Exhaled nitric oxide (NO) is highly dependent on exhalation flow; thus, exchange dynamics of NO have been described by multi-compartment models and a series of flow-independent parameters which describe airway and alveolar exchange. Since 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 (A_I,II) from the airways following five different breathhold times (5 to 30 seconds) in healthy adults (21-38 years, n=9) using air and heliox as the insufflating gas, and then modeled A_I,II as a function of breathhold time to determine airway NO exchange parameters. Increasing breathhold time results in an increase in A_I,II for both air and heliox, but AI,II is reduced by a mean (SD) of 31 (6) % (p<0.04) in the presence of heliox, independent of breathhold time. However, mean (SD) values (air, heliox) for the airway wall diffusing capacity (3.70 (4.18), 3.56 (3.20) pl^.s^-1.ppb^-1), the airway wall concentration (1439 (487), 1503 (644) ppb), and the maximum airway wall flux (4156 (2502), 4412 (2906) pl/s) using a single path trumpet-shaped airway model which considers axial diffusion were independent of the insufflating gas (p>0.55). We conclude that a single path trumpet model which 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 physiologic concentrations capable of modulating smooth muscle tone.