Pathophysiology of Respiratory Diseases - COPD and Pneumonia

Question 1

What is Chronic Obstructive Pulmonary Disease (COPD)?

Answer 1

• Umbrella term for patients with respiratory diseases e.g emphysema
• Characterised by a progressive, long-term decline in respiratory function

Question 2

Outline three possible causes of COPD

Answer 2

• Smoking
• Exposure to pollution
• Genetic disorders e.g alpha-1-antitrypsin deficiency

Question 3

Why is smoking considered dangerous?

Answer 3

• Contains harmful chemicals which cause acute damage
• Repeated exposure can cause irreversible injury

Question 4

Outline COPD inflammation.

Answer 4

• 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.

Question 5

What is the effect of an impairment in mucociliary clearance due to smoking?

Answer 5

• Cilia are damaged
• Increased secretion of mucus
• Increases likelihood of further respiratory infections - causing further inflammation

Question 6

What is the effect of long-term tissue damage?

Answer 6

Tissue remodeling
- Reduced ventilation and gas exchange

Question 7

What is chronic bronchitis?

Answer 7

Long-term inflammation of the airways

Question 8

What is the main effect of chronic bronchitis?

Answer 8

• 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.

Question 9

Why are asthma treatments such as salbutamol less effective for COPD?

Answer 9

• 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.

Question 10

Define emphysema

Answer 10

• Pathological enlargement of alveolar airspaces

Question 11

What is the effect of emphysema?

Answer 11

• Loss of elastin causing compliance to increase and recoil to decrease
• Reduced surface area and damage to pulmonary vasculature (reduced gas exchange)

Question 12

Why is COPD considered progressive?

Answer 12

• 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

Question 13

Outline the way in which COPD places burden on the CVS - PART 1

Answer 13

• Alveoli are hypoventilated
• This causes hypoxic vasoconstriction
• Vascular resistance rises so force and pressure at which blood is pumped rises - pulmonary hypertension

Question 14

Outline the way in which COPD places burden on the CVS - PART 2

Answer 14

• 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.

Question 15

What is pneumonia an infection of?

Answer 15

Alveoli and surrounding lung tissue

Question 16

Outline the steps involved in the development of pneumonia.

PART 1

Answer 16

• 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

Question 17

Outline the steps involved in the development of pneumonia.

PART 2

Answer 17

• 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

Question 18

Outline the steps involved in the development of pneumonia.

PART 3

Answer 18

• 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

Question 19

Outline the steps involved in the development of pneumonia.

PART 4

Answer 19

• 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.

Question 20

Why is simultaneous loss of airway patency and elastic recoil problematic in COPD?

Answer 20

• 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