Asthma is a chronic inflammatory disease of the airways that causes airway obstruction and hyper-responsiveness, mucosal edema and mucus production. The inflammation ultimately leads to recurrent episodes of asthma symptoms; cough, chest tightness, wheezing and dyspnea.
Asthma differs from other obstructive lung diseases in that it is largely reversible, either spontaneously or with active treatment. Patients with asthma may experience symptom free episodes alternating with acute exacerbations that last from minutes to several hours or even a couple of days with progressive onset . Asthma is the most common chronic disease of childhood and can occur at any age. Despite increased knowledge regarding the pathology of asthma and the development of better medications and management plans, the death rate from this disease, nevertheless continues to increase.
The link between allergy and asthma
For most individuals, asthma is a disruptive disease affecting school and work attendance, occupational choices, physical activity and work attendance and generally the overall quality of life. Allergy is the strongest predisposing factor for asthma. Chronic exposure to airway irritants or allergens also increases the risk of asthma. Common allergens can be seasonal (grass, tree, and weed pollens) or perennial (mold, dust, roaches, animal dander). Common triggers for asthma symptoms and exacerbations include airway irritants (air pollutants, cold, heat, weather changes, strong odors or perfumes, smoke), exercise, stress or emotional upset, sinusitis with post nasal drip, medications and viral respiratory tract infections. A person’s asthma changes depending on the environment, activities, management practices and other factors.
Pathophysiology of asthma
The underlying pathology in asthma is reversible and diffuse airway inflammation. The inflammation leads to obstruction due to the following factors; (1) swelling of the membranes that line the airways (mucosal edema, which reduces the airway diameter; (2) contraction of the bronchial smooth muscle that encapsulates the airways (bronchospasm), which causes further narrowing, and (increase mucus production, which diminishes airway size and may entirely plug the bronchi. The bronchial muscles and mucus glands enlarge, thick tenacious sputum is produced; and the alveoli hyper inflate. This is referred to as fibrotic changes that lead to the airway narrowing which further leads to irreversible airflow limitation.
Clinical manifestations and complications of asthma
The three most common symptoms of asthma are difficulty in breathing (dyspnea), persistent coughing and wheezing. In some occasions, a cough may be the only visible manifestation of the symptom. An asthma attack often occurs at night or early in the morning, possibly because of circadian variations that influence airway receptor thresholds. Asthma is categorized according to symptoms and objective measures of airflow obstruction, hence care and management of patients suffering from asthma is highly individualized.
Complications of asthma may include status astmaticus (severe and persistent asthma attacks), respiratory failure, pneumonia and atelectasis. Airway
obstruction, particularly during acute asthmatic episodes, often results in hypoxemia (low oxygen levels in the blood due to inadequate gas exchange) which can lead to respiratory acidosis requiring the administration of oxygen and monitoring of pulse oximetry and arterial blood gases. Fluids are administered because people with asthma are frequently dehydrated from profuse sweating and insensible fluid loss with hyperventilation.