Pathophysiology of Respiratory Diseases - COPD and Pneumonia Flashcards
What is Chronic Obstructive Pulmonary Disease (COPD)?
- Umbrella term for patients with respiratory diseases e.g emphysema
- Characterised by a progressive, long-term decline in respiratory function
Outline three possible causes of COPD
- Smoking
- Exposure to pollution
- Genetic disorders e.g alpha-1-antitrypsin deficiency
Why is smoking considered dangerous?
- Contains harmful chemicals which cause acute damage
- Repeated exposure can cause irreversible injury
Outline COPD inflammation.
- Tobacco smoke causes acute local inflammation due to tissue damage
- Immune cells, such as neutrophils and macrophages, are attracted to damaged tissues
- These cells release proteolytic enzymes to breakdown dead cells and attempt to resolve inflammation. However these enzymes can also degrade structural proteins
- Smoke contains chemicals that inactivate antiproteases. Protease burden increases and tissue damage also increases.
What is the effect of an impairment in mucociliary clearance due to smoking?
- Cilia are damaged
- Increased secretion of mucus
- Increases likelihood of further respiratory infections - causing further inflammation
What is the effect of long-term tissue damage?
Tissue remodeling
- Reduced ventilation and gas exchange
What is chronic bronchitis?
Long-term inflammation of the airways
What is the main effect of chronic bronchitis?
- Coughing due to irritation of sensory neurons
- Mucus hypersecretion due to stimulation of mucus glands
- Weakened airway structure due to degradation of elastin by proteases
- Decreased luminal area - increased resistance to airflow.
Why are asthma treatments such as salbutamol less effective for COPD?
- In asthma, airway lumen size is reduced by smooth muscle contraction
- In COPD, airway lumen size is reduced by inflammation, mucus secretion. Smooth muscle contraction only plays a limited role
- Salbutamol works by causing a relaxation in smooth muscle of the airways. This would have very little effect in COPD.
Define emphysema
- Pathological enlargement of alveolar airspaces
What is the effect of emphysema?
- Loss of elastin causing compliance to increase and recoil to decrease
- Reduced surface area and damage to pulmonary vasculature (reduced gas exchange)
Why is COPD considered progressive?
- Patients usually suffer frequent exacerbations of symptoms
- Lung function fails to return to previous levels which can cause respiratory failure
- Smoking cessation only slows, not stops decline in function
Outline the way in which COPD places burden on the CVS - PART 1
- Alveoli are hypoventilated
- This causes hypoxic vasoconstriction
- Vascular resistance rises so force and pressure at which blood is pumped rises - pulmonary hypertension
Outline the way in which COPD places burden on the CVS - PART 2
- Increased RV afterload. Greater effort required to maintain normal blood flow against increased resistance. RV hypertrophy occurs
- Heart eventually unable to cope with increased burden. Causes heart failure/myocardial infarction.
What is pneumonia an infection of?
Alveoli and surrounding lung tissue
Outline the steps involved in the development of pneumonia.
PART 1
- Pneumonia follows weakening of host defences e.g immune suppression, HIV
- Alveoli become colonised by pathogens
- Alveolar macrophages are activated and release cytokines, such as IL-6 and IL-8
Outline the steps involved in the development of pneumonia.
PART 2
- IL-6 and IL-8 recruit neutrophils to the lungs, releasing pro-inflammatory cytokines
- They also recruit reactive oxygen species to kill the pathogens
- However, this will injure surrounding tissues such as the alveoli
Outline the steps involved in the development of pneumonia.
PART 3
- The damage causes an ‘acute lung injury’
- Inflammation signal and injury to alveolar walls and capillary endothelium causes fluid to be drawn into alveoli and interstitial tissue
- This causes oedema. Diffusion distance increases so rate of gas exchange decreases
Outline the steps involved in the development of pneumonia.
PART 4
- Damage to alveolar walls and accumulation of dead cells cause a hyaline membrane to form
- The hyaline membrane is thick and impermeable. This also reduces diffusion distance.
- These changes causes hypoxaemia.
Why is simultaneous loss of airway patency and elastic recoil problematic in COPD?
- The airways are connected to the surrounding lung tissue.
- These connections help keep the airways open (as they are joined by various elastin).
- So the lungs increase in size and the airways are compressed (during expiration).
- In COPD the airways begin to lose patency
- Due to loss of elastic recoil, lungs need to be compressed harder during expiration
