What is Chronic Obstructive Pulmonary Disease (COPD)?
- COPD is an umbrella term used for a mixture of chronic bronchitis and emphysema, and emcompasses a long-term, progressive and accelerated decline in respiratory function.
Why does smoking damage the respiratory system?
- The many harmful constituents of tobacco smoke cause acute damage to respiratory tissue, generating an inflammatory response.
- With repeated exposure, the inflammation becomes pathological and generates chronic and irreversible dysfunction.
How does the inflammation observed within the lungs of COPD patients develop due to tobacco smoke?
- Excessive and repeated exposure to tobacco smoke induces respiratory tissue damage, initiating an inflammatory response characterised by macrophages and neutrophils.
- These cells release proteolytic enzymes that degrade structural proteins.
- Exposure to specific chemicals in tobacco smoke also inactivates antiprotease enzymes, further increasing protease burden within the lung, leading to further tissue damage.
- Over the long term, this leads to tissue remodelling (irreversible changes in lung and airway structure) that reduces ventilation and gas exchange.
- Finally, other protective / defensive pathways within the airways, such as mucociliary clearance, are impaired by the remodelling (e.g. due to the loss of cilia and hypersecretion of mucus).
- This renders the respiratory system vulnerable to infections that lead to exacerbations, during which inflammation increases (in response to the infection) and respiratory function declines rapidly.
Mucociliary clearance meaning - It is the removal of particles from the airways as the result of the movement of the mucus coating due to the beating of the underlying cilia.
Exacerbations meaning - an increase in the severity of a disease or its signs and symptoms.
What is chronic bronchitis?
- Chronic bronchitis (long-term inflammation of the bronchi/airways) is characterised by chronic and excessive sputum production, coughing and airway obstruction.
- The coughing and mucus production is a consequence of inflammation (due to smoke exposure or infection) within the airway tissue, activating sensory neurons and stimulating mucus glands.
What pathological features are observed within the airways of COPD (chronic bronchitis) patients?
- Damage to cilia - so mucus cannot be pushed out of the lungs properly.
- Mucus hypersecretion (there is an increase in goblet cells and there is also an increase in mucus gland activation.
- Inflamed, swollen airway tissue and oedema.
- Weakened airway structure (loss of elastin) and loss of patency (airway colapse).
- Impaired mucociliary clearance, leading to an increased risk of infection (and recurrent infections).
- Irritation of sensory neurons, leading to coughing (smokers cough).
- Decreased luminal area, leading to increased airway resistance and obstruction.
What is emphysema?
- The term emphysema describes pathological enlargement of alveolar airspaces due to destruction and degradation of lung tissue.
What pathological features are observed within the lungs of COPD (emphysema) patients?
- The alveoli have decreased surface area and perfusion, leading to decreased gas exchange.
- There is loss of elastin fibres, leading to increased compliance and decreased recoil.
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 when you inspire the lungs increase in size and the airways in the middle of your lungs are being stretched slightly (during inspiration) and they are compressed (during expiration).
- In COPD this compression can mean that the lungs begin to loose patency or compress too much.
- At the same time as your looseing elastic recoil in order to ventilate your gas exchange structures you need to compress your lungs harder during expiration.
What are the effects of COPD on respiratory function?
Respiratory function declines in a progressive and irreversible manner, resulting in gradually increasing disability due to hypoxaemia and acidosis.
What are the effects of COPD on the body?
What are the effects of COPD on cardiovascular function?
- Chronic hyperventilation of alveoli results in prolonged and widespread hypoxic vasoconstriction.
- The constriction of the pulmonary vasculature increases vascular resistance.
- This requires the heart to work harder to maintain normal blood flow against increased resitance, resulting in right ventricle hypertrophy and worsening efficiency.
- Eventually, the heart becomes unable to cope with the increasing demands placed upon it, resulting in right heart failure (cor pulmonale).
- This also greatly increases the risk of devastating cardiovascular events such as a myocardial infarction, a common cause of death in COPD patients.
Cor pulmonale meaning - abnormal enlargement of the right side of the heart as a result of disease of the lungs or the pulmonary blood vessels.
How effective is smoking cessation in treating COPD patients?
Smoking cessation only halts the acceleration of decline, however lung function doesn't regenerate and the decline continues (just not as rapidly).