Airway remodeling is the structural changes that occur in the large and small airways as a result of chronic asthma inflammation. This damage often leads to a thickening of the airway wall and a decline in lung function (the ability to move air in and out of the lungs). According to the American Academy of Allergy, Asthma and Immunology, as many as 92 percent of patients with asthma experience some thickening of the bronchial wall in the large and small airways.

Airway remodeling usually occurs as a result of chronic asthma or COPD (chronic obstructive pulmonary disease). However, smoking cigarettes is also linked to airway remodeling. Acute asthma can cause less damage associated with minor airway remodeling.

The damage sustained during airway remodeling often results in asthma exacerbations such as increased asthma attacks and sensitivity to triggers (e.g., dander, pollen, mold), as well as difficulty breathing. This damage can also cause a diminished response to asthma medications. Airway remodeling often results in the following types of damage:

• Cellular inflammation. Cells dilate and grow larger, constricting airways.
  
  
• Airway wall thickening. The walls of both the large and small airways can grow thicker as cellular growth is stimulated by perceived damage.
  
  
• Smooth muscle growth. The muscle mass of the smooth muscle increases in both the large and small airways, reducing the patient’s ability to inhale air into the lungs.
  
  
• Epithelium erosion. This thin layer of protective cells that lines the airways becomes fragile and begins to erode and slough (shed). This further blocks the airways.
  
  
• Mucus increase. The number and size of mucous glands located throughout the airways increases, reducing the diameter of airways and generating greater amounts of mucus than normal.

The permanent destructive changes associated with airway remodeling involve several different mechanisms. Unfortunately, little is known about why these mechanisms are triggered and clinical studies are ongoing. These changes include:

• Destruction of elastic tissue in the airways. As the smooth muscles contract, the elastic tissue normally works as an opposing force to keep the muscles in check. However, once the elastic tissue is damaged (which is believed to be due to inflammation), the contracting muscles tighten without opposition, constricting the airways.
  
  
• Thickened airways. This often leads to hyperresponsiveness in the bronchial tubes, which leads to more frequent asthma attacks.
  
  
• Increase in the bulk of the smooth muscles, cellular growth and the increased production of mucus. These changes block the airways, increasing the number of breathing difficulties as well as sensitivity to attacks.