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Safety of the ADS1292r

Krzysztof Sitko
Prodigy 130 points
Other Parts Discussed in Thread: ADS1292R

Hi,

I am looking for data or documentation that can help establish the ethicacy and safety of the ADS1292r for use in a human study. Specifically I'm looking for any information which can show that the right leg drive (RLD) feature as well as the impedance based respiration monitoring of ADS1292r are safe for humans.

Thanks,

K

  • 0
    TI__Mastermind 38745 points
    Hey Krzysztof,

    Unfortunately I am not aware of any documentation that specifically qualifies this particular product for medical use. We did have widely accepted medical standards in mind when designing the chip, but most patient protection mechanisms that qualify any end equipment for diagnostic use are system level designs rather than being inherent in the chip.

    I understand your concern about both the RLD amplifier and the respiration measurement circuitry as they both involve sending signals to the body. For the RLD amplifier, it's output voltage will typically be centered around mid analog supply and it has a typical short circuit current of 1 mA. A medical application might protect the patient from unsafe currents by placing a current limiting resistor in series between the output of the amplifier and the patient.

    The RESP_MODP and RESP_MODN pins will alternate between VREF and AVSS at either 32 kHz or 64 kHz (AC current likely has a different standard than DC current). The short circuit current that can appear from the modulation block is 100 uA. That being said, we recommend AC coupling the modulator outputs as well as putting patient protection resistors in series with the electrodes.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 130 points
    Brian,

    I understand if there is no documentation for medical use, but surely there must be something that at least documents the 1 mA figure as well as the 100uA figures. If not, then would you have any recommendations on how to capture the possible worse case, in order to document the maximum potential amperage that someone could be exposed to?

    Our current implementation uses .1uF cap connected to each RESP inputs as well as a 2200pF cap and 40K resister in series to between the .1uF cap and the RESSP_MOD pin. The RLD out pin has a 100K resistor in series with the patient. According to the AAMI/ANSI ES1 standard, the safe root mean square current is 10 μA from 0 to 1kHz and increases linearly from 1 kHz to 100 khz. Being able to document our adherence to the standard would allow us to have a successful IRB application.

    Thanks,
    K
  • 0 in reply to Krzysztof Sitko
    TI__Mastermind 38745 points
    Hey Krzysztof,

    The short circuit currents I cited were taken from the Electrical Characteristics table of the ADS1292R datasheet (both on page 4). For testing of the current coming out of the RLD amplifier, I could imagine a scenario in which the voltage across that 100 kOhm resistor was studied under a variety of scenarios possible for your application. As for the current from the RESP_MOD pins with your current setup, you could study the voltage across a few different impedance values simulating the body impedance and the electrode contact impedance and make sure the voltage never exceeds the threshold even in the worst case. Do those sound like workable test setups?

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 130 points
    Brian,

    They do sound like fine test setups. Do you have any recommendations as to methods to create different scenarios for RLD testing? I'd imagine that ideally to test the RLD amp, different levels of common mode would be fed into the ECG inputs, with different RLD amplifications. I'm just not entirely certain how to generate different controllable levels of common mode. The RESP_MOD measurement seems simple enough to simulate using a resistor in parallel with a resistor and capacitor in series.

    Thanks,
    K
  • 0 in reply to Krzysztof Sitko
    TI__Mastermind 38745 points
    Hey Krzysztof,

    You can generate different output voltage levels on the RLD amplifier by sweeping the voltage at the RLDIN/RDLREF pin and clearing the RLDREF_INT bit in the RESP2 register. If you look at Figure 52 in the datasheet, you can see that the voltage on that pin will set the DC bias of the RLD output signal.

    However, I'm not sure if input common mode will be as important is RL electrode contact impedance. The input common mode will be set by the RLD output and I don't anticipate the current changing much with different RLD output voltage levels. I see the value in this measurement coming from how different contact impedance affects how effectively the RLD amplifier can regulate the input common mode and how much current will be required to regulate that voltage. If you had a way of simulating different contact impedance that could be within the range of what your application could see, that could be a worthwhile test.

    Regards,
    Brian Pisani