Chronic obstructive pulmonary disease

Disease class: lung diseases, Obstructive

Also known as 

• COPD

 

Subtypes

• bronchitis, Chronic
• Pulmonary emphysema

 

Physiology

 

Pathophysiology

Reduced ventilation of the lungs

As the airways are narrowed, the flow rate of air entering and leaving the lungs is significantly reduced. This is an obstructive disease. Furthermore the inflammation of the alveoli (the air sacks) causes them to lose elasticity, preventing adequate recoil and exhalation of CO2 gas. Some alveoli rupture to form large dilated airspaces called bullae. These are useless for gas exchange but they occupy useful intrathoracic volume.

 

Reduced lung perfusion

Since the alveoli are not being properly ventilated, the tiny blood vessels around them will try to divert blood away so that it can perfuse healthy alveoli. The body does not "know" if a patient has no remaining well-ventilated alveoli. Since every pulmonary blood vessel has elevated resistance, the heart has to pump very hard to force blood through the pulmonary circulation. Eventually this causes the heart to become dysfunctional (Pulmonary heart disease).

 

Hypoxic drive

Eventually COPD patients develop a chronic high level of CO2 (hypercapnia) in the body. The brain becomes desensitised and no longer promotes a significantly high respiration rate, despite the hypercapnia. However, the hypoxic drive remains. Consequently, the respiratory rate is maintained at a rate high enough to prevent hypoxia. If these patients are given oxygen supplemenation and the hypoxia is corrected, their respiratory drive slows to a significantly low rate. This causes their CO2 levels to rise to dangerous levels.

 

Causes

• Tobacco smoking: about 50% of tobacco smokers will develop COPD eventually. The majority of COPD patients are former and current smokers.
• Alpha-1 antitrypsin deficiency

 

Symptoms

• Cough
• Dyspnoea

 

Complications

• Pulmonary heart disease

 

Management

Medical

• Antimuscarinics, bronchodilators
• Beta2-agonists
• Compound (β2-agonist–corticosteroid) inhalers
• Corticosteroids (glucocorticoids), inhaled
• Antibiotics
• Oxygen, Venturi mask
• Long-term oxygen 

 

Surgical

• Bullectomy 
• Pneumonectomy
• Lung transplant

 

See also 

• World Health Organisation fact sheet