Exhaled nitric oxide--is it really a good marker of airway inflammation in bronchial asthma?

Fractional Exhaled Nitric Oxide Testing: Diagnostic Utility in Asthma, Chronic Obstructive Pulmonary Disease, or Asthma-chronic Obstructive Pulmonary Disease Overlap Syndrome

Asthma and chronic obstructive pulmonary disease (COPD) can present as unique conditions or as a combination known as asthma-chronic obstructive pulmonary disease overlap syndrome (ACOS). These condition(s) can be categorized as obstructive conditions, causing inflammation of small airways leading to decrease airflow, mucus production, and bronchoconstriction. Asthma and COPD affect every age, gender, ethnicity, and socioeconomic status, thus increasing mortality and morbidity burden in our society. Fractional exhaled nitric oxide (FeNO) is an endogenous gaseous molecule which can be measured in the human breath test because of airway inflammation. It has been studied extensively as a marker of inflammation and has been incorporated into an algorithm for asthma management. The purpose of this study was to investigate whether FeNO testing can lead to a change in the diagnosis. A retrospective chart review of 95 patients with asthma, COPD, and ACOS was performed, and FeNO levels were recorded. Out of 95 patients, 36%, 24%, and 22% of the patients had an initial diagnosis of asthma, COPD, and ACOS, respectively. After the FeNO testing, the number of patients with the final diagnosis of asthma and ACOS increased, and COPD decreased. Our results support the utility of FeNO as a viable marker in diagnosing and managing complex cases of asthma, COPD, and ACOS.

Exhaled eicosanoid profiles in children with atopic asthma and healthy controls

RATIONALE

Chronic endobronchial inflammation is a hallmark of pediatric asthma and involves the arachidonic acid pathway. Its non-volatile metabolites can be quantified in the exhaled breath condensate (EBC), and single substances have been studied as non-invasive biomarkers for the diagnosis and monitoring of children with asthma. The aim of this study was to compare the content and profile of a wider range of eicosanoids in the EBC between patients and a control group.

MATERIALS AND METHODS

EBC was sampled from 33 children (aged 12.4 ± 3.1 years) with stable atopic asthma (26 on inhaled steroid treatment) and 25 healthy controls (11.8 ± 3.2 years). Validated high performance liquid chromatography coupled with a tandem mass spectrometry platform (HPLC-MS2 ) was used to measure 13 different compounds. In addition, exhaled nitric oxide levels (FeNO) were measured and bronchial hyperresponsiveness (BHR) was assessed by an exercise challenge test in all subjects. An analytical approach was used for multivariate regression modeling of disease status using the most relevant variables.

RESULTS

The levels of PGEM (P < 0.001), PGD2 (P < 0.001), 6keto-PGF1α (P = 0.03), LTC4 (P < 0.001), trans-LTC4 (P = 0.04), and 5HETE (P = 0.02) were significantly higher in asthmatics compared to healthy children, while 11-dehydro TXB2 was significantly less abundant (P = 0.02). The eicosanoids asthma classification ratio (EACR) was computed as the logistic regression function using four variables: PGEM, PGD2, LTC4, and 5HETE. This composite parameter discriminated asthmatic from healthy children better than FEV1, FeNO, or BHR.

CONCLUSION

Complementary measurements of PGEM, PGD2, LTC4, and 5HETE in small-volume EBC samples are feasible by HPLC-MS2 and showed a specific profile in our study population. EACR should be evaluated further in the context of diagnosing and monitoring childhood asthma.

Fractional exhaled nitric oxide measurements in rhinitis and asthma in children

Exaled nitric oxide (FeNO) is considered a good noninvasive marker to assess airway inflammation in asthma and allergic rhinitis. In asthma, exhaled NO is very useful to verify adherence to therapy, and to predict upcoming asthma exacerbations. It has been also proposed that adjusting anti-inflammatory drugs guided by the monitoring of exhaled NO, could improve overall asthma control. Other studies showed increased FeNO levels in subjects with allergic rhinitis.

Does asthma control as assessed by the asthma control test reflect airway inflammation?

BACKGROUND AND AIMS

The treatment of asthmatic patients is particularly focused on the control of symptoms as well as functional and inflammatory parameters. In our study, we investigated the relationship between the asthma control test (ACT) which evaluates symptoms and airway inflammation and functional parameters.

MATERIALS AND METHODS

Stable asthmatic patients admitted to our pulmonary outpatient clinic were enrolled in the study consecutively and underwent the ACT, pulmonary function tests and methacholine bronchial provocation test (MBPT). Additionally, fractional exhaled nitric oxide level (FeNO) and induced sputum cell distribution were assessed. All these parameters were re-evaluated at the third month after adjusting medications of the patients according to baseline ACT scores.

RESULTS

Of the 101 patients screened, we analyzed 83 who proceeded to the follow up visit. At the baseline visit, 8 were totally controlled, 36 partially controlled and 39 uncontrolled according to ACT. At the follow up visit, 10 were totally controlled, 39 partially controlled and 34 uncontrolled. Comparison of the two visits in terms of all parameters revealed significant reductions only in the percentages of patients with MBPT positivity (p = 0.029) and FeNO levels > 20 ppb (p = 0.025) at follow up. The percentages of patients with FeNO > 20 ppb, MBPT positivity, induced sputum eosinophilia or induced sputum neutrophilia did not show significant differences between totally controlled, partially controlled and uncontrolled groups at both baseline and follow up visits.

CONCLUSION

Although the ACT scores did not show significant correlations with the airway inflammation parameters tested in this study, a marked reduction in the percentage of patients with MBPT positivity and FeNO > 20 ppb at follow up may suggest the importance of the control concept in the management of asthma.

Is it necessary to treat all asthmatic children with raised levels of exhaled nitric oxide?: treating the patient or the data

BACKGROUND

The aim of the present study is to assess whether a single determination of the fraction of exhaled nitric oxide (FENO), added to the measurements usually taken during a routine checkup, helps in the prediction of the recurrence of asthma attacks in controlled patients who are not receiving any baseline treatment; and whether or not treatment of the said latent inflammation is appropriate.

METHODS

Observational study of prospective cohorts. Over a period of three months, data was collected from 28 patients (6 to 14 years) who met the conditions of the inclusion criteria, with a follow up appointment after six months.

RESULTS

Patients were divided into two groups: 13 with FENO values of 49 and over, and 15 with values of under 49. Five patients in the subgroup with low FENO values suffered recurrence, in contrast to only one in the group with high values. The positive predictive value of the high values of the FENO was 7.69, with no significant differences between the two groups.

CONCLUSIONS

Certain doubts were raised about the usefulness of the FENO, as opposed to the traditional methods of asthma control with regard to the therapeutic management of clinically controlled patients who are not receiving treatment and who have high FENO values. It would appear unwise to recommend the systematic treatment of patients with high FENO values, when measured during a routine check-up, in cases of asthma with an allergic component and are asymptomatic or in a phase of asthma under good control.

Exhaled breath temperature, a new biomarker in asthma control: a pilot study

OBJECTIVE

To evaluate whether the exhaled breath temperature (EBT), measured by a noninvasive method, is an effective means of monitoring patients with uncontrolled asthma.

METHODS

A pilot study comprising nine patients (seven women and two men; mean age: 39 years) diagnosed with asthma at least one year prior to the beginning of the study and not having been under maintenance therapy for the last three months. In the first visit, the patients underwent spirometry and measurement of EBT. The patients were then instructed to use inhaled budesonide/formoterol (200/6 µg) every 12 h for six weeks. In addition, the patients with severe asthma (FEV1 < 60% of predicted) were instructed to use oral prednisolone (40 mg/day) for five days. After six weeks, the patients underwent the same tests.

RESULTS

All of the patients reported an improvement in the symptoms of asthma, as confirmed by a statistically significant increase in FEV1 from the first to the second visit (mean, 56.1% vs. 88.7% of predicted; p < 0.05). Five patients used oral prednisolone for the first five days of the treatment period. Six patients used additional doses of inhaled budesonide/formoterol (mean duration, 2.5 weeks). The EBT decreased significantly from the first to the second visit (mean EBT: 35.1 ºC vs. 34.1 ºC; p < 0.05).

CONCLUSIONS

Uncontrolled asthma, especially during exacerbations, is followed by an increase in EBT, which decreases after appropriate asthma control, as demonstrated by an increase in FEV1 and an improvement of the reported symptoms. These preliminary results suggest that EBT can be used as a parameter for the assessment of asthma control.

Association of alveolar nitric oxide levels with pulmonary function and its reversibility in stable asthma

BACKGROUND

Inflammation of peripheral airways is implicated in the pathophysiology of severe asthma. However, contributions of peripheral airway inflammation to airway caliber/function in patients with stable asthma, including those with mild to moderate disease, remain to be confirmed.

OBJECTIVES

To determine whether peripheral airway inflammation affects airway function in patients with asthma.

METHODS

In 70 patients with mild to severe asthma, alveolar nitric oxide [CANO(TMAD)] levels were examined as a noninvasive biomarker of peripheral airway/alveolar inflammation. CANO(TMAD) and maximal nitric oxide (NO) flux in the airway compartment, J'awNO, were estimated with a model that incorporated trumpet-shaped airways and axial diffusion using exhaled NO output at different flow rates. Measures of pulmonary function were then assessed by spirometry and an impulse oscillometry system, and their bronchodilator reversibility was examined.

RESULTS

CANO(TMAD) levels were not correlated with pre- or postbronchodilator spirometric values, but were significantly associated with prebronchodilator reactance at low frequency (Xrs5) (rho = -0.31, p = 0.011), integrated area of low-frequency Xrs (AX) (rho = 0.35, p = 0.003) and negative frequency dependence of resistance (Rrs5-Rrs20) (rho = 0.35, p = 0.004). Furthermore, CANO(TMAD) levels were associated with bronchodilator reversibility of FEV(1), FEF(25-75%), Xrs5 and AX (rho = 0.35, 0.31, -0.24 and -0.31, respectively; p ≤ 0.05 for all). No variables were related to J'awNO.

CONCLUSIONS

Elevated CANO(TMAD), but not J'awNO, partly reflects reversible airway obstruction originating in the peripheral airway. These findings indicate the involvement of peripheral airway inflammation in physiological abnormalities in asthma.

Subcellular and cellular locations of nitric oxide synthase isoforms as determinants of health and disease

The effects of nitric oxide in biological systems depend on its steady-state concentration and where it is being produced. The organ where nitric oxide is produced is relevant, and within the organ, which types of cells are actually contributing to this production seem to play a major determinant of its effect. Subcellular compartmentalization of specific nitric oxide synthase enzymes has been shown to play a major role in health and disease. Pathophysiological conditions affect the cellular expression and localization of nitric oxide synthases, which in turn alter organ cross talk. In this study, we describe the compartmentalization of nitric oxide in organs, cells, and subcellular organelles and how its localization relates to several relevant clinical conditions. Understanding the complexity of the compartmentalization of nitric oxide production and the implications of this compartmentalization in terms of cellular targets and downstream effects will eventually contribute toward the development of better strategies for treating or preventing pathological events associated with the increase, inhibition, or mislocalization of nitric oxide production.

The relationship between exhaled nitric oxide measured with an off-line method and airway reversible obstruction in Japanese adults with asthma

BACKGROUND

Exhaled nitric oxide (eNO) is a useful marker of eosinophilic airway inflammation in asthma patients. There is no study to show the relationship between the eNO measured by using an off-line method and the degree of reversibility of airflow limitation in Japanese asthma patients. We sought to investigate the relationship between the eNO level measured by using an off-line method and the degree of reversibility of bronchial constriction in Japanese asthma patients.

METHODS

The study population comprised 97 asthma patients in our outpatient clinic with some patients in both groups who received inhaled corticosteroid treatment. We measured eNO levels, forced expiratory volume in one second (FEV1) before and after treatment, reversible airway obstruction (DeltaFEV1) after inhalation of bronchodilator, and other parameters.

RESULTS

eNO was significantly correlated with peripheral blood eosinophil counts in asthma patients (in steroid-naïve asthma patients, r=0.544, p<0.0001; in asthma patients treated with inhaled corticosteroid, r=0.463, p=0.026), and subjects with severe eosinophilia in sputum showed high levels of eNO (mild eosinophilia versus severe, p=0.0152). Among patients with obstructive impairment, eNO levels were correlated with DeltaFEV1 regardless of whether patients received (r=0.527, p=0.0435) or did not receive (r=0.64, p = 0.0056) inhaled corticosteroid. In subjects with normal pulmonary function, there was no significant relationship between eNO and DeltaFEV1 with or without inhaled corticosteroid.

CONCLUSIONS

In patients with obstructive impairment, eNO reflects the degree of reversible airflow limitation. In subjects with normal pulmonary function, eNO may facilitate the diagnosis and management of asthma, rather than indicate reversible bronchial obstruction. eNO measurement by off-line methods is applicable as a potential tool for the diagnosis of asthma and management of asthma patients.

Validation study of fractional exhaled nitric oxide measurements using a handheld monitoring device

We tested reproducibility of exhaled nitric oxide (FE(NO)) and inter-operator handling when measured with a handheld device, NIOX MINO. We enrolled 20 volunteers using a priori goals of acceptable reproducibility to be mean within-subject standard deviation less than 3 parts per billion (ppb) for FE(NO) measurements less than 30 ppb, and mean coefficient of variation less than 10% for FE(NO) measurements more than 30 ppb. Seventeen subjects with measurements less than 30 ppb displayed a mean standard deviation of 1.15, and 3 subjects with FE(NO) more than 30 ppb had a mean coefficient of variation of 2.4%. We conclude that NIOX MINO demonstrates excellent reproducibility for all ranges of FE(NO).

Quality of life and inflammatory markers in mild asthma

STUDY OBJECTIVES

The aim of this study was to explore the relationship between quality of life and measures of asthma, such as lung function, reversibility to bronchodilation, exhaled nitric oxide (NO), and bronchial responsiveness to direct and indirect stimulus in patients with mild asthma in a primary care setting.

PATIENTS AND MEASUREMENTS

Seventy-seven asthmatic patients not treated with glucocorticosteroids completed the Asthma Quality of Life Questionnaire. Spirometry was performed before and after bronchodilation, and bronchial challenges with methacholine and eucapnic dry air hyperventilation were conducted on separate days. NO in exhaled air and serum IgE were also analyzed.

RESULTS

We found no correlation between quality of life and any of the other parameters. There was a significant covariation between exhaled NO and bronchial responsiveness to methacholine and dry air, and also between FEV(1) (percentage of predicted) and reversibility to a bronchodilator. The levels of exhaled NO were higher in the asthmatic subjects with atopy than in the nonatopic asthmatics.

CONCLUSIONS

The measures used in our study do not reflect health-related quality of life in subjects with mild asthma. We conclude that in the clinical situation, quality of life and other measures of asthma provide complementary information.

Relationship between exhaled nitric oxide levels and compliance with inhaled corticosteroids in asthmatic children

Levels of exhaled nitric oxide (eNO) are elevated in subjects with asthma and fall in response to oral or inhaled steroids. This study explored the possibility the measurement of eNO levels could be used to identify subjects who were not adhering to their treatment regimen. Twenty children with asthma attending the respiratory clinic were recruited. Each attended on four occasions 1 month apart when eNO levels were measured. A data logger attached to a pressurised metered dose inhaler was used to objectively monitor use of inhaled corticosteroids (ICSs). The correlation between day and dose compliance with eNO was assessed. The data demonstrated a weak but non-significant correlation between eNO and both day (r = 0.055, P = 0.67) and dose (r = 0.153, P = 0.23). A recorded value of eNO less than 12 was associated with day compliance rates of 3-97%. Of the 19 recorded eNO values greater than 12 ppb almost 80% were from subjects with a day compliance of less than 50% during the preceding month. Of the four values greater than 12 ppb and day compliance > 60% one subject had a poor inhaler technique, one had a mild viral exacerbation and one appeared to be associated with increase pollen exposure. The measurement of eNO may prove to be a useful tool in helping to manage children with asthma but further work is required to define its precise role. Elevated eNO levels in asthmatic children taking ICSs are likely to reflect poor compliance but confounding factors such as disease activity and inhaler technique need to be carefully considered.

Examining axial diffusion of nitric oxide in the lungs using heliox and breath hold

Exhaled nitric oxide (NO) is highly dependent on exhalation flow; thus exchange dynamics of NO have been described by multicompartment models and a series of flow-independent parameters that describe airway and alveolar exchange. Because the flow-independent NO airway parameters characterize features of the airway tissue (e.g., wall concentration), they should also be independent of the physical properties of the insufflating gas. We measured the total mass of NO exhaled ( AI,II) from the airways after five different breath-hold times (5–30 s) in healthy adults (21–38 yr, n = 9) using air and heliox as the insufflating gas, and then modeled AI,II as a function of breath-hold time to determine airway NO exchange parameters. Increasing breath-hold time results in an increase in AI,II for both air and heliox, but AI,II is reduced by a mean (SD) of 31% (SD 6) ( P < 0.04) in the presence of heliox, independent of breath-hold time. However, mean (SD) values (air, heliox) for the airway wall diffusing capacity [3.70 (SD 4.18), 3.56 pl·s−1·ppb−1 (SD 3.20)], the airway wall concentration [1,439 (SD 487), 1,503 ppb (SD 644>)], and the maximum airway wall flux [4,156 (SD 2,502), 4,412 pl/s (SD 2,906)] using a single-path trumpet-shaped airway model that considers axial diffusion were independent of the insufflating gas ( P > 0.55). We conclude that a single-path trumpet model that considers axial diffusion captures the essential features of airway wall NO exchange and confirm earlier reports that the airway wall concentration in healthy adults exceeds 1 ppm and thus approaches physiological concentrations capable of modulating smooth muscle tone.

Time-Dependent Effect of Nitrate-Rich Meals on Exhaled Nitric Oxide in Healthy Subjects

BACKGROUND

Exhaled nitric oxide (eNO) is a convenient noninvasive marker for airway inflammation in several pulmonary diseases. However, external factors such as nitrate-rich nutrition can affect the levels of eNO and thus compromise its diagnostic value.

STUDY OBJECTIVES

The objective of this investigation was to have a better understanding of the time-dependent effect of nitrate-rich meals on eNO in healthy subjects.

STUDY DESIGN

Forty-two healthy, nonsmoking volunteers (age range, 25 to 62 years) were recruited for the study. They had no recent respiratory tract infections and were free of pulmonary history, rhinitis, and atopic disorders. eNO was measured before, and 0.5, 2, 4, 12, 15, and 20 h after the intake of a nitrate-rich meal equivalent to 230 mg of nitrate.

RESULTS

The intake of a nitrate-rich meal increased eNO by 60% 2 h after the meal. Even after 15 h, the mean eNO value was still 22% higher than the baseline value. Only after 20 h did eNO return to the normal baseline level.

CONCLUSION

This finding stresses the importance of advising patients to avoid nitrate-rich nutrition at least 20 h before a scheduled measurement of eNO.

Fractional exhaled nitric oxide (FENO), lung function and airway hyperresponsiveness in naïve atopic asthmatic children

BACKGROUND

Measurement of fractional exhaled nitric oxide (FENO) is a noninvasive, simple, well-tolerated, and reproducible marker of airway inflammation. Asthmatic children with normal respiratory function could be affected by airway inflammation. The aim of this study was to assess the correlation between FENO and bronchial hyperesponsiveness (BHR) to methacholine, and between FENO and lung function in atopic children with intermittent asthma.

METHODS

Thirty-seven children (21 male), aged 7.2-14.4 years (median: 10.9 years), suffering from mild intermittent atopic asthma with a physician-diagnosed history of wheezing and/or chest tightness were studied. None had taken anti-asthmatic therapy for at least three months before the study. No child had symptoms of respiratory tract infection in the month before the study. All subjects underwent FENO measurement, pulmonary function testing and the methacholine provocation tests.

RESULTS

The mean percentages of FEV1 and FEF25-27 were 91.9+/-10.5 and 88.3+/-11.8, respectively. The mean FENO was 62.2+/-39.2 ppb and PC20 methacholine was 0.93 mg/ml+/-0.54. Significant correlations were identified between FENO and FEV1 (p<0.0059, r=0.468) and between FENO and FEF25-75 (p<0.0098, r=0.439). There was no correlation between FENO and logPC20 (p=0.14).

CONCLUSIONS

A single FENO measurement is probably of scarce prognostic and predictive value and it is not surprising to find discordance with BHR. We suggest that FENO measurement could represent a good marker of airway inflammation also in naïve atopic children with intermittent asthma. Repeated measurements over time are probably necessary to understand better the clinical implications of the data obtained in this study.

Exhaled nitric oxide continues to reflect airway hyperresponsiveness and disease activity in inhaled corticosteroid-treated adult asthmatic patients

OBJECTIVE

Exhaled nitric oxide (eNO) has been used as a surrogate of airway inflammation in mild asthma. However, whether eNO levels reflect disease activity in symptomatic asthmatics receiving moderate doses of inhaled corticosteroid (ICS) is more uncertain.

METHODOLOGY

To examine the relationship between eNO levels, sputum and blood eosinophils (SpE and PbE), PD(20) methacholine as a marker of airway hyperresponsiveness (AHR) and clinical status in 28 ICS-treated asthmatic subjects with persistent asthma compared to that in 25 symptomatic asthmatics managed with beta2-agonists alone.

RESULTS

As expected, eNO levels were normalized in ICS-treated subjects and significantly elevated in the beta2-agonist only group (P < 0.001). SpE, PbE and PD20M did not differ between asthmatic groups but FEV1 was significantly worse in ICS-treated subjects (P < 0.01). Exhaled NO levels correlated with PbE within both asthmatic groups (P < 0.005), but with SpE only in ICS-untreated subjects (r(s) = 0.6, P < 0.05). In contrast, PD20M was negatively correlated with eNO and PbE in ICS-treated subjects only (r(s) = - 0.4, r(s) = - 0.4, respectively, P < 0.05). SpE and PbE were strongly correlated in both asthmatic groups (r(s) = 0.8, r(s) = 0.7, respectively, P < 0.005). Exhaled NO levels, SpE and PbE were all positively associated with increased nocturnal awakenings ( P < 0.05) in ICS-treated subjects, but not in ICS-untreated subjects.

CONCLUSIONS

In ICS-treated asthma, eNO reflects clinical activity, PbE and AHR but not eosinophilic airway inflammation. Exhaled NO levels are quantitatively and relationally different in asthmatic subjects treated with ICS and continue to have potential for use as a surrogate of asthma pathophysiology in this group.

Assessment of inhaled BDP-dose dependency of exhaled nitric oxide and local and serum eosinophilic markers in steroids-naive nonatopic asthmatics

The aim of the present study was to assess the dose-dependency from inhaled steroids of changes of airways inflammation [eosinophils count and eosinophil cationic protein (ECP)] measures in induced sputum and in serum, as well as that of exhaled nitric oxide. Twenty steroid-naive patients with nonatopic asthma of mild to moderate degree [forced expiratory volume in 1 s (FEV1) = 70% of predicted] and with negative response to the standard tests for allergy were selected; after a 1-week run-in period they were randomized to receive a 12-week treatment period of inhaled beclomethasone dipropionate dry powder given with the Pulvinal inhaler (Clenil P, Chiesi Farmaceutici S.p.A., Parma, Italy) in two different dose regimens, 400 microg bid (high dose) or 200 microg bid (low dose), over a double blind, parallel groups design. The following outcome measures were assessed in baseline and after 1, 6 and 12 weeks of treatment: FEV1 (l), eosinophils count in sputum (%), is ECP (microg/l), serum eosinophils count (%), serum ECP (microg/l) and exhaled NO (ppb). The results showed that all the considered parameters improved in both groups: the increase over baseline of FEV1 and the decrease of NO were significant at any time in the high-dose group and only at week 12 in the low-dose group (NS between groups), whereas the markers of eosinophilic activity showed more consistent reductions in the high-dose than in the low-dose group when measured in induced sputum (P < 0.05 between groups after 6 and 12 weeks for eosinophils count and after 12 weeks for ECP). Decreases over baseline of markers measured in serum were more rapid in the high-dose group, without differences between groups. A marked trend towards a negative correlation was found between FEV1 and ECP, (r = -0.72, P < 0.05), between FEV1 and eosinophils in sputum (r = -0.31, NS) and between FEV1 and exhaled NO (r = -0.38, NS), all of them only in the high-dose group. The results of the study demonstrate that changes of levels of eosinophilic activity in the airways are dependent from the daily dose of inhaled steroids when measured in induced sputum and that the local assessment can therefore represent a practical and noninvasive method to monitor the extent of airways inflammation.

Comparison of cadmium and enzyme-catalyzed nitrate reduction for determination of NO2-/NO3- in breath condensate

BACKGROUND

Analysis of NO2-/NO3- in expired breath condensate (EBC) has been proposed as a marker of inflammation in various lung diseases.

METHODS

NO2- and total NO3-/NO2- concentrations were determined in EBC collected from healthy and asthmatic subjects. The NO3- was first reduced to NO2-, and total NO2- was detected by colorimetric Griess reaction. Two methods of NO3- reduction were compared. To reduce NO3-, cadmium (600 microl EBC-macromethod) and enzyme-NADPH-nitrate reductase (60 microl EBC-micromethod) were used.

RESULTS

Macromethod: Mean NO2- concentrations in EBC were 1.64 +/- 0.24 micromol/l in healthy subjects and 0.42 +/- 0.17 micromol/l in asthmatic patients. Mean total NO2-/NO3- levels were 3.64 +/- 0.43 micromol/l in healthy subjects and 3.27 +/- 0.34 micromol/l in asthmatic. Micromethod: NO2- level: 1.69 +/- 0.23 micromol/l in healthy subjects and 0.53 +/- 0.21 micromol/l in asthmatics. Total NO2-/NO3- levels: 3.56 +/- 0.37 micromol/l in healthy subjects and 3.57 +/- 1.17 micromol/l in asthmatics. Variability index was 27% and 6% for macro- and micromethod, respectively. Recovery of NO3- added to EBC was 100% for enzymatic and almost 88% for cadmium reduction. There was no correlation between total NO2-/NO3- levels determined by macro- and micromethod.

CONCLUSIONS

We recommend enzymatic reduction as a better method for NO3- determination in EBC.

Measurement of airway inflammation in asthma

Chronic airway inflammation is considered responsible for symptoms and disorders of airway function associated with asthma. This process is the target of anti-inflammatory therapy, so a number of standardized, noninvasive techniques have been developed to assess it. More recent approaches include the measurement of exhaled gases and nonvolatile substances in breath condensate. Results from studies using a wide variety of inflammatory markers have shown group differences between patients with asthma and healthy control subjects, but evidence for the diagnostic use of these markers in individual patients is scarce. Similarly, despite many studies demonstrating some correlation between markers of airway inflammation and a measure of disease control, none has yet convincingly shown a place for the use of these markers in an individual with corticosteroid-treated asthma. However, application of these markers continues to further our understanding of the disease process and provides the potential for more appropriate, customized therapy.

Exhaled monoxides as a pulmonary function test: use of exhaled nitric oxide and carbon monoxide

Although there has been tremendous improvement in the technologic ability to measure exhaled gases and monitor biologic processes in the lung, it has not yet found a clinical role outside the research laboratory. Common themes seem to be significant overlap in the amount of exhaled gases in clinically distinct populations, confounding variables such as infection, smoking, and environmental exposure, and lack of consistent change with disease management. If these tests are ever to be used by the general pulmonologist, consistent links between the measurements and the response to disease modification will need to be demonstrated at the very least and, ideally, the clinician would like to see improved outcomes when these noninvasive tests are employed regularly.