Physiology and function in restrictive lung disorders Flashcards
What is a restrictive disorder?
A disorder in which prevents normal expansion of the lungs
What can cause lung restriction?
- Extra-pulmonary disease (visceral pleura, pleural space, chest wall including parietal pleura, bones, muscles, nerves)
- Intra-pulmonary disease (alveolar spaces)
What are the 5 examples of extra-pulmonary restriction?
- Integrity of nerves to respiratory muscles (high cervical dislocation)
- Impaired neuromuscular junctions (myasthenia gravis)
- Impaired muscles (muscular dystrophy)
- Pleural thickening (asbestos exposure)
- Skeletal abnormalities (scoliosis)
Examples of diseases causing increased fibrous tissue in the lungs (intra-pulmonary)
- Silicosis in a stonemason
- Asbestosis
- Drug-induced lung fibrosis
- Coal-workers pneumoconiosis
- Rheumatoid-lung
- Bird-fanciers lung
- Idiopathic pulmonary fibrosis
How do fibrotic lung diseases cause restrictive disorders?
- Inflation pressure
- Pulmonary compliance (the ability of the lungs to stretch during a change in volume relative to an applied change in pressure= stretchability)
- Elastic recoil pressure (=alveolar pressure minus pleural pressure)
What is the relationship between inflation pressure, compliance and elastic recoil?
- A lower compliance means greater inflation pressure required to inflate which means higher elastic recoil
- Elastic recoil not the same as elastance
- Elastance is the reciprocal of compliance hence= change in pressure/ change in volume
What is the effect of decreased compliance on inflation?
- Increased fibrous tissue (more rigid)
- Decreased compliance (requires high pressure to inflate)
- Increased elastic recoil (deflates easily)
What is the effect of increased compliance on inflation?
- Associated with an obstructive defect, particularly emphysema
- Decreased elastic tissue (more floppy)
- Increased compliance (inflates at low pressures)
- Decreased elastic recoil (difficult to deflate)
How are lungs different to balloons?
- Alveoli are moist
- Alveoli are of different sizes
How does moisture affect alveoli?
-Moisture causes surface tension which influences the pressure inside a sphere
-Inward force generated by fluid layer surface tension (sT)
-Laplace’s Law for a sphere:
P = (2 x sT)/ radius
How does size affect alveolar pressure?
- Same inflation pressure and same surface tension
- Well-inflated alveolus, large radius= relatively low alveolar pressure
- Under-inflated alveolus, small radius= relatively high alveolar pressure
How does having different sized alveoli affect instability?
- Air moves from high pressure area to low pressure area
- Smaller alveolus empties into larger alveolus
- There is instability of adjacent alveoli
What is surfactant?
- Surface Active Agent
- Produced by alveolar Type 2 cells
- Composed of lipids (90%, mainly phospholipids) and proteins (10%)
- Reduces surface tension
- Hydrophobic end (fatty acids) in gas and hydrophilic end (glycerol, phosphate and choline) in liquid
What are the mechanisms of action of surfactant in well-expanded alveoli?
- Surfactant spread evenly over alveolar surface but molecules spread out
- Surfactant has little effect on surface tension
- Large radius= high surface tension
What are the mechanisms of action of surfactant in deflated alveoli?
- Tightly packed surfactant molecules
- Some surfactant molecules extruded from the surface
- Surfactant significantly reduces surface tension with accompanying lower pressure
- Small radius= low surface tension
What is Respiratory Distress Syndrome of the New-born?
- Surfactant deficiency
- Surfactant first produced 210 days (30 weeks), c.f. full term= 280 days (40 days) so preterm birth
- Low compliance
- High inflation pressures
- Rapid shallow breathing (fatigue)
- Hypoxaemia
What is primary surfactant deficiency?
-Very rare in adult disease Impaired surfactant biology contributes to pathogenesis of -Adult respiratory distress syndrome -pneumonia -idiopathic pulmonary fibrosis -lung transplant
Describe the patterns of abnormal lung function of mild/moderate obstructive disease
FVC, TLC, VC all normal
FEV1, FEV1/FVC ratio decreased
RV, RV/TLC ratio increased
Describe the patterns of abnormal lung function of severe obstructive disease
FVC, VC normal or small or decreased
FEV1, FEV1/FVC ratio decreased
TLC, RV, RV/TLC ratio increased
Describe the patterns of abnormal lung function of restrictive disease
FEV1, FVC, TLC, VC decreased
RV normal or decreased
FEV1/FVC ratio, RV/TLC ratio normal or increased
What are predicted values based on?
Age
Gender
Height
Ethnic origin
What is the effect of age on FEV1?
0-18 increased in children
40+ decreases in adults
What is the Gas Transfer Measurement?
Gas transfer is a measure of the diffusing capacity of the lung
Requires a measurement of gas exchange and alveolar volume
What is the ideal gas for gas exchange?
-Rapidly taken up by haemoglobin with very high affinity
-Not produced by the body
-Non-toxic
-Easy to measure
Carbon monoxide
What is the ideal gas for alveolar volume?
-Not taken up by haemoglobin
-Not produced by the body
-Non-toxic
-Easy to measure
Helium
Describe the Carbon Monoxide Gas Transfer Measurement
Single breath method Inspired test gas contains 0.3% CO, 10% helium and air Breathhold at TLC approx. 10 secs Washout Alveolar sample
What does the CO Gas Transfer Measurement help to calculate?
TLCO (mmol/min/kPa) Total gas exchange capacity
Va Alveolar volume= number of contributing lung units
KCO Efficiency of gas transfer per unit of lung
How does TLCO and KCO help differentiate between extra and intra pulmonary diseases?
Extra- TLCO low (lungs are smaller), KCO high (alveoli are normal and tightly packed with blood vessels)
Intra- TLCO low (lungs are smaller), KCO low (alveoli are abnormal)
