Entry and Exit: how the larynx protects the airway
January 6, 2021
“The tumor turned out to be a wheel from a children’s designer”, “A birthday gift with serious consequences — a mysterious patient”, “Doctors after 40 years extracted a part from a child’s designer from a lung” — under similar headlines last summer, reports appeared in newspapers and on websites of many countries of the world. What happened? The Englishman, aged 47, had to undergo lung surgery due to persistent coughing and darkening on an X-ray. Doctors assumed that the long-term smoker had a malignant tumor. But during a bronchoscopy before the operation, they found in the bronchus a part from a children’s designer, which more than forty years ago the man, as he himself believed, “swallowed”, and then safely forgot about it. When, many years later, he developed a chronic cough, the first suspicion fell on smoking. Thus, a piece of plastic remained in his lungs for many decades. Admittedly, this is a very unusual case of foreign objects entering the lower respiratory tract, but it demonstrates that the lungs can be threatened not only by penetrating wounds, chemicals and fine dust, but also by such unexpected things. Although the larynx usually protects against such incidents.
Without the larynx, we would not be able to speak and our communication would be very limited. Moreover, a person would not have heard the soprano Montserrat Caballe, the falsetto of Klaus Nomi or the Bee Gees, the hoarse voice of Anastasia, the bass of Ivan Rebrov or the growl of Lemmy from the band Motorhead. I wouldn’t have heard any voices at all. The larynx is capable of amazing things. Our vocal cords vibrate the exhaled air, filling it with life and unique individual character. For me, as a pulmonologist, the larynx is a prosaic and rather clumsily arranged valve that has two states: “open” and”closed”. The first is used for breathing, and the second is used for swallowing, coughing, and effectively straining when you’re sitting on the toilet.
If the nose is an important filter for the smallest particles contained in the air, then the larynx specializes in large things, and this is no less important. On the contrary! From a design point of view, however, it seems a little strange that in the respiratory tract, the coarse filter is located after the fine filter, and not vice versa. This is about the same as if the drinking water treatment plants first filtered out bacteria and chemicals, and only then — the spaghetti left over from yesterday’s dinner. Doesn’t make sense, but only at first glance. The fact is that in humans, the respiratory tract and digestive tract are not completely separated from each other and cross just in the larynx. Would it not be better to have two separate tubes, one for breathing and the other for eating, as in animals? There are several arguments against this decision. First, the nasal cavity, due to its small size and the need to perform filtering functions, is prone to clogging. Therefore, “plan B” in this case becomes vital. Secondly, man, in comparison with animals, is a universal from a physiological point of view. It can withstand both extremely long loads and short-term maximum power peaks. Two small nostrils are clearly not enough to fully use the reserves of breathing. Therefore, at maximum load, it is necessary to switch to mouth breathing in order to supply the muscles with sufficient oxygen. This is where the problem lies: if there is a connection between the respiratory tract and the digestive tract, then there may be an undesirable exchange of their contents. Air can enter the esophagus, and food can enter the respiratory tract. In the first case, you are threatened with burping, and in the second-death from suffocation. To prevent this, and there is a larynx.
Let’s take a quick look at how the larynx works. What in men prominently protrudes on the front of the neck and is called the “Adam’s apple” is the largest part of the larynx, its thyroid cartilage. It, like a shield, covers the glottis with two vocal cords and together with the cricoid cartilage located just below, forms the transition to the trachea. In the upper part, the thyroid cartilage connects to the epiglottis, and that, in turn, with the tongue. When swallowing, the tongue completely presses the epiglottis to the opening of the larynx and thereby prevents food from entering the trachea.
Instead, the food slips elegantly into the esophagus located behind the trachea and disappears into the possession of gastroenterologists. An ingenious mechanism, unless you want to try eating and talking at the same time. Or take a deep breath while holding a piece from a children’s designer in your mouth. In this case, you are in danger of so — called aspiration-ingress of liquid substances or solid objects into the respiratory tract. If the object is so large that it overlaps the trachea or one of the two main bronchi, there is a threat of immediate death. Similarly, a large amount of fluid in the lungs (for example, when drowning) quickly leads to death due to lack of oxygen. In such a case, the airways do not overlap, but the liquid glues the alveoli and blocks the flow of oxygen into the blood. Getting into the lungs of small objects or a small volume of fluid threatens serious complications that can develop after a few days or weeks. Along with a painful cough, there is usually difficulty breathing and infection in the blocked parts of the bronchi. If the patient can’t remember exactly when a foreign object got into the respiratory tract (which is usually the case in young children), then making the correct diagnosis for the doctor turns into a detective story. To make matters worse, small plastic parts and food items (such as peanuts) are invisible on the X-ray. In doubtful cases, it is necessary to resort to bronchoscopy to find out the causes.
Despite sensational media reports, incidents like the one when US President Bush choked on a pretzel in 2002 are relatively rarely life-threatening. In 2015, the Federal Statistics Office counted 1,149 deaths in Germany caused by foreign objects entering the respiratory tract. Among the victims were many elderly people in need of medical care, whose food during the meal got into the respiratory tract and caused pneumonia. In general, as a rule, the defense mechanism works effectively, and to get around it, you need to try hard, even if unintentionally. However, many experts fear that in the future such cases will occur more often, and smartphones are cited as the reason. A person talking on the phone while eating is easier to confuse when to speak and when to swallow. Thus, it is better to turn off your mobile phone during meals and generally keep quiet — if this theory is correct. Although it can be doubted, because then southern Europeans should die in large numbers. And in women, such cases should occur more often than in men. And what about Asians with their habit of noisily sucking in food? What about oyster lovers? And can we say that Finns and Estonians never choke on food at all, because they never talk at the table? It is also necessary to take into account cultural characteristics, which largely determine what items enter the respiratory tract. In Muslim countries, for example, these are usually hair clips. Covering their heads, women hold them in their mouths, and if they inhale carelessly, some of them may disappear. In Southeast Asia, duck eggs with an already formed embryo inside (balut) are considered a delicacy. When they are drunk, pieces of the shell (or embryo!) they can get into the respiratory tract. In Europe, children’s constructors Playmobil and Lego remain out of competition.
When a foreign object is mistakenly placed in the larynx, there is another safety mechanism — reflex cough. In most cases, it does not allow foreign objects to enter the respiratory tract through the glottis. Therefore, people who have this reflex weakened or absent are particularly vulnerable to aspiration. This happens in certain nervous diseases (for example, multiple sclerosis), as well as in bedridden patients. In healthy people, the most common cause is alcohol or drugs. When a person gets drunk to the point of insensibility, there is a direct threat to life, because three factors come together: the likelihood of vomiting due to poisoning with a large amount of alcohol, suppression of the swallowing reflex and saving reflex cough. A deadly combination, the victims of which have already fallen many talented cultural figures, as evidenced, for example, the infamous “Club 27”.
The larynx, or rather the vocal cords, plays an important role in the occurrence of not only reflex, but also any other type of cough. How does this happen and what is the role of the vocal cords? Coughing is, simply put, a controlled explosion inside the airway. The shock wave generated by the explosion should remove foreign objects, mucus or pathogens from the bronchi in the direction of the oral cavity. The vocal cords perform the function of a pressure valve in this process. If somewhere in the body you need to create pressure, then you can not do without a tightly closed glottis. And pressure is required in many cases. Will a large number of children be born if the woman in labor does not push? Apparently, not very much. And the administration of natural needs without pressure from above? Possible, but difficult.
Lifting weights? Well, it’s not that vital. But back to the cough. To cough, you first need to take a deep breath with the vocal cords open, and then quickly close the glottis, creating a sealed barrier for air to escape from the lungs. After that, a sharp exhalation begins, but it is prevented by the closed vocal cords, as a result of which high pressure is created inside. When it becomes too large, the vocal cords open and compressed air with force and with a characteristic sound escapes from the bronchi to the outside.
When it is necessary to strain during childbirth or during defecation, the same mechanism is involved, but the glottis remains closed, in addition to everything there is a contraction of the muscles of the abdomen and back. Since the abdominal cavity has nowhere to compress further (the diaphragm is in the position of maximum inspiration and is not supplied by a single centimeter due to the closed glottis), the pressure of its walls is transmitted directly to the internal organs, which contributes to the exit of the fetus or feces-depending on the need. Sometimes it happens both at the same time, which is a real nightmare for any woman in labor!