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Transcription de la vidéo
- 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.