What is mucus?

Every single person produces 30 mm or two tablespoons of mucus a day. This sticky mucus coats the inside of the pipelines of the lungs like a spider's web. When we breathe in, every day we breathe in up to 1 million microorganisms, and this is up to over 100,000 different type of organisms that we breathe in every day. The sticky mucus that coats the inside of the lungs acts like a spider's web to filter the air and to capture all of these microorganisms out of the air before they get further down into the body, into the alveoli and into the bloodstream. So this mucus is constantly filtering the air.’

If you want to learn more about this topic, you can watch Mitch Taylor's lecture here:

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Mucociliary escalator

The mucus then has an escalator, which is called the Muco-ciliary clearance layer in the lungs which is similar to an escalator at a shopping center. This escalator carries the mucus with all of the organisms in it, up the lungs at a rate of 1 mm/minute, up to the throat, where it's either coughed out or the mucus is swallowed into the stomach, where the acid in the stomach kills all of the organisms. This is happening in every person's lungs without us knowing subconsciously, every day. We are breathing in, microorganisms are caught by the mucous, the mucous is escalated out of the lungs, keeping the lungs nice and clear. This is our natural respiratory defense mechanism.

Vicious cycle of bronchiectasis

 As we know, in bronchiectasis, the bronchioles are damaged, and they produce more mucus. So if we come back to the escalator analogy, in normal lungs, single file, the mucus is moving up the escalator nicely. In someone with bronchiectasis, it's like ten or 20 people trying to get on the escalator at the same time. This causes a traffic jam or a backlog of mucus. And as we call it in bronchiectasis, mucus stasis. So this mucus that is stuck in the lungs, with all of the pathogens in it provides a harbour for these infectious pathogens to grow and to turn into chest infections. With chest infections, we get more mucus, and this creates the recurrent respiratory exacerbations, leading to the vicious cycle of bronchiectasis.

Something always happens to cause bronchiectasis in the first place. Whether it's an infection or pneumonia when someone was young, some smoke inhalation or a genetic cause, something causes the initial disruption of the bronchial wall. And this causes when we have that destruction, we get an abnormal mucus clearance mucus stasis. Because of the mucus being stuck in the lungs, we have bacterial infections and colonization of a variety of bacteria. Because of the recurrent infections, we have an increase in neutrophilic inflammation in the lungs. With this increase in inflammation, we get worsening destruction of the bronchioles and this can create worsening bronchiectasis, worsening mucus clearance, worsening infections, and the cycle continues.

Antibiotic resistance

  Patients with bronchiectasis have worsening lung function, worsening symptoms, and last but not least, they can develop antibiotic resistance. And this is really important to talk about because antibiotic resistance can be one of the leading causes of mortality in these patients. So we really want to try and break this cycle as early as we can to avoid the need for recurrent use of antibiotics in this cohort. Physiotherapists play an important role in breaking this vicious cycle by using airway clearance techniques to cause expectoration and thus clear the airways and the accumulation of mucus thereby breaking the cycle.

If you want to learn more about this topic, you can watch Mitch Taylor's lecture here:

Click here

SOURCES:

1. ‘Respiratory physiotherapy – bronchiectasis‘ lecture by Mitch Taylor