Hi there!
In this video, we’re going to
be talking about a medical device.
Now, I am not a healthcare professional of any sort and
have absolutely
no qualifications to be giving medical advice whatsoever.
And so, I won’t.
This video, like nearly all of mine, is borne from simple curiosity about how something works.
My goal is to show you an example of
how everyday technologies can be used in clever
ways which improve our lives,
not to make suggestions on how to do so.
To that end, I’ll be explaining what the device does and how it works, but not how
- or even whether -
it should be used in any given situation.
And with that, let’s continue.
If you’ve ever made an unplanned visit to
a hospital, you might have had this happen to you;
someone appears with a clip-like device,
puts it around your finger, and it lights up with a couple of numbers.
That device was a pulse oximeter,
or oxy-meter if you want to say it that way,
and it measures your
blood’s oxygen saturation as a percentage.
This serves as a quick-but-limited snapshot
of how well your respiratory system is functioning.
I’ve got one right here, and simply by pressing
this button and then sticking my finger into it,
it tells me my heartrate and my oxygen saturation
in moments, and completely noninvasively.
Now, if you know a thing or two about blood,
you’ll probably know that in general
it should be inside your body, and not outside
of it.
Usually to analyze something about your blood
you’ll need to get a sample of
it through means of various unpleasantness,
but this device manages to do without that.
How?
Well, with a sensor.
And a very, very ordinary
one at that.
So first, what is a sensor?
(or, as they say in Star Trek the Motion Picture,
a Sensore)
That’s a surprisingly complicated question.
Our bodies are filled with sensors,
like the light sensors in our eyes,
the temperature and pressure sensors in our skin,
or the pressure
sensors in our ears.
"Wait," you ask, "pressure sensors? Don’t you mean sound sensors?"
No, and that’s precisely the point.
A sensor is on a very low level something that reacts to a change in its environment or stimulation.
But it’s how we interpret that change that makes a useful sensor.
For example, our ears
detect rapid changes in air pressure,
but that alone isn’t sound.
It's the way that
our brains interpret that change that produces
the sensation we call sound.
Similarly, the photodetectors in our eyes simply send stimulation to the brain.
It’s up to our visual cortex
to synthesize that stimulation into a useful image.
Moving into the artificial realm, our human-made
sensors work in essentially the same fashion.
For example, take a thermistor. Its electrical
resistance changes depending on its temperature.
That by itself isn’t useful to us, but if
we study how that change occurs,
and learn the correlation between a given resistance
and a given temperature,
we can measure its resistance in order to determine its temperature.
In that way, we can design a temperature sensor using a thermistor.
A pulse oximeter is one of countless examples
where we use a simple electrical device
as a means to determine… something.
In this case, we use light.
If you take a look inside where you put your finger you’ll find a little blinking LED.
As your finger approaches it it lights up solid.
Now look on the other
side and you’ll see a photodiode opposite the LED.
Your finger goes between the LED
and that photodiode,
and the oximeter shines light through your finger.
If you were ever a child
(which, you were)
you’ll have discovered that your skin is
actually quite translucent, and you can shine
light through your thinner parts like fingers
or earlobes.
It comes out red on the other
side because -
BLOOD!
[said all spookily]
And that of course means
you’re shining light through your blood,
and it’s absorbing some of that light.
And because scientists can’t help themselves
from asking questions and performing experiments
(to which we owe them our thanks),
we learned that the absorption spectrum of hemoglobin
(that’s the protein in our blood that carries
oxygen around the place)
is quite different between its oxygenated and non-oxygenated states.
In layman’s terms this means it changes colors,
but it’s not nearly as drastic as the pop-culture myth that deoxygenated blood is blue.
‘Cause it’s not.
But it is enough of a difference to be measurable.
And you can make the difference quite obvious if you measure it with two different wavelengths of light.
Here comes a twist - there are actually two LEDs down there!
There’s a red one, and
an infrared red one.
And they’re actually pulsing, not steady.
The light flashes red,
then infrared, and then off over and over again.
And by analyzing what the photodiode on the other side sees after the light passes thorugh your finger,
we can actually determine how
oxygenated your blood is with fairly good accuracy.
Look at this graph!
This is the absorption
spectra for oxygenated and deoxygenated hemoglobin.
The red LED’s output is right about here.
Oxygenated hemoglobin absorbs hardly any of this wavelength,
but deoxygenated hemoglobin
absorbs a fair bit.
As we move into the infrared range, this actually flips.
The infrared LED’s
output is right about here, where oxygenated
hemoglobin actually absorbs a little more
light than deoxygenated hemoglobin.
But there’s more in your finger than just
blood.
There’s skin, there’s bone, there’s a finger nail, and other goodies,
so how can
light alone tell us anything?
Well, because your blood isn’t just sitting there in your
finger!
It’s pulsing thanks to that heart thing in your chest cavity.
With a little signal analysis, the microprocessor inside the pulse oximeter
can isolate that pulsing
component of the signals it's receiving
and ignore all the not-blood.
That allows it to tell
you your heart rate,
but more importantly it allows for the next most important bit;
(more important? Or next-most? This was a bad line)
determining what percentage of the hemoglobin is oxygenated.
Once the microprocessor isolates the pulsing
of your blood, it simply has to make a comparison
between how much infrared light passes through,
and how much red light passes through your blood
during that pulse.
That ratio itself will change
over time as your cells absorb the oxygen
and each new pulse refreshes the blood.
A simple look-up table can then convert the peak ratio observed to the percentage of hemoglobin which is oxygenated,
and then that value is displayed as SpO2,
or peripheral oxygen saturation.
This method has good-enough accuracy to make
this an acceptable tool for a quick snapshot
of someone’s respiratory function.
There are many applications for this technology.
A device like this is a simple indicator meant to give a one-time reading.
This would be useful in an application like patient triage or a simple health checkup,
in fact the display is oriented for it to be read more easily by someone other than you.
But there are also
styles where the sensor is placed separately
from the microprocessing unit to allow for things
like logging of oxygenation data over time,
which can help with diagnosing things like
sleep disorders.
Pilots who fly unpressurized aircraft may
use these as a sort-of early warning device.
If your blood oxygenation falls too much you may be
near hypoxia and when flying a plane that’s not good.
I mean, it’s never good, but it’s
especially not good when you’re piloting
something that can fall from the sky.
So, wearing a monitor like this one or otherwise checking
your pulse ox every once in a while can help
you to not get in that situation by alerting
you that you need supplemental oxygen or otherwise need to descend.
But you should know that these are not perfect
devices.
There are situations where they can give false readings.
One such situation is
with carbon monoxide poisoning.
To the pulse oximeter,
hemoglobin carrying carbon monoxide looks the same as hemoglobin carrying oxygen,
so it may tell you your SpO2 is fine when
in fact it’s very not.
There are specialized versions of these devices
which use additional wavelengths of light to look for carbon monoxide poisoning,
but the common pulse oximeter cannot
do this.
Some finger nail polishes purportedly interfere
with the device’s ability to function.
In theory it should be able to filter out the
influence of such a polish like it can your
skin and bones,
but depending on what the
polish might absorb that may be impossible.
Of course there are other places where a device
like this could work like your earlobes,
but the fingertip is the most common.
And there are other situations where it might not be able to get a good reading.
To help with this,
many oximeters like this one will have some
sort of pulsing indicator like this or other
means to show you roughly how good of a reading
it’s getting.
But the most important thing these can’t
do is tell you anything else about your blood.
Arterial blood gas sampling, where you actually
get some of your arterial blood out of you
and analyze it in a lab, is the only way to
know oxygen saturation precisely, as well
as learn other things things like carbon dioxide
concentration, blood pH,
or even how much hemoglobin is in your blood.
However, the
process of getting blood from your arteries is…
unpleasant.
You can’t just draw it from your veins because then that’s not oxygenated blood so…
well you get the picture.
However, as a first-check, these are quite
useful.
And since they’re really just two LEDs, a light sensor, some sort of display,
and a basic microprocessor,
they’re essentially commodities at this point and are accordingly pretty cheap.
When demand hasn’t peaked, anyway.
All it took to create this device was someone
studying hemoglobin, discovering that its
absorption spectrum is very different between
its oxygenated and deoxygenated states, and
then applying that knowledge.
Knowing that red and infrared wavelengths would be affected differently between the two states,
and making the connection with available light emitting
diodes,
allowed Takuo Aoyagi and Michio Kishi to develop the modern pulse oximeter in 1972.
I say “all it took” like it was easy,
but it goes to show that our world is made
of discoveries built on top of one another.
When we learn things about ourselves, we often find ways to apply that knowledge.
Sometimes it happens long after we’ve made the first discovery, or perhaps
(as was the case with pulse oximetry)
we knew the basics of it since the 1930’s but it took until the modern technological age
for it to become truly practical.
But learning new thigns and applying that
knowledge is what makes us human.
When we do it, it can not only blow your mind,
but can save your life.
I’d like to end by saying that these are
obviously an invaluable tool.
They provide quick access to vital information about our
bodies,
and because they’ve been refined through the decades
and the technology that’s
inside them is very cheap at this point,
they’re easy to purchase.
But I’m not about to say
that you should run out and buy one.
If it interests you, I would encourage you to do
your own research on what to look for,
both in terms of the devices themselves and how to interpret the data they provide.
Because again, I am not a healthcare professional. I’m not an authority. And I don’t want to be perceived as one.
The only conclusion I want to lead
you to today,
is that these are pretty neat,
and human ingenuity is awesome.
Thanks for watching.
♫ oxygenatedly smooth jazz ♫
[off-camera]
OK, this video is something like...
11 - 12 minutes long. If I cannot record this in less
than a half-hour I’m gonna be very upset with myself.
Hi there!
Hi there!
Hi there!
Hi there!
[this repeats a total of 15 times]
...discovering that its absorption spectrum
is very different between its oxygenated and
deoxygenated degenerated
...hemoglobin, discovering that its absorption
spectrum is very different between its oxygenated
and deoxygenated
genated
genated
genated
degenated
This videl, like nearly all of mine, is borne
from simp… nope, don’t like THAT
As your finger approaches it, it lights up
solid.
And it stopped.
...to percentage of hemoglobin which is oxygenated…
eughh there are a lot of big words.
No!
[said in a cartoonish voice]
So, wearing a monitor like this or otherwise
checking your pul ba buhhh
...finger in it, it tells me my heartrate
and my oxygen sat, ah be be dah be deuhhh
But this device manages to do that… without!
Eh, ooo.. Nope.
...terpret that change that produces the sensation
we call sound.
Similarllll….
Similarly..
That… don’t write that word.
Boopydoopy
Boopydoopy
Boopydoopy
Boopydoopy
That's what always goes through my head at this part.
be bah da daaaaahhh
daaaaaaaaahhhhhhhh
ba da DAA
ba da DAA
DAA
da da daaahhhh
boo
BAAAAAAAAAAAAAAA
boopy doopy
