Pathophysiology Of COPD Flashcards
What does COPD stand for?
Chronic obstructive pulmonary disease
What is COPD?
Umbrella term used to describe a mixture of chronic bronchitis (airway problems) and emphysema (affects lungs). It causes a long term, progressive and accelerated decline in respiratory function.
What can cause COPD?
- Smoking - 90% of COPD cases are associated with tobacco smoke exposure
- Environmental hazards e.g pollution
- Genetic factors e.g Alpha-1 antitrypsin deficiency. This enzyme is needed to protect the lungs from neutrophil elastase.
With age, everyone’s passage of air through airways declines but smoking makes thus decline worse.
Why does smoking harm the respiratory system?
Burning organic matter like tobacco plant releases toxic compounds which cause acute damage to respiratory tissue which generates an inflammatory response.
With long repeated and long term exposure, this inflammation becomes chronic and pathological causing irreversible dysfunction.
Give steps of effects of tobacco smoke.
- Tobacco smoke causes inhalation of toxic chemicals and reactive oxygen species causing tissue damage
- This tissue response causes an inflammatory response which releases cytokines such as IL8 and TNF-a which recruit macrophages and neutrophils which attempt to resolve the inflammation and repair damaged tissue by releasing proteolytic enzymes that breakdown dead cells.
- Due to constant smoking, the inflammation continues, causing the WBC to release more enzymes (e.g trypsin elastase and metalloproteases) causing increased protease burden, causing more tissue damage.
- The smoke from tobacco also causes inactivation of antiproteases, increasing the activity of the enzymes.
- Also, due to the tobacco smoke particles constantly irritating the airways, you get hypersecretion of mucus which also damages cilia function. Mucus builds up in the airway, reducing the lumen size so less air can get through. There is impaired mucociliary clearance meaning mucus with microbes trapped in the airways isn’t removed which can cause respiratory infections. This then triggers the inflammation pathway again
Explain chronic bronchitis
- It’s a long term inflammation of bronchi
- Characterised by chronic and excessive sputum production, coughing and airway obstruction
- There is damage to cilia
- There is mucus hypersecrection due to increased goblet cell and mucus gland activation
- There is inflamed and swollen airways - oedema
- There is weakened airway structure and loss of patency caused by loss of elastin
Impaired mucociliary clearance means increases risk of infection leading to recurrent infection
Irritation of sensory neurones (due to e.g smoke exposure) causing cough
Decreased luminal area means increased airway resistance and airway obstruction
Causes reduced FEV1; also reduced FEV1/FVC ratio
How are chronic bronchitis and asthma different?
Both have impaired airflow through airways due to reduced airway lumen and increased resistance. In asthma it is reversible but not in chronic bronchitis.
In chronic bronchitis, airway lumen size is reduced due to excessive mucus secretion, tissue swelling and degradation of overall airway structure.
But in asthma, the airway lumen size is reduced primarily because of smooth muscle contraction.
This means different therapies are used.
In asthma, beta-2 agonist bronchodilators are used which relax airway smooth muscle. These are less effective in COPD.
What is emphysema?
This is the pathological enlargement of alveolar airspaces due to destruction and degradation of lung tissue.
Results in loss of loss of elastin needed to lung recoil, causing increased compliance so it becomes more difficult to compress lungs so expiration is harder.
There is also reduced surface area and damage to pulmonary capillaries decreasing gas exchange.
What is the overall effect of COPD on respiratory function?
- There will be airway obstruction and mucus build up causing reduced ventilation. This leads to alveolar hypoxia
- There is reduced lung recoil so expiratory effort increases trying to compress lungs, which also compresses the airway and since there’s no elastin surrounding the alveoli to keep open the airways, the airways will collapse, causing obstruction.
COPD exacerbations?
Patients get acute exacerbations which causes temporary but drastic decline in respiratory function caused by acute inflammation brought about by infection.
The exacerbations do resolve but the damage is already now done to the respiratory function, so patients with COPD are at risk of death.
What are the effects of chronic respiratory failure on the body?
- Chronic alveolar hypoxia
- Leads to hypoxic vasoconstriction (to increase blood flow to areas that have sufficient ventilation). This causes increased pulmonary vascular resistance (especially because so much of the alveoli are hypoxic, there’s little area where ventilation is occurring so there is a lot of hypoxic vasoconstriction).
- This causes pulmonary hypertension because more force is needed to overcome the resistance so the pressure increases.
- This causes the heart to work harder to maintain normal blood flow against increased resistance and causes increased afterload, resulting in right ventricular hypertrophy which causes right heart failure.
Quality of life is reduced because of hypoxia, hypercapnia and academia because it means reduced exercise tolerance and there’s increased fatigue.
Give symptoms of right sided heart failure
- Fatigue
- Increased peripheral venous pressure
- Enlarged liver and spleen
- Distended jugular veins
- Anorexia and complaints of GI distress
- Weight gain
- Dependent oedema
Why don’t we see chronic bronchitis and emphysema too differently?
They used to say that chronic bronchitis is the Blue Bloater and that emphysema was the Pink Puffer.
However, due to oxygen therapy, the Blue Bloater phenotype on its own is barely ever seen.
In fact, both phenotypes have some degree of underlying chronic bronchitis and emphysema.
What is the most effective way to slow down COPD progression?
Stop smoking. This will slow down the decline but the lung function won’t regenerate so decline still continues.
Oxygen therapy is helpful sometimes but stop smoking is the biggest effect.
Explain COPD lungs
Alveolar airspaces would be very large compared to normal.
