1. EXHALED NITRIC OXIDE IN ASTHMA
DR. MUKHTAR A. ADEIZA
DEPARTMENT OF MEDICINE
Ahmadu Bello University Teaching Hospital,Zaria
Thoracic club meeting, 17th march 2011

2. OUTLINE Introduction History Synthesis of NO Functions of NO
Measurement of NO
Uses in Asthma
Other uses
Conclusion

3. Introduction
Asthma is a chronic inflammatory disease of the airways that involves a complex interaction of recurrent episodes of reversible airflow obstruction, bronchial hyperresponsiveness and an underlying inflammation.
Clinical manifestations include:
Episodic wheezing
Coughing
Shortness of breath
Chest tightness

4. Introduction
In the United States, asthma affects more than 22 million people and is one of the most common chronic diseases of childhood, affecting more than 6 million children. (NHLBI, 2007)
In the United Kingdom, 20% of school age children are affected.
West Africa, 5.7%
Nigeria, 5.4%

5. Introduction
Decisions regarding asthma management are currently based on symptoms and conventional lung function tests.
Exhaled nitric oxide (FeNO) measured in a breath test has recently emerged as a potentially useful tool in the assessment and management of patients with asthma.

6. Modern view of asthma Mucus hypersecretion Hyperplasia Allergen
Eosinophil
Mast cell
Allergen
Th2 cell
Vasodilatation
New vessels
Plasma leak
Oedema
Neutrophil
Mucus plug
Macrophage/
dendritic cell
Bronchoconstriction
Hypertrophy / hyperplasia
Cholinergic
reflex
Epithelial shedding
Subepithelial
fibrosis
Sensory nerve
activation
Nerve activation
Barnes PJ

8. Th2 cytokine pattern

9. Nitric Oxide (NO)
NO is a biomarker of eosinophilic airway inflamation.
Produced by the action of proinflammatory cytokines on inducible nitric oxide synthase both in vivo and in vitro.

10. Structure of NO

11. Properties of NO Small highly reactive molecule (“radical molecule”)
Made up of one atom each of N and O
Uncharged with an unpaired electron
Can diffuse freely across membranes
T1/2 is 2-30 seconds
Decays into nitrate after spontaneously transmitting signal

12. History
1987, EDRF shown to posesss biological and chemical properties similar to NO.
1992, NO was named “Molecule of the Year” by the journal Science.
1998, Furchgott, Ignarro and Murad were awarded the Nobel Prize for Medicine for their work on this molecule.

13. History
1990s, numerous authors reported that fractional exhaled nitric oxide concentration (FeNO) was:
Higher in asthmatic patients than in healthy controls.
levels decreased in asthmatic patients treated with inhaled corticosteroids.
Closely linked to eosinophilic airway inflammation.

14. Synthesis of NO
Mammals synthesize NO by way of the NO synthase enzyme (NOS)
NOS converts the amino acid L-arginine into L-citrulline and NO.
The 3 known isoforms of the NOS are classified according to their:
activity,
Location
molecular cloning
Two are constitutive & the third is inducible.

15. Synthesis of NO
L-Arginine ↓
↓←← iNOS
Nitric Oxide + L-Citrulline

16. Regulation of NO production

17. NOS isoforms iNOS eNOS nNOS SOURCE
Macrophages, Bronchial epithelial cells, hepatocytes
Blood vessels, platelets
Nerve cells, skeletal muscles
EXPRESSION
Inducible
Constitutive
CALCIUM
Ca ²+ independent
Ca ²+ dependent
CONCENTRATION
Nanomolar
Picomolar
INHIBITION BY CORTICISTEROIDS
Yes No

18. MOA of NO on smooth muscles
NO is an endogenous and diffusible simple free radical that stimulates the enzyme guanylate cyclase.
Increased generation of cyclic guanosine monophosphate (cGMP).
Relaxation of smooth muscles results in bronchodilation and vasodilatation.

19. Functions of NO Weak bronchodilator effect. Vasodilatation.
Neurotransmitter.
Increased host resistance (deaminates DNA).
Upregulates TH2 & Downregulates TH1.
Intensify edema, plasma exudation and cause denudation and desquamation of the epithelial lining.

20. Factors affecting FeNO levels
Age
Sex
Anthropometry and race
Smoking and diet
Medications
Circadian rhythm & seasonal variation
Others
FeNO decreases after spirometry, sputum induction, bronchoprovocation and within 30mins of exercise.

21. Measurement of FeNO PREPATATION
Do not eat, drink, or do strenuous exercise for 1 hour before the test is scheduled.
Do not perform spirometry or peak flow for 1 hour before the test is scheduled.
Continue to take all your medicine as you usually do, unless you have been told to withhold medications for other testing you will be doing.

22. Procedure Differ depending on the patients condition:
ONLINE: In patients who are able to cooperate, exhale directly.
OFFLINE: In patients who are unable to cooperate, exhale into a reservoir.
Single-breath online measurement (SBOL) is the technique of choice in adults and children able to cooperate.

23. Experimental setup used to measure FeNO

24. Measurement of FeNO
NO can be measured precisely using chemiluminescence.
NO and ozone react in a cooled chamber to form NO2 .
This photochemical reaction emits infrared light that can be detected by a photomultiplier tube with a linear response.

25. Procedure
Inhales NO-free air (NO <5 ppb) for 2 to 3 seconds through a mouthpiece.
Exhale completely at a constant flow rate of 50ml/s for 10seconds (ATS, 20005).
Values are then captured and recorded in real time.
A variability of no more than 10% over 3 measurements or no more than 5% over 2 measurements is recommended.

26. Equipment NIOX analyzer NIOX-MINO
Standard stationary chemoluminiscence analyzer
NIOX-MINO
Based on electrochemical analysis
portable hand held device

27. Comparison of NIOX & NIOX-MINO
Dimension,(hwd, cm)
50 × 30 × 40
24 × 13 × 10
Weight of the analyzer, kg 40
0.8
Accuracy :
Measurements <50 ppb
Measurements >50 ppb
±2.5%
±5%
±10%
Range of measurements, ppb
0-200
5-300
Lower detection limit, ppb
1.5 5

28. Reference range
The establishment of reference values for a population is difficult because of the numerous confounding factors as discussed above.
The average normal level of eNO in different studies ranges from 20 to 30 parts per billion.

29. Refernce range
Olin et al, defined a value of 24.0 to 54.0 ppb depending on age and height.
Abba et al, 7.66 to 46.6 ppb among nonsmoking, nonatopic adult male Saudi subjects.

30. Clinical application
The availability of cheap, portable and reliable equipment for the measurement of FeNO has led to widespread use of FeNO as a noninvasive diagnostic and management tool particularly in bronchial asthma.

31. Diagnosis of asthma
Malberg et al. observed that high FENO values ( ≥3SD) correlated with clinical asthma (p<0.0001)
More than 90% specificity for the diagnosis of asthma in both adults and children.
Excellent correlation with esinophilic airway inflammation as represented by blood, sputum, and mucosal esinophilia.

32. Diagnosis of asthma
Higher diagnostic sensitivity (88%) when compared to various LFTs like induced sputum (86%) and forced spirometry (47%).
Atopy limits the clinical utility of the test in children.

33. Monitoring of asthma Monitor antiinflammatory treatment with ICS.
Identify patients who will respond to ICS (FeNO >47ppb).
When tailoring ICS dose in asthma, mean daily dose if ICS was lower in the FeNO group compared to symptoms/spirometry.

34. Diseases & factors that affect FeNO
INCREASED
DECREASED
VARIABLE
Asthma
Cystic fibrosis
COPD
Exposure to pulmonary allergens
Primary ciliary dyskinesia
Bronchiectasis
Pollution
Pulmonary hypertension
Fibrosing alveolitis
Apnea
Pneumonia
Sarcoidosis
Bronchodilators (transient)
Gastroesophageal reflux
Systemic sclerosis
Viral respiratory infection
Laryngeal tracheomalacia
Pulmonary tuberculosis
Sputum induction
Allergic rhinoconjunctivitis. Nasal polyposis
Bronchoconstriction

35. Diseases & factors that affect FeNO
INCREASED
DECREASED
VARIABLE
Posttransplant bronchiolitis
Forced spirometry (transient)
Chronic inflammatory intestinal disease
HIV infection
Hepatopulmonary syndrome
Smoking
Liver cirrhosis
Alcohol
Caffeine
Menstruation
Nebulizer therapy with distilled water

36. Conclusion
FeNO measurements are quick and easy to perform and may be readily incorporated into routine pulmonary function test procedures.
This advance offers the possibility that a diagnosis of asthma may be performed more easily and confirmed with much greater confidence than has been possible to date.

37. Conclusion
The possibility of easily taking measurements of FeNO in an office setting even by relatively young children, and the availability of a portable device, opens a significant perspective for the routine use of FeNO evaluation in daily practice.

38. The future Development of local reference values
Integration of FeNO use into medical practice in both primary care and specialist settings in Nigeria.

39. THANK YOU