What is Airflow Limitation?
You hear the term bandied around. It’s described by the GOLD COPD guidelines as a key component of COPD. If you have it, and it’s always there to some degree, you probably have COPD. So, what is it? Here’s all you need to know.
What is airflow limitation?
It’s when flow through a tube is limited. By limited, we mean “to slow down.”
Imagine a tube. Imagine it with a large lumen. A lumen is the cavity or inside of a tube. It’s the opening of the tube.
Now, imagine that tube is completely clean. Like, there is nothing obstructing the flow of air through the lumen. Air flows nice and easy in either direction.
Now, imagine this tube is your airway. When you inhale air flows nice and easy through the tube. When you exhale it also flows nice and easy. This is how it is in people with healthy lungs. Breathing is easy.
Now, imagine this same airway is narrowed somehow. When an airway is narrow, it is said to be obstructed.
Now, when you inhale, air can easily get past the obstruction. This is because you have lots of inspiratory muscles. If your usual muscles of inspiration need help, there is lots of help available. So, air can easily make it in through the narrowed airway.
But, when you exhale this flow has a hard time getting through. It is slowed by the obstruction. This is what we refer to as airflow limitation. It makes you feel short of breath. How short of breath you will be depends on the severity of the narrowing.
So, what causes narrowed airways?
There are five things that might cause airway narrowing in COPD. The first four here are components of chronic bronchitis. The fourth is a component of emphysema.
- Inflammation. COPD airways are chronically (always) inflamed to some degree. This inflammation makes airway walls abnormally thick. This makes the lumen abnormally narrow. This inflammation may improve with corticosteroids therapy. This is why inhaled corticosteroids are often recommended for COPD.
- Scarring. Chronic inflammation can irritate cells lining airways. Over time, they may become scarred. This airway scarring makes airways abnormally thick. There is no treatment for this. So, this can cause some degree of shortness of breath that’s always there. Researchers are currently studying to learn more about this. Their goal is to find a treatment and cure.
- Bronchospasm. The muscles that wrap around airways may spasm. When this happens, they squeeze airways. This may happen during COPD flare-ups. Bronchodilators relax these muscles, opening airways. One bronchodilator is albuterol. Another that seems to work well for COPD is Atrovent or Spiriva. Other options are combination medicines like Combivent or Duoneb.
- Mucus. Many people with COPD have an elevated number of goblet cells. These are special cells lining airways. They secrete mucus. People with COPD may have extra mucus in their airways. It can block airways, causing obstructions. A treatment for this is to work on your cough. A good cough may clear the mucus out of your airways.
- Stretched airway. In emphysema, lung tissue breaks down. This occurs gradually over time. This causes your lungs to stretch out all the way to your rib cage. As it stretches out, it pulls airways, stretching them taut. This causes airways to become abnormally narrowed. At the present time there is no treatment for this. So, it may cause some degree of shortness of breath that is always there.
How do you know you have it?
All people with COPD have some degree of airflow limitation. If you do, it will show up when you do a pulmonary function test (PFT). This is why PFTs are said to be required to properly diagnose COPD. They are not always ordered, as a diagnosis can be made without them. But, according to the experts, a PFT should be performed at some point.
What is persistent airflow limitation?
Asthmatics may experience airflow limitation too. But, part of the definition of asthma is it is completely or almost completely reversible with time or treatment. Their lung function may be normal between attacks. With COPD, some degree of airflow limitation remains between attacks. So, this is a key indicator that a person has COPD.
How is it treated?
COPD medicines, such as the ones listed above, may help open airways. They should to be taken every day. They may improve lung function. This may make breathing easier. They may also help control COPD long-term. They can help you live better with this lung disease.
What to make of this?
So, this is some of what researchers now know about COPD. This is what they know about airflow limitation. They have come up with some nice medicines for treating it. Still, there is plenty more to be learned. There are more treatments to be discovered.
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