The purpose of this study is to determine fractional exhaled nitric oxide (FeNO) level in healthy subjects among Thai populations.

Fractional exhaled nitric oxide (FeNO) were produced from epithelial cells of inflammatory airways and eosinophils and this gas was discovered since 1991.

Fractional exhaled nitric oxide (FeNO) has direct association with severity of inflammation of bronchial trees and sputum eosinophils and use for additional investigation for diagnosis asthma or inflammatory airway diseases.

There are many factors from previous studies that associate with level of fractional exhaled nitric oxide (FeNO), one of that factors is race therefore we can't use level from another studies with different race for use as reference and there is no study about level of fractional exhaled nitric oxide in Thai population.

It is therefore desirable to examine level of fractional exhaled nitric oxide (FeNO) in healthy subjects among Thai population and will be the main objective of this research.

Inclusion Criteria:

• healthy subjects in community

Exclusion Criteria:

• smoker or past history of smoking
• asthma, allergic rhinitis, chronic respiratory disease or other chronic illness
• history of wheezing within 12 months before enrollment
• history of upper or lower respiratory tract infection within 6 weeks before enrollment
• drink ethanol within 48 hours before enrollment
• drink caffeine within day before enrollment
• during pregnancy
• chronic use of any drugs
• participate other project within 30 days

community sample