Nasal Nitric Oxide Measurements in Airway Inflammation

Nitric oxide (NO) in the upper airway arises chiefly from paranasal sinus epithelium and is released into the nasal cavity where it can be quantified non-invasively as nasal nitric oxide (nNO). Endogenous NO synthesis is driven by three isoforms of nitric oxide synthase, with inducible NOS upregulated during inflammation. Measurement may be achieved by chemiluminescence or electrochemical sensors, often incorporating controlled aspiration flows or exhalation against resistance to isolate nasal emission. Clinically, very low nNO levels are a hallmark of primary ciliary dyskinesia, whereas elevated levels are seen in type 2-mediated allergic rhinitis. In chronic rhinosinusitis, particularly with nasal polyps, nNO is typically suppressed, reflecting ostial obstruction and altered NOS expression. Standardisation of measurement technique and reference ranges remains a challenge, yet nNO is increasingly recognised as a versatile biomarker for diagnosis, endotype stratification and monitoring of therapeutic response in diverse airway inflammatory conditions.

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Nasal Nitric Oxide Measurements in Airway Inflammation publication trend

The graph below shows the total number of articles in nasal nitric oxide measurements in airway inflammation across all publications each year (not limited to Nature Index journals).

Technical terms

Nasal nitric oxide (nNO): The fractional concentration or flow rate of NO released from the nasal cavity, measured as a non-invasive marker of upper airway inflammation.

Inducible nitric oxide synthase (iNOS/NOS2): An enzyme isoform upregulated by pro-inflammatory cytokines that catalyses NO production in airway epithelium.

Primary ciliary dyskinesia (PCD): A genetic disorder of ciliary structure or function characterised by impaired mucociliary clearance and markedly reduced nNO levels.

Chronic rhinosinusitis (CRS): A condition of persistent sinonasal mucosal inflammation, often phenotyped by presence or absence of nasal polyps, affecting nNO dynamics.

Allergic rhinitis (AR): An immunoglobulin E-mediated nasal disorder driven by type 2 immunity, typically associated with elevated nNO due to increased iNOS activity.

References

1. Role of Nasal Nitric Oxide in Primary Ciliary Dyskinesia and Other Respiratory Conditions in Children. International Journal of Molecular Sciences (2023).
2. Nasal Nitric Oxide in Chronic Rhinosinusitis with or without Nasal Polyps: A Systematic Review with Meta-Analysis. Journal of Clinical Medicine (2020).
3. The roles of nasal nitric oxide in diagnosis and endotypes of chronic rhinosinusitis with nasal polyps. Journal of Otolaryngology (2020).
4. The Functional Diversity of Nitric Oxide Synthase Isoforms in Human Nose and Paranasal Sinuses: Contrasting Pathophysiological Aspects in Nasal Allergy and Chronic Rhinosinusitis. International Journal of Molecular Sciences (2021).
5. Clinical Applications of Nasal Nitric Oxide in Allergic Rhinitis: A Review of the Literature. Journal of Clinical Medicine (2023).
6. Predictive Value of Nasal Nitric Oxide and Serum NOS2 Levels in the Efficacy of Subcutaneous Immunotherapy in Pediatric Patients with Allergic Rhinitis. Mediators of Inflammation (2022).