Mucociliary clearance in health and disease

What are the defence mechanisms of the upper airway?

The upper airway has several defence mechanisms to prevent the passage of particles and irritants to the lungs. These include a sneeze if larger particles enter nasal passage, ciliated epithelium lining nose and turbinates to trap dust and foreign particles, the epiglottis covers trachea during swallowing preventing aspiration of food and drink into the trachea and a cough if irritants do manage to enter the trachea/lungs.

The mucociliary escalator provides an effective defence mechanism for the airways against the inhalation of foreign bodies and pathogens. What are the three components of the mucociliary escalator?

There are 3 essentials for an effective mucociliary escalator: ciliated epithelium, aqueous sol layer/peri-ciliary fluid, mucous/gel layer.

To which generation of the airways does the mucociliary escalator extend?

The mucociliary escalator extends as far as the respiratory bronchioles. Below this level there is no means of protection from dust and debris.

How does dehydration effect the mucociliary escalator?

Dehydration drys out the aqueous sol layer. This means cilia are bathed in less fluid so do not beat as efficiently and effectively as normal. The mucous layer also becomes dehydrated, resulting in thick, sticky secretions. The combination of thick secretions and ineffective cilia result in impaired mucocilary clearance and secretion retention.

What is the average volume of secretions produced daily to line the airways of healthy adults? [change to MCQ?]

Up to 100mls of secretions are produced daily to line and lubricate healthy airways. These secretions are often cleared and swallowed subconsciously.

How does aging effect mucociliary clearance?

As we age, ciliary beat frequency decreases, meaning secretion clearance is slower. This combined with the other effects of aging on the respiratory system predisposes older people to the develeopement of lower respiratory tract infections.

The epiglottis descends horizontally, covering the larynx and protecting the airway during expiration true or false? [change to T/F?]

False, during swallowing the larynx rises and the epiglottis folds downwards, covering the larynx and protecting the airway from the aspiration of food, drink or saliva.

List the factors that may impair normal mucociliary clearance.

Age, fluid balance, hypersecretory conditions, general anaesthesia, uncoordinated (dyskinetic) cilia, cold air, infection / inflammation, smoking.

What are the possible consequences of impaired mucociliary clearance?

Possible consequences of impaired mucociliary clearance include: secretion retention, the development of a potential breeding ground for bacteria, increased production of secretions in response to infection, increased airflow obstruction imapairing ventilation and work of breathing, breathlessness.

Do atmospheric conditions have any impact on mucociliary clearance and if so which patient groups may this be problematic for?

Cold air tends to result in a running nose as the nasal passages produce more fluid and secretions in attempt to warm and humidify the colder than usual inspired air. Hot, dry conditions will lead to dehydration of the nasal mucosa and mucociliary escalator, impairing secretion clearance. This can be particularly problematic for patient with pre-existing hypersecretory lung conditions such as cystic fibrosis, bronchiectasis and COPD.