Exhaled Nitric Oxide: An Adjunctive Tool in the Diagnosis and Management of Asthma Jason Debley, MD, MPH Assistant Professor, Pediatrics Division of Pulmonary Medicine University of Washington School of Medicine Seattle Children s Hospital
Bronchial Reactivity Symptoms / Exacerbations ASTHMA Airway Inflammation Airway Remodeling Measure to assist with Dx and guide treatment? Airflow Obstruction (Limitation: 50% of children with mild-mod asthma have normal spirometry at baseline) Treatment (steroids) Diagnosis and Assessment of Asthma Control
Nitric Oxide: ubiquitous signaling molecule with many physiologic effects Regulation of vascular tone (e.g. pulmonary vascular bed) Regulation of platelet aggregation airway smooth muscle relaxation Neurotransmitter (e.g. memory formation) Host Defense: macrophage dependent antimicrobial effects (viral, bacterial, parasitic) Tumoricidal effects
Nitric Oxide Synthesis L-arginine 3 isoforms NOS (nitric oxide synthase) NO Neuronal (nnos): constitutive, greatest expression by neuronal cells in CNS Endothelial (enos): constitutive, greatest expression endothelial cells but present in many cells types Inducible (inos): inducible, expressed primarily by airway epithelial cells (eosinophils, mast cells)
Fraction of Exhaled Nitric Oxide (FENO): A Noninvasive Marker of Airway Inflammation in Asthma FENO higher in asthmatic than in healthy individuals (first described in early 1990 s) FENO decreases after corticosteroid treatment Baraldi et al. J Pediatr 1997;131:381-5
Excess FENO in Asthma Produced Predominantly by inos Expressed by Airway Epithelial Cells
What is the Physiologic Role of Nitric Oxide in the Lower Airways? Freely diffusible signaling molecule that appears to play a homeostatic role in several aspects of airway physiology Basal airway tone Airway responsiveness Host defense/innate immunity Pro-inflammatory or Counter-regulatory? A clear understanding of the physiologic roles of airway nitric oxide in health and disease is lacking (animal models contradictory - less data from humans)
Airway Nitric Oxide and Host Defense NO is a toxic free radical with antimicrobial properties - believed to be important in host defense. Limited human data suggests rhinovirus infection stimulates increased nasal inos and NO production, and that higher NO levels are associated with reduced symptoms and faster viral clearance Sanders et al. J Allergy Clin Immunol. 2004;113:697-702
Pro-inflammatory vs. Counter-regulatory Properties of NO in the Airways Under physiologic conditions, endogenous NO release appears to tonically suppress microvascular permeability of the airway mucosa. At high concentrations, NO appears to: increased vascular permeability cytotoxic effects on respiratory epithelial cells evidence that NOS inhibitors suppress in vitro chemotaxis of human blood eosinophils, monocytes, and neutrophils
The biologic properties of nitric oxide in the upper and lower airways are complex Which of its properties predominates in health or disease, and whether NO in the airways should always be regarded as primarily beneficial or harmful, are still unanswered questions
FENO as a Biomarker of Inflammation in Asthma
FENO in Exhaled Breath is Flow Dependent FENO is expiratory flow rate dependent ( expiratory flow rate > FENO) NO flux (flow independent) Single breath on-line FENO measurements must be at a constant expiratory flow rate (very low) ATS/ERS recommends on-line FENO measurements be performed at an expiratory flow rate of 50 ml/sec Many published studies (especially prior to 2005) did not use a flow rate of 50mL/sec. Be careful when comparing FENO values between studies Flow Dependent
FENO: Relationship Between FENO, Asthma, and Atopy atopic asthma > atopic without asthma nonatopic asthma > non-atopic Jouaville et al. Clin Exp Allergy 2003;33:1506-11 Nordvall et al. Allergy 2005;60:469-75
FENO Associated with Airway Reactivity in Asthmatics FENO associated with airway reactivity to inhaled histamine and methacholine Dupont et al. Am J Respir Crit Care Med 1998;157:894-98.
FENO Associated with Eosinophilic Airway Inflammation in Asthmatics FENO associated with eosinophils in bronchial mucosa (bronchial biopsy) and sputum Payne et al. Am J Respir Crit Care Med 2001;164: 1376-81 Covar et al. J Allergy Clin Immunol 2004;114:575-82 Jatakanon et al. Thorax.1998;53(2):91-5
Potential Clinical Uses of FENO as a Biomarker in Asthma Adjunctive diagnostic test for asthma Predictor of steroid responsiveness Identification of a distinct asthma phenotype? Predictor of loss of asthma control Longitudinal monitoring to adjust therapy Marker of compliance with steroid therapy
240 steroid naïve adults referred for evaluation of respiratory symptoms Equivalent FENO at 50mL/sec 32 ppb
FENO as a Diagnostic Test for Asthma Sensitivity Specificity Peak Flow Variability Peak Flow improvement with steroid 0% 24% 93% 93% Spirometry (FEV1 <80%) 29% 93% Improvement in spirometry (>15%) with steroid 12% 100% Sputum eosinophils > 3% 86% 88% FENO > 20 ppb (flow = 50mL/sec) 88% 79% Gold Standard: Airway reactivity to methacholine + >12% improvement in FEV1 with albuterol Smith et al. Am J Respir Crit Care Med 2004;169(4):473-8
Equivalent FENO at 50mL/sec 30 ppb
FeNO Eos count FEV1
Nonsmokers Smokers
FENO Measurement to Determine Steroid Responsiveness
Steroid Responsiveness in Relationship to FENO in Patients with Non-specific Respiratory Symptoms Am J Respir Crit Care Med 2005;172:453-59.
61% of subjects used ICS prior to study participation Relatively low baseline FENO and sputum eosinphil %
FENO as a marker of a distinct asthma phenotype?
Can Markers of Airway Inflammation in Exhaled Breath Predict Response of Childhood Asthma to Fluticasone vs. Montelukast? Characterizing the Response to a Leukotriene Receptor Antagonist and an Inhaled Corticosteroid (CLIC) trial J Allergy Clin Immunol 2005;115:233-42.
Predictors of Response to Fluticasone vs. Montelukast J Allergy Clin Immunol 2005;115:233-42.
Pediatric Asthma Controller Trial (PACT) Predictors of response to fluticasone vs. montelukast (ACD = asthma control days)
Baseline FEV 1 <80% pred Baseline FEV 1 80% pred r=- 0.62, p=0.001
FENO measured in 495 adult asthmatics in Severe Asthma Research Program Aim: Determine whether FENO identified a unique asthma phenotype Methods: Cohort classified by FENO 35ppb vs. >35ppb Results: Subjects with FENO >35ppb Younger patients; Younger when diagnosed with asthma More atopic (greater skin test positivity, higher IgE and blood eosinophils) Greater airway reactivity Greater sputum eosinophilia Greater bronchodilator responsiveness Greatest hyperinflation (RV, RV/TLC) Most frequent ED visits for exacerbations (OR 2.5)
FENO to predict loss of asthma control
FENO and asthma control assessed using ACQ in prospective study of 341 unselected adult asthmatics followed in an asthma and allergy clinic (Belgium)
24 wk observational study 40 children with stable asthma on inhaled corticosteroids eligible for ICS reduction Every 8 weeks ICS dose cut by 50% if clinically indicated Sputum eosinophils, ENO, and bronchial hyperreactivity at each visit to predict success/failure of ICS dose reduction Odds of Exacerbation during ICS Reduction Zacharaslewicz et al. Am J Respir Crit Care Med 2005;171:1077-82
eno as a Marker of Patient Compliance with Prescribed Inhaled Steroid in Childhood Asthma r 2 =0.56, p=0.001 r 2 =0.59, p=0.0003 Eur Respir J 2002;19:1015-19 Pediatr Crit Care Med 2004;5:48-52
Can We Use FENO as a Tool to Monitor Asthma Longitudinally?
Asthma Management Based on Measures of Airway Inflammation vs. Symptom/Lung Function-Based Strategy 74 adults moderate-severe asthma RCT of 2 management strategies to titrate inhaled corticosteroids (ICS) British Thoracic Society asthma management guidelines vs. Minimum ICS dose to maintain sputum eosinophils <3% (induced sputum) No difference in average daily dose of ICS between groups Green et al. Lancet 2002;360:1715-21
Which FENO cut-off to use in a RCT?? (expiratory flow = 50mL/sec) FENO cut-off of between 25-35 ppb seems to discriminate between healthy individuals and atopic asthmatics FENO of > 35 ppb reasonable predictor of > 3% eosinophils in sputum FENO > 35-45 ppb seems to be best cut-off to: Predict steroid responsiveness Predict a loss of asthma control Should cut-off be customized for individual patients?? (e.g. 30 or 50% increase from baseline)
Summary of RCTs Comparing FENO to Guideline Based Management Approach No trial to data has assessed a FENO based approach in a cohort of purely atopic asthmatics No trial has looked at change from best baseline FENO
FENO Measurement: How is it Done? Single breath maneuver at a constant expiratory flow rate from a deep inspiration Standardized procedures established/published (ATS) Approved by FDA in 2004 for clinical use CPT code. Reimbursement still somewhat problematic Most patients age 6 years and older can perform Patient with Asthma
Strength of Evidence Supporting Utility of FENO in the Diagnosis and Management of Asthma Marker of airway eosinophilic/allergic airway inflammation Adjunctive diagnostic test for atopic asthma A- Predictor of steroid responsiveness B+ Identification of a distinct asthma phenotype B+ Predictor of loss of asthma control C+ A- Assist in assessing compliance with steroid therapy B Longitudinal monitoring to adjust therapy * D+ * Contradictory results from published RCTs may reflect differences in algorithms and FENO cut-offs used
Unanswered Questions RCT using change from a subject s best baseline FENO to guide therapy? RCT in atopic asthmatics Peripheral/ alveolar FENO measurements?better correlation with asthma control
Development of Wheezing Phenotypes in Early Childhood Prevalence of Wheezing in Early Childhood eno to identify?
Active Study: FeNO in Wheezy Infants & Toddlers Ongoing study (2005- ) Longitudinal Study of FeNO,Symptoms, Exacerbations, and Lung Function in Infants & Toddlers with Recurrent Wheezing Aims: Can FeNO predict: 1. persistence of wheezing? 2. wheezing frequency or severity? 3. change in lung function? 4. assist in the diagnosis of asthma in infants and toddlers? Study Design: - Prospective observational study - 47 infants (9-24 months of age) with history of at least 3 episodes of wheezing - Study visits every 6 months from enrollment through age 3 yrs, then annually through age 6 years. PI: Debley - NIH/NHLBI K23 HL077626
Noninvasive Measures in Wheezy Infants and Toddlers Predictors FeNO -single breath during ipft -tidal breathing awake and asleep Outcome measures Lung function (infant lung function testing) Albuterol responsiveness during lung function testing Asthma symptoms during follow-up Exacerbations of wheezing during follow-up
SB-eNO (ppb) Enrollment FeNO Levels Acceptable FeNO plateau achieved in 86% of SB-eNO exhalation manuevers 3 acceptable FeNO plateau values achieved in 44 subjects SB-eNO Reproducibility: Mean Intrasubject Coefficient of Variation (CV%) = 6.2% (range 0.9-13.1%) Intraclass Correlation Coefficient = 0.92 80 70 60 50 40 30 20 10 0 Enrollment SB-eNO Levels Mean SB-eNO level = 27.8 ppb (s.d. 16.7) Range 3 76 ppb
Association Between Enrollment FeNO and Change in Lung Function Over 6 Months in Wheezy Infants/Toddlers Multivariable Linear Regression FEV 0.5 ß Coefficient ( FEV 0.5 z-scores) P value Enrollment SB-eNO (10ppb increments) -0.4 0.007 Gender 0.01 0.9 Age at enrollment (1 month increments) FH Asthma (yes/no) Eczema (yes/no) Sustained ICS use during follow-up (yes/no) Tobacco Smoke Exposure (yes/no) -0.03 0.5 0.25 0.5 0.05 0.9 0.77 0.1-0.58 0.2
SB-eNO and Bronchodilator Responsiveness in Wheezy Infants/Toddlers Pre- and post-bronchodilator ipfts completed in 37 of 44 subjects Bronchodilator response: > 12% improvement in FEV 0.5 or > 25% improvement in FEF 25-75
Enrollment SB-eNO and Subsequent Exacerbations of Wheezing Treated with Oral Steroids by Primary Care/ED Physicians Over First 6 Months of Follow-up
FeNO as a Predictor of Persistence of Wheezing at Age 3 Years ROC curve for enrollment FeNO as a predictor of persistence of wheezing at age 3 years (defined as treatment of wheezing with bronchodilators or corticosteroids over at least the last 6 months of follow-up prior to age 3 years). Sensitivity of 77%, specificity of 92%, positive predictive value (PPV) of 94%, and negative predictive value (NPV) of 71%