5th January 2024

Background

Epidemiology

Asthma affects over 8 million people, approximately 12% of the population in the UK. As the incidence of asthma is higher in children than in adults, some ‘grow out’ of the condition. In adulthood, the ratio between males and females is equal.

Occupational asthma is the most common industrial lung disease in the developed world.

Pathophysiology

Asthma is a complex disease with multigene association interacting with environmental exposure.

Pathophysiology of asthma involves two major elements: inflammation and airway hyper-responsiveness. The large airways and small airways of <2 micrometres are the sites of inflammation and airway obstruction.

Airway inflammation is secondary to interaction of inflammatory cell mediators and cells in the airways. An initial trigger causes release of inflammatory mediators, which leads to activation and migration of inflammatory cells. This inflammatory reaction is a T-helper type2 lymphocytic response. Other white cells involved are eosinophils, basophils, mast cells, macrophages, neutrophils, and natural killer cells. Neutrophils are important in near-fatal exacerbation of asthma. These cells cause changes in airways’ epithelium, tone, autonomic neuronal control and hypersecretion of mucus. They also alter the mucocilliary function and increase smooth muscle responsiveness.

Products of the inflammatory response induce smooth muscle contraction and airway hyper-responsiveness. Finally, airway smooth muscle in asthmatic people is increased in mass due to hypertrophy and hyperplasia.

Risk factors

Factors that may contribute to airway hyperresponsiveness and asthma may include the following:

• Environmental allergens
• Family history
• Viral respiratory infections
• Exercise, hyperventilation
• Gastroesophageal reflux disease
• Chronic sinusitis or rhinitis
• Aspirin or nonsteroidal anti-inflammatory drug (NSAID) hypersensitivity, sulphate sensitivity
• Obesity
• Tobacco smoke
• Occupational exposure: Insects, plants, latex, gums, diisocyanates, anhydrides, wood dust, and fluxes
• Irritants (e.g., household sprays, paint fumes)
• Emotional stress
• Perinatal factors such as prematurity and increased maternal age; maternal smoking, and prenatal exposure to tobacco smoke