SEARCH

SEARCH BY CITATION

Keywords:

  • asthma;
  • breath test;
  • children;
  • epidemiology;
  • nitric oxide;
  • spirometry

Abstract

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

Exhaled nitric oxide (NO) reflects inflammation in the lower airways and is well adapted for use in children. The aims of this study were to investigate the distribution of the fraction of expired NO (FENO) in school children and to compare FENO and spirometry in relation to the International Study of Asthma and Allergies in Childhood questionnaire. The study was performed in 959 randomly selected 13–14-year-old school children in Uppsala, Sweden. Exhaled NO was measured at an inhalation rate of 0.1 l/s (FENO0.1) and a spirometric test was performed and data from these measurements were related to questionnaire data. Exhaled NO was measured according to American Thoracic Society recommendations, except the use of a mouth wash and an exhalation flow rate of 0.1 l/s. The distribution of the mean FENO0.1 values was skewed, with a preponderance of very low levels and a widespread tail of values ranging up to 102 parts per billion (ppb). Boys exhibited significantly higher mean FENO0.1 values than girls, 5.2 (4.7–5.7) vs 4.4 (4.0–4.8) ppb (geometric mean and 95% CI), P < 0.01). Children who reported wheezing in the last year had higher FENO0.1 values than children that had not, 8.5 (7.1–10.2) vs 4.3 (4.0–4.6) ppb, P < 0.001). The same association was found to most symptoms indicating hay fever and eczema. In contrast to this, only weak or inconsistent associations were found between asthma and spirometric indices. Exhaled NO levels were found to be independently related to male gender, wheeze and rhinoconjuctivitis but not to current eczema. In conclusion, exhaled NO was closely associated with reported asthma and allergy symptoms whereas spirometric indices such as percent predicted forced expiratory volume in 1 s were not. As most asthma cases in a population are mild, the findings suggest that exhaled NO is a sensitive marker of asthma and allergy.

A primary objective of the International Study of Asthma and Allergies in Childhood (ISAAC) was to describe the prevalence and to some extent severity of asthma, rhinitis and eczema in children living in different areas, to enable comparisons within and between countries (1). To achieve this objective, a simple questionnaire was developed that has evolved into a widely used standard for pediatric epidemiological work. In addition to a world wide study of the prevalence of asthma, rhinitis and eczema in schoolchildren (2, 3), a large number of national studies have been undertaken using this standard questionnaire.

Apart from questionnaires, various methods of assessing bronchial hyper-reactivity have been utilized in epidemiological studies in children and young adults. In recent studies these have included challenges with hypertonic saline, methacholine, histamine, cold air and physical exercise tests. Allergy tests have also been used in epidemiological studies, primarily skin prick tests.

To date, it has not been possible to use methods that directly reflect inflammation in asthma in epidemiological research. Levels of exhaled nitric oxide (NO) have been found to be elevated in asthma (4, 5); this seems to be primarily a feature of allergic asthma (6, 7) and appears to reflect eosinophilic inflammation (8–10). The measurement of exhaled NO is one of few methods that are suitable for use in epidemiological studies in children. In the present study, we used the results of the ISAAC questionnaire to compare clinical allergological characteristics with measurements of exhaled NO and pulmonary function in schoolchildren.

General design

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

The investigation was performed in community schools in Uppsala, Sweden, from October 1998 to December 1999. The schools were randomized prior to the investigation. For practical reasons, the investigation was started in one school located adjacent to the Children's hospital. A random order of inclusion was followed for the remainder of the schools, with the aim of including approximately 1000 school children in the study. The headmasters of 11 schools were approached and nine schools were finally included in the study. Two schools declined to participate because of the lack of a suitable examination room.

A questionnaire previously used as a part of the world wide ISAAC study (http://isaac.auckland.ac.nz/PhaseOne/Manual/Section7/Sec7Frame.html)was translated into Swedish, adapted for use in 13–14-year-old school children (3), and was distributed within the schools to all adolescents in the appropriate age range. The children completed the forms at school and then took them home to their parents, together with a letter of information about the study. Of 1164 pupils and parents approached, 959 (83%) agreed to participate, submitted a completed questionnaire and were finally included in the study. Following inclusion, exhaled NO and pulmonary function were measured by a study nurse who, on the same occasion, also carried out a short structured interview with the young person regarding current medication, signs of respiratory tract infection, smoking habits, etc.

Measurements of exhaled NO

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

Measurements of exhaled NO were performed in accordance with the recommendations for online NO measurements published by the American Thoracic Society (ATS), with the exceptions of target flow rate and a mouthwash procedure (11). We used the Aerocrine NO system (Aerocrine AB, Stockholm, Sweden), including the CLD 77 AM chemiluminescence analyser [Eco Physics AG, Dürnten, Switzerland; sensitivity, 0.1 parts per billion (ppb) NO; rise time 0–90%, <0.1 s; sample flow rate, 110 ml/s; lag time from mouthpiece, 0.7 s] for online NO measurements, and the monitoring of flow and pressure. A two-point calibration was performed before each study session using a certified calibration gas (10 parts per million NO in N2; AGA AB, Älvsjö, Sweden). Immediately before the experiments, the mouth was rinsed for 20 s with 25 ml of 10% sodium bicarbonate (12). Within 5 min of the mouthwash, the children, comfortably seated, inhaled NO-free air from a reservoir and subsequently exhaled against a linear resistor (Hans Rudolph Inc., Kansas City, KS).

Mean oral pressure for all exhalations was 9.2 (±0.4) cmH2O. Three exhalations of 10 s duration were performed consecutively at a target flow rate of 0.1 l/s with the help of visual guidance from the computer screen, and an average value was calculated. Values are presented as NO concentrations (fraction of expired NO; FENO) at an exhalation flow rate of 0.1 l/s (FENO0.1). Two children were unable to perform an accepted exhaled NO experiment successfully, 23 performed only one and 218 performed only two accepted experiments.

Measurements of pulmonary function

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

Pulmonary function measurements were performed according to ATS criteria using a Spirolab spirometer (Medical International Research, Rome, Italy), following a routine procedure carried out by a research nurse experienced in the method. The best of three experiments was automatically chosen by the spirometer programme. Forced expiratory volume in 1 s (FEV1), the ratio of FEV1 to forced vital capacity (FVC) and forced expiratory flow at 25, 50 and 75% of FVC (FEF25 and FEF50 and FEF75) were measured. Values were normalized for age, sex and body height and weight and expressed as percent, using the spirometer programme and Knudson's normal values for children (13).

Statistical methods

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

All data were processed using a Microsoft Office Access database. Statistical analyses were performed using SPSS 10.0 (SPSS Inc., Chicago, IL, USA) and StatView 5.0 (SAS Institute, Cary, NC, USA). Seven cases without measurable levels of NO were arbitrarily assigned a value of 0.05 ppb to permit analysis. NO values were log-transformed prior to analyses. Geometric mean and 95% confidence limits were calculated and transformed back after that. Percent predicted values of spirometric indices were used untransformed in the statistical analyses. Student's t-test and anova were used for comparisons between groups. The associations between FENO0.1 and different explanatory variables were tested using different multiple linear regression models. The significance of the slope in the multivariate regression model was based on the t distribution.

Results

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

The demographic characteristics and lung function values of the study population are presented in Table 1.

Table 1.  Demographic characteristics and lung function [forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC) and forced expiratory flow (FEF)] [mean ± SD or n (%)]
Age (years)13.6 ± 0.4
Male gender476 (49.7)
Passive smoking313 (32.8)
Active smoking10 (1.0)
FEV1 (% predicted)98.0 ± 11.5
FEV1/FVC (% predicted)107 ± 6.5
FEF25 (% predicted)88.5 ± 16.9
FEF50 (% predicted)97.2 ± 20.8
FEF75 (% predicted)102 ± 41.8

Exhaled NO values

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

The mean intraindividual coefficient of variation (CV) of the measured FENO0.1 levels was 9.8% (9.0–10.6), when there were three successful experiments. The distribution of the mean FENO0.1 values was skewed, with a preponderance of very low levels and a widespread tail of values ranging up to 102 ppb, but after logarithmic transformation, a symmetric distribution was achieved (Fig. 1). Boys exhibited significantly (P < 0.01) higher mean FENO0.1 values than girls, 5.2 (4.7–5.7) vs 4.4 (4.0–4.8) ppb. No relationships were found between FENO0.1 values and active or passive smoking, respectively.

image

Figure 1. Histogram of levels of exhaled nitric oxide (10log ppb) in population of school children. The theoretical normal distribution is given by the line.

Download figure to PowerPoint

ISAAC questionnaire prevalence data

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

Wheezing during the last year (‘wheezing last year’ group) was reported by 13.1% of the children (12.0% of boys; 14.3% of girls, P = 0.28) (Table 2). The corresponding values for noninfectious rhinitis and for symptoms indicative of eczema (itching rash) during the last year were 25.6% (26.3% of boys; 24.9% of girls, P = 0.66) and 20.5% (17.1% of boys; 24.0% of girls, P = 0.01), respectively (Table 3).

Table 2.  Exhaled nitric oxide [FENO0.1 = fraction of expired nitric oxide at exhalation flow rate 0.1 l/s expressed as parts per billion (ppb)] (geometric mean and 95% confidence intervals) and forced expiratory volume in 1 s (FEV1) (mean and 95% confidence intervals) in relation to asthma questions in the ISAAC questionnaire*
Question numberISAAC question summaryPrevalenceFENO0.1 (ppb)FEV1 (% pred)
Without symptomWith symptom)P-valueWithout symptomWith symptom)P-value
A1Ever wheezing24.6 (21.9–27.3)4.3 (4.0–4.6)6.4 (5.5–7.5)<0.00198 (97–99)98 (96–99)0.51
A2Wheezing last year13.1 (11.0–15.3)4.3 (4.0–4.6)8.5 (7.1–10.2)<0.00198 (97–99)97 (94–99)0.22
A5Wheeze-impairing speech1.9 (1.0–2.7)4.7 (4.4–5.0)8.8 (5.1–15.1)0.00998 (97–99)103 (97–110)0.052
A6Ever asthma12.1 (10.0–14.1)4.5 (4.2–4.8)7.7 (6.1–9.1)<0.00198 (97–99)97 (95–100)0.39
A7Exercise-induced wheeze last year18.3 (15.9–20.8)4.3 (4.0–4.6)7.3 (6.1–8.7)<0.00198 (97–99)98 (96–100)0.73
A8Dry cough at night11.3 (9.3–13.3)4.6 (4.3–5.0)5.6 (4.5–7.0)0.0798 (97–99)99 (96–101)0.58
Table 3.  Exhaled nitric oxide [FENO0.1 = fraction of expired nitric oxide at exhalation flow rate 0.1 l/s expressed as parts per billion (ppb)] (geometric mean and 95% confidence intervals) in relation to rhinitis and eczema questions in the ISAAC questionnaire*
Question numberISAAC question summaryPrevalenceFENO0.1 (ppb)
Without symptomWith symptomP-value
N1Ever rhinitis without cold?31.4 (28.5–34.4)4.4 (4.1–4.7)5.7 (5.0–6.5)0.001
N2Rhinitis last year25.6 (22.8–28.4)4.4 (4.0–5.0)6.2 (5.3–7.1)<0.001
N3Rhinitis and conjunctivitis last year13.4 (11.2–15.6)4.5 (4.2–4.8)7.1 (5.9–8.5)<0.001
N6Ever hay fever18.5 (16.1–21.0)4.5 (4.2–4.8)6.1 (5.1–7.2)0.003
E1Ever itching rash27.1 (24.3–29.9)4.5 (4.2–4.8)5.6 (4.9–6.3)0.003
E2Itching rash last year20.5 (18.0–23.1)4.6 (4.3–4.9)5.5 (4.7–6.3)0.03
E3Typical location16.5 (14.1–18.8)4.6 (4.2–4.9)5.8 (5.0–6.9)0.005
E6Ever eczema46.9 (43.8–50.1)4.9 (4.5–5.4)4.6 (4.1–5.1)0.28

Exhaled NO in relation to symptoms of asthma

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

There were strong and significant associations between the questions regarding asthma symptoms and exhaled NO levels. FENO0.1 was significantly higher in children who had ever experienced wheezing (‘ever-wheezing’ group) compared with those who had never experienced wheezing, and in the ‘wheezing last year’ group compared with those who reported no wheezing in the previous year (Table 2). Likewise, children who had suffered from asthma sometime during their life (‘ever asthma’) had elevated FENO0.1 levels compared with those who had never experienced asthma. Of the 611 children who reported no asthma symptoms in the ISAAC questionnaire, 23 had FENO0.1 values of 20 ppb or higher, and five had FENO0.1 values of 40 ppb or higher.

Only 21 of the children had used any inhaled corticosteroids during the week preceding the investigation. In these children, FENO0.1 values were significantly higher than those in children not using corticosteroids, 9.7 (5.8–16.0) vs 4.7 (4.4–5.0) ppb; P = 0.001. Within the ‘last-year wheezing’ and ‘ever asthma’ groups, FENO0.1 values did not differ in relation to inhaled corticosteroid use.

Spirometric data in relation to the symptoms of asthma

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

In contrast to exhaled NO, pulmonary function test results showed only weak or inconsistent associations with the answers to the ISAAC questionnaire (Tables 2 and 4). The FEV1 values normalized for height and sex were found to be totally unrelated to symptoms, and normalized FEF values exhibited only weak associations with reported ‘ever wheezing’ and ‘ever asthma’ and a somewhat stronger association with ‘wheezing last year’ (Table 4).

Table 4.  Forced expiratory flow (FEF) (mean and 95% confidence intervals) in relation to asthma questions in the ISAAC questionnaire*
Question numberISAAC question summaryFEF25FEF50FEF75
Without symptomWith symptomP-valueWithout symptomWith symptomP-valueWithout symptomWith symptomP-value
A1Ever wheezing89 (88–90)87 (84–89)0.0498 (96–99)95 (92–98)0.10103 (100–108)99 (96–103)0.21
A2Wheezing last year89 (88–90)84 (81–87)0.00398 (96–99)94 (90–98)0.05103 (100–106)99 (94–105)0.37
A5Wheeze-impairing speech88 (87–90)93 (83–103)0.2497 (96–98)107 (94–120)0.06103 (100–105)112 (96–128)0.34
A6Ever asthma89 (88–90)85 (82–89)0.0498 (96–99)94 (90–98)0.07103 (100–106)96 (91–101)0.08
A7Exercise-induced wheeze last year89 (88–90)87 (84–89)0.0998 (96–99)94 (91–97)0.02103 (100–106)99 (95–103)0.24
A8Dry cough at night88 (87–89)90 (87–93)0.3197 (96–99)97 (93–101)0.79102 (99–105)102 (96–107)0.90

Exhaled NO and symptoms of hay fever and eczema

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

Positive answers to the ISAAC questions about hay fever were associated with elevated FENO0.1 levels (Table 3), but the increased levels were not as high as those seen in children experiencing asthma. Eye symptoms in conjunction with nasal symptoms exhibited the highest FENO0.1 values. A positive answer to all the ISAAC eczema questions except ever having had eczema was significantly associated with higher exhaled NO levels (Table 3).

Exhaled NO, spirometry and combination of symptoms

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

Exhaled NO levels were significantly higher in children who had both a history of asthma and experienced wheeze in the last 12 months than in children who had either a history of asthma but no current wheeze, or current wheeze but no history of asthma, 11.8 (9.0–15.5) vs 4.7 (3.4–6.5) and 6.5 (5.3–8.1) ppb, respectively (P < 0.001). No corresponding difference between these groups was seen when measuring FEV1 (Fig. 2).

image

Figure 2. Levels of exhaled nitric oxide and forced expiratory volume in 1 s in the relation to ever asthma and wheeze within the last 12 months (10th, 25th, 50th, 75th and 90th percentile).

Download figure to PowerPoint

The FENO0.1 levels were significantly higher in both children with asthma without rhinoconjunctivitis and wheeze, and with wheeze without rhinoconjuctivitis, than in children without both wheeze and rhinoconjuctivitis, 5.3 (4.3–6.6) and 7.0 (5.6–8.6) vs 4.2 (3.9–4.6) ppb (P = 0.04 and <0.0001, respectively). Children with the combination of wheeze and rhinoconjuctivitis had exhaled NO levels that were significantly higher than any of the three other groups, 11.9 (8.8–16.0) ppb, P < 0.0001) (Fig. 3). When performing multiple variable analysis, exhaled NO levels were found to be independently related to male gender, wheeze and rhinoconjuctivitis, but not to current eczema (Table 5).

image

Figure 3. Levels of exhaled nitric oxide in the relation to rhinoconjunctivitis and wheeze within the last 12 months (10th, 25th, 50th, 75th and 90th percentile).

Download figure to PowerPoint

Table 5.  Multiple linear regression model with log transformed fraction of expired nitric oxide at exhalation flow rate 0.1 l/s expressed as parts per billion as the dependent variable
 Coefficient (95% CI)P-value
Male gender0.09 (0.03, 0.10)0.002
Wheeze in the last 12 months0.25 (0.17, 0.34)<0.001
Rhinoconjuctivitis in the last 12 months0.13 (0.05, 0.22)0.002
Rash in the last 12 months0.04 (−0.03, 0.11)0.26

Discussion

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

The results of the present population-based cross-sectional study of schoolchildren show strong relationships between exhaled NO levels and reported clinical characteristics of allergic disease, especially symptoms indicative of asthma. As exhaled NO seems to reflect inflammation in the airways (8–10), a key feature of asthma, the results are especially promising. The data are particularly interesting in view of the finding that the corresponding correlates between symptoms and spirometry were surprisingly poor. Although the study sample included almost 1000 schoolchildren, no significant correlation was found between symptoms of asthma and the most commonly used spirometric index, FEV1. The results of the present epidemiological study would seem to suggest that a single spirometric measurement appears to add little to the evaluation of a child's asthma, in contrast to the measurement of exhaled NO. The poor achievement of spirometry is likely to be a consequence of the population-based design and the possibility that particularly mild cases of children with wheezing who may not fulfill present asthma criteria were recruited to the study. This indicates that NO measurements may be useful in the primary care setting. In hospital clinics the situation is likely to be different. The data may also be seen to indicate that exhaled NO measurement may be particularly useful in the assessment of mild asthma.

In previous studies in Australia, asthma was defined as recent wheeze and bronchial hyper-responsiveness (14). Exhaled NO values were significantly higher among asthmatic individuals than among healthy controls, but tended only toward an increase in those that experienced wheezing but had no bronchial hyperresponsiveness. These authors also reported a number of participants who experienced bronchial hyperresponsiveness but no asthma symptoms; these patients are of interest as they may, at least in part, correspond to the children in our study who had high levels of exhaled NO but no symptoms according to the ISAAC questionnaire. These individuals may well represent ‘early asthma’ and will be subject to further studies.

Our results are in accordance with previous studies reporting elevated exhaled NO levels in allergic asthma (5–7). In our analysis exhaled NO levels were, however, also significantly increased in schoolchildren with current rhiniconjunctivitis that did not report wheezing in the last 12 months. This is in accordance with Henriksen et al. (15) who also found that patients with seasonal allergic rhinoconjunctivitis exhibit elevated exhaled NO levels even out of season, which was particularly true for those with a perennial sensitization. Like Steerenberg et al. (10), we found increased exhaled NO levels in children with eczema. In the present analysis the relationship between eczema and NO levels was, however, no longer significant after adjusting for wheeze and rhinoconjunctivitis. It appears not to be atopy, per se, that results in a high production of NO, but the combination of an allergic state plus exposure to the relevant allergen causing an allergic inflammation (16–19). The importance of cat, our major perennial allergen, which is ubiquitous in our society, can probably not be underestimated in the context (20, 21). The issue is however not addressed by the ISAAC questionnaire. In the present study we have also seen that boys have higher FENO0.1 values than girls. This is in line with previous data from adults (22, 23). One explanation for this gender difference could be that males have larger lung volumes including larger respiratory dead space volumes relative body indices (24). Expiratory NO originates mainly in the dead space compartments and the size of this compartment may influence the total NO airway diffusing capacity, a factor that will influence the resulting FENO0.1 value (25). Another possible explanation for the sex difference would be higher degree of atopy among males, a factor at least partly compensated for in our study by including rhinoconjunctivitis in the statistical model.

We used a research prototype for the measurement of exhaled NO with voluntary flow control, following the ATS recommendations for online measurements (11), with the exception that we used an exhalation flow rate of 0.1 instead of 0.05 l/s. Only two of the 959 children were unable to perform the procedure adequately, and the technique was surprisingly reproducible even in this epidemiological setting. It may be suggested from the data that one successful exhalation is sufficient in an epidemiological study and in clinical practice. Dynamic flow control may make the procedure even easier and may further improve the technique. Mouth washing, which was used in the present study, may be of some importance as the oral contribution when measuring exhaled NO is diminished (12).

In summary, our results from a cross-sectional study of almost 1000 13–14-year-old schoolchildren indicate that the measurement of exhaled NO is far superior to spirometry in identifying children with asthma, particularly allergic mild asthma. The technique therefore seems suitable as an adjunct to questionnaires when screening for asthma in large population groups. However, the importance of diagnosing mild asthma is currently unknown as the natural course of mild asthma in this age group has yet to be determined.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References

This study was supported by grants from the Swedish Medical Research Council (Project No. 10354), The Swedish Foundation for Health Care Sciences and Allergy Research, The Swedish Asthma and Allergy Association's Research Foundation, The Swedish Heart Lung Foundation and AstraZeneca. An Aerocrine NO System was provided by Aerocrine AB, Solna, Sweden.

References

  1. Top of page
  2. Abstract
  3. Material and methods
  4. General design
  5. Measurements of exhaled NO
  6. Measurements of pulmonary function
  7. Smoking
  8. Statistical methods
  9. Ethics
  10. Results
  11. Exhaled NO values
  12. ISAAC questionnaire prevalence data
  13. Exhaled NO in relation to symptoms of asthma
  14. Spirometric data in relation to the symptoms of asthma
  15. Exhaled NO and symptoms of hay fever and eczema
  16. Exhaled NO, spirometry and combination of symptoms
  17. Discussion
  18. Acknowledgments
  19. References
  • 1
    Asher MI, Keil U, Anderson HR, Beasley R, Crane J, Martinez F et al. International Study of Asthma and Allergies in Childhood (ISAAC): rationale and methods. Eur Respir J 1995;8: 483491.
  • 2
    The International Study of Asthma and Allergies in Childhood (ISAAC) Steering Committee. Worldwide variation in prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and atopic eczema: ISAAC. Lancet 1998;351: 12251232.
  • 3
    Strachan D, Sibbald B, Weiland S, Ait-Khaled N, Anabwani G, Anderson HR et al. Worldwide variations in prevalence of symptoms of allergic rhinoconjunctivitis in children: the International Study of Asthma and Allergies in Childhood (ISAAC). Pediatr Allergy Immunol 1997;8: 161176.
  • 4
    Alving K, Weitzberg E, Lundberg JM. Increased amount of nitric oxide in exhaled air of asthmatics. Eur Respir J 1993;6: 13681370.
  • 5
    Lundberg JO, Nordvall SL, Weitzberg E, Kollberg H, Alving K. Exhaled nitric oxide in paediatric asthma and cystic fibrosis. Arch Dis Child 1996;75: 323326.
  • 6
    Ludviksdottir D, Janson C, Högman M, Hedenström H, Björnsson E, Boman G. Exhaled nitric oxide and its relationship to airway responsiveness and atopy in asthma. BHR-Study Group. Respir Med 1999;93: 552556.
  • 7
    Gratziou C, Lignos M, Dassiou M, Roussos C. Influence of atopy on exhaled nitric oxide in patients with stable asthma and rhinitis. Eur Respir J 1999;14: 897901.
  • 8
    Piacentini GL, Bodini A, Costella S, Vicentini L, Mazzi P, Sperandio S et al. Exhaled nitric oxide and sputum eosinophil markers of inflammation in asthmatic children. Eur Respir J 1999;13: 13861390.
  • 9
    Mattes J, Storm van's Gravesande K, Reining U, Alving K, Ihorst G, Henschen M et al. NO in exhaled air is correlated with markers of eosinophilic airway inflammation in corticosteroid-dependent childhood asthma. Eur Respir J 1999;13: 13911395.
  • 10
    Steerenberg PA, Janssen NAH, de Meer G, Fischer PH, Nierkens S, van Loveren H et al. Relationship between exhaled NO, respiratory symptoms, lung function, bronchial hyperresponsiveness and blood eosinophilia in school children. Thorax 2003;58: 242245.
  • 11
    Recommendations for standardized procedures for the on-line and off-line measurement of exhaled lower respiratory nitric oxide and nasal nitric oxide in adults and children. Am J Respir Crit Care Med 1999;160: 21042117.
  • 12
    Zetterquist W, Pedroletti C, Lundberg JON, Alving K. Salivary contribution to exhaled nitric oxide. Eur Respir J 1999;13: 327333.
  • 13
    Knudson RJ, Slatin RC, Lebowitz MD, Burrows B. The maximal expiratory flow-volume curve. Normal standards, variability, and effects of age. Am Rev Respir Dis 1976;113: 587600.
  • 14
    Salome CM, Roberts AM, Brown NJ, Dermand J, Marks GB, Woolcock AJ. Exhaled nitric oxide measurements in a population sample of young adults. Am J Respir Crit Care Med 1999;159: 911916.
  • 15
    Henriksen AH, Sue-Chu M, Lingaas Holmen T, Langhammer A, Bjermer L. Exhaled NO levels in allergic rhinitis: relation to sensitization, pollen season and bronchial hyperresponsiveness. Eur Respir J 1999;13: 301306.
  • 16
    Baraldi E, Carra S, Dario C, Azzolin N, Ongaro R, Marcer G et al. Effect of natural grass pollen exposure on exhaled nitric oxide in asthmatic children. Am J Respir Crit Care Med 1999;159: 262266.
  • 17
    Piacentini GL, Bodini A, Costella S, Vicentini L, Peroni D, Zanolla L et al. Allergen avoidance is associated with a fall in exhaled nitric oxide in asthmatic children. J Allergy Clin Immunol 1999;104: 13231324.
  • 18
    Leuppi JD, Downs SH, Downie SR, Marks GB, Salome CM. Exhaled nitric oxide levels in atopic children: relation to specific allergic sensitisation, AHR, and respiratory symptoms. Thorax 2002;57: 518523.
  • 19
    Olin A-C, Alving K, Torén K. Exhaled nitric oxide: relation to sensitization and respiratory symptoms. Clin Exp Allergy 2004;34: 221226.
  • 20
    Lindfors A, van Hage-Hamsten M, Rietz H, Wickman M, Nordvall SL. Influence of interaction of environmental risk factors and sensitization in young asthmatic children. J Allergy Clin Immunol 1999;104: 755762.
  • 21
    Berge M, Munir AK, Dreborg S. Concentrations of cat (Fel d1), dog (Can f1) and mite (Der f1 and Der p1) allergens in the clothing and school environment of Swedish school children with and without pets at home. Pediatr Allergy Immunol 1998;9: 2530.
  • 22
    Palm JP, Graf P, Lundberg JON, Alving K. Characterization of exhaled nitric oxide: introducing a new reproducible method for nasal nitric oxide measurements. Eur Respir J 2000;16: 236241.
  • 23
    Tsang KW, Ip SK, Leung R, Tipoe GL, Chan SL, Shum IH et al. Exhaled nitric oxide: the effects of age, gender and body size. Lung 2001;179: 8391.
  • 24
    Harris EA, Hunter ME, Seelye ER, Vedder M, Whitlock RM. Prediction of the physiological dead-space in resting normal subjects. Clin Sci Mol Med 1973;45: 375386.
  • 25
    Pedroletti C, Högman M, Meriläinen P, Nordvall SL, Hedlin G, Alving K. Nitric oxide airway diffusing capacity and mucosal concentration in asthmatic school children. Ped Research 2003;54: 496501.