Pathology of Restrictive Lung Disease - UIP Flashcards
What is UIP
Usual interstitial pneumonitis
In which diseases can UIP be seen
Connective tissue diseases Drug reaction Post infection Industrial exposure Others
In what main types of connective tissue diseases can UIP be seen
Scleroderma and Rheumatoid disease
What type of industrial exposure can cause UIP
Asbestos
Why can UIP be called IPF or CFA, What do they stand for
Most cases of UIP are cryptogenic or idiopathic
Iiopathic pulmonary fibrosis (IPF)
Cryptogenic fibrosing alveolitis (CFA)
What will the histopathology of UIP show
Patchy interstitial chronic inflammation
Type II pneumocyte hyperplasia
Smooth muscle and vascular proliferation
Give 6 common features of UIP
Occurs in the elderly (over 50)
Males affected more than females
Progressive disease – many die within 5 years of presentation
CXR shows Basal/Posterior, Diffuse infiltrates, Cysts, ‘Ground Glass’
Restrictive PFT & Reduced Gas Transfer
Poor Prognosis
What are the symptoms of UIP
Dyspnoea Cough Basal Crackles Cyanosis Clubbing
Which agents have been effective in UIP and which are ineffective
Effective - anti-angiogenic agents
Ineffective - Steriods
In what two forms can the air in the airways move and what is it dependent on
Laminar or Turbulent
Dependent on the pressure difference
How is gas exchanged beyond the terminal bronchiole
Diffusion
What does the affinity of Hb for oxygen allow
The blood which leaves the capillary bed is 98% saturated for FIO2 of only 0.21
What does the soulbility of CO2 allow
CO2 can rapidly equilibrate between the blood and air
What are normal PaO2 levels
10.5 - 13.5 kPa
What are normal PaCO2 levels
4.8-6.0 kPa
What are PaO2 levels in type I respiratory failure
PaO2 <8 kPa (PaCO2 normal or low)
What are PaCO2 levels in type I respiratory failure
PaCO2 >6.5 kPa (PaO2 usually low)
What are the 4 abnormal states associated with hypoxaemia
Alveolar Hypoventilation
Shunt
Ventilation / Perfusion imbalance - V/Q
Diffusion impairment
What is FIO2
The Fraction of Inspired air which is Oxygen
What is alveolar hypoventilation
The amount of air moved in and out of the lungs
What happens in alveolar hypoventilation
PACO2 increases so PaCO2 increases. The increase in PACO2 causes a decrease in PAO2 causing PaO2 to fall
How is a fall in PaO2 due to hypoventilation corrected
By raising FIO2
What is the normal V/Q level
We normally breath 4L/min and CO is 5L/min so normal V/Q is 4/5 or 0.8
What is the commonest cause of hypoxaemia encountered clinically
Low V/Q
How can low V/Q in some alveoli arise
Due to local alveolar hypoventilation due to some focal disease
What does hypoxaemia due to low V/Q respond to
Small increases in FIO2
What is diffusion impairment
When it takes longer for blood and alveolar air to equilibrate, particularly for oxygen.
What is the gas flow through a membrane dependent on
The thickness and surface area of the membrane and the gas pressure across it.
Why can CO2 diffuse 20 times faster than O2
Due to its greater solubility
Do diseases which impair gas diffusion change CO2 levels
Normally no
What does diffusion impairment mean
That it takes longer for blood and alveolar air to equilibrate, particularly for oxygen.
How long does equilibration normally take
0.25 seconds
What is the normal capillary transit time
0.75 seconds
How long can equilibration take in disease
May take close to 0.75 seconds so PaO2 is maintained at rest however there can be serious falls in PaO2 on exercise as RBC are spending less time in the capillary bed
How can hypoxaemia be corrected in diffusion impairment
Increasing FIO2
This increases PAO2, thus increasing rate of diffusion
What is a shunt
When blood passes from the right side to the left side of the heart without contacting ventilated alveoli
What is a normal shunt size
2-4%
What can cause pathological shunts
AV malformations
Congenital heart disease
Pulmonary disease
How will a large shunt respond to increases in FIO2
Poorly
The blood leaving the normal lung is already 98% saturated
