This World Asthma Day, we take a look at the causes and reasons why people are affected by this disease.
Around 8 million of us Brits have been diagnosed with asthma at some point in our lives. If you are one of those 8 million today is a reminder that you are not alone. The main symptoms of asthma are breathlessness, wheezing when breathing, tightness in the chest and coughing.
To understand asthma, we first need to understand our lungs.
As we breathe in that air travels down our bronchial tree. From our nose and mouth, air then passes down our larynx, past our vocal cords, into our trachea. It then splits into the main bronchi going into the left and right lung, branching off like tree branches into the secondary and then tertiary bronchi. Finally, into the alveolar ducts and alveoli. Gas exchange takes place in the alveolar ducts and alveoli.
Where does asthma begin in the lungs?
The secondary and tertiary bronchi are where our journey into asthma begins. The bronchi are made up of several layers, the innermost layer is called the epithelium - this contains cells called goblet cells that produce mucus. Next moving outwards, is the lamina propria. The layer you can see in green is the smooth muscle layer of the ‘muscularis mucosa’.
When someone has asthma, we see changes in these three layers of the bronchi. The bronchi themselves become narrower causing a bottle neck, which in turn means less air gets through to the alveoli and the alveolar ducts. This is what causes wheezing, coughing and breathlessness in asthma.
The narrowing of these bronchi is due to the build of excess smooth muscle in the muscularis mucosa layer.
What happens when an asthma attack occurs?
When an asthma attack is happening, the smooth muscle is contracting narrowing the bronchi even further, a lot like pulling shut a drawstring bag. There are changes in the other tissues too.
The epithelium goblet cells divide at an increased rate meaning there are more of them. Ordinarily, the goblet cells produce just enough mucus to trap bacteria, pollen, dust and dust preventing them from entering the lungs. But with a larger number of them, too much mucus is produced making it harder for air to flow freely through the bronchi.
In the lamina propria with asthma, we see immune cells invading this layer. There are a large number of eosinophils, a white blood cell that causes inflammation along with mast cells. Mast cells release histamine which encourages mucus to build up in the airways and causes allergic reactions. This is why antihistamine drugs are used to treat mild allergies
What causes asthma?
No two cases of asthma are quite the same although we can broadly categorise them either by their severity or by their triggers. Going back to those mast cells, we can have allergy induced asthma.
Where breathing in an allergen such as dust mites, pollen or pet dander - this triggers the bronchi to narrow and constrict. 80% of people with allergy-induced asthma have a related condition such as hay fever, eczema or food allergies. Similar to this is seasonal asthma where the specific trigger or cold is only around at a certain time of year.
There are also more uncommon irritants that trigger asthma. These are usually only encountered during manufacturing and not through everyday life. This is classified as occupational asthma. With occupational asthma, it is triggered in adulthood and no symptoms are seen with time away from work. The irritants can be a variety of things in different industries from fabric particles of cotton, hemp and flax in the textile industry to soldering fumes, chromium, nickel sulphate and platinum dust in construction. These are just a few examples, there is one for every industry. Occupational asthma accounts for 10-15% of asthma cases in adults.
Asthma when exercising
Exercise is a big trigger of asthma - 90% of all those with asthma will experience symptoms with exercise, leading to the term exercise-induced asthma. While the rate of respiration is increased, what’s really at play here is temperature and humidity.
When you are at rest you breathe primarily through your nose and your nose has three ridges in it called choanae they help to swirl the air moistening, slowing and warming it. However, when doing more strenuous exercise we breathe more through our mouth which doesn’t moisten, slow and warm the air as much as the nose. That means the lungs come into contact with fast, dry cold air which causes that smooth muscle layer to constrict narrowing the bronchi.
Temperature is a big factor in triggering asthma. There are some asthma cases that are not easy to classify and the mechanism behind them needs to be further investigated.
Different forms of Asthma and genetics
Asthma can behave slightly differently depending on when it presents. In childhood before puberty, asthma is more common in boys. When compared to girls of a similar height and weight, boys were found to have narrower and more sensitive airways. This means that it is possible to grow out of it. In around a third of childhood asthma cases, the asthma goes into remission, with the patient experiencing no symptoms in their adult life. However, in this case, asthma can come back in later life. Other risk factors that contribute to the presentation of childhood asthma include being born premature and smoking and high sugar intake by the mother during pregnancy.
For both childhood and adult asthma, there is a genetic factor in developing asthma, this involves multiple genes.
Obesity is also a risk factor in developing asthma. The mechanism is not completely understood, but the mild inflammation seen throughout the body with obesity triggers inflammation in the lungs. Smoking and air pollution are big factors when it comes to the development of asthma. After puberty asthma is more commonly present in women. The reason for this has not yet been fully understood. Although it is thought to do with oestrogen and hormonal changes. With adults presenting with asthma, it can be managed but does not go into remission.
Cure for Asthma?
There is no cure for asthma only management. Asthma can be fatal in some cases. In 2018 1,422 people died of an asthma attack in England and Wales alone.
The key to living with asthma is management. Attending yearly asthma reviews and keeping asthma plans allow patients, GP and asthma nurses to monitor changes and ensure inhalers are the right dose and taken correctly. People with asthma tend to be prescribed more than one type of inhaler. There are preventer inhalers that are taken daily even if the person feels well. These administer a low dose of steroids into the bronchi and bring down any inflammation. Secondly, there are the reliever inhalers that are taken as soon as symptoms present themselves. They work by relaxing the smooth muscle layer that contracts and narrows the bronchi building up the asthma attack.
Remember if you or someone you know has asthma, they should always have their reliever inhaler on them regardless of how long it has been since they experienced symptoms.
Want to learn more about anatomy? The Post Mortem Live is coming to a town near you soon - can you stomach it?