Basic Science and Pathohysiology

Asthma is a disorder of the airways that is complex and still not fully understood. However, it is characterised by:

• Bronchial hypersensitivity
• Broncho-constriction
• Bronchial inflammation
• Recurring symptoms of reversible airway obstruction that vary in severity

A large number of cells and mediators have been implicated in the airway inflammation pathway, including the following:

• Eosinophils
• Mast cells
• Leukotrienes
• Prostaglandins
• T-lymphocytes
• Macrophages
• Adhesion molecules

Increased mucous secretion and bronchial oedema also contribute to airflow obstruction. Chronically, desquamation of the epithelium and smooth muscle hyperplasia may result in airway re-modelling.³

Why do some asthmatics develop a cardiac arrest?

Mucous plugging from severe bronchospasm causing asphyxia is a common cause of death in asthmatic patients. Prolonged hypoxia can precipitate cardiac arrhythmia causing death.⁴

Due to bronchoconstriction, airway pressures in the lungs in acute asthma are high. Air can enter the lungs, but cannot escape. This leads to breath stacking, which causes an increase in intrathoracic pressure. Raised intrathroracic pressure may consequently cause pneumothoraces to develop or it can decrease venous return to the heart precipitating circulatory collapse.⁴