Asthma Definition and Etiology

Definition and Etiology

• Asthma is characterized by recurring paroxysms of wheezing, dyspnea, and cough resulting from inflammation and spasmodic contractions of the bronchi.
• Asthma is caused by reversible episodes of airway inflammation, mucosal edema, increased viscid secretions, and smooth muscle contraction.
• Etiologic categories of asthma include extrinsic, intrinsic, exercise-induced, occupation-induced, drug-induced, cardiac, and triad asthma.

Extrinsic and Intrinsic Asthma

• Extrinsic and intrinsic are the two most common forms of asthma, both associated with release of inflammatory chemicals from mast cells in the airways.
• Extrinsic asthma (allergic asthma) accounts for one third to one half of all cases, commonly affects children and young adults, and is an IgE-mediated response to specific antigens.
• Intrinsic asthma often develops in middle age, has a less favorable prognosis, and is not IgE mediated, with respiratory infections as possible causes.

Pathogenesis

• Asthma is characterized by obstruction and narrowing of airways due to bronchospasm, increased mucus secretion, and mucosal edema.
• Severe hypoxemia may result from intense narrowing of the bronchi.
• In extrinsic asthma, IgE production in response to a specific antigen leads to the release of inflammatory chemicals (e.g., histamine, leukotrienes) from mast cells.

Clinical Manifestations

• Common signs and symptoms of asthma include wheezing, dyspnea, hyperinflation, productive cough, tachypnea, and tachycardia.
• More severe attacks may be accompanied by the use of accessory muscles, intercostal retractions, distant breath sounds, and agitation.
• Pulmonary function tests demonstrate decreased forced expiratory volume (FEV1) and peak expiratory flow rate (PEFR).

Treatment Implications

• Prevention of asthma attacks by avoiding triggers is an important part of therapy.