PT  - JOURNAL ARTICLE
AU  - CA Byrnes
AU  - S Dinarevic
AU  - C Busst
AU  - A Bush
AU  - EA Shinebourne
TI  - Is nitric oxide in exhaled air produced at airway or alveolar level?
AID  - 10.1183/09031936.97.10051021
DP  - 1997 May 01
TA  - European Respiratory Journal
PG  - 1021--1025
VI  - 10
IP  - 5
4099  - http://erj.ersjournals.com/content/10/5/1021.short
4100  - http://erj.ersjournals.com/content/10/5/1021.full
SO  - Eur Respir J1997 May 01; 10
AB  - The aim of this study was to determine whether the nitric oxide (NO) measured in exhaled air is produced at airway or alveolar level. Exhaled NO was measured using a chemiluminescence analyser, and carbon dioxide (CO2 concentration using a Morgan capnograph in single exhalations in 12 healthy subjects (mean age 32 yrs; 6 males and 6 females). For each subject, five exhalations were made directly into the NO analyser and five were made through a T-piece system, which allowed measurement of expiratory flow rate. The peak NO levels measured via the T-piece system were 41.2 (SEM 10.8) parts per billion (ppb), significantly lower than direct levels 84.8 (14.0) ppb (p<0.001). The levels of NO tended to rise to an early peak and plateau, while the CO2 levels continued to rise to peak late in the exhalation. The mean times to reach peak NO levels were 32.2 s (direct) and 23.1 s (T-piece), which were significantly different from that of peak CO2 levels 50.5 s (direct) and 51.4 s (T-piece) (p<0.001). At peak NO level, the simultaneous CO2 level mean 4.9% (SEM 0.14)%, was significantly lower than the peak CO2 reached, 5.8 (0.21)% (p<0.001). We conclude that peak nitric oxide levels are dependent on measurement conditions. There are significant differences between the time to peak of carbon dioxide and nitric oxide. Therefore, most nitric oxide, unlike carbon dioxide, is produced in airways and not at alveolar level.