Allergy in the lung

Question 1

What are the limitations of the anatomy of the human lungs?

Answer 1

Air inlet and outlet (mouth) are the same, so can only breathe in half the time.
When we exhale we force air out and the airways collapse.

Question 2

What is allergy?

Answer 2

An immune system mediated intolerance.

There is always a trigger.

Question 3

Why does chronic allergy lead to tissue remodelling?

Answer 3

As you get recurrant inflammation, repair and fibrosis.

Question 4

What is the best investigation for allergy in the airways?

Answer 4

Spirometry.

Question 5

What causes wheeze/stridor?

Answer 5

Turbulence in the lungs.

Turbulance happens at junctions.

Question 6

Why is there wheeze in asthma?

Answer 6

Due to asymetrical narrowing of the airways. Air can start going in circular motions rather than moving down the airway in a linear fashion.
wheeze shows there is expiratory phase narrowing,

Question 7

When does stridor occur?

Answer 7

In extra-thoracic airway problems that affects air getting in. It only occurs in inspiration.

Question 8

Why is extrathoracic lung problems less common than intrathoracic?

Answer 8

As extrathoracic airways have cartilage rings to hold the airways open so isnt as vunerable to pressure changes.

Question 9

Draw the characteristic flow volume loops of

1. Normal lungs
2. extrathoracic disease
3. intrathoracic disease

Answer 9

1. normal = beauty blender shape
2. Smaller rectangle
3. L shape

Question 10

What % of the adult population have asthma?

Answer 10

15%

Question 11

What are the pathological features of asthma?

Answer 11

Inflammation
Scabby epithelium
Thickened BM and smooth muscle.
Mast cells in smooth muscle.

Question 12

What is the physiological features of asthma?

Answer 12

Reversible/variable airflow obstruction
Yello mucus
Non-elastic airways
Increases responsiveness and sensitivity

Question 13

What are the clinical features of asthma?

Answer 13

Cough 
Wheeze 
Hyper-reactivity (e.g. aspirin)
Hyper-sensitivity 
Triggers 
SOB and exercise intolerance
Diurnal - worse at night/noctural wakening.

Question 14

Describe the histology of the airways seen in asthma?

Answer 14

Airway lumen filled with mucus 
Destroyed airway epithelium
Thick BM and sub-epithelial  fibrosis 
SM hypertrophy 
Mass cells in SM.

Question 15

What do mast cells in the SM in asthma release?

Answer 15

Histamine

Question 16

What physiological tests can be done to support a diagnosis of asthma?

Answer 16

1. Give patient diary and peak flow meter and track readings. Look for diurnal variation.
2. Look for hypersensitivity by inducing an ‘asthma attack’ to look for bronchial hyper-responsiveness. Give histamine/metacholine/manitol through a mask and look for a drop in FEV1 of 20%.
3. Spirometry - look for an improvement of >15% of FEV1 after 5mg nebulised sulbutamol/
4. Can allergy test e.g. cat scratch test.

Question 17

Airway allergy drives eosinophillic inflammation. What cytokines are increased? What is the result of this?

Answer 17

TNF-alpha
TGT-beta
VEGF

These activate the ells protecting the lung (mast cells, lymphocytes, macrophages and epithelial cells) resulting in airway remodelling, fibrosis, SM hypertrophy and epithelial damage.

Question 18

Some biological therapies can be used in asthma. What does Anti-IgE therapy target?

Answer 18

Mast cells.

Question 19

What cells do corticosteroids target?

Answer 19

Mast cells, macrophages and smooth muscle.

Question 20

What do anti-leukotriene receptor drugs target?

Answer 20

macrophages and smooth muscle.

Question 21

What do bronchodilators target?

Answer 21

SM and autonomic nerves.

Question 22

List future treatments for asthma?

Answer 22

Biological therapy: Specific cytokine targets e.g. TNF, IL-5
Thermoplasty
Nerve ablation.

Question 23

What is Extrinsic Allergic Alveolitis (EAA)?

Answer 23

Inhalation of an allergen causing immune-complex formation which activates complement causing inflammation and damage to the lung.

Question 24

In EAA, What does complement activation in the lung cause?

Answer 24

Remodelling and fibrosis.

Question 25

In EAA what effect do immune complexes have on the rest of the body?

Answer 25

Activate complement. | Circulate round the body and damage small capillaries e.g. in the lung and the kidney.

Question 26

List some common triggers of EAA?

Answer 26

Bird Dander e.g. pigeon fanciers lung. Farmers lung (fungal spores) Malt workers lung (barley allergy) Humidifier lung

Question 27

When does the acute ilness of EAA come on?

Answer 27

Not instant like a type 1 allergic reaction - occurs 4-6h after exposure.

Question 28

What are the symptoms of EAA?

Answer 28

``` Wheeze Cough Fever Chills Headache Myalgia Malaise Fatigue Hypoxia. ```

Question 29

Why is there hypoxia in EAA?

Answer 29

As the alveoli fill with inflammatory fluid. | Due to thickening of septae due to inflammatory response and neutrophil infiltration.

Question 30

Is there a systemic response in EAA?

Answer 30

Yes

Question 31

What can be seen on CXR in EAA??

Answer 31

Airspace shadowing

Question 32

What can result from chronic exposure to the trigger in EAA?

Answer 32

Fibrosis and interstitial scarring. | Emphysema due to interstitial destruction from neutrophil enzyme release.

Question 33

What is Ficks Law?

Answer 33

rate of diffusion = surface area X concentration difference | DIVIDED BY membrane thickness

Question 34

What are the clinical consequences of EAA see in tests?

Answer 34

- Decreased oxygen transport to the blood stream (CO2 stays ok). Seen in carbon monoxide gas transfer in PFT's. - Airspace shadowing on CXR - Restrictive lung defect on spirometry due to reduced elasticity

Question 35

What is the management of EAA?

Answer 35

Avoid triggers. Corticosteroids for inflammation (neutrophils often steroid responsive) O2 supplementaton.