Exhaled Nitric Oxide Measured using TDLAS Insensitivity to High Atmospheric Nitric Oxide Concentrations

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Exhaled Nitric Oxide Measured using
TDLASInsensitivity to High Atmospheric Nitric
Oxide Concentrations
Mark Camp, M.D., F.A.C.P., F.C.C.P. The Lung
Center, Norman, OK James D. Jeffers, Chad Roller,
Khosrow Namjou, Ph.D. Ekips Technologies, Inc.,
Norman, OK Patrick J. McCann, Ph.D. University of
Oklahoma, School of Electrical and Computer
Engineering
ACAAI Annual Meeting San Antonio, Texas November
18, 2002
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Study Objectives

• Evaluate Tunable Diode Laser Absorption
  Spectroscopy (TDLAS) as a new tool for exhaled
  nitric oxide (eNO) measurements.
• Use eNO to assess airway inflammation and monitor
  therapy.
• Determine if high levels of ambient NO affect eNO
  measurements.

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Motivation

• Asthma is a chronic inflammatory disorder of the
  lower airways
• Working definition (NHLBI, 1995)
• High eNO levels are linked to inflammation.
• Spirometry provides only limited and indirect
  information regarding airway inflammation.

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Nitric Oxide Biochemistry
Healthy Subjects cNOS L-arginine ? L-citrulline
NO
Effects of NO Vasodilatation Host Defense Smooth
Muscle Relaxation
Asthmatics cNOS L-arginine ? L-citrulline NO
iNOS L-arginine ? L-citrulline NO
Excessive NO is associated with airway
inflammation.
Constitutive and inducible nitric oxide
synthases (cNOS and iNOS) are genetically-produce
d enzymes

• iNOS Inhibitors
• Inhaled corticosteroids

iNOS Expression Caused by epithelial cell
exposure to specific cytokines and endotoxins
Epithelial Cell
? Inflammation ? High exhaled NO

• Inflammation
• Lower eNO

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NO Measurement Techniques

• Chemiluminescence
• Reaction with ozone
• Patients must exhale at constant flow rates
• Requires NO-free air to zero the instrument
• Requires calibration using standard reference
  gases
• Unreliable calibration gases can result in
  unreliable data.
• NO degrades to NO2

• TDLAS
• Molecules absorb IR light
• Simultaneous NO and CO2 detection improves
  reliability
• Patients can exhale at different flow rates
• No consumables

NO O3 ? NO2 h? (light)
Spectral Signals
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eNO Measurements with TDLAS
Results in 20 seconds
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Asthmatic Examples
Age 14, Male, Mild-Persistent Non-Treated
Age 5, Female, Mild-Persistent Corticosteriod
Treated
Normal Airway
Inflamed Airway
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Treatment Monitoring
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Air Pollution Effects?

• Nitric Oxide is a major component of smog.
• Automobile exhaust is primary source.
• Ambient NO (aNO) concentrations will vary with
  geography, weather conditions (inversion layers),
  and time of day.

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eNO not Affected by aNO
Low aNO (2 ppb)
High aNO (24 ppb)
Untreated Asthmatic
Untreated Asthmatic
Non- Asthmatic
Non- Asthmatic
Ambient Air Displaced by Breath
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Replication Precision

• TDLAS provides good replication precision in
  spite of varying atmospheric NO levels.

Non-asthmatic volunteer over a three-month period
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Biochemistry of NO Absorption

• Ambient NO is rapidly absorbed by the airways and
  not subsequently exhaled.

Airway Tissue
NO ROS ? NO2 and NO3
Endogenously-produced NO scavenges cytotoxic
reactive oxidative species (ROS). Dweik et
al., Proc. Natl. Acad. Sci. 98, 2622 (2001)
High eNO is possibly associated with a
protective mechanism in asthmatic airways.
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Conclusions and Future Work

• TDLAS successfully measured high eNO in untreated
  asthmatics and low eNO in treated asthmatics and
  non-asthmatics.
• A reduction in eNO from more than 40 ppb to less
  than 20 ppb over a 7-day period was observed
  following anti-inflammatory treatment.
• High levels of ambient NO are rapidly absorbed
  and not subsequently exhaled.
• Clinical trials are continuing.