Exhaled Nitric Oxide:

ApplicationMeasurement

Interpretation

Marshall B Dunning III PhD, MS, RPFT, RCP

53rd AARC Congress

Nitric oxide (NO):

•1987 discovered that NO was the previously described endothelial- derived relaxing factor (EDRF)

•Colorless, odorless gas, slightly soluble in water

•Half-life is a few seconds

•NO promotes both vascular and bronchial dilation in the respiratory system

•Facilitates coordinated ciliary beating

•Serves as a neurotransmitter for NANC neurons in the bronchial wall

Drs. Robert F. Furchgott,Louis Ignarro & Ferid Murad1998 Nobel Prize inPhysiology or Medicine

Biology of NO:

Formed by action of nitric oxide synthase (NOS) on L-arginine

3 isoforms-

•type I or neuronal NOS, NOS-1, nNOS•type II or inducible NOS, NOS-2, iNOS•type III or constitutive NOS, NOS-3, cNOS, eNOS

nNOS and eNOS produce low amounts of NO

iNOS can generate large amounts of NO

Stronger affinity for hemoglobin than CO•up to 1,000 times more

Biosynthesis of NO:Under basal conditions:

NO continually being produced by eNOS (calcium dependent)Activity of iNOS is very low (calcium independent)

Stimulation of eNOS:Shear forces (increase in blood flow) flow-dependent NO formationEndothelial receptor ligands (vasoactive substances)

receptor-stimulated NO formation

Stimulation of iNOS:Inflammation by bacterial endotoxins, and cytokines and interleukinsAmount of NO produced may be 1,000-fold greater than that produced by eNOS

Source: Klabunde RE: Cardiovascular Physiology Concepts, Philadelphia, LWW 2005

Mechanism of action:Mediated via cGMP

Produced by: •Vascular endothelial cells•Airway neurons •Airway inflammatory cells•Airway epithelial cells

Vascular Effects of NO:

•Direct vasodilation•Anti-thrombotic activity•Anti-inflammatory

Nitric oxide, nitrogen monoxide

N=O

Clinical use of FENO:

• Adjuvant diagnostic tool

• Non-invasive inflammatory biomarker

• Observe response to anti-inflammatory therapy

• Monitor treatment compliance

• Detect “occult” airway inflammation

• Predict potential asthma exacerbations

• Guide step-down treatment of asthma

Online measurement:

“…exhalations where the expirate is continuously sampled by the NO analyzer, and the resultant NO profile versus time or exhaled volume…is captured and displayed in real time…” (ATS)

FENO

= fractional concentration of exhaled NO

Expressed as ppb (equivalent to nl/L)

NIOX® Flex, Aerocrine, New Providence, NJ

Offline measurement:

“…fractional NO concentration in exhalate from a vital capacity collection…” (ATS)

FENO

= fractional concentration of NO

Expressed as ppb (equivalent to nl/L)

ATS/ERS Recommendations for standardized procedures for the online and offlinemeasurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005.Am J Respir Crit Care Med 171:912-930, 2005.

•Ambient NO at the time of test should be <5 ppb

•Inhale to TLC, over 2-3 seconds, through mouth avoiding nasal inspiration

•Exclude nasal NO by exhaling against a resistance: 5 cmH2O

•Recommended expiratory flow rate: 50 mL/sec or 0.05 L/sec (+10%)

•The duration of exhalation must be sufficient (>6 sec) to obtain plateau

•3 second NO plateau: <10% or 1 ppb change

•Single-breath NO profile: exhaled NO vs time plot

•Suboptimal exhalations: identified and discarded

•3 repeated with 2 reproducible (+10%) plateau values

•30 sec relaxed tidal breathing between exhalations

•Mean of 2 NO concentration expressed in ppb

ATS recommendations for online measurement of FENO

NO concentration (ppb) and airway opening pressure versus time for three separate exhalations by the same subject, showing reproducible profiles and plateaus

ATS/ERS Recommendations for standardized procedures for the online and offlinemeasurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005.Am J Respir Crit Care Med 171:912-930, 2005.

Left-hand tracing performed with oral inspiration of gas containing <5 ppb NORight-hand tracing performed after subject asked to inhale nasallyNO plateau essentially unchanged once peak washed out

ATS/ERS Recommendations for standardized procedures for the online and offlinemeasurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005.Am J Respir Crit Care Med 171:912-930, 2005.

•Ambient NO at the time of test should be <20 ppb

•Nose clips are not required

•Inhale orally to TLC and than immediately perform a slow VC

•Exclude nasal NO by exhaling against a resistance: 5 cmH2O

•Recommended expiratory flow rate: 350 mL/sec or 0.35 L/sec (+10%)

•Reservoir for collection must be nonreactive and relatively impermeable

•Reservoir bag should be stable for at least 48 hours

•NO concentration expressed FENO,0.35

ATS recommendations for offline measurement of FENO

Technical factors that affect FENO values:

Method of collection•online vs. offline•nasal nitric oxide•expiratory flow rate

Time of day•circadian rhythm

Age/sex •no consistent relationship

Food and beverages•nitrate-containing food•Avoid for 1 hour

Medications•Oral corticosteroids

Respiratory tract infections•Wait until recovery

Exercise•Avoid for 1 hour

Deykin A, Massaro AF, Drazen JM, Israel E: Exhaled nitric oxide as a diagnostic test for asthma; Online versus offline techniques and effect of flow rate. Am J Respir Crit Care Med 165:1597-1601, 2002

ATS/ERS Recommendations for standardized procedures for the online and offlinemeasurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005.Am J Respir Crit Care Med 171:912-930, 2005.

FENO contamination

Sinus: 1,000-30,000 ppbMouth: 5-15 ppb

Nasal: 15-40 ppb

Trachea: <3 ppb

Am J Respir Crit Care Med 176:238-242, 2007

Chemoluminescence analyzerSIR N-6008, Madrid, Spain

Fortuna AM, Feixas T, Gonzalez M, Casan P: Diagnostic utility in asthma: Exhaled nitric oxide and induced sputum eosinophil count. Resp Med 101:2416-2421, 2007

Respiratory Research 7:94;2006

What about me

Mr. I. Novent

Therapeutic•Pulmonary hypertension in newborn•Hypoxic respiratory failure in near-term

•Reduce PVR and enhance RV stroke volume post cardiac transplant•Ischemic-reperfusion injury•Acute respiratory distress syndrome

Diagnostic•Pulmonary vasoreactivity in cardiac cath lab

Datex-Ohmeda INOvent, INO Therapeutics, Inc., Clinton, NJ

Conclusions

• Marker of airway inflammation

• Multiple factors contribute to variation in FENO values

• Should be used in conjunction with other pulmonary function tests

• Monitor treatment compliance

• Research tool useful tool clinical practice

References:

1) ATS/ERS Recommendations for standardized procedures for the online and offlinemeasurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005.Am J Respir Crit Care Med 171:912-930, 2005.2) Deykin A, Massaro AF, Drazen JM, Israel E: Exhaled nitric oxide as a diagnostic test for asthma; Online versus offline techniques and effect of flow rate. Am J Respir Crit Care Med 165:1597-1601, 20023) Ichinose F, Roberts JD, Zapol WM: Inhaled nitric oxide: a selective pulmonaryvasodilator, current uses and therapeutic potential. Circulation 109:3106-3111, 20044) Smith AD, Cowan JO, Brassett K, Herbison GP, Taylor DR. Use of exhaled nitricoxide measurements to guide treatment in chronic asthma. N Engl J Med 352:163-73,2005.5) Travers J, Marsh S, Aldington S, et al: Reference ranges for exhaled nitric oxide derived from a random community survey of adults. Am J Respir Crit Care Med 176:238-242, 20076) Yates DH. Role of exhaled nitric oxide in asthma. Immunol Cell Bio 79:178-90, 2001