Obstructive VS Restrictive Lung Diseases (Where Does Asthma Fit In?)

If you do a Google search you’ll learn there are two categories of lung diseases. They are obstructive and restrictive. So, what do these terms mean? Where does asthma fit in? Here’s what to know.

The anatomy of the lung

A quick review of lung anatomy may prove helpful here. Inside your chest is a set of lungs. When you take in a breath, air enters in your nose or mouth. The back of your nose or mouth is your pharynx. From there air enters your larynx and passes through your vocal cords. It then enters your bronchial airways.

Bronchial airways get smaller and smaller the further down you go. They continue getting smaller all the way to the terminal bronchioles. Air then passes to your respiratory bronchioles. These are surrounded by balloon-like sacs called alveoli. Alveoli are grouped together in grape-like clusters.

Respiratory bronchioles and alveoli are interconnected with small blood vessels. These are called capillary blood vessels. So, it’s here where gas exchange occurs. When you exhale air goes back all the way up and leaves your mouth or nose.

The difference between obstructive and restrictive lung disease

Obstructive Diseases. These are diseases that affect the airways. Something happens that obstructs the flow of air through them.^1-3

Restrictive Diseases. These are diseases that do not affect airways. Something is happening outside airways. But, this “something” may squeeze airways, making it hard to breathe.^1-3

What are obstructive diseases?

Say you swallow a hotdog. But, it doesn’t travel down your esophagus to your stomach. Instead, it goes down your airway. At some point it will get stuck. So, it’s the most basic form of obstruction. This hotdog may completely block your airway making you unable to breathe.

But, if it gets lodged just right, you may still be able to breathe. Air can get in past this hotdog obstruction, but it will have a hard time getting out. So, when you have an obstruction, air can get in but has a hard time getting back out.

When you exhale, the obstruction resists the flow of air. So, it causes increased resistance to the flow of air. So, it may seem you can exhale forever and never get all your air out. Air is therefore slowed when you exhale. A medical term for this is airflow limitation. It is this that makes you feel short of breath.

There are diseases that may obstruct airways. Chronic bronchitis (COPD) fits into this category. Asthma also fits into it. They both cause inflammation and increased sputum that make airways narrow. So, they both obstruct airways. They are obstructive diseases.^1-5

Obstructive Sleep Apnea causes your upper airway to collapse while your sleeping. So, it obstructs the flow of air. Croup causes inflammation of your upper airways. So, it’s certainly an obstructive disease. Rhinitis causes inflammation in your nasal passages. So, it also qualifies. ⁵

Cystic fibrosis, emphysema, and bronchiectasis also qualify.⁵

What are restrictive diseases?

These are diseases that occur outside your airways. The best example I can think of here is pregnancy. It’s not a disease, but it certainly does restrict your airways. You have a baby inside you. It grows larger and larger. At some point, it begins to push up on your diaphragm.

It acts to squeeze or restrict your lungs. This makes it so your lungs are less compliant. This means they are unable to fully expand because of the baby taking up space. So, that’s the most basic form of a restriction.

Obstructive diseases make it hard to exhale. Restrictive diseases make it hard to inhale. They cause less lung compliance. Another good example is kyphoscoliosis. People with this have deformed chest walls. This acts to limit the ability of the lungs to expand. Rheumatoid arthritis may also qualify.^1,4,5

Neuromuscular diseases like ALS may impact inspiratory muscles. So, this can make it hard to inhale. Drug overdoses qualify here. They relax you so you weaken your drive to inhale.^1,3

Pneumonia is inflammation of your alveoli. So, it takes up space making it hard to inhale. Obesity certainly may cause less room for lungs to expand, so it qualifies. Lung cancer takes up space outside airways, so it qualifies. ⁵

What to make of this?

So, asthma is an obstructive disease. Asthma attacks cause increased inflammation and increased sputum production. These act to obstruct airways. This obstruction resists the flow of air when you exhale, making it hard to exhale.