Exhaled nitric oxide: a biomarker integrating both lung function and airway inflammation changes

Area of Science:

• Pulmonary Medicine
• Allergy and Immunology
• Respiratory Physiology

Background:

• Elevated fraction of exhaled nitric oxide (Feno) in asthma often indicates airway inflammation.
• However, reduced airway caliber can bias Feno measurements, complicating asthma control assessment.

Purpose of the Study:

• To investigate how airway caliber and inflammation changes affect Feno values.
• Utilizing an allergen challenge model in mild allergic asthma patients.

Main Methods:

• Measured FEV1 and Feno during early and late airway responses post-allergen challenge.
• Employed single-breath washout tests with Helium and Sulfur Hexafluoride (SF6) to assess airway constriction sites.

Main Results:

• Both FEV1 and Feno decreased significantly during early and late airway responses.
• Airway caliber changes (indicated by Helium/SF6 washout) correlated with Feno alterations.
• Feno levels returned to baseline earlier than FEV1, with a later increase observed.

Conclusions:

• Airway caliber significantly modulates Feno values in mild allergic asthma.
• Feno should be viewed as a biomarker integrating inflammation and lung function, not solely inflammation.
• Allergen-induced early and late airway responses involve similar lung regions.