Exhaled nitric oxide

Nitric-oxide-2D

Exhaled nitric oxide (eNO) is a biomarker used in the diagnosis and management of various respiratory conditions, particularly asthma. Nitric oxide (NO) is a gaseous molecule produced by the epithelial cells in the respiratory tract. The measurement of eNO levels provides valuable information about the inflammatory status of the airways.

Physiology

Nitric oxide is synthesized in the body by the enzyme nitric oxide synthase (NOS). There are three isoforms of NOS: neuronal (nNOS), inducible (iNOS), and endothelial (eNOS). In the respiratory system, iNOS is primarily responsible for the production of NO in response to inflammatory stimuli. Elevated levels of eNO are often associated with eosinophilic inflammation, which is a hallmark of asthma.

Measurement

The measurement of exhaled nitric oxide is performed using a device called a nitric oxide analyzer. The patient is required to exhale into the device at a constant flow rate, and the concentration of NO in the exhaled breath is recorded. The results are typically expressed in parts per billion (ppb).

Clinical Significance

Asthma

In patients with asthma, elevated levels of eNO are indicative of airway inflammation. Monitoring eNO levels can help in assessing the effectiveness of anti-inflammatory treatments such as inhaled corticosteroids. A decrease in eNO levels after treatment suggests a reduction in airway inflammation.

Other Respiratory Conditions

While eNO is most commonly used in the management of asthma, it can also be elevated in other respiratory conditions such as chronic obstructive pulmonary disease (COPD), allergic rhinitis, and bronchiectasis. However, its role in these conditions is less well-defined compared to asthma.

Limitations

The interpretation of eNO levels can be influenced by various factors including age, gender, smoking status, and atopy. Therefore, it is important to consider these factors when interpreting the results. Additionally, eNO measurement is not a standalone diagnostic tool and should be used in conjunction with other clinical assessments and tests.

Related Pages

• Asthma
• Nitric oxide synthase
• Eosinophilic inflammation
• Inhaled corticosteroids
• Chronic obstructive pulmonary disease
• Allergic rhinitis
• Bronchiectasis