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

Nasal Nitric Oxide Measurement in Primary Ciliary Dyskinesia. A Technical Paper on Standardized Testing Protocols

Nasal nitric oxide concentrations are extremely low in primary ciliary dyskinesia (PCD), and measurement of this nasal gas is recommended as a PCD diagnostic test in cooperative patients aged 5 years and older. However, nasal nitric oxide measurements must be performed with chemiluminescence analyzers using a standardized protocol to ensure proper results, because nasal nitric oxide values can be influenced by various internal and external factors. Repeat nasal nitric oxide testing on separate visits is required to ensure that low diagnostic values are persistent and consistent with PCD. This technical paper presents the standard operating procedures for nasal nitric oxide measurement used by the PCD Foundation Clinical and Research Centers Network at various specialty centers across North America. Adherence to this document ensures reliable nasal nitric oxide testing and high diagnostic accuracy when employed in a population with appropriate clinical phenotypes for PCD.

Head-to-head comparison of single-breath and tidal-breath exhaled nitric oxide measurements

BACKGROUND

Exhaled nitric oxide (eNO) is an endogenous gas involved in airway pathophysiology and is determined in orally exhaled air by various techniques. However, traditional single-breath technique (eNO(SB)) requires active cooperation and is not always easily practicable (especially in young children); simpler techniques including tidal breathing measurements (eNO(TB)) are not standardized. The aim of this study was to evaluate the possible correlation and correspondence between eNO(SB) and eNO(TB) and the impact of potential confounders in children with chronic adenotonsillar disease.

METHODS

Eighty-six children (mean age 8.7 ± 3.2 y) underwent eNO assessment by means of eNO(SB) and eNO(TB). The correlation among eNO(TB), eNO(SB), and other potential confounders (i.e., gender, age, weight, height, BMI, and passive smoking exposure) were studied.

RESULTS

The analyses showed a poor correspondence between eNO(SB) and eNO(TB), with the latter underestimating (P < 0.001) mean eNO values: 6.4 parts per billion (ppb) (95% confidence interval (CI): 8.4-11.4 ppb) vs. 9.8 ppb (95% CI: 5.6-7.3 ppb). A greater correlation was found between eNO(SB) and eNO(TB) in children younger than 6 y. Only eNO(SB) and age predicted eNO(TB) (R2 = 43.6%).

CONCLUSION

eNO(TB) is not a good predictor of eNO(SB) in children. Constant-flow eNO(SB) is the technique of choice for eNO assessment in young children.

Exhaled nitric oxide in pediatrics: what is new for practice purposes and clinical research in children?

Fractional exhaled NO (FeNO) is universally considered an indirect marker of eosinophilic airways inflammation, playing an important role in the physiopathology of childhood asthma. Advances in technology and standardization have allowed a wider use of FeNO in clinical practice in children from the age of four years. FeNO measurements add a new dimension to the traditional clinical tools (symptoms scores, lung function tests) in the assessment of asthma. To date a number of studies have suggested a possible use of FeNO in early identification of exacerbation risk and in inhaled corticosteroids titration. The aim of this paper is to address practical issues of interest to paediatric clinicians who are attempting to use FeNO measurements as an adjunctive tool in the diagnosis and management of childhood airway diseases.

Exhaled nitric oxide in the diagnosis and management of asthma: clinical implications

Exhaled nitric oxide (eNO) used as an aid to the diagnosis and management of lung disease is receiving attention from pulmonary researchers and clinicians alike because it offers a noninvasive means to directly monitor airway inflammation. Research evidence suggests that eNO levels significantly increase in individuals with asthma before diagnosis, decrease with inhaled corticosteroid administration, and correlate with the number of eosinophils in induced sputum. These observations have been used to support an association between eNO levels and airway inflammation. This review presents an update on current opportunities regarding use of eNO in patient care, and more specifically on its potential usage for asthma diagnosis and monitoring. The review will also discuss factors that may complicate use of eNO as a diagnostic tool, including changes in disease severity, symptom response, and technical measurement issues. Regardless of the rapid, convenient, and noninvasive nature of this test, additional well-designed, long-term longitudinal studies are necessary to fully evaluate the clinical utility of eNO in asthma management.

A flow- and pressure-controlled offline method of exhaled nitric oxide measurement in children

BACKGROUND

Exhaled nitric oxide (eNO) is a noninvasive marker of airway inflammation. However, previous studies show that the offline value is lower than the online value.

OBJECTIVE

To compare a standard offline eNO measurement apparatus with a modified apparatus that can monitor flow volume and respiratory pressure.

METHODS

We studied 73 cooperative individuals aged 5 to 28 years (32 children: mean age, 8.3 years; 41 adults: mean age, 21.5 years). We modified the standard device by including a flow meter with a manometer and attaching a plastic tube connected to a 3-way valve to control the resistance. The online and offline (measured using the modified device and the standard device) eNO determinations were compared in a single session and were analyzed using a nitric oxide analyzer.

RESULTS

There was a good relationship between the online and modified offline eNO measurements in children. The modified offline method showed a stronger correlation with the online method (r = .97 vs. r = .92), and the modified offline eNO value was more similar to the online eNO value than to the standard offline value. The mean difference between the online and standard offline eNO values was 52%, whereas the mean difference between the online and modified offline eNO values was only 10%.

CONCLUSIONS

Using the offline method, we can easily control the resistance and flow volume to reach the same value measured by the online method in childhood respiratory diseases.

Exhaled nitric oxide in childhood asthma: a review

As an 'inflammometer', the fraction of nitric oxide in exhaled air (Fe(NO)) is increasingly used in the management of paediatric asthma. Fe(NO) provides us with valuable, additional information regarding the nature of underlying airway inflammation, and complements lung function testing and measurement of airway hyper-reactivity. This review focuses on clinical applications of Fe(NO) in paediatric asthma. First, Fe(NO) provides us with a practical tool to aid in the diagnosis of asthma and distinguish patients who will benefit from inhaled corticosteroids from those who will not. Second, Fe(NO) is helpful in predicting exacerbations, and predicting successful steroid reduction or withdrawal. In atopic asthmatic children Fe(NO) is beneficial in adjusting steroid doses, discerning those patients who require additional therapy from those whose medication dose could feasibly be reduced. In pre-school children Fe(NO) may be of help in the differential diagnosis of respiratory symptoms, and may potentially allow for better targeting and monitoring of anti-inflammatory treatment.

Exhaled nitric oxide: sources of error in offline measurement

Delayed offline measurement of exhaled nitric oxide (eNO), although useful in environmental and clinical research, is limited by the instability of stored breath samples. The authors characterized sources of instability with the goal of minimizing them. Breath and other air samples were stored under various conditions, and NO levels were measured repeatedly over 1-7 d. Concentration change rates varied positively with temperature and negatively with initial NO level, thus "stable" levels reflected a balance of NO-adding and NO-removing processes. Storage under refrigeration for a standardized period of time can optimize offline eNO measurement, although samples at room temperature are effectively stable for several hours.

Single-breath exhaled nitric oxide in preschool children facilitated by a servo-controlled device maintaining constant flow

Fractional concentration of exhaled nitric oxide (FENO), an index of airway inflammation, is optimally measured in adults and school-age children using a single-breath online (SBOL) exhalation at constant flow. However, preschool-aged (<6 years old) children have difficulty exhaling at constant flow, and alternative methods are needed. We employed a servo-controlled variable resistance device (servo device) that controls expiratory flow while allowing the child to vary expiratory pressure. To validate this device, 8 children (aged 6-12 years) performed SBOL exhalations with and without the servo device at expired flow rates between 20-50 ml/sec. We then studied 32 young children aged 24-71 months with the servo device alone at exhalation flows of 30, 40, and 50 ml/sec. Test difficulty (TD) with each method was rated by questioning the older children, or as observed by the physician obtaining the data in the younger children (0 = no difficulty, 1 = mild difficulty, 2 = moderate difficulty, and 3 = unable to perform test). In the older children, SBOL exhalations with and without the servo device demonstrated equivalent flow-dependence of FENO values. Test difficulty was low (0.125-0.625) at all flow rates, with excellent agreement between the two methods (P < 0.001). Twenty-eight young children (<6 years old) were able to complete measurements at all three flow rates evaluated. The 4 subjects who were not able to successfully complete all the measurements were between 2-3 years old (mean 2.75 +/- SD). Exhaled NO (mean +/- SD; ppb) was 8.8 (+/-6.2), 10.6 (+/-6.7), and 13.2 (+/-8.8) ppb at flows of 50 ml/sec, 40 ml/sec, and 30 ml/sec, respectively. Mean values of SD scores were 1.00, 1.14, and 1.43 at flows of 50, 40, and 30 ml/sec, respectively (P = NS). In conclusion, exhaled NO measurement by the SBOL method was facilitated in preschool children by the use of a servo-controlled variable resistance device. This device may allow these measurements to be applied to aid in the diagnosis and treatment of asthma in the preschool child, where spirometry is generally impossible.

Sinus computed tomography scan and markers of inflammation in vocal cord dysfunction and asthma

BACKGROUND

The inappropriate closure of the vocal cords is characteristic of vocal cord dysfunction (VCD). These patients present with wheezing and frequently receive a misdiagnosis of asthma.

OBJECTIVE

To demonstrate the ability of computed tomography (CT) scored for the presence and extent of sinus disease and markers of inflammation to distinguish patients with VCD from patients with asthma.

METHODS

Comparisons of 13 patients with VCD were made to 77 patients presenting to the emergency room with acute asthma, 31 non-acute asthmatic patients, and 65 nonasthmatic controls. Evaluation consisted of exhaled nitric oxide gas (eNO), circulating eosinophils, and total serum immunoglobulin (Ig)E, as well as the sinus CT scan.

RESULTS

Extensive sinus CT changes were present in 23 of 74 acute asthmatic patients, 5 of 29 non-acute asthmatic patients, and 2 of 59 nonasthmatic controls. In addition, absolute eosinophil counts, eNO, and total IgE were significantly elevated among the asthmatic patients. Sinus symptoms reported by questionnaire did not predict sinus CT findings. Among the patients with VCD, none had extensive sinus disease. They also had normal eNO, low IgE, and normal eosinophil count. Five of the patients presenting to the emergency room who were identified as acute asthmatic were identified with VCD by laryngoscopy and were all characterized by the absence of significant inflammation on their sinus CT scan, low IgE, and normal eosinophil count.

CONCLUSIONS

Among patients presenting with intermittent or reversible airway obstruction, patients with VCD can be distinguished from asthma by minimum or absence of inflammation in their sinuses as shown by CT scan. Clinical symptom scores are not predictive of presence or extent of sinus disease in most cases.

Exhaled nitric oxide as a diagnostic test for asthma: online versus offline techniques and effect of flow rate

Measurement of the fraction of exhaled nitric oxide (FENO) has been proposed as a noninvasive assessment of asthmatic airway inflammation. The influence of the expiratory flow rate during the collection maneuver on the ability of FENO to discriminate healthy subjects from those with asthma is unknown. We compared online and offline measurement of FENO at different flow rates. FENO was collected with expiratory flows of 50-500 ml/second in 34 patients with asthma (PC(20) of less than 8 mg/ml) and 28 healthy subjects (PC(20) of more than 10 mg/ml) using offline collection techniques. In a subgroup of 18 individuals with asthma and 17 healthy subjects, we additionally measured FENO at multiple expiratory flow rates (47-250 ml/second) using online methods. FENO fell with an increasing expiratory flow rate; FENO was higher in subjects with asthma as compared with healthy subjects at each flow rate studied with both techniques (p < 0.001). Receiver operating characteristic (ROC) curves for the diagnosis of asthma indicated that FENO is a robust discriminator between individuals with asthma and healthy subjects (area under the ROC curves 0.79 +/- 0.06 to 0.86 +/- 0.06, p for significant discrimination < 0.0001). Neither expiratory flow rate nor collection technique (online versus offline) significantly altered this discriminatory capacity (area under the ROC curves = 0.84 +/- 0.07 with the slowest online method versus 0.80 +/- 0.07 with the fastest offline method, p = 0.46). These data indicate that the choice of expiratory flow rate and collection method can be based on practicality and patient comfort without compromising the utility of this test for asthma.

Exhaled nitric oxide concentrations: online versus offline values in healthy children

Exhaled nitric oxide (FE(NO)) is a noninvasive and practical method to assess airway inflammation. We conducted this investigation to determine the most appropriate flow rate to measure FE(NO) and to obtain reference values for FE(NO) in children. FE(NO) was measured in 112 healthy 6-18 year olds (60 males) at 4 expiratory flow rates (46, 31, 23, and 15 mL/sec) using a chemiluminescent nitric oxide analyzer. Offline and online analyses were done to determine FE(NO) intraclass correlation coefficients, the relationship between FE(NO) and expiratory flow rates, and the effects of age and gender on these measurements. The major findings were: 1) intraclass correlation coefficients for FE(NO) and flow rates ranged from 0.92-0.99 for offline values, and 0.99 for all online values; 2) variation at an expiratory flow rate of 46 mL/sec (SD, 9.39) was considerably less than at other flows, especially at 15 mL/sec (SD, 26.55); 3) FE(NO) increased as flow rates decreased for both offline and online values; 4) there were no significant differences and good agreement between offline bag and online FE(NO) values at 31 and 46 mL/sec expiratory flows; and 5) using multiple regression, significant predictors of FE(NO) were flow, body surface area, age, and FEF(25-75). We have provided FE(NO) values in healthy children and propose that the ideal expiratory flow rate for FE(NO) measurements in children using the single breath technique is between 30-50 mL/sec.

Nitrogen redox balance in the cystic fibrosis airway: effects of antipseudomonal therapy

Denitrifying bacteria metabolize nitrogen oxides through assimilatory and dissimilatory pathways. These redox reactions may affect lung physiology. We hypothesized that airway colonization with denitrifying bacteria could alter nitrogen balance in the cystic fibrosis (CF) airway. We measured airway nitrogen redox species before and after antimicrobial therapy for Pseudomonas aeruginosa in patients with CF. We also studied ammonium (NH(4)(+)) and nitric oxide (NO) metabolism in clinical strains of P. aeruginosa in vitro and in CF sputum ex vivo. Ammonium concentrations in both sputum and tracheal aspirates decreased with therapy. Nitric oxide reductase (NOR) was present in clinical strains of P. aeruginosa, which both produced NH(4)(+) and consumed NO. Further, NO consumption by CF sputum was inhibited by tobramycin ex vivo. We conclude that treatment of pseudomonal lung infections is associated with decreased NH(4)(+) concentrations in the CF airways. In epithelial cells, NH(4)(+) inhibits chloride transport, and nitrogen oxides inhibit amiloride-sensitive sodium transport and augment chloride transport. We speculate that normalization of airway nitrogen redox balance could contribute to the beneficial effects of antipseudomonal therapy on lung function in CF.

Exhaled nitric oxide in asthmatic and non-asthmatic children: influence of type of allergen sensitization and exposure to tobacco smoke

Asthmatic bronchial inflammation is associated with increased nitric oxide concentrations in exhaled air (eNO). Recent data suggest that this effect arises from atopy. Our aim in this study was to find out whether atopy and sensitization to particular allergens influences eNO levels. A total of 213 subjects (41 asthmatics and 172 controls) (96 boys and 117 girls, 7.3-14 years of age) were studied. Parents completed a questionnaire that sought information on their children's respiratory symptoms and exposure to tobacco smoke. Subjects underwent skin-prick tests for the following common allergens: Dermatophagoides pteronyssinus (Dpt), cat fur, Aspergillus fumigatus, Alternaria tenuis, mixed grass, mixed tree pollen, Parietaria officinalis, egg, and cow's milk. eNO was collected in 1-l mylar bags (exhaled pressure 10 cmH2O, flow 58 ml/s) and analyzed by using chemiluminescence. Atopic and non-atopic children without a history of chronic respiratory symptoms had a similar geometric mean eNO (atopics, n = 28, 11.2 p.p.b.; non-atopics, n = 96, 10.0 p.p.b.; mean ratio 1.1, 95% confidence interval [CI]: 0.7-1.6). Conversely, atopic asthmatic subjects had significantly higher eNO values than non-atopic asthmatic subjects (atopics, n = 25, 24.8 p.p.b.; non-atopics, n = 16, 11.4 p.p.b.; mean ratio 2.2, 95% CI: 1.2-3.9, p= 0.000). In children with rhinitis alone (n = 15) and those with lower respiratory symptoms other than asthma (n = 33), eNO increased slightly, but not significantly, with atopy. eNO levels correlated significantly with Dpt wheal size (r = 0.51) as well with the wheal size for cat, mixed grass, and Parietaria officinalis (r = 0.30-0.29), and with the sum of all wheals (r = 0.47) (p= 0.000). Subjects sensitized only for Dpt (but not those subjects sensitized only for grass pollen or other allergens) showed significantly higher eNO levels than non-atopic subjects (16.4 p.p.b. vs. 10.2 p.p.b., mean ratio 1.6, 95% CI: 1.1-2.3, p= 0.002). In asthmatic subjects, Dpt sensitization markedly increased eNO levels (Dpt-sensitized subjects: 28.0 p.p.b.; Dpt-unsensitized subjects: 12.2 p.p.b.; mean ratio 2.3, 95% CI: 1.5-3.5, p= 0.000). Non-asthmatic Dpt-sensitized subjects also had significantly higher eNO values than non-asthmatic, non-Dpt-sensitized subjects (14.2 p.p.b. vs. 10.1 p.p.b.; mean ratio 1.4, 95% CI: 1.1-1.9, p= 0.008). No difference was found between eNO levels in asthmatic subjects and control subjects exposed or unexposed to tobacco smoke. In conclusion, eNO concentrations are high in atopic asthmatic children and particularly high in atopic asthmatics who are sensitized to house-dust mite allergen.

Off-line exhaled nitric oxide measurements in children

The concentration of exhaled nitric oxide (eNO) is a useful marker of asthmatic bronchial inflammation. eNO can now be measured away from the laboratory (off-line), even in children. Short exhalation maneuvers (8 sec) and small samples (1 L) of exhaled gas are probably sufficient in children, but more information is needed about the effect of different measurement conditions. As a preliminary step before conducting epidemiological studies in schoolchildren, we investigated the effects of expiratory flow, dead space, and expiratory time on eNO concentrations collected in 1-L mylar collection bags. We studied 101 cooperative subjects (62 males) aged 5-18 years (30 healthy volunteers, 51 asthmatics, and 20 children with various other respiratory diseases) in our pulmonary function laboratory. On-line and off-line eNO were compared in a single session, and analyzed with a Sievers NOA 280 nitric oxide analyzer. For both methods of collecting expired gas, subjects did a single exhalation without breath-holding against an expiratory pressure 10 cm H(2)O. We investigated the effects of expiratory flow, dead space, and exhalation time on eNO; we also compared on-line and off-line eNO measurements, and the repeatability of both techniques at a given flow rate. Expiratory flows of 58 mL/sec provided more reproducible data than lower flows (coefficient of repeatability 1.1 ppb for 58 mL/sec vs. 2.8 for 27 mL/sec vs. 5.7 for 18 mL/sec). eNO concentrations were about 25% higher in off-line than in on-line recordings if the initial 250 mL of exhaled gas were not eliminated, and 37% higher if exhalation lasted longer (16 sec vs. 8 sec). Eliminating 250 mL of dead space and shortening the filling time to 8 sec yielded off-line eNO values close to those on-line (geometric mean off-line eNO 14.4 ppb, 95% confidence interval: 12.2-17.0) vs. on-line eNO 13.8 ppb (95% confidence interval: 11.6-16.5). On-line and off-line results were highly correlated (r = 0.996, P = 0.000) and had similar coefficients of variation (on-line eNO 2.6%, off-line 2.8%). Neither agreement nor repeatability of eNO measurements were affected by disease status or baseline FEV(1) (% predicted values). Once standardized, the off-line eNO technique using 1-L gas collection bags will provide results similar to those recorded on-line.

Controlled low flow off line sampling of exhaled nitric oxide in children

BACKGROUND

The aim of this study was to validate exhaled nitric oxide (eNO) values obtained with an alternative off line, single breath, low flow balloon sampling method against on line sampling according to ERS and ATS guidelines in children who could perform both methods.

METHODS

One hundred and twenty seven white children of median age 14.1 years, all pupils of a secondary school, participated in the study. They performed the two different sampling techniques at three different flows of 50, 100, 150 ml/s. Additional measurements were done in random subgroups to determine the influence of the dead space air on eNO values obtained off line by excluding the first 220 ml of exhaled air. All children completed a questionnaire on respiratory and allergic disorders and underwent spirometric tests.

RESULTS

The off line eNO values were significantly higher than the on line values at all flows. At 50 ml/s the geometric mean (SE) off line eNO was 18.7 (1.1) ppb and the on line eNO was 15.1 (1.1) ppb (p<0.0001). However, when dead space air was discarded, off line and on line values were similar: at 50 ml/s off line eNO was 17.7 (1.0) ppb and on line eNO 16.0 (1.2) ppb. There was a good agreement between off line eNO values without dead space air and on line eNO: for 50 ml/s the mean on/off line ratio was 0.95 (95% agreement limits 0.63 to 1.27). The off line eNO level at 50 ml/s in 80 children with negative questionnaires for asthma, rhinitis, and eczema was 13.6 (1.0) ppb compared with 33.3 (1.1) ppb in the remaining children with positive questionnaires on asthma and allergy and/or recent symptoms of cold (p<0.0001).

CONCLUSIONS

In children, off line assessment of eNO using constant low flow sampling and excluding dead space air is feasible and produces similar results as on line assessment with the same exhalation flow rate. Both sampling methods are sufficiently sensitive to differentiate between groups of otherwise healthy school children with and without self-reported asthma, allergy, and/or colds. We propose that, for off line sampling, similar low flow rates should be used as are recommended for on line measurements.

A simple flow-driven method for online measurement of exhaled NO starting at the age of 4 to 5 years

NO is increased in exhaled air of asthmatic patients, and may be used as a marker of airway inflammation. The online method is a standardized technique for measuring exhaled nitric oxide (ENO). However, this method has proven difficult for some children, who may have trouble maintaining a constant expiratory flow. The aim of this study was to validate a modified technique for online ENO measurement that utilizes a flow regulator to overcome the patient problem of having to actively maintain a constant expiratory flow. We measured ENO levels with two methods in 105 asthmatic and 10 healthy subjects, comparing the standardized (ST) single-breath method with a modified single-breath, flow-driven (FD) method. With the ST method and visual monitoring, the subjects inhaled NO-free air to TLC, and exhaled with a target flow of 50 ml/s. With the FD method, the subjects exhaled from TLC and flow was kept constant (50 ml/s) by the operator, using a flow regulator. The subjects were divided into two groups, one consisting of children aged 4 to 8 yr (n = 74) and the other of children aged 9 to 16 yr (n = 41). In the group aged 4 to 8 yr, 38 children (51%) were unable to perform the ST method, whereas only five children (7%) failed to perform the FD technique. In the group aged 9 to 16 yr, only four children (10%) were unable to perform the ST maneuver, and all successfully performed the FD maneuver. The mean concentrations of ENO in the 73 children who performed both types of maneuver were similar (36.1 +/- 3.4 [mean +/- SEM] ppb with the ST method and 33.8 +/- 3.3 ppb with the FD technique, p = NS) and were highly correlated with one another (r = 0.99, p < 0.0001). ENO values were significantly higher in steroid-naive than in steroid-treated asthmatic children. In conclusion, we describe a modified online method for measuring ENO that is simple, does not require active cooperation to maintain a constant expiratory flow, and can be easily performed by children from 4 to 5 yr of age onward.

Exhaled nitric oxide as an indicator of severity of asthmatic inflammation

Traditional assessment of severity of asthma relies on an evaluation of signs and symptoms and pulmonary function tests. These pulmonary function tests, such as peak expiratory flow rates, forced vital capacity, and forced expiratory flow rates, are indirect measures of airway caliber only, and not inflammation. Since asthma is an inflammatory disease, a measure of the degree of inflammation would be helpful in quantitating severity and titrating of anti-inflammatory therapy. A noninvasive method for measuring pulmonary inflammation would therefore be helpful to assist the emergency physician in initial treatment and assist in titration of anti-inflammatory therapy during repeat visits. Exhaled nitric oxide (NO) assays are convenient and practical and may fulfill this role. In this review, we discuss the role of NO in asthmatic inflammation and the role that exhaled NO values may play in the emergency management of asthma.

FE(NO): relationship to exhalation rates and online versus bag collection in healthy adolescents

Measurement of exhaled nitric oxide (FE(NO)) is a noninvasive and practical method for assessing airway inflammation. We conducted this investigation to determine the most appropriate flow rate for FE(NO) measurement and to obtain normal values for FE(NO). We determined which expiratory flow was easy to sustain, generated reproducible values, and provided good correlation between offline and online measurements. Thirty-two healthy subjects (15- 18 yr old) underwent spirometry and FE(NO) measurements, using a chemiluminescent NO analyzer at expiratory flow rates of 46, 31, 23, 15, 10, 7, 5, and 4 ml/s. The major findings were as follows: (1) FE(NO) increased as flow rates decreased, with strong correlation between FE(NO) values and flow rates at the four highest flows (0. 85- 0.93, p < 0.001); (2) there were no significant differences and good agreement between offline bag and online FE(NO) values for the four highest flows (p < 0.09-0.83); (3) online FE(NO) values increased with age 15-17 yr at all flow rates, but decreased at age 18 yr; and (4) using multiple regression, significant predictors of FE(NO) were flow, body surface area, age, and FEF(25-75). On the basis of these results, we provide FE(NO) values for healthy adolescents and propose that the ideal flow rate for children is between 30 and 50 ml/s.

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 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.

Endogenous nitric oxide in allergic airway disease

There has been intense research into the role nitric oxide (NO) plays in physiologic and pathologic mechanisms. The presence of NO in exhaled breath and the high concentrations in nasal airways stimulated many studies examining exhaled and nasal NO as potential markers of airway inflammation, enabling repeated monitoring of airway inflammation not possible with invasive tests (eg, bronchoscopy). In airway inflammation, NO is not merely a marker but may have anti-inflammatory and proinflammatory effects. Nasal NO measurement may be used in the noninvasive diagnosis and monitoring of nasal disease. This review was compiled by speakers who gave presentations on NO at the annual meeting of the American Academy of Allergy, Asthma, and Immunology in 1999 on exhaled and nasal NO, in vitro studies of NO, the chemistry of airway NO formation, and standardized measurement of exhaled mediators.

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.