- Now bronchiolitis is a common respiratory tract
infection in young children.
But what exactly do I mean by this
and how does it differ from a common cold?
Well, in order discover this,
let's break down the word.
Bronchiolitis can be broken down into two parts.
Bronchial and itis.
Now bronchial refers to an anatomic location in the lungs.
So to describe this, let me just bring in
a cartoon of the respiratory tract.
Up here in blue is the oral and
nasal cavity in the upper part of the throat.
That's our upper respiratory tract.
And then as you go down you encounter
the airways and the lung tissue itself.
And so this is the lower part of the
respiratory tract, the lower respiratory tract.
And the bronchials, as you go down through
the trachea here into the bronchi,
these kind of ending branches out here,
these are bronchials.
So you can imagine that bronchiolitis
has something to do with the bronchials.
But what does itis mean?
Well generally speaking in medicine,
any time you see a word that ends in itis,
it refers to inflammation.
Now what do I mean by inflammation?
In order to describe inflammation,
let me use an example here.
Imagine this guy over here hits his head.
Now what's gonna happen over time?
Well the area of his head underneath
where he got hit, it's gonna kind of bulge up.
And you're gonna get a little swelling.
So you have some swelling, and it's gonna turn red,
and the area's gonna become painful,
and even a little bit warm.
And those are the characteristics of inflammation.
Pain, tenderness, warmth, and redness.
And what inflammation is, it's the body's
reaction to injury.
So in bronchiolitis, you get that same
kind of inflammation, but in the bronchials.
Let me show you that.
So here we have a zoomed-in image
of the bronchials here.
So in bronchiolitis, you're gonna have
inflammation of these.
So we now know that bronchiolitis is inflammation
of the bronchials, but what causes bronchiolitis?
Well bronchiolitis is a viral infection.
And the most common virus that causes bronchiolitis
is known as respiratory syncytial virus.
But that's a little bit difficult to say.
So we're just gonna call it RSV.
Now RSV causes bronchiolitis by
entering the respiratory tract.
And it can enter the respiratory tract
either from someone who's infected who coughs
and then coughs the virus out into the air
and then this guy over here will inhale it,
or that virus can be sitting on something
and this person may touch it with their hand
and get the virus on their hand,
then touch their mouth, and that is the way
they get the virus into their respiratory tract.
And the first part of bronchiolitis is actually
an infection and inflammation of the upper airway.
So even though bronchiolitis is inflammation
of the bronchials, it starts out as this
infection and inflammation of the upper airway.
And this makes sense because the first signs
and symptoms of bronchiolitis are actually
a runny nose and nasal congestion.
Now at this point if you're thinking bronchiolitis
just kinda looks like the common cold,
you'd be right because the common cold
is a viral infection of this upper airway,
just like what we just happened.
But in bronchiolitis, the virus actually
makes its way down from the upper respiratory tract
down into the bronchials, and it causes
the infection down here.
And so that's what differentiates
bronchiolitis from the common cold.
And it's this infection and subsequent
inflammation of the bronchials that produces
a few more symptoms that are a little more
characteristic of bronchiolitis.
And these symptoms are cough and wheezing.
Now a cough can occur in an upper airway infection
because you have some secretions from the
infection that fall down the airway and that
irritates the airway so you cough it up,
but wheezing only happens if you have
disease in this lower airway.
So wheezing is a very important symptom
for bronchiolitis 'cause it lets you know that
something's going on in the lower respiratory tract.
Well these symptoms don't really seem that bad,
so what's the big deal with bronchiolitis?
The big deal is that sometimes in bronchiolitis
the child's lungs have a hard time getting oxygen,
and that can cause some problems.
So let me show you how that happens.
Now imagine that this part right here
is where oxygen in the air is exchanged in the body.
And in order to get there, the air is gonna
have to travel through the bronchials.
But in bronchiolitis, sometimes this inflammation
gets so bad that these bronchials are blocked.
So the air can't get into the lung tissue itself,
and you have no oxygen there.
And if the oxygen in the air can't reach
the lung tissue, it can't get into the blood.
And this is known as hypoxemia.
And the child's body does two things
to try and compensate for this low oxygen.
And that's to increase his or her heart rate
and increase his or her breathing rate.
And this increase in heart rate and breathing
takes up a lot of energy.
And over time the child can get kind of tired
and gets a little bit sleepy.
And sleepiness is a sign in bronchiolitis
that the child's getting really sick.
So any time any of these symptoms like
increased heart rate or a child just having
a hard time breathing or becomes really sleepy,
any time those are present it's probably
time to call the doctor because the child
may require treatment in the hospital.
So now that we know that bronchiolitis is
inflammation of the bronchials that's caused by
viral infection, what are some of the risk factors
for developing bronchiolitis?
Well since bronchiolitis is a viral infection,
the most common risk factors have to do with
being in contact with the virus.
So being around other children that are sick
is a big risk factor.
So I'm gonna just label that as sick contacts.
And another risk factor that has to do with
exposure to the virus is season.
And RSV is most common in the fall and winter months.
Now this is a little misleading because
the reason we think RSV is most common
in the fall and winter is because children
tend to be inside and in kind of more closed spaces,
so they're in closer contact with the sick contacts.
So this may actually be just a representation
of sick contacts, but it's good to remember
that children are most commonly infected
with RSV in the fall and winter.
But what are some of the other risk factors?
Well since the RSV infection that leads to
bronchiolitis first starts in this upper airway,
if a child's immune system isn't working properly
that infection is more likely to start here.
So I'm gonna put poor immune system.
Now there's also some risk factors that
have to do more with the lower respiratory tract.
The first one I want to talk about is age,
because bronchiolitis is most common in children
under the age of two years.
Now the next one is prematurity.
So any child who's born premature,
especially less than 35 weeks gestation,
their lungs just aren't quite as developed
as children who were born mature.
And part of this is that their airways
are just narrower.
And if you imagine that this inflammation
is occurring in the airways and the bronchials,
that's gonna decrease the size of the airway
and air is gonna have a harder time getting through.
So if you have a narrower airway to start with,
less inflammation causes this blockage
of air flow and results in hypoxemia,
like we talked about earlier.
And another risk factor that affects the
lower respiratory tract is pre-existing lung disease.
And the last one I want to mention
is smoke exposure.
And smoke exposure causes small amounts
of injury to the lower airways
and lower respiratory tract here.
So children exposed to smoke will already have
a little bit of inflammation.
And this pre-existing low level of inflammation
due to second-hand smoke exposure makes them
more susceptible to infection of this area.
So to recap, bronchiolitis is a very common
respiratory tract infection in children,
especially under the age of two years old.
And if you can remember to break down the word,
you can remember what's going on.
Remember, it's inflammation, or itis,
of the bronchials, which are the end part
of the airway before we get to the lung tissue.
And this inflammation is caused by
viral infection, mostly commonly RSV.
It presents with runny nose, nasal congestion,
cough, and wheezing.