Examining axial diffusion of nitric oxide in the lungs using heliox and breath hold

Hye Won Shin, Peter Condorelli, Steven George

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Exhaled nitric oxide (NO) is highly dependent on exhalation flow; thus exchange dynamics of NO have been described by multicompartment models and a series of flow-independent parameters that describe airway and alveolar exchange. Because the flow-independent NO airway parameters characterize features of the airway tissue (e.g., wall concentration), they should also be independent of the physical properties of the insufflating gas. We measured the total mass of NO exhaled (AI,II) from the airways after five different breath-hold times (5-30 s) in healthy adults (21-38 yr, n = 9) using air and heliox as the insufflating gas, and then modeled AI,II as a function of breath-hold time to determine airway NO exchange parameters. Increasing breath-hold time results in an increase in AI,II for both air and heliox, but AI,II is reduced by a mean (SD) of 31% (SD 6) (P < 0.04) in the presence of heliox, independent of breath-hold time. However, mean (SD) values (air, heliox) for the airway wall diffusing capacity [3.70 (SD 4.18), 3.56 pl·s-1·ppb-1 (SD 3.20)], the airway wall concentration [1,439 (SD 487), 1,503 ppb (SD 644>)], and the maximum airway wall flux [4,156 (SD 2,502), 4,412 pl/s (SD 2,906)] using a single-path trumpet-shaped airway model that considers axial diffusion were independent of the insufflating gas (P > 0.55). We conclude that a single-path trumpet model that considers axial diffusion captures the essential features of airway wall NO exchange and confirm earlier reports that the airway wall concentration in healthy adults exceeds 1 ppm and thus approaches physiological concentrations capable of modulating smooth muscle tone.

Original languageEnglish (US)
Pages (from-to)623-630
Number of pages8
JournalJournal of Applied Physiology
Issue number2
StatePublished - Feb 1 2006


  • Gas exchange
  • Trumpet model

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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