Extended NO analysis in asthma

Longitudinal hierarchical Bayesian models of covariate effects on airway and alveolar nitric oxide

Biomarkers such as exhaled nitric oxide (FeNO), a marker of airway inflammation, have applications in the study of chronic respiratory disease where longitudinal studies of within-participant changes in the biomarker are particularly relevant. A cutting-edge approach to assessing FeNO, called multiple flow FeNO, repeatedly assesses FeNO across a range of expiratory flow rates at a single visit and combines these data with a deterministic model of lower respiratory tract NO to estimate parameters quantifying airway wall and alveolar NO sources. Previous methodological work for multiple flow FeNO has focused on methods for data from a single participant or from cross-sectional studies. Performance of existing ad hoc two-stage methods for longitudinal multiple flow FeNO in cohort or panel studies has not been evaluated. In this paper, we present a novel longitudinal extension to a unified hierarchical Bayesian (L_U_HB) model relating longitudinally assessed multiple flow FeNO to covariates. In several simulation study scenarios, we compare the L_U_HB method to other unified and two-stage frequentist methods. In general, L_U_HB produced unbiased estimates, had good power, and its performance was not sensitive to the magnitude of the association with a covariate and correlations between NO parameters. In an application relating height to longitudinal multiple flow FeNO in schoolchildren without asthma, unified analysis methods estimated positive, statistically significant associations of height with airway and alveolar NO concentrations and negative associations with airway wall diffusivity while estimates from two-stage methods were smaller in magnitude and sometimes non-significant.

Improved prediction of asthma exacerbations by measuring distal airway inflammation

Introduction

Partitioning parameters measured from exhaled nitric oxide, such as the alveolar concentration of nitric oxide (CalvNO), may provide better predictors of future asthma exacerbation than exhaled nitric oxide fraction at an expiratory flow rate of 50 mL·s−1 (FENO50). We aimed to determine whether any partitioned nitric oxide parameters were more closely associated than FENO50 with subsequent asthma exacerbations.

Methods

68 asthmatic children (mean±sd age 9.0±2.4 years) were followed prospectively (134 visits) and exacerbations were recorded. Childhood Asthma Control Test (cACT), spirometry, FENO50, CalvNO, bronchial flux of nitric oxide (JawNO), transfer factor of nitric oxide (DawNO) and airway wall concentration of nitric oxide (CawNO) were measured.

Results

No exacerbation was recorded in 99 visits (Group 1) and an exacerbation was recorded in 35 visits (Group 2). The median (range) FENO50, JawNO, CalvNO, DawNO and CawNO of Group 1 versus Group 2: 12.7 (4–209) versus 13.5 (3.8–149.9) ppb, 715 (10–12 799) versus 438 (40–7457) pL·s−1, 3.4 (0.2–10.8) versus 5.2 (1.7–23.6) ppb, 38.3 (0.2–113.3) versus 38 (1.3–144.5) pL·s−1·ppb−1 and 26.8 (4.1–2163) versus 29.9 (5.5–3054) ppb, respectively. Other than for CalvNO (p<0.001), there was no difference between the two groups. CalvNO >7 ppb predicted asthma exacerbation with specificity 90.9% and positive likelihood ratio (LR) 3.1. Conversely, CalvNO <4 ppb excluded an exacerbation with sensitivity 71.4% and negative LR 0.48. An increase of CalvNO by 0.5 ppb between visits could also predict an exacerbation with sensitivity 92%, specificity 92%, positive LR 11.8 and negative LR 0.08.

Conclusions

Assessment of CalvNO improved prediction of subsequent exacerbation, highlighting the importance of distal inflammation in asthma outcomes in children.

Small airway function in Finnish COVID-19 survivors

Follow-up studies of COVID-19 patients have found lung function impairment up to six months after initial infection, but small airway function has not previously been studied. Patients (n = 20) hospitalised for a severe SARS-CoV-2 infection underwent spirometry, impulse oscillometry, and multiple measurements of alveolar nitric oxide three to six months after acute infection. None of the patients had small airway obstruction, nor increased nitric oxide concentration in the alveolar level. None of the patients had a reduced FEV₁/FVC or significant bronchodilator responses in IOS or spirometry. In conclusion, we found no evidence of inflammation or dysfunction in the small airways.

Hierarchical Bayesian estimation of covariate effects on airway and alveolar nitric oxide

Exhaled breath biomarkers are an important emerging field. The fractional concentration of exhaled nitric oxide (FeNO) is a marker of airway inflammation with clinical and epidemiological applications (e.g., air pollution health effects studies). Systems of differential equations describe FeNO—measured non-invasively at the mouth—as a function of exhalation flow rate and parameters representing airway and alveolar sources of NO in the airway. Traditionally, NO parameters have been estimated separately for each study participant (Stage I) and then related to covariates (Stage II). Statistical properties of these two-step approaches have not been investigated. In simulation studies, we evaluated finite sample properties of existing two-step methods as well as a novel Unified Hierarchical Bayesian (U-HB) model. The U-HB is a one-step estimation method developed with the goal of properly propagating uncertainty as well as increasing power and reducing type I error for estimating associations of covariates with NO parameters. We demonstrated the U-HB method in an analysis of data from the southern California Children’s Health Study relating traffic-related air pollution exposure to airway and alveolar airway inflammation.

Clinical Utility of Central and Peripheral Airway Nitric Oxide in Aging Patients with Stable and Acute Exacerbated Chronic Obstructive Pulmonary Disease

Purpose

Exhaled nitric oxide has been used as a marker of airway inflammation. The NO concentration in the central and peripheral airway/alveolar can be measured by a slow and fast exhalation flow rate to evaluate inflammation in different divisions within the respiratory tract. We hypothesized that FeNO₂₀₀ (exhaled NO at a flow rate of 200mL/s) could be used as an evaluation tool for peripheral airway/alveolar inflammation and corticosteroid therapy in chronic obstructive pulmonary disease (COPD) patients.

Methods

We recruited 171 subjects into the study: 73 healthy controls, 59 stable COPD patients, and 39 acute exacerbations of COPD (AECOPD) patients. Exhaled nitric oxide (FeNO₅₀ (exhaled NO at a flow rate of 50mL/s)), FeNO₂₀₀ and CaNO (peripheral concentration of NO/alveolar NO) and clinical variables including pulmonary function, COPD Assessment Test (CAT), C-reactive protein concentration (CRP) and circulating eosinophil count were measured among the recruited participants. FeNO_50, FeNO₂₀₀ and CaNO were repeatedly evaluated in 39 AECOPD patients after corticosteroid treatment.

Results

FeNO₂₀₀ was significantly higher in stable COPD and AECOPD patients than in healthy controls. Nevertheless, CaNO could not differentiate COPD from healthy controls. No correlation was found between circulating eosinophil counts or FEV1 and exhaled nitric oxide (FeNO_50, FeNO₂₀₀, CaNO) in COPD patients. For AECOPD patients, 64% of patients had eosinophil counts >100 cells/µL; 59% of patients had FeNO₂₀₀ >10 ppb; only 31% of patients had FeNO₅₀ > 25 ppb. Among AECOPD patients, the high FeNO₅₀ and FeNO₂₀₀ groups’ levels were significantly lower than their baseline levels, and significant improvements in CAT were seen in the two groups after corticosteroid treatment. These implied a good corticosteroid response in AECOPD patients with FeNO₂₀₀>10ppb.

Conclusion

FeNO₂₀₀ is a straightforward and feasible method to evaluate the peripheral NO concentration in COPD. FeNO200 can be a type 2 inflammation biomarker and a useful tool for predicting corticosteroid therapy in COPD.

Usefulness of extended nitric oxide analysis in children with allergic rhinitis

OBJECTIVE

Evaluation of airway inflammation and dysfunction is important in management of allergic rhinitis (AR) since AR is a risk factor for developing asthma. Theoretical nonlinear modeling of exhaled nitric oxide (NO) has revealed extended flow-independent NO parameters that could explain where or how NO metabolism was altered. We aimed to evaluate the association between extended NO parameters and bronchial hyperresponsiveness (BHR) in children with AR.

METHODS

Exhaled NO was measured in 74 children with AR on the same day they underwent the provocholine challenge test (PCT). Extended NO was measured in three different exhaled flow rates (30, 100, 200 mL/s) and calculated using the Högman-Meriläinen model. We compared the extended NO parameters including bronchial NO (JawNO), airway tissue NO (CawNO), alveolar tissue NO (CaNO), and diffusing capacity of NO (DawNO) between AR with and without BHR groups, and analyzed the correlation between extended NO parameters and the response-dose ratio (RDR) of the PCT. We additionally evaluated 49 respiratory healthy controls.

RESULTS

Among the 74 children with AR, nine showed BHR. JawNO increased more in children with AR than the control group. In children with AR, JawNO was higher in the AR with BHR than without BHR group, and was correlated positively with log RDR (r = 0.373, p = .001).

CONCLUSIONS

Extended NO analysis including JawNO can be a useful tool for assessing BHR in AR.

Onset of action of inhaled glucocorticoids on bronchial and alveolar nitric oxide output

Fractional exhaled nitric oxide (F_ENO) is a marker of airway inflammation. Measuring F_ENO at multiple flow rates enables calculation of NO parameters: bronchial NO output (J _awNO), bronchial wall (C _awNO) and alveolar (C _ANO) NO concentrations, and bronchial diffusion factor of NO (D _awNO). F_ENO is known to rapidly reduce after the commencement of inhaled corticosteroid (ICS) treatment. However, little is known on the effect of ICS on the other NO parameters. We assessed (1) the onset of action of ICS treatment on the NO parameters and (2) whether the changes in bronchial NO output are due to changes in bronchial wall NO concentration or diffusion factor. F_ENO and other NO parameters were measured at baseline and after 1, 3 and 7 d of treatment with inhaled fluticasone propionate 250 μg b.i.d. in 23 allergic children with a history of asthma-like symptoms. There was a decrease in J _awNO (from 680 (244/1791) (median (1st/3rd quartile)) to 357 (165/753) pl s^-1, p < 0.001) and F_ENO₅₀( from 13.8 (7.5/35) to 8.3 (5.36/17.0) ppb, p < 0.001) in 3 d from the first dose of ICS. Also, C _awNO seemed to reduce after 3 d (from 171 (89/328) to 79 (54/157) ppb, p = 0.041), while D _awNO remained unchanged. Furthermore, C _ANO reduced during the 7 d treatment (from 3.0 (2.0/5.0) to 2.3 (1.9/2.6) ppb, p = 0.004). ICS treatment reduced F_ENO₅₀ and J _awNO rapidly and the decline was caused by decreased bronchial wall NO concentration while bronchial NO diffusion factor remained unchanged. These findings suggest that C _awNO could be a more specific marker of airway inflammation and treatment response than J _awNO or F_ENO₅₀, which are both determined also by D _awNO that seems to be resistant to the treatment with ICS.

Accurate real-time FENO expirograms using complementary optical sensors

The fraction of exhaled nitric oxide (F_ENO) is an important biomarker for the diagnosis and management of asthma and other pulmonary diseases associated with airway inflammation. In this study we report on a novel method for accurate, highly time-resolved, real time detection of F_ENO at the mouth. The experimental arrangement is based on a combination of optical sensors for the determination of the temporal profile of exhaled NO and CO₂ concentrations. Breath CO₂ and exhalation flow are measured at the mouth using diode laser absorption spectroscopy (at 2 μm) and differential pressure sensing, respectively. NO is determined in a sidestream configuration using a quantum cascade laser based, cavity-enhanced absorption cell (at 5.2 μm) which simultaneously measures sidestream CO₂. The at-mouth and sidestream CO₂ measurements are used to enable the deconvolution of the sidestream NO measurement back to the at-mouth location. All measurements have a time resolution of 0.1 s, limited by the requirement of a reasonable limit of detection for the NO measurement, which on this timescale is 4.7 ppb (2 σ). Using this methodology, NO expirograms (F_ENOgrams) were measured and compared for eight healthy volunteers. The F_ENOgrams appear to differ qualitatively between individuals and the hope is that the dynamic information encoded in these F_ENOgrams will provide valuable additional insight into the location of the inflammation in the airways and potentially predict a response to therapy. A validation of the measurements at low-time resolution is provided by checking that results from previous studies that used a two-compartment model of NO production can be reproduced using our technology.

Impact of different fixed flow sampling protocols on flow-independent exhaled nitric oxide parameter estimates using the Bayesian dynamic two-compartment model

Exhaled nitric oxide (FeNO) is an established respiratory biomarker with clinical applications in the diagnosis and management of asthma. Because FeNO depends strongly on the flow (exhalation) rate, early protocols specified that measurements should be taken when subjects exhaled at a fixed rate of 50 ml/s. Subsequently, multiple flow (or "extended") protocols were introduced which measure FeNO across a range of fixed flow rates, allowing estimation of parameters including Caw NO and CA NO which partition the physiological sources of NO into proximal airway wall tissue and distal alveolar regions (respectively). A recently developed dynamic model of FeNO uses flow-concentration data from the entire exhalation maneuver rather than plateau means, permitting estimation of Caw NO and CA NO from a wide variety of protocols. In this paper, we use a simulation study to compare Caw NO and CA NO estimation from a variety of fixed flow protocols, including: single maneuvers (30, 50,100, or 300 ml/s) and three established multiple maneuver protocols. We quantify the improved precision with multiple maneuvers and the importance of low flow maneuvers in estimating Caw NO. We conclude by applying the dynamic model to FeNO data from 100 participants of the Southern California Children's Health Study, establishing the feasibility of using the dynamic method to reanalyze archived online FeNO data and extract new information on Caw NO and CA NO in situations where these estimates would have been impossible to obtain using traditional steady-state two compartment model estimation methods.

Flow-independent nitric oxide parameters in asthma: a systematic review and meta-analysis

INTRODUCTION

Fractional exhaled nitric oxide (F_ENO) has been proposed as a non-invasive marker of inflammation in the lungs. Measuring F_ENO at several flow rates enables the calculation of flow independent NO-parameters that describe the NO-exchange dynamics of the lungs more precisely. The purpose of this study was to compare the NO-parameters between asthmatics and healthy subjects in a systematic review and meta-analysis.

METHODS

A systematic search was performed in Ovid Medline, Web of Science, Scopus and Cochrane Library databases. All studies with asthmatic and healthy control groups with at least one NO-parameter calculated were included.

RESULTS

From 1137 identified studies, 33 were included in the meta-analysis. All NO-parameters (alveolar NO concentration (C_ANO), bronchial flux of NO (J_awNO), bronchial mucosal NO concentration (C_awNO) and bronchial wall NO diffusion capacity (D_awNO)) were found increased in glucocorticoid-treated and glucocorticoid-naïve asthma. J_awNO and C_ANO were most notably increased in both study groups. Elevation of D_awNO and C_awNO seemed less prominent in both asthma groups.

DISCUSSION

We found that all the NO-parameters are elevated in asthma as compared to healthy subjects. However, results were highly heterogenous and the evidence on C_awNO and D_awNO is still quite feeble due to only few studies reporting them. To gain more knowledge on the NO-parameters in asthma, nonlinear methods and standardized study protocols should be used in future studies.

Influence of mouthwashes on extended exhaled nitric oxide (FENO) analysis

Fractional exhaled nitric oxide (F_ENO) is used to assess eosinophilic inflammation of the airways. F_ENO values are influenced by the expiratory flow rate and orally produced NO. We measured F_ENO at four different expiratory flow levels after two different mouthwashes: tap water and carbonated water. Further, we compared the alveolar NO concentration (C_ANO), maximum airway NO flux (J'_awNO) and airway NO diffusion (D_awNO) after these two mouthwashes. F_ENO was measured in 30 volunteers (healthy or asthmatic) with a chemiluminescence NO-analyser at flow rates of 30, 50, 100 and 300 mL/s. A mouthwash was performed before the measurement at every flow rate. The carbonated water mouthwash significantly reduced F_ENO compared to the tap water mouthwash at all expiratory flows: 50 mL/s (p < .001), 30 mL/s (p = .001), 100 mL/s (p < .001) and 300 mL/s (p = .004). J'_awNO was also significantly reduced (p = .017), however, there were no significant differences in C_ANO and D_awNO. In conclusion, a carbonated water mouthwash can significantly reduce oropharyngeal NO compared to a tap water mouthwash at expiratory flows of 30-300 mL/s without affecting the C_ANO and D_awNO. Therefore, mouthwashes need to be taken into account when comparing F_ENO results.

Bayesian estimation of physiological parameters governing a dynamic two-compartment model of exhaled nitric oxide

The fractional concentration of nitric oxide in exhaled breath (fe_NO) is a biomarker of airway inflammation with applications in clinical asthma management and environmental epidemiology. fe_NO concentration depends on the expiratory flow rate. Standard fe_NO is assessed at 50 mL/sec, but “extended NO analysis” uses fe_NO measured at multiple different flow rates to estimate parameters quantifying proximal and distal sources of NO in the lower respiratory tract. Most approaches to modeling multiple flow fe_NO assume the concentration of NO throughout the airway has achieved a “steady‐state.” In practice, this assumption demands that subjects maintain sustained flow rate exhalations, during which both fe_NO and expiratory flow rate must remain constant, and the fe_NO maneuver is summarized by the average fe_NO concentration and average flow during a small interval. In this work, we drop the steady‐state assumption in the classic two‐compartment model. Instead, we have developed a new parameter estimation approach based on measuring and adjusting for a continuously varying flow rate over the entire fe_NO maneuver. We have developed a Bayesian inference framework for the parameters of the partial differential equation underlying this model. Based on multiple flow fe_NO data from the Southern California Children's Health Study, we use observed and simulated NO concentrations to demonstrate that our approach has reasonable computation time and is consistent with existing steady‐state approaches, while our inferences consistently offer greater precision than current methods.

Altered levels of exhaled nitric oxide in rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is an autoimmune disorder characterized by bone and joint destruction, but other organ systems can also be involved. Recent studies have suggested that the disease may start in the lungs. Exhaled nitric oxide (F_ENO) is a marker of inflammation. The aims of the study were to compare the NO parameters between subjects with RA and healthy control subjects, and to examine whether the NO parameters correlated with lung function and disease activity in the subjects with RA.

METHODS

Subjects with RA (n = 35) were recruited during their regular outpatient visits to the rheumatology department. The nitric oxide (NO) parameters: alveolar NO concentration (C_ANO), airway compartment diffusing capacity of NO (D_awNO), and tissue concentration of NO in the airway wall (C_awNO), were algorithmically estimated. Healthy subjects (n = 35) matched by age, gender and height were used as controls. Data are given in median, (quartile 25, 75). Wilcoxon Matched Pairs test was used for group comparisons. Mann-Whitney U test was used to make comparisons between any two groups and for pairwise comparisons. Correlations were tested with Spearman rank order correlation.

RESULTS

C_ANO was significantly lower in the RA subjects compared with healthy subjects; 1.1 (0.5, 1.8) ppb versus 2.4 (2.0, 3.0) ppb, (p < 0.001). C_awNO was significantly lower in the RA subjects with 51 (22, 87) ppb versus 120 (76, 162) ppb in the control group. D_awNO was significantly higher at 25 (15, 36) mL/s in the RA group versus the control group's 7.7 (5.3, 10.7) mL/s.

CONCLUSIONS

There are significant differences between subjects with RA and matched healthy control subjects regarding the exhaled NO parameters. It is unclear if this can be explained by the pathogenesis of RA, consequences of long-term disease, and/or due to drug treatment.

Association of extended nitric oxide parameters with bronchial hyperresponsiveness and bronchodilator response in children with asthma

Theoretical non-linear modeling of exhaled nitric oxide has revealed extended flow-independent parameters that could explain where or how nitric oxide is produced in the lung and transferred to the airway gas stream. We aimed to evaluate the associations of bronchial hyperresponsiveness and bronchodilator response with extended flow-independent nitric oxide parameters. Nitric oxide (30, 50, 100, 200 ml s^-1) was measured in 432 children with asthma on the same day with either a methacholine challenge test (n = 156) or spirometry with bronchodilator (n = 276; 96 previously diagnosed with asthma and treated with inhaled corticosteroid, 37 with acute exacerbation treated with systemic corticosteroid). We additionally included 107 healthy controls for evaluation of the suitability of the non-linear model of exhaled nitric oxide. In asthmatic children, the response-dose ratio of the methacholine challenge test was correlated positively with bronchial nitric oxide (JawNO) and airway tissue nitric oxide (CawNO) (r = 0.367 and r = 0.299, respectively; both p < 0.001), while the change in forced expiratory volume in 1 s, representing bronchodilator response, was associated positively with only JawNO (r = 0. 216, p < 0.001). On multiple regression, JawNO, CawNO, and the diffusing capacity of NO (DawNO) were significantly associated with the response-dose ratio. JawNO was significantly associated with change in forced expiratory volume in children with stable asthma but not those with acute exacerbation. Our findings suggest that bronchial hyperresponsiveness is associated with CawNO while factors other than airway tissue inflammation could affect bronchodilator response in children with mild asthma. Systemic corticosteroid use during asthma exacerbation could affect the association of bronchodilator response with extended nitric oxide parameters.

Inducible nitric oxide synthase expression is increased in the alveolar compartment of asthmatic patients

INTRODUCTION

Increased exhaled nitric oxide (NO) levels in asthma are suggested to be through inducible NO synthase (iNOS). The aim of this study was to investigate the expression of iNOS in bronchoalveolar lavage (BAL) cells and tissue from central and peripheral airways and compare it with the exhaled bronchial and alveolar NO levels in patients with asthma vs a control group.

METHODS

Thirty-two patients with asthma (defined as controlled or uncontrolled according to Asthma Control Test score cut-off: 20) and eight healthy controls were included. Exhaled NO was measured, and alveolar concentration and bronchial flux were calculated. iNOS was measured in central and peripheral lung biopsies, as well as BAL cells. Bronchoalveolar lavage macrophages were stimulated in vitro, and iNOS expression and NO production were investigated.

RESULTS

Expression of iNOS was increased in central airway tissue and the alveolar compartment in uncontrolled as compared to controlled asthmatics and healthy controls. There were no differences, however, in iNOS mRNA levels in total BAL cells in uncontrolled as compared to controlled asthma. Bronchoalveolar lavage cell mRNA levels of iNOS or iNOS expression in central and alveolar tissue did not relate to alveolar NO, nor to bronchial flux of NO. In vitro stimulation with leukotriene D₄ increased iNOS mRNA levels and NO production in cultured BAL macrophages.

CONCLUSION

The levels of both bronchial and alveolar iNOS are increased in uncontrolled as compared to controlled asthma. However, levels of iNOS in BAL macrophages were not reflected by alveolar NO. Both central and distal iNOS levels may reflect responsiveness to steroid treatment.

Optimal flow rate sampling designs for studies with extended exhaled nitric oxide analysis

INTRODUCTION

The fractional concentration of exhaled nitric oxide (FeNO) is a biomarker of airway inflammation. Repeat FeNO maneuvers at multiple fixed exhalation flow rates (extended NO analysis) can be used to estimate parameters quantifying proximal and distal sources of NO in mathematical models of lower respiratory tract NO. A growing number of studies use extended NO analysis, but there is no official standard flow rate sampling protocol. In this paper, we provide information for study planning by deriving theoretically optimal flow rate sampling designs.

METHODS

First, we reviewed previously published designs. Then, under a nonlinear regression framework for estimating NO parameters in the steady-state two compartment model of NO, we identified unbiased optimal four flow rate designs (within the range of 10-400 ml s^-1) using theoretical derivations and simulation studies. Optimality criteria included NO parameter standard errors (SEs). A simulation study was used to estimate sample sizes required to detect associations with NO parameters estimated from studies with different designs.

RESULTS

Most designs (77%) were unbiased. NO parameter SEs were smaller for designs with: more target flows, more replicate maneuvers per target flow, and a larger range of target flows. High flows were most important for estimating alveolar NO concentration, while low flows were most important for the proximal NO parameters. The Southern California Children's Health Study design (30, 50, 100 and 300 ml s^-1) had ≥1.8 fold larger SEs and required 1.1-3.2 fold more subjects to detect the association of a determinant with each NO parameter as compared to an optimal design of 10, 50, 100 and 400 ml s^-1.

CONCLUSIONS

There is a class of reasonable flow rate sampling designs with good theoretical performance. In practice, designs should be selected to balance the tradeoffs between optimality and feasibility of the flow range and total number of maneuvers.

Online Measurement of Exhaled NO Concentration and Its Production Sites by Fast Non-equilibrium Dilution Ion Mobility Spectrometry

Exhaled nitric oxide (NO) is one of the most promising breath markers for respiratory diseases. Its profile for exhalation and the respiratory NO production sites can provide useful information for medical disease diagnosis and therapeutic procedures. However, the high-level moisture in exhaled gas always leads to the poor selectivity and sensitivity for ion spectrometric techniques. Herein, a method based on fast non-equilibrium dilution ion mobility spectrometry (NED-IMS) was firstly proposed to directly monitor the exhaled NO profile on line. The moisture interference was eliminated by turbulently diluting the original moisture to 21% of the original with the drift gas and dilution gas. Weak enhancement was observed for humid NO response and its limit of detection at 100% relative humidity was down to 0.58 ppb. The NO concentrations at multiple exhalation flow rates were measured, while its respiratory production sites were determined by using two-compartment model (2CM) and Högman and Meriläinen algorithm (HMA). Last but not the least, the NO production sites were analyzed hourly to tentatively investigate the daily physiological process of NO. The results demonstrated the capacity of NED-IMS in the real-time analysis of exhaled NO and its production sites for clinical diagnosis and assessment.

Spirometry effects on conventional and multiple flow exhaled nitric oxide in children

OBJECTIVE

Clinical and research settings often require sequencing multiple respiratory tests in a brief visit. Guidelines recommend measuring the concentration of exhaled nitric oxide (FeNO) before spirometry, but evidence for a spirometry carryover effect on FeNO is mixed. Only one study has investigated spirometry carryover effects on multiple flow FeNO analysis. The objective of this study was to evaluate evidence for carryover effects of recent spirometry on three exhaled NO summary measures: FeNO at 50 ml/s, airway wall NO flux [J'awNO] and alveolar NO concentration [CANO] in a population-based sample of schoolchildren.

METHODS

Participants were 1146 children (191 with asthma), ages 12-15, from the Southern California Children's Health Study who performed spirometry and multiple flow FeNO on the same day. Approximately, half the children performed spirometry first. Multiple linear regression was used to estimate differences in exhaled NO summary measures associated with recent spirometry testing, adjusting for potential confounders.

RESULTS

In the population-based sample, we found no evidence of spirometry carryover effects. However, for children with asthma, there was a suggestion that exhaled NO summary measures assessed ≤6 min after spirometry were lower (FeNO: 25.8% lower, 95% CI: -6.2%, 48.2%; J'awNO: 15.1% lower 95% CI: -26.5%, 43.0%; and CANO 0.43 parts per billion lower, 95% CI: -0.12, 0.98).

CONCLUSIONS

In clinical settings, it is prudent to assess multiple flow FeNO before spirometry. In studies of healthy subjects, it may not be necessary to assess FeNO first.

A practical approach to the theoretical models to calculate NO parameters of the respiratory system

Expired nitric oxide (NO) is used as a biomarker in different respiratory diseases. The recommended flow rate of 50 mL s⁻¹ (F(E)NO₀.₀₅) does not reveal from where in the lung NO production originated. Theoretical models of NO transfer from the respiratory system, linear or nonlinear approaches, have therefore been developed and applied. These models can estimate NO from distal lung (alveolar NO) and airways (bronchial flux). The aim of this study was to show the limitation in exhaled flow rate for the theoretical models of NO production in the respiratory system, linear and nonlinear models. Subjects (n = 32) exhaled at eight different flow rates between 10-350 mL s⁻¹ for the theoretical protocols. Additional subjects (n = 32) exhaled at tree flow rates (20, 100 and 350 mL s⁻¹) for the clinical protocol. When alveolar NO is calculated using high flow rates with the linear model, correction for axial back diffusion becomes negligible, -0.04 ppb and bronchial flux enhanced by 1.27. With Högman and Meriläinen algorithm (nonlinear model) the corrections factors can be understood to be embedded, and the flow rates to be used are ≤20, 100 and ≥350 mL s⁻¹. Applying these flow rates in a clinical setting any F(E)NO can be calculated necessitating fewer exhalations. Hence, measured F(E)NO₀.₀₅ 12.9 (7.2-18.7) ppb and calculated 12.9 (6.8-18.7) ppb. In conclusion, the only possibility to avoid inconsistencies between research groups is to use the measured NO values as such in modelling, and apply tight quality control to accuracies in both NO concentration and exhaled flow measurements.

Estimation of parameters in the two-compartment model for exhaled nitric oxide

The fractional concentration of exhaled nitric oxide (FeNO) is a biomarker of airway inflammation that is being increasingly considered in clinical, occupational, and epidemiological applications ranging from asthma management to the detection of air pollution health effects. FeNO depends strongly on exhalation flow rate. This dependency has allowed for the development of mathematical models whose parameters quantify airway and alveolar compartment contributions to FeNO. Numerous methods have been proposed to estimate these parameters using FeNO measured at multiple flow rates. These methods—which allow for non-invasive assessment of localized airway inflammation—have the potential to provide important insights on inflammatory mechanisms. However, different estimation methods produce different results and a serious barrier to progress in this field is the lack of a single recommended method. With the goal of resolving this methodological problem, we have developed a unifying framework in which to present a comprehensive set of existing and novel statistical methods for estimating parameters in the simple two-compartment model. We compared statistical properties of the estimators in simulation studies and investigated model fit and parameter estimate sensitivity across methods using data from 1507 schoolchildren from the Southern California Children's Health Study, one of the largest multiple flow FeNO studies to date. We recommend a novel nonlinear least squares model with natural log transformation on both sides that produced estimators with good properties, satisfied model assumptions, and fit the Children's Health Study data well.

Multiple-flow exhaled nitric oxide, allergy, and asthma in a population of older children

"Extended" (multiple-flow) measurements of exhaled nitric oxide (FeNO) potentially can distinguish proximal and distal airway inflammation, but have not been evaluated previously in large populations. We performed extended NO testing within a longitudinal study of a school-based population, to relate bronchial flux (J'awNO) and peripheral NO concentration (CalvNO) estimates with respiratory health status determined from questionnaires. We measured FeNO at 30, 50, 100, and 300 ml/sec in 1,640 subjects aged 12-15 from eight communities, then estimated J'awNO and CalvNO from linear and nonlinear regressions of NO output versus flow. J'awNO, as well as FeNO at all flows, showed influences of asthma, allergy, Asian or African ancestry, age, and height (positive), and of weight (negative), generally corroborating past findings. By contrast, CalvNO results were inconsistent across different extended NO regression models, and appeared more sensitive to small measurement artifacts.

CONCLUSIONS

Extended NO testing is feasible in field surveys of young populations. In interpreting results, size, age, and ethnicity require attention, as well as instrumental and environmental artifacts. J'awNO and conventional FeNO provide similar information, probably reflecting proximal airway inflammation. CalvNO may give additional information relevant to peripheral airway, alveolar, or systemic pathology. However, it needs additional research, including testing of populations with independently verifiable peripheral or systemic pathology, to optimize measurement technique and interpretation.

Guidance for a personal target value of F(E)NO in allergic asthma: case report and theoretical example

In clinically stable asthma the exhaled NO values (F(E)NO) are generally higher than in control subjects. Therefore, reference values are of limited importance in clinical practice. This is demonstrated in this case report, but it is also shown that NO parameters from non-linear modelling do have a clinical value. A subject with asthma was treated with inhaled corticosteroids for 1 week. The non-linear NO model was used to measure the response to treatment. The NO parameters from subjects with atopic rhinitis and asthma were fed into a computer program to generate theoretical F(E)NO₀.₀₅ values, i.e. target values. There was a dramatic decrease in F(E)NO₀.₀₅ due to treatment, from 82 to 34 ppb, but it remained higher than in healthy controls. This is due to the elevated diffusion rate of NO, unchanged by treatment. When the NO parameters are known, a personal best value of F(E)NO₀.₀₅ (fractional concentration of exhaled NO in the gas phase, 0.05 L/s) can be calculated, which can be the target value when only F(E)NO₀.₀₅ can be monitored. In conclusion, reference values for NO parameters are shown to be clinically useful. It is essential that every patient receives his/her target value of F(E)NO₀.₀₅, when only a single NO measurement is available. In our opinion, this is the reason why there are few successful studies of trying to target the NO value with inhaled corticosteroids.

Methods of NO detection in exhaled breath

There is still an unexplored potential for exhaled nitric oxide (NO) in many clinical applications. This study presents an overview of the currently available methods for monitoring NO in exhaled breath and the use of the modelling of NO production and transport in the lung in clinical practice. Three technologies are described, namely chemiluminescence, electrochemical sensing and laser-based detection with their advantages and limitations. Comparisons are made in terms of sensitivity, time response, size, costs and suitability for clinical purposes. The importance of the flow rate for NO sampling is discussed from the perspective of the recent recommendations for standardized procedures for online and offline NO measurement. The measurement of NO at one flow rate, such as 50 ml s(-1), can neither determine the alveolar site/peripheral contribution nor quantify the difference in NO diffusion from the airways walls. The use of NO modelling (linear or non-linear approach) can solve this problem and provide useful information about the source of NO. This is of great value in diagnostic procedures of respiratory diseases and in treatment with anti-inflammatory drugs.

Comparison of online single-breath vs. online multiple-breath exhaled nitric oxide in school-age children

INTRODUCTION

Standards for online multiple-breath (mb) exhaled nitric oxide (eNO) measurements and studies comparing them with online single-breath (sb) eNO measurements are lacking, although eNOmb requires less cooperation in children at school age or younger.

METHODS

Online eNOmb and eNOsb were measured in 99 healthy children and (in order to observe higher values) in 21 children with suspected asthma at a median age of 6.1 and 11.7 y, respectively. For eNOmb, we aimed for 20 tidal breathing maneuvers; eNOsb was measured according to standards. The two techniques were compared by standard methods after computing NO output or extrapolating eNOmb to the standard flow of 50 ml/s (eNOmb(50)).

RESULTS

Measurements were acceptable in 82 (eNOmb) and 81 (eNOsb) children. Paired data were available for 65 children. On a log-log scale, eNOmb(50) (geometric mean ± SD 13.1 ± 15.5 parts per billion, ppb) was correlated with eNOsb (12.5 ± 15.8 ppb), with r(2) = 0.87. The mean difference between eNOsb and eNOmb(50) was -0.7 ppb, with limits of agreement (LOAs) of 4.0 and -5.3 ppb.

DISCUSSION

Despite its correlation with eNOsb, the LOA range hampers eNOmb use in research, where exact values across the whole range are warranted. However, eNOmb might be an alternative tool especially at preschool age, when cooperation during measurements is crucial.

Exhaled nitric oxide monitoring by quantum cascade laser: comparison with chemiluminescent and electrochemical sensors

Fractional exhaled nitric oxide (F(E)NO) is considered an indicator in the diagnostics and management of asthma. In this study we present a laser-based sensor for measuring F(E)NO. It consists of a quantum cascade laser (QCL) combined with a multi-pass cell and wavelength modulation spectroscopy for the detection of NO at the sub-part-per-billion by volume (ppbv, 110(-9)) level. The characteristics and diagnostic performance of the sensor were assessed. A detection limit of 0.5 ppbv was demonstrated with a relatively simple design. The QCL-based sensor was compared with two market sensors, a chemiluminescent analyzer (NOA 280, Sievers) and a portable hand-held electrochemical analyzer (MINO, Aerocrine AB, Sweden). F(E)NO from 20 children diagnosed with asthma and treated with inhaled corticosteroids were measured. Data were found to be clinically acceptable within 1.1 ppbv between the QCL-based sensor and chemiluminescent sensor and within 1.7 ppbv when compared to the electrochemical sensor. The QCL-based sensor was tested on healthy subjects at various expiratory flow rates for both online and offline sampling procedures. The extended NO parameters, i.e. the alveolar region, airway wall, diffusing capacity, and flux were calculated and showed a good agreement with the previously reported values.

Added value with extended NO analysis in atopy and asthma

INTRODUCTION

Assessments of the usefulness of exhaled nitric oxide (NO) in the treatment of asthma have given conflicting results. It is not always obvious if atopic status has been tested in these evaluations.

OBJECTIVES

The aim of the study is to use extended NO analysis to characterize subjects from a random sample populations with focus on rhinitis and asthma.

METHODS

Data were extracted from the European Community Respiratory Health Survey II. A subgroup from the Uppsala site that had had their NO measured at multiple flow rates was included (n = 284). The nonlinear model for NO parameters was used. Atopy was defined as having a titre against at least one of the tested allergens ≥0·35 kU l(-1) . Bronchial responsiveness was assessed by methacholine challenge.

RESULTS

Subjects with non-atopic rhinitis or non-atopic asthma could not be separated from healthy subjects regarding NO parameters. There was a gradual increase with atopy in airway diffusion rate (D(aw) NO); healthy subject 8·0 (7·3, 8·8), healthy atopic 8·8 (6·7, 11·5), atopic rhinitis 10·6 (9·0, 12·4) and atopic asthma 11·2 (9·9, 28·3) ml s(-1) [geometrical mean (CI(95%) )]. There was a correlation between bronchial responsiveness and D(aw) NO in atopic rhinitis (r = -0·41, P<0·01), and bronchial responsiveness and airway wall content of NO (C(aw) NO) in atopic asthma (r = -0·56, P<0·001).

CONCLUSION

It is of importance to characterize atopic status when evaluating the association between NO and asthma. Our results indicate that the use of extended NO analysis, with particular attention to D(aw) NO and C(aw) NO, may be useful in monitoring treatment for rhinitis and asthma.

Multicomponent Breath Analysis With Infrared Absorption Using Room-Temperature Quantum Cascade Lasers

Breath analysis is a powerful noninvasive technique for the diagnosis and monitoring of respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD). Nitric oxide (NO) and carbon monoxide (CO) are markers of airway inflammation and can indicate the extent of respiratory diseases. We have developed a compact fast response laser system for analysis of multiple gases by infrared absorption. The instrument uses room temperature quantum cascade lasers to simultaneously measure NO, CO, carbon dioxide (CO(2)) and nitrous oxide (N(2)O) in exhaled breath. Four breath flow rates are employed to explore their exchange dynamics in the lungs and airways. We obtain 1-s detection precisions of 0.5-0.8 parts-per-billion (ppb) for NO, CO, and N(2)O with an instrument response time of less than 1 s. The breath analysis system has been demonstrated in a preliminary study of volunteers. It is currently deployed in a trial clinical study.

Extended exhaled nitric oxide analysis in field surveys of schoolchildren: a pilot test

Extended exhaled nitric oxide (eNO) analysis can distinguish proximal and distal airway contributions to FeNO. Thus, it has the potential to detect effects of different environmental influences, allergic phenotypes, and genetic variants on proximal and distal airways. However, its feasibility in field surveys has not been demonstrated, and models for estimating compartmental NO contributions have not been standardized. In this study we verified that extended NO tests can be performed by children in schools, and assessed different analytical models to estimate bronchial flux and alveolar NO concentration. We tested students at a middle school, using EcoMedics NO analyzers with ambient NO scrubbers, at flows of 50 (conventional), 30, 100, and 300 ml/sec, with 2-3 trials at each flow. Data from 65 children were analyzed by two linear and four nonlinear published models, plus a new empirical nonlinear model. Bronchial NO flux estimates from different models differed in magnitude but were strongly correlated (r >or= 0.95), and increased in subjects with allergic asthma. Alveolar concentration estimates differed among models and did not consistently show the same effects of allergy or asthma. A novel index of nonlinear behavior of NO output versus flow was significantly related to asthma status, and not strongly correlated with bronchial flux or alveolar concentration. Field-based extended NO testing of children can yield useful information about NO in different regions of the respiratory tract that is not obtainable from conventional FeNO. Extended NO analysis holds promise for investigating environmental and genetic determinants of regional airway inflammatory states.

Nitric oxide in exhaled and aspirated nasal air as an objective measure of human response to indoor air pollution

The concentration of nitric oxide (NO) in exhaled and aspirated nasal air was used to objectively assess human response to indoor air pollutants in a climate chamber exposure experiment. The concentration of NO was measured before exposure, after 2, and 4.5 h of exposure, using a chemiluminescence NO analyzer. Sixteen healthy female subjects were exposed to two indoor air pollutants and to a clean reference condition for 4.5 h. Subjective assessments of the environment were obtained by questionnaires. After exposure (4.5 h) to the two polluted conditions a small increase in NO concentration in exhaled air was observed. After exposure to the reference condition the mean NO concentration was significantly reduced compared to pre-exposure. Together these changes resulted in significant differences in exhaled NO between exposure to reference and polluted conditions. NO in nasal air was not affected by the exposures. The results may indicate an association between polluted indoor air and subclinical inflammation.

PRACTICAL IMPLICATIONS

Measurement of nitric oxide in exhaled air is a possible objective marker of subclinical inflammation in healthy adults.

Basal and induced NO formation in the pharyngo-oral tract influences estimates of alveolar NO levels

The present study analyzed how models currently used to distinguish alveolar from bronchial contribution to exhaled nitric oxide (NO) are affected by manipulation of NO formation in the pharyngo-oral tract. Exhaled NO was measured at multiple flow rates in 15 healthy subjects in two experiments: 1) measurements at baseline and 5 min after chlorhexidine (CHX) mouthwash and 2) measurements at baseline, 60 min after ingestion of 10 mg NaNO3/kg body wt, and 5 min after CHX mouthwash. Alveolar NO concentration (CalvNO) and bronchial flux (J′awNO) were calculated by using the slope-intercept model with or without adjustment for trumpet shape of airways and axial diffusion (TMAD). Salivary nitrate and nitrite were measured in the second experiment. CalvNO [median (range)] was reduced from 1.16 ppb (0.77, 1.96) at baseline to 0.84 ppb (0.57, 1.48) 5 min after CHX mouthwash ( P < 0.001). The TMAD-adjusted CalvNO value after CHX mouthwash was 0.50 ppb (0, 0.85). The nitrate load increased J′awNO from 32.2 nl/min (12.2, 60.3) to 57.1 nl/min (22.0, 119) in all subjects and CalvNO from 1.47 ppb (0.73, 1.95) to 1.87 ppb (10.85, 7.20) in subjects with high nitrate turnover (>10-fold increase of salivary nitrite after nitrate load). CHX mouthwash reduced CalvNO levels to 1.15 ppb (0.72, 2.07) in these subjects with high nitrate turnover. All these results remained consistent after TMAD adjustment. We conclude that estimated alveolar NO concentration is affected by pharyngo-oral tract production of NO in healthy subjects, with a decrease after CHX mouthwash. Moreover, unknown ingestion of dietary nitrate could significantly increase estimated alveolar NO in subjects with high nitrate turnover, and this might be falsely interpreted as a sign of peripheral inflammation. These findings were robust for TMAD.

Extended NO analysis in a healthy subgroup of a random sample from a Swedish population

INTRODUCTION

There is an interest in modelling exhaled nitric oxide (NO). Studies have shown that flow-independent NO parameters i.e. NO of the alveolar region (C(A)NO), airway wall (C(aw)NO), diffusing capacity (D(aw)NO) and flux (J(aw)NO), are altered in several disease states such as asthma, cystic fibrosis, alveolitis and chronic obsmuctive pulmonary disease (COPD). However, values from a healthy population are missing.

OBJECTIVES

To calculate NO parameters in a healthy population by collecting NO values at different exhalation flow rates.

METHODS

A random sample from the ECRHS II study was investigated. Among the 281 subjects that had performed a bronchial hyperreactivity (BHR)-test, FEV(1.0), IgE and NO-analyses 89 were found to be healthy.

RESULTS

There were no differences in F(E)NO(0.05) or NO parameters between men and women. There were weak correlations between height and both F(E)NO(0.05) (r = 0.23, P = 0.03) and C(aw)NO (r = 0.22, P = 0.04). There was also a correlation between age and C(A)NO (r = 0.28, P = 0.007). When controlled for gender, this correlation was more powerful in women (r = 0.51, P = 0.001) but did not remain for male subjects.

CONCLUSION

Extended NO analysis is a simple non-invasive tool that gives by far more information than F(E)NO(0.05). Based on our results, we suggest that the values for healthy subjects should be considered to fall between the following ranges: F(E)NO(0.05), 10-30 ppb; C(aw)NO, 50-250 ppb; D(aw)NO, 5-15 ml s(-1); J(aw)NO, 0.8-1.6 nl s(-1); and C(A)NO, 0-4 ppb. Values outside these intervals indicate the need for further investigation to exclude a state of disease.