Airway Clearance - Pathophysiology Flashcards
What is the difference between mucus and sputum?
Sputum is mucus from the respiratory tract outside the body (aka phlegm)
What is the normal level of airway mucus?
10-100mL mucus produced each day by submucosal glands, goblet cells, clara cells and tissue fluid exudate
What is the function of mucus?
- Mechanical barrier trapping particles
- Chemical screen (filter/diffusion)
- Biological barrier (bacterial adhesion/clearance)
- Airway hydration
What are the characteristics of mucus?
- Normally white/clear (mucoid)
- Altered colour indicates infection
- Smell (normally none)
- Thickness/viscosity
- Adhesivity
- Amount
What is the only illness that will produce pink, frothy sputum?
Pulmonary oedema
Where are goblet cells located?
In the epithelium of the mucosal layer (make up 10% of epithelium in proximal airways, decrease in number in peripheral airways)
What happens to goblet cells in COPD?
Increased number, extending peripherally
How can the structure of the alveolar region be described?
A pocket of air surrounded by a thin membrane
What channels connect the bronchioles and alveoli?
Pores of Kohn: Connect adjacent alveoli
Canals of Lambert: Connect terminal bronchioles
Inter-segmental respiratory bronchioles
What are the 4 mechanisms of airway clearance?
- Alveolar clearance: Removes insoluble particles
- Two phase flow: Airway narrowing on expiration create shear force that moves mucus towards the mouth
- Mucociliary clearance (MCC): Clears conducting airways
- Cough: Backup system when MCC fails
What 2 mechanisms of airway clearance can we influence?
MCC and cough
What cells clear the respiratory tract?
Ciliated cells of the periciliary (sol) layer of the mucosa (carry out mucociliary clearance)
Why is the depth of the periciliary (sol) layer important?
So the cilia can function correctly and move the mucus along the airways
What do the cilia use to move the mucus/particles?
Mucus blanket
What does the speed of MCC depend on?
Airway generation (fast movement in central airways)
What happens if the airways are not adequately hydrated?
The cilia cannot carry out their function
What is the mucus blanket composed of?
95% water, 1% salts, 4% lipids, foreign particles, cellular debris
In cystic fibrosis, what does the mucus blanket also contain?
DNA
How does the airway surface fluid (ASF) differ between healthy people and CF/infected patients?
Healthy: ASF is hypotonic
CF/infected: ASF is isotonic (dehydrated airway mucus secretions)
What are the factors that affect MCC?
**Exam Q!
- Age (slows in elderly)
- Sleep (decreases)
- Hairspray (decreases)
- Posture (gravity increases MCC if MCC impaired)
- Exercise (increases)
- Pollutants
- Smoking (variable)
- Medications
- Disease
In chronic bronchitis, what percentage does cough increase sputum clearance by?
20% (compared to 2.5% increase in healthy people)
What are the 4 steps of a quality cough?
**Need to know
- Inspiration of volume of air
- Glottis closed (opening btwn vocal cords)
- Simultaneous contraction of expiratory muscles resulting in large increase in intrathoracic pressure
- Glottis is open, rapid expiratory flow of air
Why is a deep breath important for an effective cough?
- More areas of lung receive ventilation
- Greater elastic recoil pressure of lungs
- Muscles at better position (length/tension relationship)
- Changes equal pressure point within airways
Where is the equal pressure point (EPP)?
- Located around the level of the trachea at high lung volumes
- Moves peripherally as lung volume decreases
What is the EPP?
The point where the pressure inside the airways is equal to the pressure surrounding the airways
Where does dynamic compression occur?
Downstream from the EPP (towards the mouth) and acts to shear the mucus from the airway walls
What happens to the EPP in a normal cough?
- Expiratory muscle activity causes dynamic compression of trachea & intrathoracic airways
- Dynamic compression increases velocity of air downstream from EPP, applying a shearing force
- Airflow causes misting of mucus
- Enhanced movement of mucus from trachea, inner/intermediate regions of lungs (not outer)
What are the adverse effects of vigorous coughing?
- CV (decrease BP, cardiac rhythm disturbances)
- Genitourinary (incontinence)
- GI (reflux, inguinal hernia)
- Musculoskeletal (rib fracture)
- Neuro (syncope, headache)
- Respiratory (airflow limitation, pneumothorax)
Why can coughing be exhausting?
It produces high intrathoracic pressures and is associated with high energy consumption
What is a huff?
Maintains open glottis, prolonged less explosive expulsion of air
What are the benefits of a huff?
- Similar effect on mucus clearance
- Energy efficient, less painful
- Manipulates EPP to pick up sputum more distally into the airway
What are the 3 main causes of impaired airway clearance?
- Excessive sputum production
- Impaired MCC
- E.g. medications, general anaesthetic, bronchiectasis, CF - Failure of cough
- Pain following surgery
- Chest wall trauma
- Denervated lungs post lung transplant
- Neuromuscular conditions e.g. Guillain Barre syndrome
- Drowsiness/confusion
What is the significance of retained airway secretions?
- Increased airway resistance (harder for lungs to expand)
- Can obstruct an airway causing distal collapse
- Site for bacterial infection
- Can cause airway destruction & cycle of impaired clearance (e.g. CF, bronchiectasis)
What is important to remember about sputum clearance problems?
Lots of sputum doesn’t always = problem
Someone can have lots of sputum, but if they can clear it effectively they don’t have a sputum clearance problem
OR
Someone can only have a little sputum, but if they can’t clear it effectively they do have a sputum clearance problem
What are the 2 phases of a pneumonia illness?
Consolidation (solid in lungs)
Resolution (sputum)
What is important to remember about the consolidation phase?
Sputum is still in a solid state, so clearance techniques will not work. Need to wait a few days until it is broken down before beginning sputum clearance
What is bronchiectasis?
When part of the airway becomes widened and floppy (ballooned-out pocket that fills with sputum)
