Increase in Alveolar Nitric Oxide in the Presence of Symptoms in Childhood Asthma. Part 1

Based on current knowledge, some modality of long-term and high degree of acid suppression or acid exclusion seems to be the most effective treatment strategy. Preselecting children with an abnormal extended pH monitoring finding and a favorable response to a therapeutic trial of aggressive anti-GER therapy seems to be the best way to implicate GER in inducing or exacerbating asthma.

Study objectives: To determine respective contributions of alveolar and proximal airway compartments in exhaled nitric oxide (NO) output (Qno) in pediatric patients with asthma and to correlate their variations with mild symptoms or bronchial obstruction.

Patients and design: In 15 asthmatic children with recent mild symptoms, 30 asymptomatic asthmatic children, and 15 healthy children, exhaled NO concentration was measured at multiple expiratory flow (V) rates allowing the calculation of alveolar and proximal airway contributions in (Qno , using two approaches, ie, linear and nonlinear models.

Measurements and results: Asymptomatic and recently symptomatic patients were not significantly different regarding FEVj and maximum V between 25% and 75% of FVC (MEF25_75): FEVX, 93.3 ± 13.4% vs 90 ± 7.5%; MEF25_75, 70 ± 22% vs 68 ± 28% of predicted values, respectively (mean ± SD). Maximal airway Qno output was significantly higher in recently symptomatic vs asymptomatic patients (p < 0.0001), and in asymptomatic patients vs healthy children (p < 0.02): 134 ± 7 nl/min, 55 ± 43 nl/min, and 19 ± 8 nl/min, respectively. In a multiple regression analysis, variables that influenced airway Qno output were symptoms (p < 0.0001) and distal airway obstruction as assessed by MEF25_75 (p < 0.05). Alveolar NO concentration (FAno) was significantly (p < 0.03) higher in recently symptomatic than in patients without symptoms, whereas it was not significantly different between asymptomatic patients and healthy children: 7.2 ± 2.4 parts per billion (ppb), 5.5 ± 2.7 ppb, and 4.2 ± 2.0 ppb, respectively.

Conclusions: An increase in FAno was observed in the presence of symptoms, and proximal airway NO output was correlated with distal obstruction during asthma.

Key words: exhaled nitric oxide; multiple flow analysis; nitric oxide

Abbreviations: ATS = American Thoracic Society; Cw,no = nitric oxide concentration in the airway wall; Dno = proximal airway nitric oxide diffusing capacity; FAno = alveolar nitric oxide concentration; FEno = exhaled nitric oxide fraction; FEno,50 = exhaled NO fraction calculated at a expiratory flow of 50 mL/s; MEF25_75 = maximal expiratory flow between 25% and 75% ofFVC; NO = nitric oxide; ppb = parts per billion; Qbr,maxNO = maximal proximal airway nitric oxide output; QNO = nitric oxide output; V = expiratory flow

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