Pulmonary Pathophysiology - Obstructive Lung Disease Flashcards
Mechanisms of airway obstruction
Secretions / fluid / foreign body within airway
Increased thickness of airway wall
Loss of radial traction of airway secondary to alveolar destruction
Examples of causes of increased airway thickness
Hypertrophy of smooth muscle
Chronic bronchitis
Example cause of alveolar destruction resulting in reduced airway radial traction
Emphysema
COPD components
Mixed picture of emphysema and chronic bronchitis
Emphysema definition
Enlargement of air spaces distal to the terminal bronchiole with destruction of their walls
Anatomical diagnosis
Distribution / types of emphysema
Centriacinar emphysema
Panacinar emphysema
Bullous emphysema
Paraseptal emphysema
Lower zone emphysema
Lower zone emphysema
Primarily lower lung zones affected by emphysema
Caused by alpha 1 antitrypsin deficiency
Possible pathogenesis of emphysema (as suggested by alpha 1 antitrypsin deficiency)
Imbalance of protease-antiprotease system
Cigarette smoking causes release of neutrophil elastase
Elastase attacks both elastin and collagen
Type IV collagen in blood gas barrier may be a critical structure
Why do neutrophils contain elastase
To break down bacteria
Chronic bronchitis definition
Excessive mucus production in the bronchial tree sufficient to cause excessive expectoration of sputum
Clinical diagnosis
Pathophysiology of chronic bronchitis
Increased mucus production by mucus glands in response to airway pollutant (cigarette smoke)
Mucus volume overwhelms mucociliary escalator
Changes in small airways in chronic bronchitis
Inflammation
Airway wall oedema
Narrowing
Cellular infiltration
Peri-bronchial fibrosis
Effect of single cigarette on airway conductance
Significantly reduces airway conductance for around 1 hour after single cigarette
Clinical presentations of COPD
Type A (Pink puffer)
Type B (Blue bloater)
Usually patients are a mix of type A and type B
Type A COPD presentation
‘Pink puffer’
SOB with high ventilation rate
Maintains relatively normal PaO2 and PaCO2
Type B COPD presentation
‘Blue bloater’
Severe chronic bronchitis
PaCO2 higher and lower PaO2
Pulmonary HTN + right heart failure
Lung volume changes in COPD
TLC, FRC and RV typically increased
Gas exchange changes in COPD
Pulmonary circulation changes in COPD
Pulmonary hypertension (Cor pulmonale)
Fluid retention with pulmonary oedema
Right heart failure
Causes of pulmonary hypertension in COPD
- Destruction of capillary bed
- Hypoxic vasoconstriction
- Polycythaemia - increases blood viscosity
- Thickening of small artery walls
Hypoxic vasoconstriction
Vasoconstriction of poorly ventilated alveoli / lung to maintain V/Q matching
Early changes in COPD early stages
Increased resistance in small airways
Management of COPD
Lung tissue destruction is irreversible
Abx + prevention of exacerbation for bronchitis
Bronchodilators for reversible bronchoconstriction
LTOT can reduce pulmonary hypertension
Lung volume reduction surgery
Rehabilitation programs
Asthma definition
Increased responsiveness of airways to various stimuli.
Manifested by inflammation and widespread airway narrowing that changes in severity either spontaneously or in response to treatment.
Clinical features of asthma
Often begins in children but can be any age
Can be related to specific allergens
General hyper-reactivity of airways
May have other atopy features
Common triggers for asthma
Smoke
Cold air
Exercise
Aspirin
Status asthmaticus
Exacerbation which may last for hours
Pathological changes in airways with asthma
Pathogenesis of asthma
Airway hyper-responsiveness
Airway inflammation
May be an allergic basis
Possible reasons for increasing incidence of asthma
Environmental factors
Pollutants
Genetic component
Inflammatory mediators involved in asthma
Cytokines associated with T helper cells
Interleukins 3, 4, 5 and 13
Arachidonic acid metabolites
Leukotrienes, prostaglandins
Histamine, platelet activating factor
Location of Beta 2 adrenergic receptors
Bronchi
Blood vessels
Uterus
Location of Beta 1 adrenergic receptors
Heart
Action of Beta 2 adrenergic receptors
Increase activity of adenyl cyclase
-> Raises concentration of cAMP in smooth muscle
Also reduce airway inflammation
Action of inhaled corticosteroids
Inhibit inflammatory and immune response
Enhance Beta 2 receptor expression or
function
(Minimal systemic absorption)
Additional bronchoactive therapies used for asthma
Methylxanthines
Anticholinergics
Leukotriene receptor antagonists
Methylxanthine examples
Theophylline
Aminophylline
Lung volume changes in asthma exacerbation
FRC and TLC increase
Lung compliance increases
RV increases as diseases airways close prematurely in expiration
Why is it helpful for lung volumes to increase in asthma exacerbation
Increase volume results in increased radial traction on airways and pulls them open to reduce airway resistance
Which airways are affected in asthma
Likely all airways of all size are constricted in asthma exacerbations
Gas exchange changes in asthma
Uneven distribution of ventilation
Ventilation perfusion mismatch
Less significant than mechanical changes in asthma mentioned earlier
