Some individuals with severe asthma can experience fixed airflow obstruction (FAO). Doctors characterize the condition as a persistent airflow limitation through the airways, especially when exhaling.

Generally, asthma is a chronic inflammatory disorder of the airways. It encompasses a spectrum of symptoms and severity levels. Typical symptoms include difficulty breathing, wheezing, and variable, reversible airflow obstruction.

Unlike typical asthma — where airflow obstruction is reversible with bronchodilator use — fixed airflow obstruction refers to a chronic and unchanging restriction in a person’s ability to exhale air from the lungs.

Asthma with FAO also has associations with an accelerated decline in lung function and other health issues. Doctors find this condition challenging to treat.

This article explores asthma with fixed airflow obstruction, including the risk factors and treatments.

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Asthma with fixed airflow obstruction is a distinct subtype of severe asthma. A person with this condition may experience airflow issues, even without other symptoms.

Doctors define severe asthma as requiring medium or high dose inhaled corticosteroids combined with other longer-acting medications to manage symptoms. Despite the proper use of bronchodilators, a person with fixed airflow obstruction may still have difficulties exhaling.

The prevalence of FAO among people with severe asthma is around 60%.


Individuals with severe asthma may experience a range of symptoms, including:

  • Shortness of breath: A hallmark symptom of asthma, individuals may feel a sense of breathlessness, especially during physical exertion or exposure to triggers.
  • Wheezing: The production of a high-pitched whistling sound during exhalation is a common symptom of asthma. In fixed airflow obstruction, a person may wheeze even when other symptoms are absent.
  • Coughing: Persistent coughing is a characteristic symptom of asthma. It may be worse at night or in response to specific triggers.
  • Chest tightness: Individuals may experience a sensation of tightness or pressure in the chest, which can contribute to feelings of breathlessness and discomfort.

Learn more about severe asthma.

The underlying causes of asthma with FAO involve a complex interplay of factors. While the exact mechanisms are not fully understood, there appear to be several critical processes involved, including:

  • Chronic airway inflammation: Asthma with FAO involves persistent airway eosinophilic inflammation, leading to structural changes in the bronchial walls.
  • Airway remodeling: Chronic inflammation contributes to airway remodeling, causing a thickening of bronchial walls and reduced flexibility of the airways.
  • Smooth muscle dysfunction: Atypical functioning of the airway smooth muscle results in excessive contraction and airway narrowing, further limiting airflow.
  • Persistent airway hyperresponsiveness: The airways become sensitive and constrict without specific triggers.
  • Structural changes to lung tissue: In some cases, FAO may involve structural changes in the lung tissue, affecting lung elasticity and limiting airflow.

Various risk factors can increase the likelihood of developing FAO in asthma, including:

  • Blood and sputum eosinophilia: Higher levels of eosinophils — a type of white blood cell involved in the immune response — can increase the risk of FAO in asthma.
  • Adult-onset asthma: Developing asthma during adulthood is a risk factor for FAO. It is different from childhood-onset asthma and may have distinct characteristics.
  • Older age and male sex: Age and sex can influence the likelihood of FAO in asthma. Older individuals and males may have a higher risk.
  • History of smoking: A smoking history increases the risk of developing FAO in asthma. Smoking can cause chronic inflammation and structural changes in the airways, leading to persistent airflow obstruction.

Other potential risk factors include airway hyperresponsiveness, allergic rhinitis, and low initial lung function, as indicated in FEV1 levels. However, more research is needed to understand the relationship between these risk factors and asthma with FAO.

There are no current treatments to reverse or prevent excessive lung function decline in people with severe asthma with FAO. Therefore, managing FAO in asthma requires a comprehensive treatment approach to reduce symptoms and enhance a person’s overall quality of life.

Asthma treatments, such as inhaled corticosteroids and bronchodilators, provide some benefits for people with asthma. However, they may not help those with FAO. This is because doctors often diagnose FAO later when irreversible damage or changes have already happened in the lungs and airways.

Additionally, current treatments primarily target the inflammatory process in asthma, which may not directly address the underlying causes of FAO.

Novel treatments

Newer treatments, such as biological therapies, may help. For example, omalizumab, an anti-immunoglobulin E monoclonal antibody, may reduce symptom flares, also known as exacerbations, in people with FAO. However, it does not significantly improve lung function.

Experts have also investigated monoclonal antibodies targeting interleukin-5 or its receptor. Interleukin- 5 usually drives the production of eosinophils. Generally, these treatments can reduce exacerbation rates and asthma symptoms.

However, their effects on lung function in people with asthma with FAO vary. These treatments are generally intended for people with severe asthma with eosinophilic inflammation resistant to corticosteroids.

Currently, no specific treatments are available that directly target the remodeling of the airways and lung tissue that happens in FAO. Therefore, people will need to work closely with their doctor to find a treatment regime that works for them. This may require a trial-and-error approach.

Asthma and allergy resources

To discover more evidence-based information and resources for living with asthma and allergies, visit our dedicated hub.

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Knowing when to seek help for asthma is crucial to ensure prompt management and prevent complications. It is best for an individual who experiences any of the following symptoms to seek medical attention:

  • worsening asthma symptoms
  • difficulty in performing daily activities
  • frequent exacerbations
  • a decline in lung function

Other signs to watch include needing to use a rescue inhaler more frequently or experiencing respiratory infections that worsen symptoms.

Asthma with fixed airflow obstruction (FAO) is a subtype of severe asthma characterized by persistent limitations in airflow when exhaling. Some causes of this condition include chronic airway inflammation, airway remodeling mechanisms, and extreme hypersensitivity of lung tissue.

Managing asthma with FAO is complex. It requires a comprehensive approach to manage symptoms, optimize lung function, and avoid triggers. Current asthma treatments may not effectively reverse or prevent FAO, highlighting the need for further research and targeted therapies.

Early recognition and appropriate management are essential to prevent asthma symptoms from worsening and decrease the risk of developing severe asthma with FAO.