The pathophysiology of asthma refers to the changes that occur in the airways and lungs that lead to asthma symptoms. Understanding the pathophysiology can help with targeting asthma treatment.

Asthma is a long-term lung disease that affects the bronchial tubes, which are the airways that carry oxygen to the lungs. People with asthma may develop inflammation and narrowing of the airways, which makes breathing difficult.

Pathophysiology refers to the ways a disease alters or affects normal bodily function.

The pathophysiology of asthma is the process or ways asthma alters the lungs. The exact process and impact on the lungs may differ slightly depending on the type of asthma someone has. However, the pathophysiology remains similar. Understanding the pathophysiology of asthma helps in determining effective treatment.

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The prevalence of asthma in the United States is about 8%. According to the National Heart, Lung, and Blood Institute (NHLBI), the exact cause of asthma remains unknown. However, a combination of environmental and genetic factors likely contribute to the development of the disease.

For instance, environmental factors, such as exposure to cigarette smoke as a young child, may affect lung development and increase the risk of asthma. Frequent viral infections as a child may also affect a person’s asthma risk.

Some people may experience environmental risks and never develop asthma. However, others may have a genetic predisposition that makes them more likely to develop the condition.

Bronchial hypersensitivity, also known as bronchial hyperresponsiveness or bronchial hyperreactivity, is a crucial feature of asthma. People with asthma have airways with an increased sensitivity to certain triggers.

Triggers are normally harmless. However, in someone with asthma, their airways are hypersensitive and become irritated. This hyperresponsiveness leads to increased mucus production and constriction or narrowing of the airways.

Additionally, some people react to environmental triggers that cause an allergic reaction, leading to asthma symptoms. About 80% of children with asthma are sensitive to environmental allergens.

Common allergens that cause hyperresponsive or hypersensitive airways include:

  • dust mites
  • pollen
  • molds
  • pet dander
  • cockroaches

Airflow obstruction, which occurs due to a reduction in the diameter of the airways, also develops as part of the asthma process.

The airways become narrow due to the activation and release of immune cells, such as eosinophils, neutrophils, and mast cells. Inflammation develops as a response to the release of the cells, leading to the airways swelling.

Once this inflammatory response develops, it causes a cascade of adverse effects on the airways. For instance, it causes the airway’s smooth muscle to contract, leading to bronchoconstriction. The inflammation also causes excess mucus production in the airways, possibly forming a mucus plug.

When persistent airflow limitation is not fully reversible, experts may refer to it as asthma with fixed airflow obstruction.

Acute asthma is reversible, which means treatment may reverse airway changes, such as inflammation and narrowing. However, in some situations, the airway changes are no longer reversible.

People with chronic asthma with recurrent asthma attacks may develop airway remodeling. With repeated asthma attacks, a prolonged immune response, and chronic inflammation, irreversible changes to the airways may occur.

Structural changes to the walls of the airways may develop. The makeup of the extracellular matrix, which is a mixture of fibrous proteins, also changes.

Airway remodeling may include:

  • increased thickness of the smooth muscle in the airways
  • an increased number of airway smooth muscle cells
  • increased airway wall thickening
  • eosinophil infiltration — a type of inflammation
  • a hardening and stiffening of the airway wall
  • abnormal growth of blood vessels

Experts associate an increase in airway smooth muscle with decreased lung function in people with severe asthma.

Doctors break down asthma symptoms into two main phases: the early and late phases. The early phase of asthma occurs when the immune system detects an allergen. Because the airways are hypersensitive in someone with asthma, this response triggers the release of immunoglobulin E (IgE) antibodies.

In turn, IgE attaches itself to certain types of white blood cells, such as basophils and mast cells. The mast cells then release prostaglandins, histamine, and leukotrienes. These cells cause the smooth muscle in the airways to contract or narrow, causing bronchospasm, which triggers an asthma attack.

The late phase is the second phase of asthma. If left untreated, the late phase of an asthma attack occurs over the next few hours after the initial response to the allergen.

The cells released by the immune system, including eosinophils, helper T cells, and mast cells, travel to the airways and increase inflammation and constriction. This leads to airflow obstruction, making it harder to breathe. The immune system response also stimulates the goblet cells, producing excess mucus.

The first step in asthma treatment involves determining the triggers and assessing the severity of symptoms and frequency of flare-ups.

Treatment for asthma should recognize the three mechanisms that develop during an asthma attack. These include:

  • inflammation, which leads to swelling in the airways
  • excess mucus production that contributes to airway obstruction
  • bronchoconstriction, which narrows the airways

Doctors may prescribe a combination of medications to treat the different physiological factors that develop in an asthma attack. For instance, medications called bronchodilators help relax the smooth muscles of the airways, allowing them to dilate or widen.

Steroids help treat inflammation, which also reduces airflow obstruction. Medications are also available that inhibit eosinophils, such as monoclonal antibody therapy.

The best treatment plan may depend on a person’s type of asthma, severity of symptoms, and response to initial treatment.

The pathophysiology of asthma is how the disease affects the normal function of the airways. It includes hypersensitivity of the airways, airflow obstruction, and reversibility.

However, in some people, if asthma remains untreated and frequent attacks develop, the inflammation can cause structural changes in the airways. Developing airway remodeling, such as thickening and stiffening of the airway smooth muscle, can further cause airflow obstruction.

Asthma treatment typically addresses both constriction and inflammation to decrease airflow obstruction.