Expired nitric oxide as a marker for childhood asthma

Airway nitrogen oxide measurements in asthma and other pediatric respiratory diseases

Markers for airway inflammation that can be measured noninvasively in expired air may be helpful in treating patients with asthma. For example, levels of nitric oxide are high in the breath of children with asthma exacerbations and decrease with anti-inflammatory therapy. Expired nitric oxide testing has now been standardized and may be useful for children with recurring wheezing that is diagnostically or therapeutically challenging. However, the results may be influenced by several biochemical and anatomic variables and must therefore be interpreted with caution.

Exhaled nitric oxide in children measured by tidal breathing method: differences between asthmatics and nonasthmatic controls

The single-breath maneuver used to measure nitric oxide (NO) in adults cannot be performed by young children. We, therefore, developed a method of measuring NO in mixed exhaled gas collected during tidal breathing. NO was measured in mixed exhaled gas during 5 min of tidal breathing in 113 children 4-14 years of age: 22 nonasthmatics, 21 asthmatic children not taking inhaled corticosteroids, and 70 asthmatic children using inhaled corticosteroids. Exhaled NO levels (median, range) were significantly lower in nonasthmatic controls (median, range: 7, 2-10 ppb) than in asthmatic children on inhaled corticosteroids (8, 3-25 ppb; 95% CI for difference in medians with those of controls, 0-4 ppb), and in those not on inhaled corticosteroids (13, 6-37, ppb; 95% CI for difference in medians, 5-17 ppb). Asthmatic children not using inhaled corticosteroids had significantly higher exhaled NO levels than asthmatic children using inhaled corticosteroids (95% CI for difference in medians, 3-10 ppb). The tidal breathing method is a useful and practical way of measuring exhaled NO levels in children regardless of their age.

Exhaled nitric oxide and exercise-induced bronchoconstriction in asthmatic children

It is known that exhaled nitric oxide (ENO) is increased in asthmatic individuals, probably as an expression of airway inflammation, but no studies have been reported of ENO and exercise-induced bronchoconstriction (EIB). We assessed the effect of a treadmill exercise challenge on ENO concentration in 24 asthmatic children aged 11.2 +/- 0.4 yr (mean +/- SEM). According to the presence or absence of EIB, the children were divided into an EIB group (n = 10) and a non-EIB group (n = 14). ENO was measured with a single-breath reservoir technique. FEV(1), ENO, and heart rate were measured at baseline and 1, 6, 12, and 18 min after the end of exercise. We also measured ENO in 18 healthy control children aged 10.8 +/- 0.6 yr, of whom nine underwent an exercise challenge identical to that of the asthmatic children. After the exercise test, the mean decrease in FEV(1) was 34% in the EIB group and 5% in the non-EIB group. The EIB group had higher baseline ENO values (12.3 +/- 1.6 ppb) than the healthy children (6.1 +/- 0.2 ppb) (p < 0.01). The time course of ENO was similar in the EIB, non-EIB, and control groups, with no significant changes after exercise (p = NS). In the overall group of asthmatic children there was a significant correlation (r = 0.61, p < 0.01) between baseline (preexercise) ENO and magnitude of the maximal decrease in FEV(1) after exercise. In conclusion, our study shows that ENO levels do not change during acute airway obstruction induced by exercise challenge in asthmatic children. In addition, baseline ENO values correlate with the magnitude of postexercise bronchoconstriction, suggesting that NO may be a predictor of airway hyperresponsiveness to exercise.

Exhaled nitric oxide before and after montelukast sodium therapy in school-age children with chronic asthma: a preliminary study

Exhaled nitric oxide (ENO) is a surrogate marker of airway inflammation in asthma. In 12 children aged 6-11 years with mild to moderate persistent asthma, ENO concentrations were measured before and after 4 weeks of treatment with montelukast sodium, a leukotriene receptor antagonist, and 2 weeks after withdrawal of therapy. Baseline ENO levels (mean and 95% confidence interval) were significantly elevated in patients with asthma compared to age-matched nonasthmatic control subjects, with levels of 83 (42-123) vs. 13 (11-15) ppb (P < 0.001). After treatment with montelukast sodium, there was a significant (P < 0.01) reduction in ENO to 58 (27-89) ppb which again rose to 69 (38-99) ppb 2 weeks after treatment was withdrawn. During treatment, the fall in ENO was accompanied by nonsignificant improvements in prebronchodilator forced expiratory volume in 1 s (FEV(1)) from 81-85% predicted or reductions in use of albuterol from a mean of 2.5 to 1.6 puffs/day. Individual ENO measurements and change in ENO concentrations with treatment did not correlate with either pulmonary function changes or use of bronchodilator. These data show that ENO is elevated in children with relatively mild asthma treated with bronchodilator alone, and that treatment with montelukast sodium for 4 weeks results in a significant reduction in ENO concentrations, even in the absence of significant changes in pulmonary function. These findings suggest an anti-inflammatory role for leukotriene D(4) receptor antagonism in the treatment of children with mild to moderate asthma.

Treatment of severe status asthmaticus with nitric oxide

The paper reports on a 13-year-old girl with chronic asthma who presented in acute respiratory failure following an exacerbation of her disease. Nitric oxide was added to the ventilator circuit at 7 ppm and then 15 ppm after the patient failed to respond to bronchodilators and steroids. This was followed by rapid improvement in respiratory mechanics and blood gases with no adverse effects. Nitric oxide appears to have a direct relaxing effect on the bronchial smooth muscle.

Concentration of nitric oxide products in bronchoalveolar fluid obtained from infants who develop chronic lung disease of prematurity

AIMS

To determine if nitric oxide (NO) products (nitrate and nitrite) are increased in bronchoalveolar lavage (BAL) fluid obtained from infants who develop chronic lung disease of prematurity (CLD).

METHODS

One hundred and thirty six serial bronchoalveolar lavages were performed on 37 ventilated infants (12 with CLD, 18 with respiratory distress syndrome (RDS), and seven control infants) who did not receive inhaled NO.

RESULTS

During the first week of life nitrate concentration was between 25-31 micromol/l in all three groups. Thereafter, the concentration of BAL fluid nitrate decreased to 14 micromol/l and 5.5 micromol/l, respectively in the RDS and control groups by 14 days of age. In contrast, nitrate in the CLD infants remained constant until 28 days of age (31.3 micromol/l at day 14; p<0.05). In all BAL fluid samples the mean concentration of nitrite was <1.2 micromol/l throughout the first 28 days with no significant differences noted among the three groups.

CONCLUSION

The similar concentration of BAL fluid nitrate in all groups during the first week of life suggest that NO may be important in the adaptation of the pulmonary circulation after birth. However, persistence of nitrate in the BAL fluid of infants with CLD during the second week may reflect pulmonary maladaptation, or, more likely, persisting pulmonary inflammation.

Serum eosinophilic cationic protein and blood eosinophil counts for the prediction of the presence of airways inflammation in children with wheezing

BACKGROUND

Serum eosinophilic cationic protein (ECP) concentrations may be useful noninvasive markers of airways inflammation in atopic asthma. However, the usefulness of serum ECP measurement for the prediction of airways inflammation in children with a history of wheezing is unknown.

OBJECTIVE

To determine the test accuracy of serum ECP and blood eosinophil percentage as noninvasive markers of eosinophilic airways inflammation.

METHODS

Bronchoalveolar lavage (BAL) fluid and peripheral blood samples for eosinophil percentages and serum ECP were obtained from children undergoing elective surgery and who gave a history of wheezing in the previous year. Sensitivity, specificity and likelihood ratios (LH) and the area under the curve (AUC) for the receiver operator characteristic (ROC) curve were calculated for each blood marker for the prediction of airways inflammation defined by a BAL eosinophil percentage > 0.86. Data were analysed on the basis of how recently symptoms had occurred.

RESULTS

Seventy-seven children (median age 6.75 years) were studied. An AUC of 0.75 (log serum ECP concentration) and 0.76 (log blood eosinophil percentage) was obtained for predicting airways inflammation. A serum ECP > 13 microg/L yielded a LH of 4.4, whereas using a cutoff blood eosinophils > 4% yielded a LH of 1.9, for the prediction of elevated eosinophils in BAL. Serum ECP and eosinophil percentages in BAL and blood were lowest (not statistically significant) when last symptoms had occurred more than 12 weeks previously.

CONCLUSIONS

Serum ECP and blood eosinophil percentages are useful markers for predicting eosinophilic airways inflammation in wheezing children.

Exhaled nitric oxide measurements in childhood asthma: techniques and interpretation

In this review, we outline the role of nitric oxide in airway inflammation in children with asthma. We also discuss the various methods reported for measuring exhaled nitric oxide and provide some insight as to the pros and cons and pitfalls of these techniques. Guidelines for measurements of exhaled nitric oxide based on our experience are provided, as well as suggestions for the use of this technique as a new "airway inflammation test."

NO in exhaled air of asthmatic children is reduced by the leukotriene receptor antagonist montelukast

Nitric oxide in exhaled air (FENO) is increased in asthmatic children, probably reflecting aspects of airway inflammation. We have studied the effect of the leukotriene receptor antagonist (LTRA) montelukast on FENO with a view to elucidate potential anti-inflammatory properties of LTRAs. Twenty-six asthmatic children 6 to 15 yr of age completed a double-blind crossover trial of 2 wk of treatment with 5 mg montelukast once daily versus placebo. FENO was measured during single-breath exhalation at a constant flow rate of 0.1 to 0.13 L/s against a resistance of 10 kPa/L/s. Eleven children were receiving maintenance treatment with inhaled steroids during the study (mean daily dose, 273 microgram), whereas the other 15 used only inhaled beta(2)-agonists as required. The within-subject coefficient of variation of FENO over a 2-wk interval for the 26 children was 38%. FENO was significantly reduced by 20% after the 2-wk treatment with montelukast as compared with placebo as well as compared with baseline. This effect occurred rapidly with a 15% fall in FENO within 2 d. The effect of montelukast on FENO was independent of concurrent steroid treatment. The effect on FENO is probably not caused by bronchodilatation since FENO increased significantly after inhalation of terbutaline. In conclusion, FENO in asthmatic children was significantly decreased from montelukast, which corroborates anti- inflammatory properties of LTRA.

Eosinophil peroxidase nitrates protein tyrosyl residues. Implications for oxidative damage by nitrating intermediates in eosinophilic inflammatory disorders

Eosinophil peroxidase (EPO) has been implicated in promoting oxidative tissue injury in conditions ranging from asthma and other allergic inflammatory disorders to cancer and parasitic/helminthic infections. Studies thus far on this unique peroxidase have primarily focused on its unusual substrate preference for bromide (Br(-)) and the pseudohalide thiocyanate (SCN(-)) forming potent hypohalous acids as cytotoxic oxidants. However, the ability of EPO to generate reactive nitrogen species has not yet been reported. We now demonstrate that EPO readily uses nitrite (NO(2)(-)), a major end-product of nitric oxide ((.)NO) metabolism, as substrate to generate a reactive intermediate that nitrates protein tyrosyl residues in high yield. EPO-catalyzed nitration of tyrosine occurred more readily than bromination at neutral pH, plasma levels of halides, and pathophysiologically relevant concentrations of NO(2)(-). Furthermore, EPO was significantly more effective than MPO at promoting tyrosine nitration in the presence of plasma levels of halides. Whereas recent studies suggest that MPO can also promote protein nitration through indirect oxidation of NO(2)(-) with HOCl, we found no evidence that EPO can indirectly mediate protein nitration by a similar reaction between HOBr and NO(2)(-). EPO-dependent nitration of tyrosine was modulated over a physiologically relevant range of SCN(-) concentrations and was accompanied by formation of tyrosyl radical addition products (e.g. o,o'-dityrosine, pulcherosine, trityrosine). The potential role of specific antioxidants and nucleophilic scavengers on yields of tyrosine nitration and bromination by EPO are examined. Thus, EPO may contribute to nitrotyrosine formation in inflammatory conditions characterized by recruitment and activation of eosinophils.

Is childhood asthma an inflammatory disease?

There is now extensive evidence that asthma results from inflammation in large and small airways, and that the degree of inflammation reflects the clinical severity of the disease. Most of this evidence, however, has come from studies in adult patients. Evidence in children comes largely from indirect studies such as measurements of peripheral blood cells and inflammatory markers, rather than from direct bronchoscopic examination. Studies in adults show that inflammation in asthma is characterized by eosinophilia, epithelial damage, and bronchial hyperresponsiveness, and that activation of allergen-specific T cells plays an important role in orchestrating the inflammatory process. In children, indirect evidence of inflammation comes from the observation that anti-inflammatory agents such as inhaled corticosteroids improve symptoms and bronchial hyperresponsiveness, reduce the number of asthma exacerbations, and limit the progressive decline in lung function. Further evidence comes from measurements of nitric oxide and hydrogen peroxide (potential inflammatory markers) in exhaled air, and of inflammatory mediators in plasma and urine. As in adults, there is evidence that lymphocytes play an important role in orchestrating the inflammatory process. The immunologic profile appears to shift from a Th1-type cytokine profile to an allergen-related Th2-type profile prior to birth. Such a Th2 predominance constitutes a risk factor for the subsequent development of bronchial hyperresponsiveness and asthma in response to allergen.

Effects of hard metal on nitric oxide pathways and airway reactivity to methacholine in rat lungs

To examine whether the development of hard metal (HM)-induced occupational asthma and interstitial lung disease involves alterations in nitric oxide (NO) pathways, we examined the effects of an industrial HM mixture on NO production, interactions between HM and lipopolysaccharide (LPS) on NO pathways, and alterations in airway reactivity to methacholine in rat lungs. HM (2.5 to 5 mg/100 g intratracheal) increased NO synthase (NOS; EC 1.14.23) activity of rat lungs at 24 h without increasing inducible NOS (iNOS) or endothelial NOS (eNOS) mRNA abundance or iNOS, eNOS, or brain NOS (bNOS) proteins. The increase in NOS activity correlated with the appearance histologically of nitrotyrosine immunofluorescence in polymorphonuclear leukocytes (PMN) and macrophages. Intraperitoneal injection of LPS (1 mg/kg) caused up-regulation of iNOS activity, mRNA, and protein at 8 h but not at 24 h. HM at 2.5 mg/100 g, but not at 5 mg/100 g, potentiated the LPS-induced increase in NOS activity, iNOS mRNA, and protein. However, HM decreased eNOS activity at 8 h and eNOS protein at 24 h. Whole body plethysmography on conscious animals revealed that HM caused basal airway obstruction and a marked hyporeactivity to inhaled methacholine by 6-8 h, which intensified over 30-32 h. HM-treatment caused protein leakage into the alveolar space, and edema, fibrin formation, and an increase in the number of inflammatory cells in the lungs and in the bronchoalveolar lavage. These results suggest that a HM-induced increase in NO production by pulmonary inflammatory cells is associated with pulmonary airflow abnormalities in rat lungs.

Exhaled nitric oxide concentrations during treatment of wheezing exacerbation in infants and young children

While it is known that exhaled nitric oxide (ENO) is increased in adults and school children with asthma exacerbation probably as an expression of disease activity, no studies have investigated whether this phenomenon also occurs in infants and young children with recurrent wheeze exacerbation. We measured ENO in 13 young children (mean age 20.2 mo) with recurrent wheeze (Group 1) during an acute episode and after 5 d of oral prednisone therapy. ENO was measured also in nine healthy control subjects (Group 2) (mean age 16.9 mo) and in six children with a first-time viral wheezy episode (Group 3) (mean age 11 mo). To measure ENO, infants inhaled NO-free air via a face mask from a reservoir and, through a nonrebreathing valve, exhaled in a collecting bag that was analyzed by chemiluminescence. To address the question of whether the levels of ENO collected in the bag are a reflection of the pulmonary airway, ENO determinations were performed in two healthy infants before and after tracheal intubation for elective surgery. During the acute episode of wheezing the mean (+/- SEM) value of ENO in children with recurrent wheeze (Group 1) was 14.1 +/- 1.8 ppb, almost threefold higher than in healthy control subjects (5.6 +/- 0.5 ppb, p < 0.001). After steroid therapy we found a mean fall of 52% in ENO (5.9 +/- 0.7 ppb, p < 0.01) compared with baseline values. ENO values measured before and after intubation in two infants were 6 ppb and 5 ppb in one child and 7 ppb and 6 ppb in the other one. The mean value of ENO of children with first-time wheeze (Group 3) was 8.3 +/- 1.3 ppb, significantly lower (p < 0.05) than the value of children with recurrent wheeze (Group 1). In conclusion, we describe a method to measure ENO in young children and show that infants with recurrent wheeze have elevated levels of ENO during exacerbation that rapidly decrease after steroid therapy. This suggests that, in these children, airway inflammation could be present at a very early stage.

Expired nitric oxide and airway obstruction in asthma patients with an acute exacerbation

Expired nitric oxide (eNO) is a marker of airway inflammation that is increased in asthma. The present study was undertaken to examine the clinical utility of eNO as an aid in the assessment of asthma in the emergency department (ED). Fifty-two adult patients with acute asthma, 53 age- and sex-matched controls, and eight patients with stable asthma were enrolled. Subjects performed spirometry, their eosinophil counts and serum total IgE were measured, and a sample of mixed VC expirate was collected for measurement of NO. Mixed expired NO was 8.2 +/- 0.5 ppb in controls, 8.8 +/- 1.5 ppb in patients with stable asthma, and 15.0 +/- 1.0 ppb in patients with acute asthma. A significant difference in eNO was observed in patients with acute asthma and controls (p < 0.001). Twenty-three of the 52 patients with acute asthma versus two of 53 controls had an eNO >/= 15 ppb (p < 0.001). Expired NO concentration correlated with FEV1% (r = -0.42, p < 0.001) and with the peripheral blood eosinophil count (r = 0.34, p < 0.001) in the group of 60 patients with acute and stable asthma. The sensitivity of eNO > 10 ppb and eosinophilia (> 200 cells/microliter) was 90% in predicting airway obstruction (FEV1/FVC < 0. 8). No relationship of eNO was found to serum IgE, self- reported smoking, or glucocorticoid use. Measurement of eNO is a promising clinical tool for assessing acute asthma.

Reference values of exhaled nitric oxide for healthy children 6-15 years old

Nitric oxide (NO) can be detected in human exhaled air, and its endogenous production is increased in patients with asthma. It may provide a noninvasive means for measuring airway inflammation. The aim of this study was to establish reference values for exhaled NO concentrations in a large number of healthy school-age children. We measured exhaled NO levels in 159 white healthy children (88 girls, 71 boys, age range 6-15 years) recruited from two public schools of Padua, Italy. Exhaled NO levels in exhaled gas were measured by a tidal breathing method with a chemiluminescence analyzer, and NO steady-state levels were recorded. Nasal NO levels were measured by direct sampling from the nose during mouth breathing. The mean concentration of endogenous NO in orally exhaled gas was 8.7 parts per billion (ppb) (95% confidence interval (C.I.), 8.1-9.2 ppb) and sampled data followed a log-normal distribution (Kolmogorov-Smirnov d = 0.77, P > 0.2). No difference was found between boys (mean value, 8.4 ppb; 95% C.I., 7.3-9.4 ppb) and girls (mean value, 8.9 ppb; 95% C.I., 7.9-9.9 ppb). No significant correlation was found between age, height, or spirometric data and exhaled NO levels (r < 0.2). The mean value of nasal NO concentrations was 216 ppb (95% C.I., 204-228 ppb). There was no correlation between exhaled and nasal NO values (r = 0.16, P = ns). In conclusion, this study establishes a reference range for exhaled NO values measured by a tidal breathing method in children between age 6-15 years. The observed levels are independent of age, gender, and lung function, and can be used to monitor airway inflammation in asthmatic children.

Vital capacity reservoir and online measurement of childhood nitrosopnea are linearly related. Clinical implications

Hypernitrosopnea, a robust marker for childhood asthma, is measured reproducibly in mixed vital capacity (VC) expirates. Recent guidelines for measurement of expired nitric oxide (NO) in adults have favored use of an online (OL), flow-dependent technique. We compared VC and OL NO measurements in 14 asthmatic and 11 control children 5 through 18 yr of age. After spirometry, subjects breathed both into an open-ended reservoir (20 cm H2O resistance) and into a tedlar bag (VC maneuver). End-expiratory pressure > 5 cm H2O was continuously maintained during VC measurements, and the velum remained shut. Eight additional children (24% of total number of subjects) were unable reproducibly to perform the OL measurement at constant flow (six asthmatics; two control children). For subjects able to perform the OL technique, OL and VC NO measurements were linearly related (r2 = 0.88). In children, VC NO assays are reproducible, sensitive in identifying asthma, and portable. Additionally, we have shown that (1) not all children are able to perform OL measurements, and (2) VC measurements vary linearly with OL measurements. These findings suggest that there may not be compelling reason to favor OL over VC measurements for hypernitrosopnea in children with asthma.

Effect of natural grass pollen exposure on exhaled nitric oxide in asthmatic children

Exhaled nitiric oxide (NO) is increased in exhaled breath of asthmatic patients. The aim of this study was to investigate the longitudinal changes of exhaled NO outside and during the pollen season in pollen-allergic asthmatic children. Twenty-one children (age 6 to 16 yr), with a seasonal allergic asthma sensitive to grass pollen, underwent measurements of exhaled NO and pulmonary function before (March), during (May), and after (November) the pollen season. Exhaled NO was measured by a tidal breathing method with a chemiluminescence analyzer and NO steady-state levels were recorded. The timing of the measurements during the pollen season was based on the atmospheric pollen count. Exhaled NO values of asthmatic children were compared with those of 21 sex- and age-matched healthy children. Pulmonary function and symptoms of asthma were also evaluated at each visit. The mean value of exhaled NO before the grass season was 12.7 +/- 5.1 ppb (mean +/- SD), significantly higher when compared with controls (7.8 +/- 2.7 ppb, p < 0.001). In the pollen season there was a significant (p < 0.001) twofold increase in exhaled NO (21.4 +/- 7.6 ppb) that, after the season, returned to values similar (12.8 +/- 5.8 ppb, p = NS) to those found before the season. There were no significant changes in FEV1 before and during the season (98.6% predicted versus 101% predicted, p = NS). We conclude that natural allergen exposure is related to an increase of exhaled NO in asthmatic grass pollen-allergic children even in absence of significant changes in airways function. We speculate that measurement of exhaled NO could be a sensitive noninvasive marker of asthma disease activity.

A community study of exhaled nitric oxide in healthy children

Exhaled nitric oxide (eNO) is elevated in patients with inflammatory pulmonary diseases and it has attracted increasing interest as a simple, noninvasive marker of airway inflammation. Little is known, however, about factors that might affect eNO in healthy subjects. We measured eNO in 157 healthy 7- to 13-yr-old children (mean 9.7 yr, 77 girls), with no history of respiratory tract disease, using a recently validated, single-breath technique. Measurements of eNO were obtained at driving (mouth) pressures of 10, 15, and 20 cm H2O and 3 eNO plateaux were achieved for each child at each pressure. Exhaled NO decreased with increasing pressure (increasing expiratory flow) (p < 0.001) and increased with age (p < 0.001). Concentrations were greater in children with a positive skin prick test (p < 0.0001). Geometric mean eNO levels were 7.2 ppb in children with no positive skin prick tests (n = 116), 10.9 ppb in children with one positive reaction (n = 24), and 20.1 ppb in children with two or more skin reactions (n = 17). Age and immunological reactions to common allergens are associated with increased eNO in children and should be controlled for in studies of eNO. The mechanisms responsible for these associations require further study.

Relationship between exhaled nitric oxide and childhood asthma

The purpose of the study was to determine if exhaled nitric oxide levels in children varied according to their asthmatic and atopic status. Exhaled nitric oxide was measured in a sample of 93 children attending the North West Lung Centre, Manchester, United Kingdom, for the clinical evaluation of a respiratory questionnaire being developed as a screening tool in general practice. The clinical assessment included full lung function, skin prick testing, and exercise challenge. Children were said to be asthmatic either by consensus decision of three independent consultant pediatricians, who reviewed all the clinical results except the nitric oxide measurements, or by positive exercise test. Atopic asthmatic children had higher geometric mean exhaled nitric oxide levels (consensus decision, 12.5 ppb [parts per billion] 95% CI, 8.3 to 18. 8; positive exercise test, 12.2 ppb 95% CI, 7.6 to 19.7) than did nonatopic asthmatic children (3.2 ppb 95% CI, 2.3 to 4.6; 3.2 ppb 95% CI, 2.0 to 5.0), atopic nonasthmatic children (3.8 ppb 95% CI, 2. 7 to 5.5; 5.7 ppb 95% CI, 4.1 to 8.0), or nonatopic nonasthmatic children (3.4 ppb 95% CI, 2.8 to 4.1; 3.5 ppb 95% CI, 3.0 to 4.1). Thus, exhaled nitric oxide was raised in atopic asthmatics but not in nonatopic asthmatics, and these nonatopic asthmatics had levels of exhaled nitric oxide similar to those of the nonasthmatics whether atopic or not.

Effect of atmospheric nitric oxide (NO) on measurements of exhaled NO in asthmatic children

The measurement of exhaled nitric oxide concentrations [NO] may provide a simple, noninvasive means for measuring airway inflammation. However, several measurement conditions may influence exhaled NO levels, and ambient NO may be one of these. We measured exhaled NO levels in 47 stable asthmatic children age 5 to 17 years and in 47 healthy children, gender and age matched. Exhaled [NO] in expired air was measured by a tidal breathing method with a chemiluminescence analyzer, sampling at the expiratory side of the mouthpiece. NO steady-state levels were recorded. In order to keep the soft palate closed and avoid nasal contamination, the breathing circuit had a restrictor providing an expiratory pressure of 3-4 cm H2O at the mouthpiece. To evaluate the effect of [NO] in ambient air, measurements were randomly performed by breathing ambient air or NO-free air from a closed circuit. Breathing NO-free air, exhaled [NO] in asthmatics (mean +/- SEM) was 23.7 +/- 1.4 ppb, significantly higher (P < 0.001) than in healthy controls (8.7 +/- 0.4 ppb). Exhaled NO concentrations measured during ambient air breathing were higher (49 +/- 4.6 ppb, P < 0.001) than when breathing NO-free air (23.7 +/- 1.4 ppb) and were significantly correlated (r = 0.89, P < 0.001) with atmospheric concentrations of NO (range 3-430 ppb). These findings show that 1) exhaled [NO] values of asthmatic children are significantly higher than in healthy controls, and 2) atmospheric NO levels critically influence the measurement of exhaled [NO]. Therefore, using a tidal breathing method the inhalation of NO-free air during the test is recommended.

Bronchodilator S-nitrosothiol deficiency in asthmatic respiratory failure

BACKGROUND

Nitric oxide (NO) gas concentrations are high in the expired air of individuals with asthma, but not consistently so in the expired air of people with pneumonia. S-nitrosothiols are naturally occurring bronchodilators, the concentrations of which are raised in the airways of patients with pneumonia. Airway S-nitrosothiols have not been studied in asthma.

METHODS

Tracheal S-nitrosothiol concentrations from eight asthmatic children in respiratory failure were compared with those of 21 children undergoing elective surgery.

RESULTS

Mean S-nitrosothiol concentrations in asthmatic children were lower than in normal children (65 [SD 45] nmol/L vs 502 [SD 429] nmol/L) and did not vary with inspired oxygen concentration or airway thiol concentration.

INTERPRETATION

Severe asthma is associated with low concentrations of airway S-nitrosothiols. This is the first reported deficiency of an endogenous bronchodilator in the human asthmatic airway lining fluid. We suggest that S-nitrosothiol metabolism may be a target for the development of new asthma therapies.

Exhaled nitric oxide measurements in normal and asthmatic children

The aim of this study was to determine whether we could measure exhaled nitric oxide (NO) levels in children, and whether the same pattern of exhaled NO concentrations was observed in asthmatic and normal children as had been seen in adults. Using a chemiluminescence NO analyzer, we measured NO in exhaled air both directly and through a T-piece allowing us to measure carbon dioxide (CO2), mouth pressure, and expiratory flows. In 39 normal children the mean peak exhaled NO was 49.6 parts per billion (ppb) (SD 37.4) when all expired gas passed directly through the NO analyzer, and 29.7 ppb (SD 27.1) when expiration occurred through a T-piece. The results were significantly higher in 15 asthmatic subjects on bronchodilator therapy only [126.1 ppb (SD 77.1) direct (P < 0.001), and 109.5 ppb (SD 106.8) via T-piece (P < 0.001)]. In 16 asthmatics on regular inhaled corticosteroids the mean peak exhaled levels were significantly lower 48.7 ppb (SD 43.3) direct (P < 0.001) and 45.2 ppb (SD 45.9) via T-piece (P < 0.01). There was no difference between the normal children and the asthmatic children on regular inhaled corticosteroids (P = 0.9 direct, P = 0.2 via T-piece). There were no significant differences in carbon dioxide levels, mouth pressure, duration of expiration and expiratory flows between the different groups, and no difference between carbon dioxide levels, mouth pressure and duration of expiration between the two methods (direct and T-piece). In 6 asthmatic children mean peak exhaled levels on NO fell from a median peak level of 124.5 ppb to 48.6 ppb when measured before and 2 weeks after commencement of inhaled corticosteroid treatment. The measurement of exhaled NO levels may be useful as a noninvasive means of monitoring children with asthma.