title: Airway diffusing capacity of nitric oxide and steroid therapy in asthma.
abstract: Exhaled nitric oxide (NO) concentration is a noninvasive index for monitoring lung inflammation in diseases such as asthma. The plateau concentration at constant flow is highly dependent on the exhalation flow rate and the use of corticosteroids and cannot distinguish airway and alveolar sources. In subjects with steroid-naive asthma (n = 8) or steroid-treated asthma (n = 12) and in healthy controls (n = 24), we measured flow-independent NO exchange parameters that partition exhaled NO into airway and alveolar regions and correlated these with symptoms and lung function. The mean (+/-SD) maximum airway flux (pl/s) and airway tissue concentration [parts/billion (ppb)] of NO were lower in steroid-treated asthmatic subjects compared with steroid-naive asthmatic subjects (1,195 +/- 836 pl/s and 143 +/- 66 ppb compared with 2,693 +/- 1,687 pl/s and 438 +/- 312 ppb, respectively). In contrast, the airway diffusing capacity for NO (pl.s-1.ppb-1) was elevated in both asthmatic groups compared with healthy controls, independent of steroid therapy (11.8 +/- 11.7, 8.71 +/- 5.74, and 3.13 +/- 1.57 pl.s-1.ppb-1 for steroid treated, steroid naive, and healthy controls, respectively). In addition, the airway diffusing capacity was inversely correlated with both forced expired volume in 1 s and forced vital capacity (%predicted), whereas the airway tissue concentration was positively correlated with forced vital capacity. Consistent with previously reported results from Silkoff et al. (Silkoff PE, Sylvester JT, Zamel N, and Permutt S, Am J Respir Crit Med 161: 1218-1228, 2000) that used an alternate technique, we conclude that the airway diffusing capacity for NO is elevated in asthma independent of steroid therapy and may reflect clinically relevant changes in airways.
authors.affiliation: Department of Biomedical Engineering, University of California, Irvine, CA 92697-2575, USA.
authors.forename: Hye-Won
authors.initials: HW
authors.lastname: Shin
authors.forename: Christine M
authors.initials: CM
authors.lastname: Rose-Gottron
authors.forename: Dan M
authors.initials: DM
authors.lastname: Cooper
authors.forename: Robert L
authors.initials: RL
authors.lastname: Newcomb
authors.forename: Steven C
authors.initials: SC
authors.lastname: George
mesh_terms: D000293:Adolescent; D000305:Adrenal Cortex Hormones / Q000627:therapeutic use*; D000328:Adult; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use; D001249:Asthma / Q000175:diagnosis / Q000188:drug therapy* / Q000503:physiopathology*; D001944:Breath Tests; D002908:Chronic Disease; D004058:Diffusion; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008954:Models, Biological; D009569:Nitric Oxide / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000378:metabolism*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D014797:Vital Capacity
chemical_list: D000305:Adrenal Cortex Hormones; D018927:Anti-Asthmatic Agents; D009569:Nitric Oxide