0:00:02.420,0:00:05.130
Let's say this person is[br]lying here in front of me.

0:00:05.130,0:00:07.870
And I'm thinking[br]about how the air is

0:00:07.870,0:00:10.830
passing through their[br]nose and their mouth

0:00:10.830,0:00:12.840
and entering their lungs.

0:00:12.840,0:00:16.260
And specifically I'm interested[br]this time in how much

0:00:16.260,0:00:20.390
oxygen is actually getting[br]to their alveolar sacs.

0:00:20.390,0:00:23.580
So, deep inside their lungs[br]they have these branches,

0:00:23.580,0:00:26.150
they're conducting in[br]respiratory bronchials.

0:00:26.150,0:00:28.750
But at the end, of course,[br]they have these alveolar

0:00:28.750,0:00:30.430
sacs that we've talked about.

0:00:30.430,0:00:34.010
And I'm interested in thinking[br]about how much oxygen is really

0:00:34.010,0:00:36.120
down there at the very ends.

0:00:36.120,0:00:38.300
And you have to excuse[br]this alveolar sac.

0:00:38.300,0:00:40.200
It really is that.

0:00:40.200,0:00:43.380
It looks a little bit like a[br]three-leaf clover, I guess.

0:00:43.380,0:00:45.100
But that's the issue.

0:00:45.100,0:00:48.972
How much oxygen is deep[br]down in here where the x is?

0:00:48.972,0:00:50.180
So how do we figure this out?

0:00:50.180,0:00:52.630
I want to first[br]think about the air

0:00:52.630,0:00:55.080
this gentleman is breathing in.

0:00:55.080,0:00:57.860
He's breathing in air[br]from the atmosphere.

0:00:57.860,0:01:01.120
So this is atmospheric[br]pressure air.

0:01:01.120,0:01:03.710
And we say ATM for short.

0:01:03.710,0:01:06.480
And we know that atmospheric[br]pressure at sea level

0:01:06.480,0:01:09.130
is 760 millimeters of mercury.

0:01:09.130,0:01:12.520
It's going to be lower[br]at higher altitudes.

0:01:12.520,0:01:14.430
So, if you're at the[br]top of a mountain,

0:01:14.430,0:01:16.140
it would be less than that.

0:01:16.140,0:01:19.540
And this pressure is made up of[br]many, many different molecules

0:01:19.540,0:01:20.680
bouncing around.

0:01:20.680,0:01:23.290
So, I've got some[br]molecules of oxygen.

0:01:23.290,0:01:25.380
Let's say this is about 21%.

0:01:25.380,0:01:27.080
This is my oxygen.

0:01:27.080,0:01:29.760
And before I move on,[br]I should mention FiO2.

0:01:29.760,0:01:31.690
You might come across this.

0:01:31.690,0:01:35.360
And FiO2 stands for the[br]fraction-- which in this case

0:01:35.360,0:01:40.170
was 21% or 0.21--[br]fraction of inspired,

0:01:40.170,0:01:43.140
meaning how much oxygen[br]you took in or air you

0:01:43.140,0:01:46.500
took in-- fraction[br]of inspired oxygen.

0:01:46.500,0:01:50.690
And the fraction happens to be[br]21%, which is, of course, much,

0:01:50.690,0:01:52.904
much lower than the nitrogen.

0:01:52.904,0:01:54.570
Now nitrogen-- when[br]I draw it this way--

0:01:54.570,0:01:55.550
it's pretty impressive.

0:01:55.550,0:01:57.250
All the purple is nitrogen.

0:01:57.250,0:02:00.810
This is about 78% of[br]what you're breathing in.

0:02:00.810,0:02:02.790
And the last little[br]tiny little bit,

0:02:02.790,0:02:05.190
I'm going to draw[br]the green line.

0:02:05.190,0:02:07.120
This is mostly argon.

0:02:07.120,0:02:09.900
And argon is-- in[br]Greek, it actually

0:02:09.900,0:02:11.850
comes from the term lazy.

0:02:11.850,0:02:14.320
But it basically reminds[br]me when I think of that,

0:02:14.320,0:02:16.340
that argon is not[br]going to do much.

0:02:16.340,0:02:21.171
It's not going to react with[br]anything that is in our body.

0:02:21.171,0:02:22.420
And of course, you have other.

0:02:22.420,0:02:24.210
You have less than 1%.

0:02:24.210,0:02:26.970
And this would be things[br]like carbon dioxide.

0:02:26.970,0:02:29.180
So, this is a[br]breakdown of the air

0:02:29.180,0:02:31.180
that my friend is breathing in.

0:02:31.180,0:02:33.170
This is my friend breathing.

0:02:33.170,0:02:36.530
And if I want to now think[br]about how much oxygen

0:02:36.530,0:02:38.180
they're taking in,[br]all I have to do

0:02:38.180,0:02:40.360
is a little tiny bit of math.

0:02:40.360,0:02:46.560
I can say OK, pO2-- this is the[br]partial pressure of oxygen--

0:02:46.560,0:02:55.110
is just 0.21, or 21%, times[br]760 millimeters of mercury.

0:02:55.110,0:02:59.930
And this turns out to be[br]160 millimeters of mercury.

0:02:59.930,0:03:03.030
Now, that oxygen kind of[br]goes down in his lungs.

0:03:03.030,0:03:06.740
And it goes through his[br]trachea and into his-- all

0:03:06.740,0:03:10.450
the little bronchials and[br]down into the alveolar sac.

0:03:10.450,0:03:12.950
And when it gets there--[br]on the way over there,

0:03:12.950,0:03:14.200
an interesting thing happens.

0:03:14.200,0:03:17.790
The body temperature here[br]is 37 degrees Celsius.

0:03:17.790,0:03:20.260
He's got a normal[br]body temperature.

0:03:20.260,0:03:23.220
And what that does[br]is-- the air is

0:03:23.220,0:03:27.640
going through these[br]bronchials and trachea.

0:03:27.640,0:03:30.370
And as it does, there's[br]a lot of moisture

0:03:30.370,0:03:32.300
in the respiratory tree.

0:03:32.300,0:03:33.425
There's moisture there.

0:03:33.425,0:03:34.800
And that moisture,[br]when it starts

0:03:34.800,0:03:37.210
heating up-- and of[br]course, 37 degrees

0:03:37.210,0:03:41.340
is pretty warm-- It's going to[br]start leaving the liquid phase

0:03:41.340,0:03:43.180
and going into the gas phase.

0:03:43.180,0:03:45.680
So all of a sudden you[br]have now little molecules.

0:03:45.680,0:03:48.510
I'm going to draw them[br]as little dots of water.

0:03:48.510,0:03:49.660
That's here.

0:03:49.660,0:03:52.660
And it's going to start[br]entering and mingling

0:03:52.660,0:03:54.750
with the gas that's[br]going through.

0:03:54.750,0:03:58.420
So, the gas that got[br]taken in, that he inhaled

0:03:58.420,0:03:59.650
is now mingling.

0:03:59.650,0:04:01.850
And what happens as a[br]result, is that water

0:04:01.850,0:04:06.340
has what we call[br]a vapor pressure.

0:04:06.340,0:04:09.420
And that vapor pressure[br]is going to change

0:04:09.420,0:04:10.740
depending on the temperature.

0:04:10.740,0:04:13.540
But at 37 degrees,[br]that vapor pressure

0:04:13.540,0:04:17.140
ends up being 47[br]millimeters of mercury.

0:04:17.140,0:04:20.760
In other words, if the[br]temperature is 37 degrees,

0:04:20.760,0:04:24.010
then we can expect that some[br]of those water molecules

0:04:24.010,0:04:27.230
will leave the liquid[br]and enter the gas phase.

0:04:27.230,0:04:31.050
And it turns out that[br]the amount of molecules--

0:04:31.050,0:04:32.680
or the number of[br]molecules-- that leave

0:04:32.680,0:04:35.400
are going to generate[br]a pressure that

0:04:35.400,0:04:37.270
is 47 millimeters of mercury.

0:04:37.270,0:04:39.000
And this is pretty standard.

0:04:39.000,0:04:40.842
This is known off of a table.

0:04:40.842,0:04:42.300
And in fact, if[br]you think about it,

0:04:42.300,0:04:44.720
if you just generated[br]lots of heat-- let's say

0:04:44.720,0:04:47.290
you actually were[br]boiling water--

0:04:47.290,0:04:49.010
that would be 100[br]degrees Celsius.

0:04:49.010,0:04:51.590
And the vapor pressure[br]there would be very high,

0:04:51.590,0:04:52.520
because it's boiling.

0:04:52.520,0:04:54.970
And it would be 760.

0:04:54.970,0:04:58.360
So boiling is actually 760.

0:04:58.360,0:04:59.530
So just keep that in mind.

0:04:59.530,0:05:06.620
Boiling water has a[br]vapor pressure of--

0:05:06.620,0:05:08.950
And what do you think[br]760 reminds you of?

0:05:08.950,0:05:11.417
That is atmospheric pressure.

0:05:11.417,0:05:12.250
So it's interesting.

0:05:12.250,0:05:15.510
Vapor pressure is going to[br]equal atmospheric pressure

0:05:15.510,0:05:17.830
when you are boiling water.

0:05:17.830,0:05:20.760
And that's actually exactly[br]what's happening as you boil.

0:05:20.760,0:05:22.610
But I don't want to[br]get too distracted.

0:05:22.610,0:05:26.350
We're not boiling water inside[br]of our bodies or our lungs.

0:05:26.350,0:05:28.120
We're actually much[br]cooler than that.

0:05:28.120,0:05:29.120
But we are warm.

0:05:29.120,0:05:30.150
We're at 37 degrees.

0:05:30.150,0:05:34.280
And so you do have some of these[br]little water molecules that

0:05:34.280,0:05:37.050
have entered the gas phase.

0:05:37.050,0:05:40.190
And so if overall it's got[br]to be-- this whole thing

0:05:40.190,0:05:41.720
has got to be 760.

0:05:41.720,0:05:45.120
So, on average,[br]our lung pressures

0:05:45.120,0:05:47.290
are going to be the same[br]as atmospheric pressure.

0:05:47.290,0:05:51.280
But now you've got[br]water taking up 47.

0:05:51.280,0:05:54.720
So if water's taking up 47,[br]the rest of those little gas

0:05:54.720,0:06:00.070
molecules have got to be 713.

0:06:00.070,0:06:03.180
So this is the rest.

0:06:03.180,0:06:04.450
What was in that rest?

0:06:04.450,0:06:05.950
It's going to be[br]the same as before.

0:06:05.950,0:06:07.845
It's going to be-- and I'm[br]going to try to sketch it

0:06:07.845,0:06:09.303
as best as possible--[br]this is going

0:06:09.303,0:06:11.930
to be my oxygen right here.

0:06:11.930,0:06:16.310
This is 21% of 713.

0:06:16.310,0:06:18.910
And then we have lots and[br]lots of nitrogen still.

0:06:18.910,0:06:21.600
Same kind of break[br]down as before.

0:06:21.600,0:06:25.142
And remember this is all[br]air that is being inhaled.

0:06:25.142,0:06:26.850
So we're not talking[br]about breathing out.

0:06:26.850,0:06:28.590
We're just talking[br]about breathing in.

0:06:28.590,0:06:32.360
And this purple right[br]here-- and this is 78%.

0:06:32.360,0:06:35.206
Again, this is 78%[br]percent of 713.

0:06:35.206,0:06:37.080
And we still have a[br]little bit of that argon,

0:06:37.080,0:06:39.515
and those other gases--[br]I won't write it all out,

0:06:39.515,0:06:40.390
but you get the idea.

0:06:40.390,0:06:42.840
That basically now[br]because water is taking up

0:06:42.840,0:06:45.880
some of the overall pressure,[br]all of the other gases

0:06:45.880,0:06:48.690
are going to have a[br]lower partial pressure.

0:06:48.690,0:06:51.710
So what is the partial[br]pressure of the air that's

0:06:51.710,0:06:54.750
entering into that alveolar sac?

0:06:54.750,0:07:00.850
It's going to be basically[br]FiO2, which is 21%.

0:07:00.850,0:07:02.730
I'll write that here.

0:07:02.730,0:07:04.890
And then we have the[br]atmospheric pressure.

0:07:04.890,0:07:06.960
This is atmospheric[br]pressure over here.

0:07:06.960,0:07:09.510
And we said that was 760.

0:07:09.510,0:07:12.730
We can draw a little arrow so[br]we know what's pointing to what.

0:07:12.730,0:07:15.210
760 millimeters of mercury.

0:07:15.210,0:07:17.960
And then, from that to account[br]for the partial pressure

0:07:17.960,0:07:18.610
of water.

0:07:18.610,0:07:21.550
Because now we have some[br]water vapor in there.

0:07:21.550,0:07:26.230
We have to subtract out 47.

0:07:26.230,0:07:30.620
So, so far, if you've[br]kept up with this math,

0:07:30.620,0:07:33.400
you see that we have-- what[br]does that work out to be?

0:07:33.400,0:07:38.150
About 150 millimeters[br]of mercury.

0:07:38.150,0:07:43.336
Now this is the partial pressure[br]of oxygen, at this spot.

0:07:43.336,0:07:45.210
Let me just make it very[br]clear with my arrow,

0:07:45.210,0:07:48.190
not at this orange x.

0:07:48.190,0:07:49.700
So far, we've[br]figured out that we

0:07:49.700,0:07:53.030
have a partial pressure that's[br]a little bit lower than when

0:07:53.030,0:07:54.280
we started.

0:07:54.280,0:07:56.600
And that was because of the[br]partial pressure of water.

0:07:56.600,0:07:59.630
Let's pick up there[br]in our next video.