Heartbeat Monitor/Detector

[[email protected]]

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.

 

[Homer J Simpson]

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.

--
..
..
..
..
..
..
..
..

 

[D from BC]

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.

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

 

[Jan Panteltje]

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.

You must have really strong brain waves ;-)

 

[andrew.barthle]

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 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.

 

[Jim Thompson]

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....

http://analog-innovations.com/SED/Earpulse.pdf

This circuit was used on an exercise bicycle around 1975.

...Jim Thompson

 

[D from BC]

You must have really strong brain waves ;-)

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

 

[[email protected]]

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.

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.

 

[Jan Panteltje]

You must have really strong brain waves ;-)

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

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...

 

[D from BC]

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

 

[Jan Panteltje]

On a sunny day (Wed, 31 Jan 2007 22:20:37 GMT) it happened D from BC

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 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',
http://en.wikipedia.org/wiki/Heart_rate
but there is also a nerve from the brain:
http://en.wikipedia.org/wiki/Vagus_nerve
Just as in electronics things get more complicated the more you look.

I did see that optical thingy on the finger on this weeks episode of
House..
Optical device was mentioned by other posters.

Yes I downloaded Jim's diagram, seems fun.

Guessing at it's construction:
Small view angle LED and phototransistor. Both parts can be SMD.
D from BC

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

 

[Frank Miles]

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.

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...

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
--

 

[Frank Miles]

You can use optical: Red-LEDs through earlobe

These can work well indoors. If there's sunlight (particularly if
the level of sunlight varies) these can have problems.

electrical: Measure three points get signal through differential

See below.

audio: Microphone

Lots of artifacts here too unless the person is quiescent.

I think the simplest way is to buy an chest "pulse belt" and receive the
signal into your project.

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
--

 

[jasen]

I did see that optical thingy on the finger on this weeks episode of
House.. Optical device was mentioned by other posters.

optical thing measures blood oxygen (oxygenated haemoglobin is red)

Bye.
Jasen

 

[D from BC]

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

 

[Jim Thompson]

Does that mean there's two types of finger clips? One for heartbeat
and one for blood 02?
D from BC

Yes.

...Jim Thompson

 

[jasen]

Does that mean there's two types of finger clips? One for heartbeat
and one for blood 02?
D from BC

The oxygen level in thhe capillaries varies as the blood is pumped -
at the same rate as the heartbeat.

Bye.
Jasen

 

[Marte Schwarz]

Does that mean there's two types of finger clips? One for heartbeat

Yes.

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

 

[Marte Schwarz]

The oxygen level in thhe capillaries varies as the blood is pumped -

at the same rate as the heartbeat.

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