Pathology of Obstructive Lung Disease Flashcards
Define alveolar hyperventilation
Amount of air moved in and out of lungs
Describe the affect of alveolar hyperventilation on blood gases
- Hypoventilation increases PACO2, and thus increases PaCO2
- Increase in PACO2 decreases PAO2, which causes PaO2 to fall
- Fall in PaO2 due to hypoventilation is corrected by raising FIO2
- FIO2 = the Fraction of Inspired air which is Oxygen
What is chronic (hypoxic) Cor Pulmonale
Hypertrophy of the Right Ventricle resulting from disease affecting the function and/or the structure of the lung, except where pulmonary alterations are the result of diseases primarily affecting the left side of the heart or congenital heart disease
How is chronic bronchitis defined clinically?
Cough productive of sputum for 3 months for 2 or more consecutive years.
Pulmonary vascular changes in Hypoxia
•Physiological pulmonary arteriolar vasoconstriction
- When alveolar oxygen tension falls
- Can be localised effect
- All vessels constrict if there is hypoxaemia
A protective mechanism do not send blood to alveoli short of oxygen
Shunt
- Blood passing from Right to Left side of Heart WITHOUT contacting ventilated alveoli
- Normally 2-4% shunt
- Pathological shunt in AV malformations, congenital heart disease and PULMONARY DISEASE
- Large shunts respond poorly to increases in FI O2 as the Blood leaving normal lung is already 98% saturated
Ventilation / Perfusion imbalance
- NORMAL V/Q
- Response to oxygen
•Normally breathing ~4 l/min
Cardiac Output is ~5 l/min
normal V/Q is 4/5 or 0.8
- LOW V/Q is the COMMONEST cause of hypoxia encountered clinically
- LOW V/Q in some alveoli arises due to local alveolar hypoventilation due to some, focal disease
- Hypoxia due to low V/Q responds well to even small increases in FIO2
What are the normal values for FEV and FVC?
- FEV1 is usually about 70-80% of FVC
- Normal FEV1 is about 3.5 – 4 litres
- Normal FVC is about 5 litres
- Normal ratio FEV1 : FVC is 0.7 – 0.8
What are the 2 types of respiratory failure?
- Type I PaO2 <8 kPa (PaCO2 normal or low) - hypoxia and hypocapnea
- Type II PaCO2 >6.5 kPa (PaO2 usually low) - hypoxia and hypercapnia
What are the 4 abnormal states associated with hypoxia?
- Ventilation / Perfusion imbalance - V/Q
- Diffusion impairment
- Alveolar Hypoventilation
- Shunt
What are the 4 forms of emphysema and describe each one? (4)
- CENTRIACINAR - primarily the upper lobes. Occurs with loss of the respiratory bronchioles in the proximal portion of the acinus, with sparing of distal alveoli. This pattern is most typical for smokers.
- PANACINAR - involves all lung fields, particularly the bases. Occurs with loss of all portions of the acinus from the respiratory bronchiole to the alveoli. This pattern is typical for alpha-1-antitrypsin deficiency
- PERIACINAR - enlarged air spaces along the edge of the acinar unit, but only where it abuts against a fixed structure such as the pleura or a vessel.
•SCAR ‘ irregular’
‘Bullous emphysema’
(a bulla is an emphysematous space greater than 1cm)
What are the normal values for PEFR?
Normal 400 – 600 litres/min
Normal range is 80-100% of best value
50-80% of best is moderate fall
<50% of best is marked fall
What differs in bronchial asthma to COPD?
Bronchial asthma is generally reversable either spontaneously or as a result of medical intervention.
COPD is irreversable.
Why does COPD cause hypoxia?
- Ventilation / Perfusion abnormality (mismatch) due to airway Obstruction
- Alveolar Hypoventilation due to reduced Respiratory Drive
- Diffusion Impairment due to loss of Alveolar Surface Area
- Shunt only during acute infective exacerbation
Why does pneumonia cause hypoxia?
•Ventilation / Perfusion abnormality (mismatch)
-Bronchitis / Bronchopneumonia
•Shunt
- Severe bronchopneumonia - Lobar pattern with large areas of consolidation
