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Re: Recovering one irregular signal in the presence of another stronger one--*in utero* pulse ox

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Christian Gollwitzer wrote:
> Am 19.05.21 um 00:31 schrieb Phil Hobbs:
>> I'm working on a completely noninvasive sensor for fetal blood oxygen, 
>> using optical sensing through the mom's abdomen.  It's a very low SNR 
>> measurement on account of all the attenuation.
>>
>> The mom's heartbeat modulates her pulse-ox signal, which is much 
>> stronger than the fetus's on account of the scattering and absorption 
>> in maternal tissue.
>>
>> The data are several time series.  The main issue is the variability 
>> of both pulses, which smear out the spectra and therefore knock the 
>> peak heights way down towards the noise.  There are weak 
>> multiplicative effects between maternal and fetal signals, as you'd 
>> expect.
> 
> How about using a second channel to detect the mother's heartbeat? For 
> example an ECG channel? It's not perfectly synchronized, though, the 
> delay between ECG and pulse oxymetry is influenced by the blood 
> pressure. So it only works if the blood pressure is constant.
> 
>      Christian
> 
> 

Thanks.  We can isolate the mom's pulse-ox signal, and as Eric 
suggested, it's possible to use that for adaptive noise cancellation 
except that (as far as we gather from the literature) it doesn't work 
well enough for a technological measurement.  We can get the mom's pulse 
rate vs. time from that, which will be a big help.

We really need to resample at the child's pulse rate in order to 
concentrate its signal into as narrow a bandwidth as possible to improve 
the SNR.

Folks have been trying this sort of thing since the late '90s without 
producing a commercial instrument.  Despite the optimistic tone of all 
scientific papers, this leads me to suppose that although an expert can 
make it work once or twice, getting it to work many times in non-expert 
hands is hard.

There's also a lot of physiological variability, including thickness of 
skin and subcutaneous fat, presentation (normal, breech, reverse, etc.)

When you're working with 150-dB path loss, a 2% change will lose you 
half your signal. :(

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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Recovering one irregular signal in the presence of another stronger one--*in utero* pulse ox Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2021-05-18 18:31 -0400
  Re: Recovering one irregular signal in the presence of another stronger one--*in utero* pulse ox theman@ericjacobsen.org (Eric Jacobsen) - 2021-05-18 22:50 +0000
    Re: Recovering one irregular signal in the presence of another stronger one--*in utero* pulse ox Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2021-05-18 19:16 -0400
  Re: Recovering one irregular signal in the presence of another stronger one--*in utero* pulse ox Christian Gollwitzer <auriocus@gmx.de> - 2021-05-19 07:37 +0200
    Re: Recovering one irregular signal in the presence of another stronger one--*in utero* pulse ox Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2021-05-19 11:31 -0400
  Re: Recovering one irregular signal in the presence of another stronger one--*in utero* pulse ox Les Cargill <lcargil99@gmail.com> - 2021-05-30 21:14 -0500
    Re: Recovering one irregular signal in the presence of another stronger one--*in utero* pulse ox Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2021-06-02 12:39 -0400

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