pascalian

hello,
i need to measure tension and blood pluse with pic
but i can not find pressure sensor that has low prince and enough response
is there anybody know it?

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stevez

I have an electronic blood pressure measuring device - Omron I think. The cuff contains no sensor and is connected to the monitor via a single flexible hose.

My guess is that there is a pressure sensor inside the monitor. The sensor would have to monitor a pressure that exceeds the highest expected BP by 20 mm or so. Many of the old mercury or gage types stopped at 300 mm so my guess would be to find a sensor in that range. I presume that the monitor looks for subtle pulses that give the same indication as the stethoscope does with the manual method of measurement.

I can explain how traditional blood pressure measurement is done if that helps.

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stevez

tansis

Measure the pulse by another means, the pressure sensor on the cuff will never be sensitive enough...
here is one idea using infra red , another way could be to use a microphone as an electronic stethoscope.
just had a thought , can blood oxygen level can be monitored by a similiar method ???

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bmcculla

Standard blood pressure measuring machines use a microphone to detect blood flow at different pressures of the cuff.

tansis: you can measure blood oxygen content with infrared leds and detectors. you use two different wavelengths. The transmision/ reflection of the first wavelength is unaffected by oxygenation of the blood, its only affected by blood voulume. The second wavelength is affected by blood oxygenation. The ration of the two give oxygenation/volume.

Brent

Roff

My digital blood pressure gauge is about 10 years old, and it measures pulse rate from the cuff. I assume it uses the same sensor for BP and rate.

tansis

Hello Ron H,
I stand corrected it would appear, have you opened it up yet ?

Roff

I guess I'm not that curious. I will open things to repair them, but rarely to see what makes them tick.

bmcculla

Pulse isn't that hard to measure with a microphone. When you take a BP measurement manualy you gradually loosen the cuff until you hear a hissing sound which means that the blood is getting through. The hissing isn't constant though. You will hear a hiss each beat of the heart. All you need to do is count the hisses and detirmine the Heart rate from that.

stevez

I took a minute to verify my understanding. I've used the old cuff, meter and stethoscope method to take my own BP a zillion times and recalled seeing the meter needle "pulse" as I went from systolic to diastolic. I found a brief description of the oscillometric method that takes advantage of this:

Not quite a quote: oscillometric relies on variations in arterial wall movement beneath an occulding cuff.

I concluded from the rest of the description that the arterial wall movement is what causes the pressure to vary with pulse (therefore the needle "pulsing") and this pressure variation is registered via a pressure sensor. Well established algorithms are used to make sense of the appearance, disappearance and frequency of the pulses.

Apparently this "oscillometric" method is common in home BP monitoring devices.

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stevez