Bronchiectasis

Definitions & Key takeaways

Bronchiectasis is a chronic inflammation of the bronchi and the bronchioles, which damages the mucociliary escalator and the walls of the airways. This causes mucus to accumulate and get stuck in the airways, and form mucus plugs that can lead to serious infections, difficulty breathing, and a variety of other health problems. Common causes of bronchiectasis include long-term exposure to cigarette smoke, respiratory infections such as pneumonia, and cystic fibrosis.

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Introduction0:00–0:32

With bronchiectasis, bronchi refers to bronchi and bronchioles, which are small airways in the lungs, while ectasis means dilation.
So in bronchiectasis, chronic inflammation in the lungs damages the smooth muscle cells and elastic tissue that support these small airways, resulting in their permanent dilation.
When you take a breath, your diaphragm moves down, creating negative pressure within your chest. This gentle vacuum in the chest pulls air in through your nose or mouth down the trachea.

Physiology0:32–1:50

From here, the air travels through the primary bronchi into the secondary bronchi, then tertiary bronchi, and finally into the bronchioles, which leads directly to the alveoli where the gas exchange occurs.
Now the walls of our airway consist of smooth muscle cells and elastic tissue that help the airways open and return to their shape as we breathe.
These walls are lined with epithelial cells which have tiny brush-like projections called cilia and goblet cells which produce sticky mucus.
The mucus traps dust, bacteria, and other unwanted particles, and the cilia move together in coordinated waves, pushing the mucus and trapped particles towards the throat so we can clear them out of the lungs.
This system is called the mucociliary escalator. This way we can either swallow or cough out foreign particles that end up in our airways.
Now bronchiectasis can develop due to chronic respiratory infections or lung obstructions. These are closely related and tend to trigger each other, setting off a cycle that slowly damages the airways over time.
First, let's look at how chronic recurrent respiratory infections can lead to bronchiectasis. When a pathogen reaches the small airways in the lungs, epithelial cells respond by releasing pro-inflammatory cytokines, which signal neutrophils to join the action.

Pathology1:50–4:48

As neutrophils fight the pathogen, they use powerful weapons like elastase and reactive oxygen species. These substances are great at killing pathogens, but they also cause collateral damage, breaking down the surrounding structures, including epithelial cilia.
As a result, epithelial cilia cannot propel the mucus and pathogens out of the lungs, causing the mucus to accumulate, which creates a perfect environment for bacteria to thrive.
With recurrent infections, chronic inflammation can destroy the surrounding smooth muscle cells and elastic tissue. Resulting in permanent dilation of bronchi and bronchioles.
Sometimes airways can dilate up to 4 times their normal size. This kind of damage is common in necrotizing pneumonia caused by Staphylococcus aureus, Klebsiella species, and Mycobacterium tuberculosis.
Another setting where bronchiectasis can develop includes immunodeficiencies, particularly the ones with low immunoglobulin levels.
It might seem surprising, but when the immune system can't effectively fight off pathogens, they keep coming back, causing repeated episodes of pneumonia.
Over time, chronic inflammation destroys the small airways, eventually resulting in bronchiectasis. Now moving on to lung obstruction, in this case, the cilia of epithelial cells cannot move mucus and debris out of the lungs.
This might happen when something is physically blocking the airway, such as tumors or foreign objects like a peanut. It can also occur if the cilia themselves are not functioning properly, as in primary ciliary dyskinesia, or if the mucus is too thick to move like in cystic fibrosis.
In all cases, mucus accumulates and becomes a breeding ground for infection and chronic inflammation. Over time, chronic inflammation leads to bronchiectasis.
In both recurrent inflammation and lung obstruction, if the inflammation continues for too long, fibroblasts step in to repair the damage by depositing collagen.
But instead of healing, this results in fibrosis and scarring of the bronchial and bronchiolar walls. In more severe cases, the fibrosis can extend to the tissues surrounding the bronchioles, a process called peribronchiolar fibrosis.
Now keep in mind that not all parts of the lungs are equally affected by bronchiectasis. In general, the lower lobes are most commonly involved, especially when the cause is a widespread condition such as infection and immunodeficiency.
However, when the cause is more localized, like with aspiration of a foreign object or a tumor, bronchiectasis tends to affect just one specific area of the lung.
Regardless of the underlying cause, the lung's ability to perform gas exchange in the affected area drops, resulting in low blood oxygen levels.
To adapt, the pulmonary arterioles constrict and redirect blood away from the damaged areas towards healthier parts of the lung where gas exchange is possible.

Symptoms4:48–5:10

However, if the damage is widespread, this vasoconstriction becomes widespread, increasing resistance throughout the pulmonary circulation and causing pulmonary hypertension.
The right ventricle must now push blood against much higher pressure so it thickens and becomes stronger. This condition is known as right ventricular hypertrophy and is often referred to as cora pulmonale.

Diagnosis5:10–5:39

Moving on to clinical manifestations, because mucus gets trapped in the lungs and the body is trying to clear it out, these individuals typically report a severe or persistent cough that brings up thick, foul smelling mucus.
Sometimes the inflammation can damage nearby small blood vessels. As a result, the person can cough up blood.

Treatment5:39–5:55

Next, the damage to the lung tissue makes gas exchange less effective, lowering oxygen levels in the blood and triggering shortness of breath.
In the worst cases, the lung damage is so bad and blood oxygen levels are so extremely low, it results in cyanosis. Diagnosis is based on imaging, more specifically a chest CT scan, which reveals dilated bronchi and bronchioles.

Recap5:55–7:23

As a result of decreased lung capacity and mucus buildup in the airways. Pulmonary function tests will reveal reduced lung capacity and the ability to force air out of the lungs.
Finally, genetic testing can help uncover hereditary causes like primary ciliary dyskinesia and cystic fibrosis. Treatment focuses on managing recurrent infections with antibiotics along with clearing excess mucus through percussion or postural drainage.
If a physical blockage like a tumor is causing problems, surgical intervention might be necessary. All right, as a quick recap, bronchiectasis can develop after severe infections such as necrotizing pneumonia caused by Staphylococcus aureus, Klebsiela, or Mycobacterium tuberculosis, or after recurrent infections like in individuals with immunodeficiencies where the immune system fails to clear pathogens.
It can also result from airway obstruction either from physical blockages like tumors or foreign objects or from impaired mucus clearance due to conditions like primary ciliary dyskinesia or cystic fibrosis.
In both cases, mucus buildup promotes persistent infection and inflammation which over time damages the airway walls and leads to permanent dilation of the bronchi and bronchioles.