Asthma Definition and Etiology

Study Notes

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 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.

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.

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).