I want to design a circuit that I can use to monitor heartbeats. I want to be able to strap a device on ones wrist or neck and be able to pick up the heartbeat. Is anyone aware of the type of sensors that are used in medical applications to measure heartbeats. For my application the sensor has to be very sensitive as contact with the body may be minimal.
The obvious choices are an infra red blood flow detector or a microphone.
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This sounds like an cheapo ebay product type of thing. (Terrorist dead man switch? As seen in the movies? :) )
But as a E project I can take a guess as to the design.. It'll have to be confirmed by other posters.. The sensors are not really sensors...just electrodes.. The 2 electrodes connect to high gain high CMRR amplifier. (Basic description.) I'm guessing without a google search.... The amp picks up the brain trigger signal. This signal propagates outward to the skin due to the body being a impedance network with electrically carrying nerves. D from BC
On a sunny day (Wed, 31 Jan 2007 18:35:03 GMT) it happened D from BC wrote in :
You must have really strong brain waves ;-)
the typical simple heartbeat monitor clips on a finger and contains an infra-red sensor. you see these on exercise equipment as well as in hospitals. i would assume that the wrist or neck would work more or less just as well as a finger.
See....
This circuit was used on an exercise bicycle around 1975.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
It's from too much lossy thinking.. My brain waves are so strong that my head overheats from I^2*R losses. I might need to put heat sink on my head.. :)
I didn't mean the electrodes go on the head but across the heart to pick up the brain trigger signal. I don't know the dominant signal... Could be the nerve to the heart.. Could be the heart itself or both.
D from BC
You can use optical: Red-LEDs through earlobe electrical: Measure three points get signal through differential audio: Microphone
I think the simplest way is to buy an chest "pulse belt" and receive the signal into your project.
On a sunny day (Wed, 31 Jan 2007 20:14:11 GMT) it happened D from BC wrote in :
My recent understanding is that the heart triggers itself (an internal feedback loop). I dunno if there is a signal from the brain too, but things like adrealine do affect the speed it runs. But I am no doctor, so...
I believe that's right... I'm thinking about it more.. IIRC I saw a documentary in which heart cells under the microscope beat.. Also...I've never heard of a head injury so severe that it stopped the heart.. Without a google search..Maybe the heart still puts out a voltage detectable on the skin. What were all those chest wires for in those old hospital movies??
I did see that optical thingy on the finger on this weeks episode of House.. Optical device was mentioned by other posters.
Guessing at it's construction: Small view angle LED and phototransistor. Both parts can be SMD. D from BC
On a sunny day (Wed, 31 Jan 2007 22:20:37 GMT) it happened D from BC wrote in :>IIRC I saw a documentary in which heart cells under the microscope
I dunno, Hollywood also had Frankenstein come alive ;-) But I had a heart test with wires too. Anyways I looked it up, indeed the heart is 'auto',
Yes I downloaded Jim's diagram, seems fun.
Or you can just feel your pulse..... I have been in danger situations where for a long time I could just feel my heartbeat really strong, no need for electronics. Emergency landing.... hehe
The myogenic (muscle de/polarization signal) dwarfs neural inputs as measured from a distance - that is, from the skin. Similarly, active skeletal muscles have potentials that can make detection of the heartbeat difficult.
When disease or other malady removes neural input, the heart can "free run" in its absence. Unfortunately, this 'default' rate is slower than what the CNS would require (and less well controlled for the body's metabolic needs).
-f
These can work well indoors. If there's sunlight (particularly if the level of sunlight varies) these can have problems.
See below.
Lots of artifacts here too unless the person is quiescent.
Agreed. But the user wanted to design his/her own. It's definitely non-trivial if you need robust results while the individual is exercising. A fun challenge! BE CAREFUL whenever attaching wires to your body!!
-f
optical thing measures blood oxygen (oxygenated haemoglobin is red)
Bye. Jasen
Does that mean there's two types of finger clips? One for heartbeat and one for blood 02? D from BC
Yes.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
The oxygen level in thhe capillaries varies as the blood is pumped - at the same rate as the heartbeat.
Bye. Jasen
No, heartbeat measurement is a collateral effect from pulsoxymetry. Last one uses light from 2 wavelength on the top and the bottom of the puls wave to calculate the partial oxigen saturation SpO2. For only heartbeat detection you only need one wavelenth. but every SpO2 Fingerclip can measure heartbeat too.
Marte
No, the variation of the light does depend on the variation og blood pressure in the arterial system. The capillar and venous blood deos make very very little variation in thickness Therefor only the atrial blood is measured by pulseoxymetry. It is based on measurements from (at least) 2 wavelenth at 2 different times of pulsating. By subtracting the two measurements only the part of thickness variation due to blood pressure variance in the arteria is left.
Marte
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