Increase in Alveolar Nitric Oxide in the Presence of Symptoms in Childhood Asthma. Part 6

By contrast, both very low-flow and very high-flow rates were not obtained in all children. FEno at a “very” high flow (> 150 mL/s) was obtained in only 20 participants, whereas measurements did not satisfy the criteria of stability in the remaining patients. Most frequent aspect in these cases was a progressive decrease in FEno without a stable plateau. FEno was only interpretable at a “very” low flow (< 40 mL/s) in 25 asthmatic children. At this very low flow, the time needed to obtain a stable NO plateau was > 12 s, and stable V was difficult to sustain for younger patients in this condition close to apnea. The mean values of the very low flows and the low flows allowing resolution of the equation of Silkoff were 25 ± 9 mL/s and 39 ± 10 mL/s, respectively. We applied the equation in these 25 children. Thus, modeling was achieved in all 60 participants using the linear method and in 25 asthmatic participants using the nonlinear method.

In the 25 asthmatic participants for whom both models were used, Dno X Cw,no, which reflected Qbr,maxNO with the nonlinear method, was significantly correlated to Qbr,maxNO calculated with the linear method (Fig 1, top, A); the mean values of these two parameters were 77 ± 68 nL/min and 81 ± 73 nL/min, respectively. Similarly, FAno computed with the linear method was significantly correlated to FAno calculated by the analysis of Silkoff(Fig 1, bottom, B); their mean values were 5.8 ± 2.5 ppb and 6.8 ± 4.6 ppb, respectively. Because the linear model could be applied to the entire population only FAno and Qbr,maxNO calculated using the linear model are reported hereafter.

Comparison of NO Indexes Between Symptomatic and Nonsymptomatic Asthmatic Patients and Healthy Children

The results of Qbr,maxNO, FAno, and FEno calculated at a V of 50 mL/s (FEno,50) are summarized in Figure 2. Symptomatic children were characterized by an increase in both Qbr,maxNO and FAno as compared to asymptomatic asthmatic patients and healthy children (Table 1). For healthy children, the observed values of Qbr,maxNO were not significantly different from predicted values that were calculated based on the relationship established for healthy nonsmoker adults:

Qbr,maxNO (nanoliters per minute) = 0.666 X height(centimeters) – 78 (see Materials and Methods).

FAno contributed substantially to FEno, the proportion of FEno due to FAno increased with the flow rate: respective contribution of FAno in FEno in symptomatic, asymptomatic, and healthy children is illustrated in Figure 3. No correlation was found between alveolar and proximal airway NO, namely FAno and Qbr,maxNO.

Correlation With Functional Respiratory Tests in Asthmatic Children

Pulmonary function tests demonstrated no significant difference between recently mildly symptomatic (n = 15) and asymptomatic (n = 30) asthmatic children: FEV1 % of predicted, 90 ± 16.5% vs 93 ± 13.5%; MEF25_75 % of predicted, 68 ± 28% vs 70 ± 22%; respectively.