Pediatric Pulmonology 41:929–936 (2006)

Exhaled Breath Condensate Nitrite/Nitrate andpH in Relation to Pediatric Asthma Control and

Exhaled Nitric Oxide

Ratnawati, MD, MCH,1,2 John Morton, MB, BS,3,4 Richard L. Henry, MD,3,4

and Paul S. Thomas, MD1,2*

Summary. Background: Combining exhaled breath condensate (EBC) and exhaled nitric oxide

(eNO) may be a useful, non-invasive method to assess airway inflammation in pediatric asthma.

This cross-sectional studyevaluated the relationship of both EBCnitrite/nitrate (NOx) andEBCpH

with asthma control and eNO in asthmatic, normal, and atopic children.

Methods: A total of 92 children were recruited, comprising 62 with asthma, 14 with atopy only, and

16 who were normal and non-atopic. All completed a questionnaire for asthma symptoms and

control. Variables measured were spirometry, EBC NOx, pH, and eNO.

Results: EBCNOx in thosewith asthma (mean8.4mM,CI 7.5–9.4)was significantlyelevatedwhen

compared with normal (4.8 mM, CI 3.4–6.2, P¼ 0.0007) and atopic children (6.5 mM, CI 4.0–9.1,

P¼0.02). The mean level of eNO was significantly higher in those with asthma (43.7 ppb,

CI 34.7–51.1,P<0.001) and atopy (24 ppb, CI 16.7–31.2,P< 0.05) when comparedwith normal

children (11.5 ppb, CI 6.7–16.2). There was a significantly lower pH in those with asthma and a

FEV1<80% predicted (P¼0.03), but no significant overall differences in EBC pH between the

three groups of children. There was a significant correlation between eNO and EBC NOx in the

group as a whole, but not between eNO and EBC pH.

Conclusions:MeanEBCNOx levels differ between childrenwith asthma, atopy, and thosewho are

normal, but it is not interchangeable with eNO. EBC pH may be an additional marker of asthma

control. Pediatr Pulmonol. 2006; 41:929–936. � 2006 Wiley-Liss, Inc.

Key words: asthma; asthma control; pH; nitrite; exhaled breath condensate; nitric oxide.

INTRODUCTION

The collection of exhaled breath condensate (EBC) toobtain samples from the lower respiratory tract through acooling system is a non-invasive method to assess airwayinflammation. The procedure is simple, safe, and easy toperform in children.1,2 Exhaled breath contains gaseouscompounds such as nitric oxide (NO) and carbonmonoxide, and breath condensate contains non-volatilesubstances including small molecular weight compoundssuch as water, hydrogen ions, nitrite and nitrates,hydrogen peroxide as well as larger molecules such aseicosanoids, proteins, and DNA.1,3 Thus, EBC may be ofvalue formonitoring the changes in the composition of thelung epithelial lining fluid and for assessing inflammatorymarkers in the airway.1,4,5

Nitric oxide is a biological messenger produced from L-arginine by theNO synthase enzymes.NOhas been shownto play an important role in the physiological regulationand pathophysiology of airway diseases. In aqueoussolutionNO reacts rapidly with reactive oxygen species toform stable oxides of nitrogen (NOx), which includenitrite (NO2) and nitrate (NO3).

6 It has been suggested thatthe concentration and bioactivity of NOx in asthmaticinflammation may be regulated by airway pH.7

Exhaled breath condensate collection is a clinicallyuseful method for the assessment of NOx as nitrite andnitrate,8 and it can also be used to assess airway

1Inflammatory Diseases Research Unit, School of Medical Sciences,

Faculty of Medicine, UNSW, Sydney, New South Wales, Australia.

2Department of Respiratory Medicine, The Prince of Wales Hospital,

Randwick, New South Wales, Australia.

3Department of Respiratory Medicine, The Sydney Children’s Hospital,

Randwick, New South Wales, Australia.

4School of Women’s and Children’s Health, Faculty of Medicine, UNSW,

Sydney, New South Wales, Australia.

Grant sponsor: Aerocrine; Grant sponsor: School of Medical Sciences,

UNSW.

*Correspondence to: Paul Thomas, Respiratory Medicine, Prince of Wales

Hospital, Randwick, NSW 2031, Australia.

E-mail: paul.thomas@unsw.edu.au

Received 26 October 2005; Revised 1 March 2006; Accepted 17 March

2006.

DOI 10.1002/ppul.20469

Published online 26 July 2006 in Wiley InterScience

(www.interscience.wiley.com).

� 2006 Wiley-Liss, Inc.

acidification (pH) which may reflect an additional featureof the airway inflammatory process in asthmaticpatients.7,9 Exhaled nitric oxide (eNO or FENO) is alsobecoming a widely accepted method of monitoringasthmatic airway inflammation.10 It provides a longerterm index of asthma control than simple spirometry, andalready data are emerging to confirm its role inmonitoringclinical asthma.11,12 We hypothesized that EBC NOx andpH as well as eNO are markers of airway inflammationwhich can be used to differentiate between asthmatic andcontrol subjects. The aim of this study was to compare thelevel of EBC nitrite/nitrate (NOx) and pH betweenasthmatic, atopic, and normal children. The study alsosought to evaluate the relationship between EBC nitrite/nitrate and eNO, as the end product of NO.

METHODS

Study Design

This cross-sectional study involved 92 children agedbetween 6 and 16 years old, which comprised 62 asthmatic,16 normal (non-atopic), and14 atopic subjects.Asthmawasdiagnosed by a pediatrician and children were recruitedfrom the respiratory clinics of Sydney Children’s Hospital,whereas the control subjects were recruited by advertise-ment (Table 1). Clinical assessments were performed on allsubjects and included a medical history, spirometry, eNOmeasurement, allergen skin prick tests (SPT), and EBC.Subjects were classified according the NHLI and GINAclassification of asthma and asthma control.13 The use ofinhaled glucocorticosteroids (GCS) was taken as anarbitrary period of any usage over the last 6 months.

Skin Prick Tests

Atopy was assessed by SPT on the volar surface of theforearm for seven common allergens (Hollister-Stier,Toronto, Canada) including house dust mite (Dermatopha-goides pteronyssinus), cockroach, cat hair, dog hair,

Altenaria tenuis, egg white, and grass mix. Histaminehydrochloride (1.0 mg/ml) and glycerol saline (50% v/vglycerin) solution were used as positive and negativecontrols, respectively. Evaluation at 10 min was performedby measuring the orthogonal axes of the wheal inmillimeters. The testwas positive if themeanwheal diameterwas 3 mm or larger than negative control. Subjects with oneor more positive allergen SPTwere classed as atopic.

eNO Measurement

The level of eNO was measured with a chemilumines-cence nitric oxide analyser (NiOX Version 2.0, AerocrineAB, Solna, Sweden) according to standard procedures.The onlinemethod displays real-time eNO, pressure, deadspace, and flow rate. Children were seated without a noseclip, and inhaled NO-free air to nearly total lung capacityand then exhaled against an expiratory resistance at aconstant expiratory flow rate of 50 ml/sec for 10 sec.Repeated exhalation to obtain three eNO plateau valueswith <10% variation was performed.14 Calibration wasperformed fortnightly using 215 ppb NO calibration gasand checked daily using a biological control.

Breath Condensate Collection

Exhaled breath condensate collection was performedusing a glass-condensing chamber in wet ice. Children wereinstructed to breathe tidally by mouth through a one-wayvalve and to expire through a glass tube for 5 min or until250 ml of EBC was obtained. The samples were thenimmediately frozen and stored at�708Cbefore processing.1

Breath Condensate Analysis

Nitrite Assays

Total nitrite/nitrate was measured by a fluorescentmethod. Briefly, 50 ml of breath condensate was mixed

TABLE 1— Subjects’ Characteristics Regarding Gender, Age, Spirometry, Allergic Status(Skin Prick Test, SPT), Regular Glucocorticosteroid (GCS) Use, and Classification ofAsthma Severity of the Study Subjects According to NHLBI Guidelines30

Asthmatic Normal Atopy

N 62 16 14

Male/female 44/17 6/10 8/6

Age (years) 12 (11.3–12.7) 9.2 (7.9–10.4) 9.8 (8.4–11.1)

FEV1% 93.1 (89.1–97.2) 92.3 (86.3–98.5) 97.4 (93.4–101.5)

FEV1/FVC 80.7 (78–82.4) 99.4 (96.9–102.0) 99.4 (95.5–103.2)

Positive SPT 54 (�) 14

Inhaled GCS 55 (�) (�)

No GCS in the last 6 months 7

Asthma classification

Mild intermittent 0

Mild persistent 49

Moderate persistent 13

Severe persistent 0

930 Ratnawati et al.

with 0.25 mM NADPH, 50 mM FAD, and 250 IU nitratereductase (Sigma, St Louis,MO). Sampleswere incubatedfor 1 hr at 378C and then mixed with 10 ml DAN (2,3-diaminonaphthalene). Samples were further incubated for10 min in the dark and then 2.8 M NaOH solution wasadded. Absorbance was measured with a Perkin-ElmerCytofluor 4000 plate reader (excitation 360/40, emission395/25, gain 50). Standard curves were generated usingsodium nitrite (range of standard 0–40 mM, limit ofdetection 2 mM, mean (SD) intra-assay coefficient ofvariation 3.11 (3.42%)).15

pH Measurement

Hydrogen ion concentration was measured by a pHmeter with a silicon chip sensor (Shindengen pH Boy-P2,Tokyo, Japan). Calibration was performed daily usingbuffers of pH 4.0, 7.0, and 10.0 before measuring thesamples. The stability of the EBC pH was measuredsequentially in 10 samples over 10months and found to bestable with a coefficient of variation of 2%. De-aerationwas not undertaken as the study was commenced prior tomany of the publications suggesting that it may bebeneficial.

Statistical Analysis

Data are presented as the mean and 95% confidenceintervals. eNO data were log transformed to the Normaldistribution. Unpaired t tests were performed on para-metric data and Mann–Whitney tests on non-parametricdata were used to compare data from different subjects.Where multiple comparisons were performed, ANOVAfollowed by Dunnet’s multiple comparison test or Fried-man analysis of variance followed by the Mann–WhitneyU tests for parametric and non-parametric data were used,respectively, and univariate analysis applied to ascertainthe influence of multiple variables. Correlation wasanalyzed for non-parametric and parametric data bySpearman’s or Pearson’s correlation coefficients, respec-tively. P< 0.05 was considered significant.

RESULTS

Exhaled Nitric Oxide

The subjects’ characteristics are summarized inTable 1.Asthmatic children had a mean level of eNO which washigher than normal subjects (43.7 ppb, CI 34.7–51.1 vs.11.5 ppb, CI 6.7–16.2, P< 0.001), and atopic children(24 ppb, CI 16.7–31.2 ppb, P¼ 0.03, Table 2, Fig. 1).There was a significant difference between eNO in atopicasthmatic children (n¼ 54) compared with non-atopicasthmatic children, although the number in this lattergroup was small (47.7 ppb CI 39.1–56.4 vs. 12.1 ppb CI2.4–21.9, n¼ 7, P¼ 0.0003).

There appeared to be a tendency for eNO to rise withage, as the values for those aged less than 10 years andthose 10 years and older were 7.4 ppb (CI 5.7–9.0) versus13.3 ppb (CI 8.5–18.1) (P¼ 0.004), respectively. Like-wise there was a significant difference based on crudeheight (<140 cm: 7.4 ppb (CI 5.9–8.9),>140 cm14.4 ppb(CI 9.2–19.6), P¼ 0.0006).Asthmatic subjectswhowere takingGCS (n¼ 55) had a

significantly lower eNO level when compared with thosewhowere not taking GCS in the preceding 6 months (39.3ppb CI 31.0–47.6 vs. 92.54 ppb CI 53.6–131.4, n¼ 7,P¼ 0.0001).

EBC NOx and EBC pH

Themean level of EBCNOxwas significantly higher inasthmatic patients (mean 8.4 mM, CI 7.5–9.4) comparedwith normal (4.8 mM, CI 3.4–6.2, P¼ 0.0007) and atopicnon-asthmatic children (6.5 mM, CI 4.0–9.1, P¼ 0.02)(Fig. 2). The mean EBC pHwas not significantly different

Fig. 1. Levels of eNO in children who were either asthmatic,

atopic, or normal. Horizontal bars indicate the mean andP-values

are indicated above the brackets. The mean levels of eNO and

95% confidence intervals for each group are also shown in

Table 2.

TABLE 2— Mean levels of eNO, EBC pH, and EBC Nitrite/Nitrate in Normal, Atopic, and Asthmatic Children

Normal Atopy Asthma

eNO (ppb) 11.5 (6.7–16.2) 24 (16.7–31.2)* 43.7 (34.7–51.1)**

EBC Nox

(mM)

4.8 (3.4–6.2) 6.5 (4–9.1) 8.4 (7.5–9.4)**

EBC pH 6.4 (6–6.8) 6.6 (6.2–7) 6.7 (6.5–6.9)

*P< 0.05, when compared with normal subjects.

**P< 0.001, when compared with normal subjects.

EBC NOx in Asthma 931

between asthmatic (6.7� 0.1), normal (6.6� 0.2,P¼ 0.8), or atopic subjects (6.4� 0.2, P¼ 0.5) (Fig. 3).

Correlation Between eNO and EBC NOxand EBC pH

In asthmatic subjects, eNO showed no significantcorrelation with EBC NOx (P¼ 0.2, r¼ 0.1), but therewas a significant correlation between eNO and NOxwhendata for the normal, atopic, and asthmatic children werecombined (P¼ 0.02, r¼ 0.3, Fig. 4). There was nosignificant correlation between EBC pH and eNO(P¼ 0.2, r¼�0.2), except in those not taking GCS, andthis group comprised only seven subjects. Likewise, there

was no relationship between pH and NOx in normal(P¼ 0.06, r¼ 0.5), atopy (P¼ 0.4, r¼ 0.2), and asthmaticchildren (P¼ 0.87, r¼ 0.02) (Fig. 5).

Relationship of pH to Indicators ofAsthma Control

Markers of satisfactory asthma control were wheezing<1 night/week, FEV1� 80% predicted or best, FEV1/FVC� 80%. In addition, an increase in rescuemedicationwas considered indicative of unsatisfactory control. MeanEBC pH in children with asthma who had a FEV1� 80%was significantly higher when compared with those whohad a FEV1< 80%, P¼ 0.03. The mean level of EBC pH,however, in those with asthma who had a FEV1/FVC� 80% was not significantly different to those whohad a FEV1/FVC< 80%, but was significantly lower inthose who had required an increase in their rescuemedication (Table 3). Asthmatic children who had

Fig. 2. Levels of EBC NOx in children who were either asthmatic,

atopic, or normal. Horizontal bars indicate the mean andP-values

are indicated above the brackets.

Fig. 3. Levels of EBC pH in children who were either asthmatic,

atopic, or normal. Horizontal bars indicate the mean andP-values

are indicated above the brackets. Relationship between eNO and

EBC NOx in all subjects (normal, atopic, and asthmatic) (n¼ 92,

P¼0.02, r¼0.3).

Fig. 4. The relationship between EBC NOx and EBC pH in all

subjects (normal, atopic, and asthmatic). There was a significant

correlation between these two variables (P¼0.02, r¼0.3).

Fig. 5. The relationship between EBC NOx and EBC pH in

children (P¼0.08, r¼0.5).

932 Ratnawati et al.

wheezing <1 night per week had mean levels of EBC pHwere similar to those who had wheezing �1 nights perweek (Table 3).

Relationship of NOx and eNO to Indicators ofAsthma Control

The level of NOx in asthmatic subjects who had aFEV1� 80%was similar to thosewho had a FEV1< 80%.Likewise, asthmaticswhohad a FEV1/FVC� 80%did nothave a significantly lower level of NOx compared withthose who had a FEV1/FVC< 80%. Asthmatic childrenwho had wheezing<1 night per week had mean levels ofNOx which were not significantly different to those whohadwheezing>1 or 2 nights perweek (Table 3). Likewise,there were no significant relationships between eNO andthe markers of asthma control.

DISCUSSION

This study has confirmed that the mean level of eNO ishigher in asthmatic children compared with those who arenormal or atopic. Previous studies have shown differinglevels of eNO in sub-groups of asthmatic children. A studyby Byrnes et al. also found that the mean eNO level washigher in asthmatic children on bronchodilator therapyonly, whereas it was significantly lower in asthmaticchildren on regular inhaled GCS, similar to those valuesseen in normal children. Levels of eNO decreased to thoseseen in normal subjects after 2weeks of inhaledGCSwereadministered.16 These findings have been confirmed in thecurrent study.

Atopic, non-asthmatic children with positive SPT havehigher eNO levels compared with those who wereunreactive, which is consistent with previous studies thatdemonstrated a positive correlation of eNO levels with thenumber of positive SPT. In this study, eNO levels weresignificantly higher in atopic asthmatic subjects comparedwith the non-atopic asthmatic group whose levels were inthe same range as normal children, suggesting that eNOmight be more useful for monitoring atopic asthma ratherthan non-atopic asthma. Other studies have also suggestedthat eNOmay be a marker of atopy, rather than asthma per

se, as the chance of asthma increases with increasingnumber of positive SPT.17,18

Exhaled nitric oxide is produced by nitric oxidesynthases (NOS) in the airways, and inducible or Type IINOS (iNOS) is thought to be upregulated by inflammatorycytokines particularly via eosinophilic activation andairway epithelium.19,20 Healthy subjects produce lowlevels of eNO, which presumably originates from cNOSactivity. GCS decrease eNO both after an acute asthmaexacerbation and in stable asthmatics, presumably viasuppression of eosinophilic inflammation and iNOS, butnot in normal subjects.21 On the other hand, a study byPayne et al.22 indicated that eNOpersists above the normallevel in a group with difficult asthma in whom symptomspersist despite the use of oral steroid treatment. A recentprospective study reported that eNO measurements maybe useful to improve monitoring of airway inflammationand to optimize treatment in asthmatic children.23

The mechanism responsible for the increased iNOSexpression in atopic asthma is probably allergic eosino-philic inflammation, whereas non-eosinophilic asthmahas been attributed to neutrophilic inflammation.24 Astudy of the effect of allergen exposure on atopic asthmaby Roberts et al.25 suggested that an increased eNOconcentration was associated with an increase in the meanpollen count in the preceding week and also inverselycorrelated with asthma control.Previous studies have shown that EBC pH is lower in

acute asthmawhen comparedwith normal subjects.7,9,26Astudy by Hunt et al. found that therapy with anti-inflammatory GCS increases the EBC pH of asthmaticsubjects towards that seen in normal subjects, andsuggested that airway inflammation is responsible forthe mechanism of acidification of breath condensate.7,26

Thus, GCS are associated with an increase in pH and adecrease in eNO.7 The reason the present study found thatthe EBC pH of asthmatic children was similar to normalsubjects is perhaps because the majority of the patientswere already using inhaledGCS.27 A recent study byOjooet al. also found that EBC pH in atopic stable asthma wassimilar to that found in healthy subjects. It has beensuggested that pH is one of the determining factors leadingto NOx formation. Hydrogen ions increase conversion of

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TABLE 3— Mean (95%CI) Levels of EBC NOx and EBC pH in Asthmatic Subjects According to Indicators of Asthma Control

n NOx (95%CI) (mM) P-value pH (95%CI) P-value eNO (95%CI) (ppb) P-value

FEV1� 80% 50 8.5 (7.3–9.7)0.7

6.8 (6.7–7.0)0.03

43.6 (34.2–53.1)0.5

FEV1< 80% 12 8.6 (5.8–11.5) 6.4 (6–6.8) 44.1 (25.5–62.7)

FEV1/FVC� 80% 36 8.4 (6.9–9.8)0.9

6.8 (6.6–6.9)0.9

37.4 (27.9–46.9)0.07

FEV1/FVC< 80% 26 8.7 (7–10.4) 6.7 (6.4–7) 52.5 (37.9–67.1)

Wheeze <1 night/week 26 8.8 (6.9–10.6)0.6

6.7 (6.6–6.9)0.5

46.6 (36.8–56.3)0.2

Wheeze >1 night/week 36 8.1 (6.7–9.5) 6.7 (6.2–7.3) 33.1 (18.9–47.2)

Short acting BD increase 14 7.8 (4.9–10.8)0.6

6.4 (6.0–6.8)0.02

44.9 (26.4–63.4)0.7

BD doses as usual 38 8.5 (7.4–9.7) 6.8 (6.6–7.0) 43.4 (33.9–52)

EBC NOx in Asthma 933

NO toNOxwhich is consistentwith elevatedNOandNOxin expired breath in acute asthma. Thus an increase in NOgeneration and a fall in pH may elevate NOx in exhaledbreath.Nitrite and nitrate, the stable metabolites of NO have

also been proposed as a tool to assess disease activity inasthmatic children.28 EBC nitrite in asthmatic children issignificantly higher than in healthy children or those whohave cough, but who are non-asthmatic.29 In the presentstudy it has been demonstrated that NOx in EBC iselevated in asthmatic children comparedwith both normaland atopic children. Thus, EBC NOx might be used as anindicator of inflammation in asthmatic children, but in thiscross-sectional study, it does not show a clear relationshipto markers of disease control.A significant correlation was seen between eNO and

EBCNOxwhen combining data from all three groups, butnot when the groups were analyzed individually. Thissuggests that such a correlation is relatively weak, and thatthe two measurements are probably not interchangeable.The present study found that a lower EBC pH is

associated with a decreased FEV1 as an indicator ofairway obstruction in asthmatic children, and with recentincreased bronchodilator usage, but not night-timewheeze. It may be that pH reflects the asthma severity atthe time of sampling, but may not necessarily be anindicator of asthma severity in the past few weeks,whereas NO and NOx may reflect longer term changes.Alternatively,NOmay bemore sensitive to the use ofGCSthan pHwhich is why pH is associated with somemarkersof poor asthma control.

In terms of a relationship between gender, age, andheight with eNO, NOx, and pH in normal, atopic, andasthmatic children, only the mean level of eNO in thenormal group had a significantly different regarding withage and height (Table 4). This study did not show the effectof gender on eNO level as mentioned in the studies byTsang et al. and Nordvall et al.30,31

An additional problem when comparing studies in theliterature is that the collection apparatusmay influence thelevels of the variables of interest. Leung et al.32 and datafrom our own laboratory suggest that there can be verypoor agreement between devices, making comparisonsdifficult. Our apparatus used a collection device whichmaintains conditions at 48C. The Jaeger EcoScreencollects samples at �15 to �208C, and the sample needsto thaw and refreeze for aliquoting and storage to takeplace. The R-tube device (Respiratory Research, Charlot-tesville, VA) starts at �15 to �208C, and graduallyincreases in temperature, collecting EBC as a liquidwhichtherefore does not undergo a freeze-thaw cycle. Our datasuggest that the EcoScreen is more efficient at collectingvariables such as protein in the EBC sample, whencompared with siliconized or plain glass at 48C.33 Leunget al.32 also indicated that there was little agreementbetween pHmeasured by the two commercial devices, andeach device use different materials which may affectadsorption, and possibly pH.In conclusion, detecting airway inflammation through

exhaled breath is non-invasive, safe, and easy to performin children.Measuring EBCNOx and eNO,may be usefulin distinguishing between asthmatic, atopic, and normal

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TABLE 4— Mean Levels (95% CI) of eNO, EBC pH, and EBC NOx According to Gender, Age, and Height in Normal, Atopic,and Asthmatic Children

eNO P-value NOx P-value pH P-value

Normal

Male 13.8 (0.2–27.8)0.79

4.39 (1.7–7.1)0.64

6.7 (5.9–7.4)0.22

Female 10.1 (6.4–13.8) 5 (3–7.1) 6.2 (5.7–6.7)

<10 year 7.4 (5.7–9)0.004

5.2 (3.2–7.1)0.5

6.7 (6.3–7.2)0.4�10 year 13.3 (8.5–18.1) 4.2 (1.4–7.0) 6.4 (5.3–7.5)

�140 cm 7.4 (5.9–8.9)0.0006

5.3 (3.5–7.0)0.31

6.7 (6.3–7.1)0.35

>140 cm 14.4 (9.2–19.6) 3.7 (0.3–7.2) 6.3 (4.9–7.8)

Atopy

Male 27.6 (16.3–38.9)0.18

5.9 (2.3–9.5)0.49

6.6 (6.2–7.0)0.6

Female 19.1 (8.5–29.7) 7.4 (2.5–12.4) 6.6 (5.7–7.5)

<10 year 25.7 (17.4–34.1)0.6

7.0 (2.8–11.2)0.7

6.2 (5.6–6.9)0.3�10 year 22.2 (7.5–36.9) 6.2 (1.9–10.3) 6.7 (5.9–7.4)

�140 cm 26.8 (17.3–36.3)0.49

5.5 (1.6–9.5)0.49

6.3 (5.4–7.1)0.39

>140 cm 21.8 (9.4–34.3) 7.3 (3.2–11.4) 6.6 (6.0–7.3)

Asthma

Male 40.1 (31.1–49.1)0.2

8.9 (7.6–10.2)0.07

6.8 (6.6–7)0.09

Female 53.4 (34.2–72.5) 6.9 (5–8.8) 6.6 (6.3–6.8)

<10 year 43.7 (27.2–60.3)0.8

7.0 (4.9–9.1)0.07

6.6 (6.3–6.9)0.3�10 year 46.7 (35.3–58.2) 9.1 (7.9–10.4) 6.7 (6.6–7.0)

�140 cm 42.7 (25.3–60.2)0.92

8.9 (6.5–11.4)0.59

6.7 (6.3–7.1)0.85

>140 cm 43.7 (33.9–53.6) 8.3 (7.0–9.5) 6.7 (6.5–6.9)

P-values shown are those using univariate analysis.

934 Ratnawati et al.

children. This study has demonstrated a correlationbetween NO and its metabolite, NOx. It would thereforeappear that although there is a weak correlation betweenEBC NOx and eNO, EBC pH, NOx, and eNO are notinterchangeable, but it is possible that simple, inexpensiveNOx devices might be a practical method of monitoringairway inflammation. EBC pHmay be of interest in futurestudies as a surrogate marker of asthma control and mightbe used in conjunction with eNO and inflammatorymarkers in EBC.

ACKNOWLEDGMENTS

The authors thank children and parents who partici-pated in this study, and also to the laboratory andoutpatient clinic staff of Sydney Children’s Hospital forassistance in conducting this study, particularly AlisonBoynton, Barbara O’Donovan, and Sharron Chow. Thisproject was supported by an equipment grant fromAerocrine, Sweden and support from the School ofMedical Sciences, UNSW.

REFERENCES

1. Mutlu GM, Garey KW, Robbins RA, Danziger LH, Rubinstein I.

Collection and analysis of exhaled breath condensate in humans.

Am J Respir Crit Care Med 2001;164:731–737.

2. Baraldi E, Ghiro L, Piovan V, Carraro S, Zaccello F, Zanconato S.

Safety and success of exhaled breath condensate collection in

asthma. Arch Dis Child 2003;88:358–360.

3. Gessner C, Kuhn H, Toepfer K, Hammerschmidt S, Schauer J,

Wirtz H. Detection of p53 gene mutations in exhaled breath

condensate of non-small cell lung cancer patients. Lung Cancer

2004;43:215–222.

4. Montuschi P, Barnes PJ. Analysis of exhaled breath condensate

for monitoring airway inflammation. Trends Pharmacol Sci 2002;

23:232–237.

5. Hunt JF. Exhaled breath condensate: An evolving tool for

noninvasive evaluation of lung disease. J Allergy Clin Immunol

2002;110:28–34.

6. Gaston B, Drazen JM, Loscalzo J, Stamler JS. The biology of

nitrogen oxides in the airways. Am J Respir Crit Care Med 1994;

149:538–551.

7. Hunt JF, Fang K, Malik R, Snyder A, Malhotra N, Platts-Mills

TAE, Gastos B. Endogenous airway acidification. Implications

for asthma pathology. Am J Respir Crit Care Med 2000;161:694–

699.

8. Ganas K, Loukides S, Papatheorodou G, Panagou P,

Kalogeropoulos N. Total nitrite/nitrate in expired breath con-

densate of patients with asthma. Respir Med 2001;95:649–

654.

9. Kostikas K, Papatheodorou G, Ganas K, Psathakis K, Panagou P,

Loukides S. pH in expired breath condensate of patients with

inflammatory airways diseases. Am J Respir Crit Care Med 2002;

165:1364–1370.

10. Silkoff PE, Robbins RA, Gaston B, Lundberg JON, Townley RG.

Endogenous nitric oxide in allergic airway disease. J Allergy Clin

Immunol 2000;105:438–448.

11. Artlich A, Busch T, Lewandowski K, Jonas S, Gortner L, Falke

KJ. Childhood asthma: Exhaled nitric oxide in relation to clinical

symptoms. Eur Respir J 1999;13:1396–1401.

12. Ratnawati, Thomas PS. Exhaled nitric oxide in paediatric asthma.

Chron Respir Dis 2005;2:163–174.

13. Global initiative for asthma. Global strategies for asthma

management and prevention. NHLBI. 2005; Publication No 02-

3659 (http://www.ginasthma.com/Guidelineitem.asp ?l1¼ 2&l2

¼1 &intId¼60).

14. American Thoracic Society ATS. ATS/ERS Recommendations

for standardized procedures for the online and offline measure-

ment of exhaled lower respiratory nitric oxide and nasal

nitric oxide. Am J Respir Crit Care Med 2005;171:912–930.

15. Misko TP, Schilling RJ, Salvemini D, Moore WM, Currie MG. A

fluorometric assay for the measurement of nitrite in biological

samples. Anal Biochem 1993;214:11–16.

16. Byrnes CA, Dinarevic S, Shinebourne EA, Barnes PJ, Bush A.

Exhaled nitric oxide measurements in normal and asthmatic

children. Pediatr Pulmonol 1997;24:312–318.

17. Franklin PJ, Taplin R, Stick SM. A community study of exhaled

nitric oxide in healthy children. Am J Respir Crit Care Med 1999;

159:69–73.

18. Thomas PS, Gibson PG, Wang H, Shah S, Henry RL. The

relationship of exhaled nitric oxide to airway inflammation and

responsiveness in children. J Asthma 2005;42:281–289.

19. Robbins RA, Barnes PJ, Springall DR, Warren JB, Kwon QJ,

Buttery LDK, Wilson AJ, Geller DA, Polak JM. Expression of

inducible nitric oxide in human lung epithelial cells. Biochem

Biophys Res Commun 1994;203:209–218.

20. Guo FH, Comhair SAA, Zheng S, Dweik RA, Eissa NT,

Thomassen MJ, Calhoun W, Erzurum SC. Molecular mechanisms

of increased nitric oxide (NO) in asthma: Evidence for

transcriptional and post-translational regulation of NO synthesis.

J Immunol 2000;164:5970–5980.

21. Yates DH, Kharitonov SA, Robbins RA, Thomas PS, Barnes PJ.

Effect of a nitric oxide synthase inhibitor and glucocorticosteroid

on exhaled nitric oxide. Am J Respir Crit Care Med

1995;152:892–896.

22. Payne DNR, Adcock IM, Wilson NM, Oates T, Scallan M, Bush

A. Relationship between exhaled nitric oxide and mucosal

eosinophilic inflammation in children with difficult asthma, after

treatment with oral prednisolone. Am J Respir Crit Care Med

2001;164:1376–1381.

23. Zacharasiewicz A, Wilson N, Lex C, Erin EM, Li AM, Hansel T,

Khan M, Bush A. Clinical use of noninvasive measurements of

airway inflammation in steroid reduction in children. Am J Respir

Crit Care Med 2005;171:1077–1082.

24. Douwes J, Gibson P, Pekkanen J, Pearce N. Non-eosinophilic

asthma: Importance and possible mechanisms. Thorax

2002;57:643–648.

25. Roberts G, Hurley C, Bush A, Lack G. Longitudinal study of

grass pollen exposure, symptoms, and exhaled nitric oxide in

childhood seasonal allergic asthma. Thorax 2004;59:752–756.

26. Carpagnano GE, Barnes PJ, Francis J, Wilson N, Bush A,

Kharitonov SA. Breath condensate pH in children with cystic

fibrosis and asthma. A new noninvasive marker of airway

inflammation? Chest 2004;125:2005–2010.

27. Ojoo JC, Mulrennan SA, Kastelik JA, Morice AH, Redington

AE. Exhaled breath condensate pH and exhaled nitric oxide

in allergic asthma and in cystic fibrosis. Thorax 2005;60:22–

26.

28. Straub DA, Ehmann R, Hall GL, Moeller A, Hamacher J, Frey U,

Sennhauser FH, Wildhaber JH. Correlation of nitrites in breath

condensates and lung function in asthmatic children. Pediatr

Allergy Immunol 2004;15:20–25.

29. Formanek W, Inci D, Lauener RP, Wildhaber JH, Frey U, Hall

GL. Elevated nitrite in breath condensates of children with

respiratory disease. Eur Respir J 2002;19:487–491.

EBC NOx in Asthma 935

30. Tsang KW, Ip SK, Leung R, Tipoe GL, Chan SL, Shum IH, Ip

MS, Yan C, Fung PC, Chan-Yeung M, Lam W. Exhaled nitric

oxide: The effects of age, gender and body size. Lung 2001; 179:

83–91.

31. Nordvall SL, Janson C, Kalm-Stephens P, Foucard T, Toren K,

Alving K. Exhaled nitric oxide in a population-based study of

asthma and allergy in schoolchildren. Allergy 2005;60:469–475.

32. Leung TF, Li CY, Yung E, Liu EKH, Lam CWK, Wong GWK.

Clinical and technical factors affecting pH and other biomarkers

in exhaled breath condensate. Pediatr Pulmonol 2006;41:87–94.

33. Liu J, Chow S, Ratnawati XX, Thurston MC, Krishnan A, Yates

DH, Thomas PS. Effect of collection materials upon markers of

inflammation in exhaled breath condensate. Respirology 2006;

11:Suppl 2(A31) .

936 Ratnawati et al.