Bronchial Asthma

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Bronchial asthma is a inflammatory disease of the airways characterized by bronchial hyperreactivity and a variable degree of airway obstruction with symptoms including wheezing, chest tightness, dyspnea and cough. The specification of the word bronchial affirms that this is caused by processes within the lungs itself, distinguishing it from other breathing issues such as cardiac asthma which is caused by heart failure.

There is considerable variation in this disease. Firstly, the causation as it can be from complex interactions between genetic predisposition and environmental exposures. And secondly, in the magnitude and manifestations of the disease within and between individuals over time. Some patients may have mild, infrequent symptoms, others prolonged, severe ones.

Etiology:

The most important risk factor for asthma is atopy, a genetic predisposition to produce IgE antibodies in response to allergen exposure, for example, pollen, dust etc.

Another risk factors is indoor exposure to dust mite or cockroach antigens. In childhood, bronchial asthma is mostly due to allergies.

Non-allergic asthma in adults can be due to development of allergic sensitization after a viral infection of the lower respiratory tract for example.

Causes of Asthma

Genetic factors may also contribute.

Pathogenesis:

Because of the variability of the disease, there isn't one single mechanism that characterizes the pathology of asthma. There are however common events that we can define.

The most prominent is airway inflammation. Local inflammatory cells get activated indirectly by other processes or directly by the IgE dependent mechanisms, releasing acute acting mediators (leukotrienes, prostaglandins, cytokines) that cause smooth muscle contraction, mucus hypersecretion, vasodilation with endothelial leakage and edema formation. Inflammatory cells are recruited, and they participate in a complex series of events that results in inflammation and hyperresponsiveness. Hyperresponsiveness is caused by exposed afferent sensory nerves due to injury to epithelial cells.

Due to this inflammatory process, there can be injury to epithelial cells, which drives tissue remodeling and fibrosis of the airways, which can lead to fixed airway obstruction, further complicating the situation.

As a consequence of airway inflammation, mucus hypersecretion and smooth muscle hyperresponsiveness, there is bronchoconstriction. The narrowed airways lead to an increase in air resistance and airflow obstruction.

Clinical Manifestations:

Asthma is a very variable disease, both within and between patients, it can be mild and intermittent or severe and chronic, sometimes even life threatening. It is important to note symptoms do not necessarily correlate with degree of airway obstruction, some of the most common ones are listed below:

• Dyspnea and chest tightness - Lung compliance falls due increased thoracic distention caused by hyperinflation. The work of breathing is increased which is detected by chest wall sensory nerves as chest tightness.
• Wheezing - It is produced by hypersecretion and retention of mucus, resulting in turbulent flow.
• Cough - to provide enough force to clear the mucus and retained particles from the narrow airways.
• Bronchial hyperresponsiveness - non-specific, present in all patients with asthma.

Investigations:

Basic diagnostic assessment is done by history taking, presence of symptoms and physical examination. Airway obstruction is measured by pulmonary function tests, most prominently by spirometry. It is worthy to note that normal spirometry values do not rule out asthma if they have been taken in a symptom free period.

Management:

Normal course of treatment for asthma is administering medication of which there are two categories:

• Relievers - taken for symptomatic relief as necessary
• Controllers - taken for preventative, maintenance therapy