Patho-Physiology Of COPD Flashcards
What is Chronic Obstructive Pulmonary Disease (COPD)?
It 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.
What pathological features are observed within the airways of COPD (chronic bronchitis) patients?
- impaired mucociliary clearance, leading to an increased risk of infection (and recurrent infections)
- irritation of sensory neurons, leading to coughing
- decreased luminal area, leading to increased airway resistance and obstruction
What pathological features are observed within the lungs of COPD (emphysema) patients?
- alveoli have decreased surface area and perfusion, leading to decreased gas exchange
- loss of elastin fibres, leading to increased compliance and decreased recoil
What are the effects of chronic respiratory failure on respiratory function?
COPD results in decreased airflow, ventilation and gas exchange due to a combination of the pathological features involved in chronic bronchitis and emphysema, eventually resulting in respiratory failure.
Respiratory function declines in a progressive and irreversible manner, resulting in gradually increasing disability due to hypoxaemia and acidosis.
Furthermore, patients experience acute exacerbations (worsening of symptoms) characterised by a temporary (days) but drastic decline in symptoms and respiratory function, due to the acute inflammation brought about by infection.
Whilst exacerbations do resolve, patients with already severe COPD are at acute risk of death, and lung function often fails to completely return to previous levels, further hastening the long-term respiratory decline.
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 capillaries increases resistance, ultimately increasing blood pressure, resulting in right heart hypertrophy.
Eventually, the heart becomes unable to cope with the increasing demands placed upon it, resulting in heart failure. This also greatly increases the risk of devastating cardiovascular events such as a myocardial infarction, a common cause of death in COPD patients.
How effective is smoking cessation in treating COPD patients?
Smoking cessation only halts the acceleration of decline - lung function doesn’t regenerate and the decline continues (just not as fast).
