- Here's an example of a family that's been exposed
to a highly contagious respiratory
infection called, Pertussis.
This disease is also called Whooping Cough
because of the distinct noise an infected person
typically makes when drawing in air
after a lengthy coughing fit.
And this isn't just a regular cough.
It's a powerful, forceful cough that continues until all
the air has been removed violently from the lungs.
And it's triggered by a reflex from the lung's
responding to a build up of mucous that occurs
when the bacteria causes damage in the airways.
So let's look into how this cough is generated.
I've sketched out the muscles
that play a role in the cough generation.
The chest muscles here, the abdominal muscles here,
and the diaphragm muscle which rests just below the lungs.
And to cough, these muscle contract inward, like this.
And this.
And the diaphragm relaxes, pushing up on the lungs.
And the consequence of these muscles actions
is to squeeze the lungs.
Let's look specifically at the lungs.
And I'm gonna erase the muscles here
so that I can bring up an image of the lungs.
All these forces from the muscles reduce
the volume of the lungs.
So I'm showing that here at the dotted line.
Think of this as like a water balloon.
If you have an untied water balloon filled with water
and then you use your muscles to squeeze it
the water comes spurting out the top.
But the airways that the air needs to travel through
are swollen from the infection.
Which means that the air can't get out easily.
And this causes air pressure in the lungs to build.
So in the water balloon example,
think about if we had tied the water balloon
off at the top and then squeezed it.
The water can't go anywhere, so as we squeeze
the balloon stronger and stronger
the pressure builds until the balloon bursts.
And the same is true for the lungs.
Even though we're not tying off the airways,
we're constricting them enough that the air pressure builds
and the lungs can actually tear.
And all the muscles squeezing can cause things,
like a rib fracture.
But remember that there's a lot of other organs
in the chest that'll be feeling
the pressure from the muscle squeezing.
The stomach, for example will respond
by emptying it's contents, like the lungs.
And result in vomiting after coughing fits.
And this is particularly a problem
because if it happens frequently,
dehydration and weight loss can occur.
The bladder also empties it's content
and leads to incontinence.
And even circulation is affected.
Blood has trouble returning to the heart
through this big vein that drains blood from the head.
And it backs up.
This means that the blood, just like the air
pushing it against lungs that cause a tear,
builds up and pushes against blood vessels.
And causes delicate blood vessels to break.
Leading to things like bloody nose,
red eyes, and free blood in the head.
And while a coughing fit is happening,
a person could cough to the point
where they faint from the sudden decrease in oxygen.
And even if fainting doesn't occur,
extremities like the fingers will cyanos,
or turn blue from a lack of oxygen.
With all these complications, you may be wondering
why a violent reflex is so important.
And it's because the mucous that I'm drawing
in the airways in pink builds in the airway.
Because airway damage from Pertussis infection
makes normal removal of the mucous difficult.
And built up mucous is dangerous because
it's the perfect place for other bacteria
that we breathe in to get stuck and cause
yet another lung infection in addition to Pertussis.
Battling multiple lung infections at the same time
is a really difficult job for the body.
So the mucus needs to be removed
with this violent coughing reflex.
And while all these complications that we just discussed
can happen to anyone with Pertussis, there are some groups
that have a higher risk of developing them.
So let's says that grandma has an underlying lung condition.
Her lung functions already compromised
and adding Pertussis to her burden
can lead rapidly to respiratory damage and failure.
Maybe dad has a weak or suppressed immune system.
And this means that his immune system
may not be strong enough to fight a Pertussis infection.
Maybe grandpa had a vaccine, but it was about 10 years ago
and his immunity to the disease has decreased
over time, making him susceptible.
Infants under one year old,
but particularly those under six months
are a high risk group.
And this is for a couple of reasons.
They have an underdeveloped immune system.
They have small airways that can't
accommodate too much swelling.
And for infants younger than two months,
they can't yet receive the protective Pertussis vaccine.
So all this means that about 50 percent
of infants who have Pertussis will be hospitalized
to stabilize complications from the infection.
To break this down further by complication,
in the 50 percent of infants who will be hospitalized
from Pertussis, the vast majority will have Apnea.
Which is stopped breathing.
The reason this probably happens so often in infants
is because muscles in their airway tend to spasm
in response to mucous building up.
When a muscle spasm happens,
it means the muscles don't allow for breathing to occur.
In the hospital, infants will be closely monitored
for Apnea and they may even need
help breathing with machines.
But if Apnea occurs, and they stop breathing
their bodies aren't receiving enough oxygen
to function correctly.
So this means they are prone to seizures
from the brain being denied oxygen.
And about a quarter of the infants hospitalized
will have a secondary respiratory infection.
This goes back to what we were talking about earlier
about how mucous in airways
a great environment for bacteria to thrive.
And unfortunately about two percent of the time
these infants will have fatal respiratory failure.
And there might actually be a way to tell
which infants are most at risk for this.
Lymphocytes are cells of the immune system
that help fight diseases.
And Pertussis releases a toxin in the body
that causes lymphocytes to divide to high levels.
So average levels in infants during the infection
can be about 20,000 lymphocytes per micro liter of blood.
And generally the higher the counts,
the more severe the infection,
and the more severe the complications
leading to respiratory failure.