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  • Author Author: fustini
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Biosensor crunch time

fustini

Our biosensor array team worked late into the night on Saturday at Pumping Station: One.  With the hackerspace challenge build deadline on Tuesday night, it's definately crunch time!

 

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Thankfully we've got a nice array of working sensors (in the order of signal speed):

 

  • EKG
  • Pulse oximeter
  • GSR (Galvanic Skin Response)
  • CO2
  • Temperature

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Dan yet again played the role of test subject:

 

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The QRD1114QRD1114 sensor from SparkFun contains an IR LED and a compatible phototransistor.  It dectects pulse via the change in the amount of infrared light reflected by finger as blood pumps through it.

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We observed a great correlation between EKG and pulse oximetry signals:

image

 

Cheers,

Drew

Parents

  • Hi Drew,

      ECG and PPG (Photoplethysmograph) signals are very highly correlated. Consider your heart like an electric pump. ECG talks about the armature current and PPG talks about the pumping action. PPG is also correlated to the pressure at which the blood has been pushed through the blood vessels. Algorithms used to calculate the BP using cuffless monitors use this correlation.

    Ventricular Depolarization happens -> ventricles contracts -> when the pressure increases more than 120mmhg -> aortic valve opens -> bloods gets squeezed out from the chamber -> it travels through the vessels and reaches you finger tip where you are measuring the PPG.

    calculate - pulse transit time (PTT). This will be proportional to the pressure (or pulse wave velocity). But we are all different and we do have slightly different anatomy. Our blood vessel thickness and elasticity is different. This is a variable parameter in the BP calculation. So we have to perform calibrations with different readings and finally make a regressive model to calculate the BP. (Blood vessels looses its elastic property over time so calibrations is required periodically)

     

    Regards,

    Aswin

Comment

  • Hi Drew,

      ECG and PPG (Photoplethysmograph) signals are very highly correlated. Consider your heart like an electric pump. ECG talks about the armature current and PPG talks about the pumping action. PPG is also correlated to the pressure at which the blood has been pushed through the blood vessels. Algorithms used to calculate the BP using cuffless monitors use this correlation.

    Ventricular Depolarization happens -> ventricles contracts -> when the pressure increases more than 120mmhg -> aortic valve opens -> bloods gets squeezed out from the chamber -> it travels through the vessels and reaches you finger tip where you are measuring the PPG.

    calculate - pulse transit time (PTT). This will be proportional to the pressure (or pulse wave velocity). But we are all different and we do have slightly different anatomy. Our blood vessel thickness and elasticity is different. This is a variable parameter in the BP calculation. So we have to perform calibrations with different readings and finally make a regressive model to calculate the BP. (Blood vessels looses its elastic property over time so calibrations is required periodically)

     

    Regards,

    Aswin

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