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Use of different exhaled nitric oxide multiple flow rate models in COPD

¹ Medicines Evaluation Unit, North West Lung Centre and ³ Medical Statistics, Wythenshawe Hospital, and ² Dept of Mathematics, University of Manchester, Manchester, UK. ⁴ Dept of Cardiology and Respiratory Medicine, Hvidovre Hospital, Hvidovre, Denmark.

CORRESPONDENCE: K. Roy, Medicines Evaluation Unit, North West Lung Centre, Wythenshawe Hospital, Southmoor Road, Manchester, M23 9QZ, UK. Fax: 44 1619461459. E-mail: kroy{at}meu.org.uk

Keywords: Chronic obstructive pulmonary disease, nitric oxide, two-compartment model

Received: November 17, 2006
Accepted January 30, 2007

Multiple flow rates of exhaled nitric oxide (eNO) fraction (F_e,NO) data can be modelled to estimate airway wall concentration of nitric oxide (C_aw,NO), diffusing capacity of nitric oxide (D_aw,NO), alveolar nitric oxide concentration (C_alv,NO) and total maximal flux of nitric oxide in the airway compartment (J'_aw,NO).

F_e,NO at 10, 30, 50, 100 and 200 mL·s^–1 from 50 chronic obstructive pulmonary disease (COPD) patients and 35 healthy controls (smokers and nonsmokers) modelled using five different methods was compared and the effect of the number of flow rates was investigated.

All methods showed that current smoking reduced C&SetFont Italic="0";_aw,NO in COPD patients, with some methods showing that smoking reduced J'_aw,NO. Smoking did not affect C_alv,NO or D_aw,NO. The methods gave similar results for C_aw,NO but there was variability between methods for J'_aw,NO, C_alv,NO and D_aw,NO&SetFont Italic="0";. The median error by least squares fitting between modelled and actual data was significantly lower for the nonlinear method (1.96) compared with the mixed methods (3.31 and 3.62). Parameters calculated using the nonlinear method using five and four flow rates were significantly different. The ratio (95% confidence interval) of C_aw,NO was 2.02 (1.45–2.83).

Nitric oxide models give different results, although airway conductance of nitric oxide is relatively model independent. Nonlinear modelling has the least error, suggesting it is the best method. The number of flow rates should be standardised.

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