Obstructive: Emphysema Flashcards
What is emphysema?
Destruction of alveolar air sacs
Loss of elastic recoil and collapse of small airways, leads to air trapping
Explain the pathogenesis of Emphysema (elastic recoil)
Physiological obstruction
Elastic recoil snaps distal air sacs back to release air
Loss of elastic recoil = rather than having lots of small alveoli you have one large one
Difficult to release the air – obstruction
Another obstruction reason is
- Cartilage helps keep wall open during exhalation so there is no collapse of bronchi
- Difference between bronchus and bronchiole = bronchiole has no cartilage
- Alveolar air sacs surrounding with elastic recoil holds open the tube walls
Loss of elastic recoil means when air goes out, the wall is dragged along with it, causing the wall to close, resulting in obstruction
Collapse of small airways due to loss of elastic recoil of the alv air sacs (air trapping)
Spongey appearance histologically
How does an imbalance of proteases and antiproteases lead to emphysema?
Emphysema occurs due to an imbalance between proteases and antiproteases
- Most of what we breathe in is filtered by the mucus keeping the distal portions of lung clean
- Base of lung doesn’t have these defence mechanisms so only way to keep it clean are via cells known as alveolar macrophages -
- Engulfing the particles causes small amounts of inflammation in the alv air sacs
- Inflammation in lung normally leads to release of proteases (including elastase) by neutrophils and macrophages
- They damage lung but body produces protein which protects against the proteases known as antiproteases
- Antiproteases incl alpha-1-macroglobulin and secretory leukoprotease inhibitor
- Most imp is called alpha-1 antitrypsin which neutralises
- Normally exists in a balance – so however many proteases are produced we have the same level of antiproteases to protect us
Emphysema can also result in one of two ways
- Either an increase in production of proteases (via smoking) destroying alv air sacs, causing excessive inflammation
- Or decrease in production of antiproteases (alpha-1 antitrypsin deficiency -A1AD) - cannot protect against normal protease damage
And over time emphysema develops
Name the types of emphysema, and what causes them with pathophysiology
There are two major categories of emphysema
- Centriacinar (95%)
- Panacinar (5%)
Smoking results in CENTRICINAR emphysema
- More severe in upper lobes
- Because smoke travels upwards
- Terminal bronchiole opens up into alv air sacs
- Both terminal bronchiole and air sac are an acinus
- So the main part hit by smoke is the beginning part near bronchioles – or proximal resp bronchioles involved, distal are spared
- So that’s why centriacinar is the most common in smokers
- Panacinar means ENTIRE acinus is affected
– Due to A1AD - Common in lower lobes
- Liver cirrhosis can also be present due to panacinar
- A1AT protein is not in the blood but the liver continues to make it
- Mutant A1AT accumulated in ER of hepatocytes
- Damaging liver and causing cirrhosis
How they may ask you in exam
- Biopsy reveals pink PAS-positive globules in hepatocytes
How is Emphysema severity based on the degree of deficiency? (Allele conformation)
- PiM is normal allele
- 2 COPIES are usually expressed OF PiM
- The PiZ is most common mutation – results in low levels of circulating A1AT
- Patients could be heterozygous, having one normal and one mutated allele – PiMZ – they are usually asymptomatic but they have a decrease in circulation of A1AT because they are only producing half of the normal amount
- They are usually fine but if they smoke, there is a very high risk of emphysema – so you treat these patients with making sure they DON’T SMOKE
PiZZ Homozygotes
- Significant risk for panacinar emphysema and cirrhosis
- Classic patient to get this
What are the signs and symptoms for emphysema?
- Dyspnoea
- Cough with minimal sputum
- Wheezing
- Pink puffer (prolonged expiration with pursed lips!!)
Pursed lips increase the airway pressure and prevents airway collapse… back pressure from above, forcing the walls open, prolonging expiration, getting air out slowly, allowing air to move in and out, requires tremendous amount of work, hence why you …… - Lose weight
- Fatigue
- Use accessory muscles to breathe
What does emphysema look like on a CXR?
- Increased AP diameter (barrel-chest)
- Flattened diaphragm
- Increased lung field lucency
Tendency of lung Is to collapse in and chest wall goes out
There is an imbalance, the set point is the functional residual capacity … more expansion.
When you lose the elastic recoil of the lung and chest goes out you reset the FRC so its now INCREASED!
NOTE: If there was fibrosis, the elastic recoil is increased therefore pulls chest wall IN a little
What occurs to the DLCO and lung compliance during emphysema
- Decreased DLCO (- Diffusing capacity of the lungs for carbon monoxide is a medical test that determines how much oxygen travels from the alveoli of the lungs to the blood stream) from destruction of alv walls
- Imbalance of proteases and antiproteases = increased elastase activity = increased loss of elastic fibres = increased lung compliance
Compliance = measure of the lung’s ability to stretch and expand
Explain the results of emphysema on gross examination
- Lungs are enlarged and overinflated
- Enlarged grossly visible air spaces
- Show formation of apical blebs and bullae (centriacinar type)
What can be the later complications of emphysema?
- Hypoxemia
Pink puffers can maintain gas exchange due to prolonged expiration and pursed lips
But if this continues, you lose air sacs and recoil
Lose the bed of oxygen exchange in capillaries within walls of air sacs,
they cant generate a good PaO2
- Cor Pulmonale
Occurs after hypoxemia, blood vessels constrict, the R heart pumps against the BV, undergoes R sided hypertrophy first then eventually r sided heart failure
