Pressure sensors

[nightwish3r]

Hi guys,

I need help with a med school project:
a) Needed to inflate a blood pressure cuff (those velcro things you wrap around your arm) to a pressure of 60mm Hg

and then stop it.
b) Detect the presence of any pulse which are over 60mm Hg, preferably with the output signal going to a bulb or

something that lights up when there is a satisfactory pulse (above 60)

How exactly would I go about doing it? I'd really really appreciate your help and a little step by step guidance,

it'd be a huge help!!

thanks

 

[Hayato]

There is no way to inflate anything, on normal conditions, to 60 mmHg. 60 mmHg is below the sea-level atmospheric pressure = 760 mmHg.

 

[KMoffett]

Me thinks nightwish3 means 60mmHg above ambient, as blood pressure was stated. Did your doctor tell you your BP was OK at "880 over 840"?

Ken

 

[KMoffett]

a) Needed to inflate a blood pressure cuff (those velcro things you wrap around your arm) to a pressure of 60mm Hg and then stop it.

Do you need to do this automatically...pressurized air source/pressure sensor/switch/pneumatic valve...or will you be doing this manually?

b) Detect the presence of any pulse which are over 60mm Hg, preferably with the output signal going to a bulb or something that lights up when there is a satisfactory pulse (above 60)

There are a couple ways to detect a pulse in this type of system. One is acoustic...an amplified microphone...similar to the standard stethoscope method. The other is to sense the variations in cuff pressure, due to the pulse, after the cuff inflation is stopped.

What are your abilities in electronic circuits/assembly?

Ken

 

[bobledoux]

Retail blood pressure units often display the pulse on the display. It should be simple to take that output and display it on an LED.

Some of these units also have battery powered air pumps. They typically inflate, look for pulse, and inflate higher if necessary. It might be possible to limit the pump to 60mm hg as you seek.

Maybe it would be easier starting with such a unit rather than starting from scratch.

 

[Hayato]

Me thinks nightwish3 means 60mmHg above ambient, as blood pressure was stated. Did your doctor tell you your BP was OK at "880 over 840"?

Ken

The blood is isolated from the ambient, inside the circulatory system, hermetically sealed, so it's valid to say that the blood pressure is 120 over 80.

 

[KMoffett]

The blood is isolated from the ambient, inside the circulatory system, hermetically sealed, so it's valid to say that the blood pressure is 120 over 80.

Of course! I was being facetious...thus my response. Actually the blood is not isolated from ambient, it's "housed" inside a very flexible container, so is always exposed to the vagaries of the atmospheric pressure. Blood pressure is always stated relative to the ambient pressure of the environment.

But, that doesn't help nightwish3r.

As bobledoux said there commercial units available over the counter.

nightwish3r, can you detail the requirements of your assigned(?) project?


Ken

 

[Hayato]

Of course! I was being facetious...thus my response. Actually the blood is not isolated from ambient, it's "housed" inside a very flexible container, so is always exposed to the vagaries of the atmospheric pressure. Blood pressure is always stated relative to the ambient pressure of the environment.

But, that doesn't help nightwish3r.

As bobledoux said there commercial units available over the counter.

nightwish3r, can you detail the requirements of your assigned(?) project?


Ken

Agreed!


nightwish3r, there isn't a real way to measure the blood pressure itself, unless you insert a pressure meter inside the patient's veins.

As far I remember, to take ones pressure, I used to insuflate the cuff until it gets to 180 mmHg ~ 220 mmHg, and then, I'd desulfflate it until I hear the heart beating through the stethoscope (placed under the cuff), this would be the systolic pressure. When the heart beats were gone then it would be the diastolic pressure.

You'll have to use pressure sensors inside the cuff and a microphone or some kind of "ECG sensor", to sense the heart beats.

 

[nightwish3r]

Guys thank u so much for the responses,

a couple of details:

the system does need to be automated - its for use on training dummies, where an artificial 'pulse' of >60mm Hg needs to be detected (during CPR compressions).

So I thought I'd inflate the cuff to 60 - hence 'blocking' any pulses under that pressure and thus only detecting pulses >60. That said however, is there anyway to detect the pulses without using the cuff - say a vibration sensor or something?

The problems I was having was:

a) how to get the pump to automatically inflate the cuff to 60mm of Hg and stop there
b) the type of sensor to use to detect the pulses - vibration sensors would be a little difficulate since ambient vibrations would interfere.. perhaps an arrangement to cancel ambient noise?

again very honestly and sincerely your help is greatly appreciated guys!! thanks a million

 

[KMoffett]

.....the system does need to be automated - its for use on training dummies, where an artificial 'pulse' of >60mm Hg needs to be detected (during CPR compressions).....

Are you saying that the dummy has a artificial artery in the arm that has a pulse, and the peak pulse pressure of which is controllable by an operator?

Ken

 

[nightwish3r]

it has the artificial artery, and the pulses are indeed controlled by the operator - though by means of chest compressions. So if the compression is hard enough it'll generate a pulse of >60.

 

[KMoffett]

Is the monitor you are seeking, for a second student to monitor the "patient" while the first student does the compressions, or for the instructor to monitor the compressing student remotely?

I used to do restorative surgery on ResusiAnnie.

Ken

 

[arhi]

nightwish3r,

You can find very precise (1.5Pa precision, that's ~0.011mmHg) pressure sensors (SCP1000 for e.g.). Connect it with the air pump to the micro controller and you can easily have cuff pressurised to needed pressure. I'm not sure if you might use the second one to measure ambient pressure but from what I recon the ambient pressure is already influencing the "soft" cuff hence single pressure sensor is enough. Note that SCP1000 is ~50$, depending on the precision you need you might use a mechanical sensor (like the one used in washing machine) that you calibrate for the desired value, you can also make your own sensor with plastic tube, some salt water and some electrodes .. even easier with Hg but that stuff is too poisons to be plaid with...

With regards to detecting the pulse, if you use precise enough sensor that's all you need as you can monitor the small changes in the calf pressure. I'v seen this done in those "pressure monitors" that you attach to your finger. On the other hand, you can put a small piezo between calf and the arm and detect the impulses from the piezo (well you will have to amplify them first).

 

[nightwish3r]

nightwish3r,

You can find very precise (1.5Pa precision, that's ~0.011mmHg) pressure sensors (SCP1000 for e.g.). Connect it with the air pump to the micro controller and you can easily have cuff pressurised to needed pressure. I'm not sure if you might use the second one to measure ambient pressure but from what I recon the ambient pressure is already influencing the "soft" cuff hence single pressure sensor is enough. Note that SCP1000 is ~50$, depending on the precision you need you might use a mechanical sensor (like the one used in washing machine) that you calibrate for the desired value, you can also make your own sensor with plastic tube, some salt water and some electrodes .. even easier with Hg but that stuff is too poisons to be plaid with...

With regards to detecting the pulse, if you use precise enough sensor that's all you need as you can monitor the small changes in the calf pressure. I'v seen this done in those "pressure monitors" that you attach to your finger. On the other hand, you can put a small piezo between calf and the arm and detect the impulses from the piezo (well you will have to amplify them first).

Thanks mate, and I apologise for the simple question, but how would I be able to stop the motor at a certain pressure?
And as far the precision goes, I simply need a binary signal - to see if pulse is there not, the value is immaterial.. long as its 'escaping' the cuff of 60mmHg, that means the pulse will be above that.


And Ken yes it is for an instructor to monitor
Though not remotely, they can be standing right next to the student

 

[KMoffett]

Is it possible to tap into the "artery", inside the "patient"? If so, it would be possible to run a piece of tubing to an electronic pressure transducer. Take the output of the transducer into an adjustable voltage comparator. Have the output of the comparator drive an LED. Every time, and as long as the pressure exceeded 60 mmHg, the LED would turn on. This can be battery powered.

If one could find a low range, low displacement, mechanical, adjustable, pressure switch, it could be done with the switch, a battery, a resistor, and an LED. I'll have to look into that.

Ken

 

[duffy]

Those fingertip sensors are IR reflective sensors. Your skin is transparent to IR, changes reflectivity with each pulse.

 

[arhi]

but how would I be able to stop the motor at a certain pressure?

If you use digital sensor like SCP1000 then you need to hook up the sensor to the micro controller and control the pump from micro controller too. Simple program would then compare the value from the sensor and control the motor accordingly.

If you go with mechanical pressure sensors, they mostly act like switches so you just hook up the motor trough the sensor and when right pressure is achieved the sensor will detach power from the pump.

And as far the precision goes, I simply need a binary signal - to see if pulse is there not, the value is immaterial.. long as its 'escaping' the cuff of 60mmHg, that means the pulse will be above that.

With regards to precision, I was referring to the precision of pressure inside the cuff, and that differs from sensor to sensor (SCP1000 will give you 1.5Pa precision which is few hundred times more then you need, analog sensor from washing machine will probably be in range of few mmHg ...)... regarding the "pulse detection", that's completely different story. You can detect pulse from the mechanical arm using pressure distortion or using acoustics...

For pressure distortion you can use sensor to detect the variations in pressure (measure them using micro controller) or you can use some pressure to electricity transducer like piezoelectric disk (the one like in buzzers, wrist watches, singing telegrams ....) that will generate small electrical pulses when pressure is applied (you place it between the arm and the cuff).

For acustics, you have to mount a microphone and "detect the sound of the pulse"... I have no idea how to do that but I'm sure audioguru knows

 

[nightwish3r]

sincere thanks guys!! Truly truly amazed at the time and thought people had put in to help someone like me out

being a total newbie to electronics may I (meekly) ask if someone could recommend a couple of websites or resource materials where I could learn (least the theory of what needs to be done) the nitty gritty details.. i.e. how to actually house the sensor.. I have a vague idea it'll need to be integrated into a circuit, some sort of power supply, perhaps soldering etc..

pretty much just point me in the right direction so to speak..
thanks again!

 

[duffy]

Jeezis, man - Google?
**broken link removed**

 

[nightwish3r]

!!!!