL-ADPD4100Z-PPG user guide

    EVAL-ADPD4100Z-PPG (Rev. 0) (analog.com)

    The test points IN7 and IN8 on the EVAL-ADPD4100Z-PPG is for connecting ECG electrodes with ECG circuit is already populated on the board. In addition, GPIO2 on the board is for control of ADXL362. Test point GPIO3 is the only one from the ADPD4100 pin. You would need to modify the board accordingly.

    Regards,

    Glen B. 

Children