Single-exhalation profiles of NO and CO2 in humans: effect of dynamically changing flow rate

Simultaneous real-time detection of fractional exhaled nitric oxide and end-tidal carbon dioxide by quantum cascade laser absorption spectroscopy

The simultaneous detection of fractional exhaled nitric oxide (FeNO) and end-tidal carbon dioxide (ETCO2) is of great importance for the distinguishing and diagnosis of asthma and chronic obstructive pulmonary disease (COPD), providing more comprehensive information on respiratory disorders. This work demonstrates a simultaneous ETCO2 and FeNO detection system based on quantum cascade laser absorption spectroscopy (QCLAS) technology was presented. The system employs wavelength modulation spectroscopy (WMS) technology and the Herriott multi-pass cell, achieving a detection limit of 2.82 ppb for nitric oxide (NO) and 0.05 % for carbon dioxide (CO2). Real-time exhalation measurements were performed on volunteers with varying ETCO2 and FeNO levels, and the results of the test can accurately distinguish whether the corresponding volunteer was healthy, had asthma or COPD. The effect of exhalation flow rate on the concentration of the two gases was explored. A range of expiratory flow rates were tested in the flow rate interval from 1 to 4 L/min, and there was always an inverse relationship between expiratory flow rate and FeNO concentration, but flow rate changes did not affect ETCO2 concentration. The results indicate that this detection system can simultaneously and effectively measure ETCO2 and FeNO concentrations in real-time.

Changes in lung mechanics and ventilation-perfusion match: comparison of pulmonary air- and thromboembolism in rats

BACKGROUND

Pulmonary air embolism (AE) and thromboembolism lead to severe ventilation-perfusion defects. The spatial distribution of pulmonary perfusion dysfunctions differs substantially in the two pulmonary embolism pathologies, and the effects on respiratory mechanics, gas exchange, and ventilation-perfusion match have not been compared within a study. Therefore, we compared changes in indices reflecting airway and respiratory tissue mechanics, gas exchange, and capnography when pulmonary embolism was induced by venous injection of air as a model of gas embolism or by clamping the main pulmonary artery to mimic severe thromboembolism.

METHODS

Anesthetized and mechanically ventilated rats (n = 9) were measured under baseline conditions after inducing pulmonary AE by injecting 0.1 mL air into the femoral vein and after occluding the left pulmonary artery (LPAO). Changes in mechanical parameters were assessed by forced oscillations to measure airway resistance, lung tissue damping, and elastance. The arterial partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2) were determined by blood gas analyses. Gas exchange indices were also assessed by measuring end-tidal CO2 concentration (ETCO2), shape factors, and dead space parameters by volumetric capnography.

RESULTS

In the presence of a uniform decrease in ETCO2 in the two embolism models, marked elevations in the bronchial tone and compromised lung tissue mechanics were noted after LPAO, whereas AE did not affect lung mechanics. Conversely, only AE deteriorated PaO2, and PaCO2, while LPAO did not affect these outcomes. Neither AE nor LPAO caused changes in the anatomical or physiological dead space, while both embolism models resulted in elevated alveolar dead space indices incorporating intrapulmonary shunting.

CONCLUSIONS

Our findings indicate that severe focal hypocapnia following LPAO triggers bronchoconstriction redirecting airflow to well-perfused lung areas, thereby maintaining normal oxygenation, and the CO2 elimination ability of the lungs. However, hypocapnia in diffuse pulmonary perfusion after AE may not reach the threshold level to induce lung mechanical changes; thus, the compensatory mechanisms to match ventilation to perfusion are activated less effectively.

Raman Spectroscopy for Urea Breath Test

The urea breath test is a non-invasive diagnostic method for Helicobacter pylori infections, which relies on the change in the proportion of ¹³CO₂ in exhaled air. Nondispersive infrared sensors are commonly used for the urea breath test in laboratory equipment, but Raman spectroscopy demonstrated potential for more accurate measurements. The accuracy of the Helicobacter pylori detection via the urea breath test using ¹³CO₂ as a biomarker is affected by measurement errors, including equipment error and δ¹³C measurement uncertainty. We present a Raman scattering-based gas analyzer capable of δ¹³C measurements in exhaled air. The technical details of the various measurement conditions have been discussed. Standard gas samples were measured. ¹²CO₂ and ¹³CO₂ calibration coefficients were determined. The Raman spectrum of the exhaled air was measured and the δ¹³C change (in the process of the urea breath test) was calculated. The total error measured was 6% and does not exceed the limit of 10% that was analytically calculated.

Numerical Simulation of the Novel Coronavirus Spread in Commercial Aircraft Cabin

Passengers carrying the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a commercial aircraft cabin may infect other passengers and the cabin crew. In this study, a cabin model of the seven-row Airbus A320 aircraft is constructed and meshed for simulating the SARS-CoV-2 spread in the cabin with a virus carrier using the Computational Fluid Dynamics (CFD) modeling tool. The passengers’ infection risk is also quantified with the susceptible exposure index (SEI) method. The results show that the virus spreads to the ceiling of the cabin within 50 s of the virus carrier’s normal breathing. Coughing makes the virus spread to the front three rows with a higher mass fraction. While the high mass fraction areas always stay on the same side of the aisle as the virus carrier, the adjacent passengers and the passengers in the back two rows are affected more than the others when the virus carrier breathes normally. Spread patterns under the carrier’s two breath conditions, normal breath and cough, were numerically simulated.

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.

Dopamine Reverses Lung Function Deterioration After Cardiopulmonary Bypass Without Affecting Gas Exchange

OBJECTIVE

To investigate the effects of dopamine on the adverse pulmonary changes after cardiopulmonary bypass.

DESIGN

A prospective, nonrandomized clinical investigation.

SETTING

A university hospital.

PARTICIPANTS

One hundred fifty-seven patients who underwent elective cardiac surgery that required cardiopulmonary bypass.

INTERVENTIONS

Fifty-two patients were administered intravenous infusion of dopamine (3 µg/kg/min) for five minutes after weaning from cardiopulmonary bypass; no intervention was applied in the other 105 patients.

MEASUREMENTS AND MAIN RESULTS

Measurements were performed under general anesthesia and mechanical ventilation before cardiopulmonary bypass, after cardiopulmonary bypass, and after the intervention. In each protocol stage, forced oscillatory lung impedance was measured to assess airway and tissue mechanical changes. Mainstream capnography was performed to assess ventilation- and/or perfusion-matching by calculating the normalized phase-3 slopes of the time and volumetric capnograms and the physiologic deadspace. Arterial and central venous blood samples were analyzed to characterize lung oxygenation and intrapulmonary shunt. After cardiopulmonary bypass, dopamineinduced marked improvements in airway resistance and tissue damping, with relatively small decreases in lung tissue elastance. These changes were associated with decreases in the normalized phase-3 slopes of the time and volumetric capnograms. The inotrope had no effect on physiologic deadspace, intrapulmonary shunt, or lung oxygenation.

CONCLUSION

Dopamine reversed the complex detrimental lung mechanical changes induced by cardiopulmonary bypass and alleviated ventilation heterogeneities without affecting the physiologic deadspace or intrapulmonary shunt. Therefore, dopamine has a potential benefit on the gas exchange abnormalities after weaning from cardiopulmonary bypass.

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.

Precision Antifungal Treatment Significantly Extends Voice Prosthesis Lifespan in Patients Following Total Laryngectomy

Indwelling silicone valves called voice prostheses (VPs) are the gold standard for speech rehabilitation in patients with laryngeal cancer following total laryngectomy. Reported VP lifespans amongst these patients are highly variable but when devices fail patients experience loss of voice and an increase risk of chest infection. Early failure of VP is a current clinical concern that is associated with regular hospital visits, reduced quality of life and associated medical cost. Poly-microbial biofilms comprised of both bacterial and fungal microorganisms readily colonize VPs and are linked to loss of device performance and its early failure in addition to providing a reservoir for potential infection. Our detailed analysis of poly-microbial biofilm composition on 159 early failing VPs from 48 total laryngectomy patients confirmed Candida albicans as the predominant fungal species and Staphylococcus aureus as the most common bacterial colonizer within our patient cohort. Using a combination of microbiological analysis, patient data and a high-throughput antifungal test assay mimicking in vivo conditions we established an evidence based precision antifungal treatment approach to VP management. Our approach has allowed us to implement a personalized VP management pathway, which increases device in situ lifespan by an average of 270%. Our study represents a significant step forward in both our understanding of the cause of VP failure and a new effective treatment pathway that offers tangible benefit to patients.

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.

Effects of Oral Supplementation With Nitrate-Rich Beetroot Juice in Patients With Pulmonary Arterial Hypertension-Results From BEET-PAH, an Exploratory Randomized, Double-Blind, Placebo-Controlled, Crossover Study

BACKGROUND

The nitrate-nitrite-nitric oxide (NO) pathway may represent a potential therapeutic target in patients with pulmonary arterial hypertension (PAH). We explored the effects of dietary nitrate supplementation, with the use of nitrate-rich beetroot juice (BRJ), in patients with PAH.

METHODS AND RESULTS

We prospectively studied 15 patients with PAH in an exploratory randomized, double-blind, placebo-controlled, crossover trial. The patients received nitrate-rich beetroot juice (∼16 mmol nitrate per day) and placebo in 2 treatment periods of 7 days each. The assessments included; exhaled NO and NO flow-independent parameters (alveolar NO and bronchial NO flux), plasma and salivary nitrate and nitrite, biomarkers and metabolites of the NO-system, N-terminal pro-B-type natriuretic peptide, echocardiography, ergospirometry, diffusing capacity of the lung for carbon monoxide, and the 6-minute walk test. Compared with placebo ingestion of BRJ resulted in increases in; fractional exhaled NO at all flow-rates, alveolar NO concentrations and bronchial NO flux, and plasma and salivary levels of nitrate and nitrite. Plasma ornithine levels decreased and indices of relative arginine availability increased after BRJ compared to placebo. A decrease in breathing frequency was observed during ergospirometry after BRJ. A tendency for an improvement in right ventricular function was observed after ingestion of BRJ. In addition a tendency for an increase in the peak power output to peak oxygen consumption ratio (W peak/VO₂ peak) was observed, which became significant in patients reaching an increase of plasma nitrite >30% (responders).

CONCLUSIONS

BRJ administered for 1 week increases pulmonary NO production and the relative arginine bioavailability in patients with PAH, compared with placebo. An increase in the W peak/VO₂ peak ratio was observed after BRJ ingestion in plasma nitrite responders. These findings indicate that supplementation with inorganic nitrate increase NO synthase-independent NO production from the nitrate-nitrite-NO pathway.

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.

Carbon dioxide accumulation inside vehicles: The effect of ventilation and driving conditions

Limiting the air exchange of passenger vehicles by closing windows and recirculating cabin air (RC) restricts the influx of roadway pollutants and reduces in-vehicle particulate concentrations. However, the carbon dioxide (CO₂) exhaled by the occupants can accumulate under these conditions to reach high concentrations. We characterized the factors (ventilation setting, vehicle age, speed, cabin volume, trip duration, and number of occupants) that allow CO₂ accumulation to reach concentration thresholds found in other studies to produce cognitive or physiological effects of concern such as fatigue or difficulty concentrating. Ventilation setting was the primary determinant of CO₂ accumulation; only the RC setting (and not outside-air intake) ever allows CO₂ accumulations to exceed thresholds of concern. Longer trips with multiple occupants are a particular concern. Even so, under RC setting, a 2500ppm threshold-the threshold consistently linked to detrimental cognitive effects-would not be exceeded for most one- or even two-occupant average-duration commutes (twenty-six minutes in the U.S.). For multiple passenger commutes and/or longer trips, RC ventilation should be periodically interrupted or partially mixed with outside air to keep CO₂ concentrations below 2500ppm.

Experimental analysis of the air velocity and contaminant dispersion of human exhalation flows

Human exhalation flow is a potential source of pathogens that can constitute a cross-infection risk to people in indoor environments. Thus, it is important to investigate the characteristics of this flow, its development, area of influence, and the diffusion of the exhaled contaminants. This paper uses phase-averaged particle image velocimetry together with a tracer gas (CO₂ ) to study two different exhalation flows over time: the exhalation of an average male (test M) and an average female (test F), using a life-sized thermal manikin in a supine position. The exhalation jets generated for both tests are similar in terms of symmetrical geometry, vorticity values, jet opening angles, and velocity and concentration decays. However, there is a difference in the penetration length of the two flows throughout the whole exhalation process. There is also a time difference in reaching maximum velocity between the two tests. It is also possible to see that the tracer gas dispersion depends on the momentum of the jet so the test with the highest velocity decay shows the lowest concentration decay. All these results are of interest to better understand cross-infection risk.

Short-range airborne transmission of expiratory droplets between two people

The occurrence of close proximity infection for many respiratory diseases is often cited as evidence of large droplet and/or close contact transmission. We explored interpersonal exposure of exhaled droplets and droplet nuclei of two standing thermal manikins as affected by distance, humidity, ventilation, and breathing mode. Under the specific set of conditions studied, we found a substantial increase in airborne exposure to droplet nuclei exhaled by the source manikin when a susceptible manikin is within about 1.5 m of the source manikin, referred to as the proximity effect. The threshold distance of about 1.5 m distinguishes the two basic transmission processes of droplets and droplet nuclei, that is, short-range modes and the long-range airborne route. The short-range modes include both the conventional large droplet route and the newly defined short-range airborne transmission. We thus reveal that transmission occurring in close proximity to the source patient includes both droplet-borne (large droplet) and short-range airborne routes, in addition to the direct deposition of large droplets on other body surfaces. The mechanisms of the droplet-borne and short-range airborne routes are different; their effective control methods also differ. Neither the current droplet precautions nor dilution ventilation prevents short-range airborne transmission, so new control methods are needed.

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.

Exercise and NO production: relevance and implications in the cardiopulmonary system

This article reviews the existing knowledge about the effects of physical exercise on nitric oxide (NO) production in the cardiopulmonary system. The authors review the sources of NO in the cardiopulmonary system; involvement of three forms of NO synthases (eNOS, nNOS, and iNOS) in exercise physiology; exercise-induced modulation of NO and/or NOS in physiological and pathophysiological conditions in human subjects and animal models in the absence and presence of pharmacological modulators; and significance of exercise-induced NO production in health and disease. The authors suggest that physical activity significantly improves functioning of the cardiovascular system through an increase in NO bioavailability, potentiation of antioxidant defense, and decrease in the expression of reactive oxygen species-forming enzymes. Regular physical exercises are considered a useful approach to treat cardiovascular diseases. Future studies should focus on detailed identification of (i) the exercise-mediated mechanisms of NO exchange; (ii) optimal exercise approaches to improve cardiovascular function in health and disease; and (iii) physical effort thresholds.

Contribution of exhaled nitric oxide measurement in airway inflammation assessment in asthma. A position paper from the French Speaking Respiratory Society

Nitric oxide (NO) is both a gas and a ubiquitous inter- and intracellular messenger with numerous physiological functions. As its synthesis is markedly increased during inflammatory processes, NO can be used as a surrogate marker of acute and/or chronic inflammation. It is possible to quantify fractional concentration of NO in exhaled breath (FENO) to detect airway inflammation, and thus improve the diagnosis of asthma by better characterizing asthmatic patients with eosinophilic bronchial inflammation, and eventually improve the management of targeted asthmatic patients. FENO measurement can therefore be viewed as a new, reproducible and easy to perform pulmonary function test. Measuring FENO is the only non-invasive pulmonary function test allowing (1) detecting, (2) quantifying and (3) monitoring changes in inflammatory processes during the course of various respiratory disorders, including corticosensitive asthma.

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.

Airway gas exchange and exhaled biomarkers

During inspiration and expiration, gases traverse the conducting airways as they are transported between the environment and the alveolar region of the lungs. The term "conducting" airways is used broadly as the airway tree is thought largely to provide a conduit for the respiratory gases, oxygen and carbon dioxide. However, despite a significantly smaller surface area, and thicker barrier separating the gas phase from the blood when compared to the alveolar region, the airway tree can participate in gas exchange under special conditions such as high water solubility, high chemical reactivity, or production of the gas within the airway wall tissue. While these conditions do not apply to the respiratory gases, other gases demonstrate substantial exchange of the airways and are of particular importance to the inflammatory response of the lungs, the medical-legal field, occupational health, metabolic disorders, or protection of the delicate alveolar membrane. Given the significant structural differences between the airways and the alveolar region, the physical determinants that control airway gas exchange are unique and require different models (both experimental and mathematical) to explore. Our improved physiological understanding of airway gas exchange combined with improved analytical methods to detect trace compounds in the exhaled breath provides future opportunities to develop new exhaled biomarkers that are characteristic of pulmonary and systemic conditions.

Induced sputum, exhaled NO, and breath condensate in occupational medicine

OBJECTIVE

Studies of fractional exhaled NO (FeNO) or induced sputum are now well standardized and the exponential increase in publications about exhaled breath condensate reflects growing interest in a noninvasive diagnosis of pulmonary diseases in occupational medicine.

METHODS

This review describes current techniques (FeNO, induced sputum, and exhaled breath condensate) for the study of inflammation and oxidative stress biomarkers.

RESULTS

These biomarkers are FeNO, cytokines, H2O2, 8-isoprostane, malondialdehyde, and nitrogen oxides. These techniques also include the study of markers of the toxic burden in the lungs (heavy metals and mineral compounds) that are important in occupational health exposure assessment.

CONCLUSIONS

In occupational medicine, the study of both volatile and nonvolatile respiratory biomarkers can be useful in medical surveillance of exposed workers, the early identification of respiratory diseases, or the monitoring of their development.

Effects of respiratory mechanics on the capnogram phases: importance of dynamic compliance of the respiratory system

INTRODUCTION

The slope of phase III of the capnogram (SIII) relates to progressive emptying of the alveoli, a ventilation/perfusion mismatch, and ventilation inhomogeneity. S(III) depends not only on the airway geometry, but also on the dynamic respiratory compliance (Crs); this latter effect has not been evaluated. Accordingly, we established the value of SIII for monitoring airway resistance during mechanical ventilation.

METHODS

Sidestream capnography was performed during mechanical ventilation in patients undergoing elective cardiac surgery (n = 144). The airway resistance (Raw), total respiratory resistance and Crs displayed by the ventilator, the partial pressure of arterial oxygen (PaO2) and S(III) were measured in time domain (S(T-III)) and in a smaller cohort (n = 68) by volumetry (S(V-III)) with and without normalization to the average CO2 phase III concentration. Measurements were performed at positive end-expiratory pressure (PEEP) levels of 3, 6 and 9 cmH2O in patients with healthy lungs (Group HL), and in patients with respiratory symptoms involving low (Group LC), medium (Group MC) or high Crs (Group HC).

RESULTS

S(T-III) and S(V-III) exhibited similar PEEP dependencies and distribution between the protocol groups formed on the basis of Crs. A wide interindividual scatter was observed in the overall Raw-S(T-III) relationship, which was primarily affected by Crs. Decreases in Raw with increasing PEEP were reflected in sharp falls in S(III) in Group HC, and in moderate decreases in S(III) in Group MC, whereas S(T-III) was insensitive to changes in airway caliber in Groups LC and HL.

CONCLUSIONS

SIII assessed in the time domain and by volumetry provide meaningful information about alterations in airway caliber, but only within an individual patient. Although S(T-III) may be of value for bedside monitoring of the airway properties, its sensitivity depends on Crs. Thus, assessment of the capnogram shape should always be coupled with Crs when the airway resistance or oxygenation are evaluated.

Exhaled nitric oxide (FeNO) as a non-invasive marker of airway inflammation

Nitric oxide (NO), previously very famous for being an environmental pollutant in the field of pulmonary medicine, is now known as the smallest, lightest, and most famed molecule to act as a biological messenger. Furthermore, recent basic researches have revealed the production mechanisms and physiological functions of nitric oxide in the lung, and clinical researches have been clarifying its tight relation to airway inflammation in asthma. On the bases of this knowledge, fractional nitric oxide (FeNO) has now been introduced as one of the most practical tools for the diagnosis and management of bronchial asthma.

Update on exhaled nitric oxide in pulmonary disease

The ability to assess the inflammatory status of a patient's airway using a noninvasive method is the ideal situation for clinicians. Owing in part to the relationship between the levels of exhaled nitric oxide to inflammation and the ease of the technique, the measurement of the fraction of exhaled nitric oxide (F(E)NO) has achieved considerable attention, particularly with respect to asthma. A multitude of studies have shown that when measured in exhaled air, this unique molecule has the potential to have both diagnostic and therapeutic roles in the clinical setting for many pulmonary diseases. The incorporation of F(E)NO into asthma management and treatment algorithms may help shed further insight on the current control and future risk of patients. Research is ongoing to determine the biology and the benefits of the use of F(E)NO in respiratory conditions in addition to asthma. This review will briefly outline the pathophysiology of nitric oxide, the measurement of F(E)NO and the potential clinical uses of F(E)NO in asthma and a number of other respiratory diseases. Despite its promise, until further research is conducted, the use of F(E)NO cannot be recommended for routine clinical management of respiratory diseases at present, but should be considered as an adjuvant to help guide therapy in certain patients with asthma and in those with eosinophilic bronchitis.

Utility of two-compartment models of exhaled nitric oxide in patients with asthma

Two-compartment models provide more precise information about the contribution of the different portions of the airways to exhaled nitric oxide (NO). Airway wall concentration of NO (Caw,NO) and maximum flux of NO in the airways (J'aw,NO) reflect the tissue production rate of NO and they can be modified by corticosteroids. The airway wall diffusing capacity of NO (Daw,NO) depends on diverse physical and anatomical determinants of the airways, such as gas exchange surface area. Daw,NO can be modified by structural and physiological changes that are characteristic of airway remodeling, which take place over the long term. The alveolar concentration of NO (Calv,NO) represents the degree of small airway inflammation. The persistence of high Calv,NO in patients treated with inhaled corticosteroids could reflect the incapacity of these drugs to reach distal locations due to the heterogeneity of the acinar ventilation. In this review, we evaluate the parameters provided by the compartmentalized analysis of exhaled NO that could be useful in characterizing asthma patients.

Increased plasma and salivary nitrite and decreased bronchial contribution to exhaled NO in pulmonary arterial hypertension

BACKGROUND

Conflicting results on exhaled NO in pulmonary hypertension (PH) exist. Therefore, we analysed exhaled NO, as well as systemic and local nitrite, a possible alternative source of NO, in PH with regard to PH aetiology.

METHODS

Exhaled NO at multiple flow-rates, as well as plasma and salivary nitrite and nitrate, was measured in 22 patients with PH and 21 healthy controls. Alveolar NO (Calv(NO) ) and bronchial flux (J'aw(NO) ) were calculated using the slope-intercept model. Patients with PH were subdivided into pulmonary arterial hypertension (PAH) and PH WHO Groups II-IV, according to the WHO clinical classification of PH.

RESULTS

Exhaled NO was reduced at flow-rates in the range of 20-200 mL s(-1) in patients with PAH (n=13) vs. PH WHO Group II-IV (n=9) (P<0·05 all). Patients with PAH had higher Calv(NO) than healthy controls [2·61 (2·23, 3·36) vs. 1.97ppb (1·22, 2·49), P=0·03] and similar to PH WHO Group II-IV (P=0·51). Patients with PAH had lower J'aw(NO) than patients with PH WHO Group II-IV or healthy controls [430 (371, 702) vs. 807 (557, 993) or 731pLs(-1) (580, 818), P<0·05 both]. Subjects with PAH were characterized by higher levels of salivary and plasma nitrite than healthy controls (P<0·05 both).

CONCLUSIONS

Patients with PAH have lower bronchial NO flux compared to healthy controls and patients with PH WHO Group II-IV along with elevated salivary and plasma nitrite compared to controls. This implies reduced bronchial NO synthase-derived NO formation in PAH. Increased alveolar NO levels were found in subjects with PH compared to controls, especially in subjects with PAH. This may reflect NO diffusion disturbances in the alveoli.

Analysis of nitrogen oxides (NOx) in the exhaled breath condensate (EBC) of subjects with asthma as a complement to exhaled nitric oxide (FeNO) measurements: a cross-sectional study

Background

The study of pulmonary biomarkers with noninvasive methods, such as the analysis of exhaled breath condensate (EBC), provides a useful approach to the pathophysiology of asthma. Although many recent publications have applied such methods, numerous methodological pitfalls remain. The first stage of our study consisted of validating methods for the collection, storage and analysis of EBC; we next sought to clarify the utility of analysing nitrogen oxides (NOx) in the EBC of asthmatics, as a complement to measuring exhaled nitric oxide (FeNO).

Methods

This hospital-based cross-sectional study included 23 controls matched with 23 asthmatics. EBC and FeNO were performed and respiratory function measured. Intra-assay and intra-subject reproducibility were assessed for the analysis of NOx in the EBC of 10 healthy subjects.

Results

The intraclass correlation coefficient (ICC) was excellent for intra-assay reproducibility and was moderate for intra-subject reproducibility (Fermanian's classification). NOx was significantly higher in asthmatics (geometric mean [IQR] 14.4 μM [10.4 - 19.7] vs controls 9.9 μM [7.5 - 15.0]), as was FeNO (29.9 ppb [17.9 - 52.4] vs controls 9.6 ppb [8.4 - 14.2]). FeNO also increased significantly with asthma severity.

Conclusions

We validated the procedures for NOx analysis in EBC and confirmed the need for assays of other biomarkers to further our knowledge of the pathophysiologic processes of asthma and improve its treatment and control.

The increase in exhaled NO following allergen challenge is not associated with airway acidification

BACKGROUND

Exhaled nitric oxide (NO), commonly accepted marker of airways inflammation, may be generated both by specific enzymes, NO synthases, as well as by nonenzymatic reduction in its metabolites. During asthma exacerbations, owing to lower airways pH, it has been reported that nitrite reduction may contribute to the increase in exhaled NO. Allergen exposure, an important cause of asthma exacerbations, is also known to increase exhaled NO.

DESIGN

To investigate whether cat allergen exposure of cat-sensitized asthmatics leads to airway acidification, which could explain the expected increase in exhaled NO. Twelve nonsmoking, cat-sensitized patients (nine women) aged 33·5 (22-54) years with mild intermittent asthma performed a cat allergen challenge. Exhaled NO at 50-200 mL s(-1), nasal NO, exhaled breath condensate (EBC) pH, nitrite and nitrate were measured before, 8 and 24 h after allergen challenge.

RESULTS

A significant increase in FE(NO 50) was observed 24 h after allergen challenge compared to baseline: 110 ppb (34, 143) vs. 60 ppb (19, 122), P = 0·006. This was mainly explained by an increase in bronchial NO flux (P = 0·02), while no changes in EBC pH were observed (P = 0·35).

CONCLUSIONS

Allergen exposure is not associated with airways acidification, implying that the observed increase in exhaled NO is probably because of enzymatic NO production.

Exhaled breath condensate nitrates, but not nitrites or FENO, relate to asthma control

BACKGROUND

Asthma is a chronic respiratory disease, characterised by airways inflammation, obstruction and hyperresponsiveness. Asthma control is the goal of asthma treatment, but many patients have sub-optimal control. Exhaled NO and exhaled breath condensate (EBC) NO metabolites (nitrites and nitrates) measurements are non-invasive tools to assess airways inflammation. Our aim was to investigate the relationships between asthma control and the above-named biomarkers of airways inflammation.

METHODS

Thirty-nine non-smoking asthmatic patients (19 women) aged 50 (21-80) years performed measurements of exhaled NO (FENO), EBC nitrates, nitrites and pH, and answered Asthma Control Questionnaire (ACQ) and Asthma Control Test (ACT)-questionnaire.

RESULTS

The ACT and ACQ score were strongly interrelated (ρ = -0.84, p < 0.001). No relationships between ACT or ACQ score and FENO were found (p > 0.05). EBC nitrates were negatively related to ACT score (ρ = -0.34, p = 0.03) and positively related to ACQ score (ρ = 0.41, p = 0.001) while no relation of EBC nitrites to either ACQ or ACT score was found (p>0.05).

CONCLUSION

EBC nitrates were the only biomarker that was significantly related to asthma control. This suggests that nitrates, but not nitrites or FENO, reflect an aspect of airways inflammation that is closer related to asthma symptoms. Therefore there is a potential role for EBC nitrates in objective assessment of asthma control.

Exhaled nitric oxide in pulmonary diseases: a comprehensive review

The upregulation of nitric oxide (NO) by inflammatory cytokines and mediators in central and peripheral airway sites can be monitored easily in exhaled air. It is now possible to estimate the predominant site of increased fraction of exhaled NO (FeNO) and its potential pathologic and physiologic role in various pulmonary diseases. In asthma, increased FeNO reflects eosinophilic-mediated inflammatory pathways moderately well in central and/or peripheral airway sites and implies increased inhaled and systemic corticosteroid responsiveness. Recently, five randomized controlled algorithm asthma trials reported only equivocal benefits of adding measurements of FeNO to usual clinical guideline management including spirometry; however, significant design issues may exist. Overall, FeNO measurement at a single expiratory flow rate of 50 mL/s may be an important adjunct for diagnosis and management in selected cases of asthma. This may supplement standard clinical asthma care guidelines, including spirometry, providing a noninvasive window into predominantly large-airway-presumed eosinophilic inflammation. In COPD, large/central airway maximal NO flux and peripheral/small airway/alveolar NO concentration may be normal and the role of FeNO monitoring is less clear and therefore less established than in asthma. Furthermore, concurrent smoking reduces FeNO. Monitoring FeNO in pulmonary hypertension and cystic fibrosis has opened up a window to the role NO may play in their pathogenesis and possible clinical benefits in the management of these diseases.

Clinical patterns in asthma based on proximal and distal airway nitric oxide categories

BACKGROUND

The exhaled nitric oxide (eNO) signal is a marker of inflammation, and can be partitioned into proximal [J'awNO (nl/s), maximum airway flux] and distal contributions [CANO (ppb), distal airway/alveolar NO concentration]. We hypothesized that J'awNO and CANO are selectively elevated in asthmatics, permitting identification of four inflammatory categories with distinct clinical features.

METHODS

In 200 consecutive children with asthma, and 21 non-asthmatic, non-atopic controls, we measured baseline spirometry, bronchodilator response, asthma control and morbidity, atopic status, use of inhaled corticosteroids, and eNO at multiple flows (50, 100, and 200 ml/s) in a cross-sectional study design. A trumpet-shaped axial diffusion model of NO exchange was used to characterize J'awNO and CANO.

RESULTS

J'awNO was not correlated with CANO, and thus asthmatic subjects were grouped into four eNO categories based on upper limit thresholds of non-asthmatics for J'awNO (>or= 1.5 nl/s) and CANO (>or= 2.3 ppb): Type I (normal J'awNO and CANO), Type II (elevated J'awNO and normal CANO), Type III (elevated J'awNO and CANO) and Type IV (normal J'awNO and elevated CANO). The rate of inhaled corticosteroid use (lowest in Type III) and atopy (highest in Type II) varied significantly amongst the categories influencing J'awNO, but was not related to CANO, asthma control or morbidity. All categories demonstrated normal to near-normal baseline spirometry; however, only eNO categories with increased CANO (III and IV) had significantly worse asthma control and morbidity when compared to categories I and II.

CONCLUSIONS

J'awNO and CANO reveal inflammatory categories in children with asthma that have distinct clinical features including sensitivity to inhaled corticosteroids and atopy. Only categories with increase CANO were related to poor asthma control and morbidity independent of baseline spirometry, bronchodilator response, atopic status, or use of inhaled corticosteroids.

Impact of analysis interval on the multiple exhalation flow technique to partition exhaled nitric oxide

Exhaled nitric oxide (eNO) is elevated in asthmatics and is a purported marker of airway inflammation. By measuring eNO at multiple flows and applying models of eNO exchange dynamics, the signal can be partitioned into its proximal airway [J' aw NO (nl/sec)] and distal airway/alveolar contributions [CA(NO)(ppb)]. Several studies have demonstrated the potential significance of such an approach in children with asthma. However, techniques to partition eNO are variable, limiting comparisons among studies. The objective of this study is to examine the impact of the analysis interval (time or volume) on eNO plateau concentrations and the estimation of J' aw NO and CA(NO). In 30 children with mild to moderate asthma, spirometry and eNO at multiple flows (50, 100, and 200 ml/sec) were measured. The plateau concentration of eNO at each flow was determined using two different methods of analysis: (1) constant time interval and (2) constant volume interval. For both methods of analysis, a two-compartment model with axial diffusion was used to characterize J' aw NO and CA(NO). At a flow of 200 ml/sec, the time interval analysis predicts values for eNO that are smaller than the volume interval analysis. As a result, there are significant differences in CA(NO) between the methods of analysis (volume > time). When using the multiple flow technique to partition eNO, the method of analysis (constant time vs. constant volume interval) significantly affects the estimation of CA(NO), and thus potentially the assessment and interpretation of distal lung inflammation.

Comparative transcript profiling of Candida albicans and Candida dubliniensis identifies SFL2, a C. albicans gene required for virulence in a reconstituted epithelial infection model

Candida albicans and Candida dubliniensis are closely related species displaying differences in virulence and genome content, therefore providing potential opportunities to identify novel C. albicans virulence genes. C. albicans gene arrays were used for comparative analysis of global gene expression in the two species in reconstituted human oral epithelium (RHE). C. albicans (SC5314) showed upregulation of hypha-specific and virulence genes within 30 min postinoculation, coinciding with rapid induction of filamentation and increased RHE damage. C. dubliniensis (CD36) showed no detectable upregulation of hypha-specific genes, grew as yeast, and caused limited RHE damage. Several genes absent or highly divergent in C. dubliniensis were upregulated in C. albicans. One such gene, SFL2 (orf19.3969), encoding a putative heat shock factor, was deleted in C. albicans. DeltaDeltasfl2 cells failed to filament under a range of hypha-inducing conditions and exhibited greatly reduced RHE damage, reversed by reintroduction of SFL2 into the DeltaDeltasfl2 strain. Moreover, SFL2 overexpression in C. albicans triggered hyphal morphogenesis. Although SFL2 deletion had no apparent effect on host survival in the murine model of systemic infection, DeltaDeltasfl2 strain-infected kidney tissues contained only yeast cells. These results suggest a role for SFL2 in morphogenesis and an indirect role in C. albicans pathogenesis in epithelial tissues.

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.

The effect of posture-induced changes in peripheral nitric oxide uptake on exhaled nitric oxide

Airway and alveolar NO contributions to exhaled NO are being extracted from exhaled NO measurements performed at different flow rates. To test the robustness of this method and the validity of the underlying model, we deliberately induced a change in NO uptake in the peripheral lung compartment by changing body posture between supine and prone. In 10 normal subjects, we measured exhaled NO at target flows ranging from 50 to 350 ml/s in supine and prone postures. Using two common methods, bronchial NO production [Jaw(NO)] and alveolar NO concentration (FANO) were extracted from exhaled NO concentration vs. flow or flow−1 curves. There was no significant Jaw(NO) difference between prone and supine but a significant FANO decrease from prone to supine ranging from 23 to 33% depending on the method used. Total lung capacity was 7% smaller supine than prone ( P = 0.03). Besides this purely volumetric effect, which would tend to increase FANO from prone to supine, the observed degree of FANO decrease from prone to supine suggests a greater opposing effect that could be explained by the increased lung capillary blood volume (Vc) supine vs. prone ( P = 0.002) observed in another set of 11 normal subjects. Taken together with the relative changes of NO and CO transfer factors, this Vc change can be attributed mainly to pulmonary capillary recruitment from prone to supine. Realistic models for exhaled NO simulation should include the possibility that a portion of the pulmonary capillary bed is unavailable for NO uptake, with a maximum capacity of the pulmonary capillary bed in the supine posture.

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.

The effect of montelukast on exhaled nitric oxide of alveolar and bronchial origin in inhaled corticosteroid-treated asthma

BACKGROUND

Inhaled corticosteroid therapy suppresses nitric oxide levels (NO) of airway origin but not necessarily NO of alveolar or small airway origin. Systemic therapy with an oral anti-leukotriene agent may suppress NO production in distal airways and alveoli not reached by inhaled therapy.

METHODS

Adult patients with mild asthma were treated for 3 weeks with inhaled fluticasone 250 microg twice daily then with inhaled fluticasone plus oral montelukast 10 mg daily for 3 additional weeks. We monitored exhaled NO (eNO), spirometry, lung volumes, and asthma symptoms scores at baseline and at the end of each treatment period. In a subset of patients, we continued with montelukast monotherapy and repeated these measurements.

RESULTS

In the 18 patients studied, pulmonary function parameters and asthma symptom scores were not altered significantly from baseline by any therapy. The total eNO at baseline was 55+/-35.3 ppb, dropping to 28.1+/-15.3 ppb (p=0.005) after 3 weeks of fluticasone and to 23.5+/-14 ppb (p=0.001 vs. baseline) after the addition of montelukast. The trend towards reduced total eNO with the combination therapy vs. monotherapy was not statistically significant. Alveolar eNO dropped from 4.2+/-2.4 at baseline to 3.0+/-1.5 (p=0.1) after fluticasone and then to 2.2+/-0.9 (p=0.08 vs. baseline) after fluticasone plus montelukast, increasing then to 3.8+/-1.8 after montelukast alone (p=0.6 vs. baseline).

CONCLUSIONS

Leukotriene receptor antagonists administered systemically might decrease small airway/alveolar sites of inflammation when combined to inhaled corticosteroid therapy.

Partitioned exhaled nitric oxide to non-invasively assess asthma

Asthma is a chronic inflammatory disease of the lungs, characterized by airway hyperresponsiveness. Chronic repetitive bouts of acute inflammation lead to airway wall remodeling and possibly the sequelae of fixed airflow obstruction. Nitric oxide (NO) is a reactive molecule synthesized by NO synthases (NOS). NOS are expressed by cells within the airway wall and functionally, two NOS isoforms exist: constitutive and inducible. In asthma, the inducible isoform is over expressed, leading to increased production of NO, which diffuses into the airway lumen, where it can be detected in the exhaled breath. The exhaled NO signal can be partitioned into airway and alveolar components by measuring exhaled NO at multiple flows and applying mathematical models of pulmonary NO dynamics. The airway NO flux and alveolar NO concentration can be elevated in adults and children with asthma and have been correlated with markers of airway inflammation and airflow obstruction in cross-sectional studies. Longitudinal studies which specifically address the clinical potential of partitioning exhaled NO for diagnosis, managing therapy, and predicting exacerbation are needed.

Effect of heterogeneous ventilation and nitric oxide production on exhaled nitric oxide profiles

Elevated exhaled nitric oxide (NO) in the breath of asthmatic subjects is thought to be a noninvasive marker of lung inflammation. Asthma is also characterized by heterogeneous bronchoconstriction and inflammation, which impact the spatial distribution of ventilation in the lungs. Since exhaled NO arises from both airway and alveolar regions, and its level in exhaled breath depends strongly on flow, spatial heterogeneity in flow patterns and NO production may significantly affect the exhaled NO signal. To investigate the effect of these factors on exhaled NO profiles, we developed a multicompartment mathematical model of NO exchange using a trumpet-shaped central airway segment that bifurcates into two similarly shaped peripheral airway segments, each of which empties into an alveolar compartment. Heterogeneity in flow alone has only a minimal impact on the exhaled NO profile. In contrast, placing 70% of the total airway NO production in the central compartment or the distal poorly ventilated compartment can significantly increase (35%) or decrease (-10%) the plateau concentration, respectively. Reduced ventilation of the peripheral and acinar regions of the lungs with concomitant elevated NO production delays the rise of NO during exhalation, resulting in a positive phase III slope and reduced plateau concentration (-11%). These features compare favorably with experimentally observed profiles in exercise-induced asthma and cannot be simulated with single-path models. We conclude that variability in ventilation and NO production in asthmatic subjects impacts the shape of the exhaled NO profile and thus impacts the physiological interpretation.

Nitric oxide metabolism and the acute chest syndrome of sickle cell anemia

OBJECTIVE

To review the role of endothelial dysfunction and nitric oxide metabolism in the pathogenesis of the acute chest syndrome.

DATA SOURCE

A thorough literature search of PubMed for publications relevant to acute chest syndrome and nitric oxide metabolism in sickle cell disease was performed using search terms that included acute chest syndrome, sickle cell disease, nitric oxide metabolism, arginine, nitrite, nitrate, exhaled nitric oxide, nitric oxide synthase, and oxidant injury. We identified randomized controlled trials, case reports, editorials, and review articles from English-language and non-English-language studies of adult, pediatric, animal, and human subjects that describe the pathophysiology of acute chest syndrome, the biology of nitric oxide relevant to the pathophysiology of sickle cell disease, and the evidence for the role of endothelial dysfunction and abnormal nitric oxide metabolism in acute chest syndrome. We identified and reviewed 350 publications by the initial search and subsequent bibliography review. The articles most pertinent to the topic of this article were selected to support the discussion.

RESULTS

Acute chest syndrome is the leading cause of acute respiratory system dysfunction and a leading cause of morbidity and mortality among patients with sickle cell disease. Evidence is available to support decreased nitric oxide production, increased nitric oxide consumption, and abnormal metabolism of nitric oxide in patients with acute chest syndrome. Moreover, substrate availability is disturbed, and alternate pathways for substrate and nitric oxide metabolism exist.

CONCLUSIONS

Abnormalities of nitric oxide metabolism are prevalent during acute illness and baseline health in patients with sickle cell disease. Further investigation is needed to understand the clinical significance of aberrant nitric oxide metabolism as well as the potential for therapeutic manipulation of the arginine-nitric oxide pathway in patients with sickle cell disease.

Peripheral nitric oxide is increased in rhinitic patients with asthma compared to bronchial hyperresponsiveness

Allergic rhinitis is a predisposing factor for developing clinical asthma. Moreover, allergic rhinitis is often associated with bronchial hyperresponsiveness (BHR). We hypothesise that patients with asthma have more small airway involvement than those with allergic rhinitis and BHR alone. The aim of this study was to assess peripheral and proximal NO concentration in rhinitic subjects, and to correlate the peripheral NO concentration to the peripheral obstruction in response to methacholine. Patients with allergic rhinitis with or without BHR, or clinical asthma were investigated in and out of the allergy season. Healthy subjects served as controls. Fractional exhaled NO was performed, and peripheral NO concentration and proximal flux of NO was calculated. Methacholine test was performed including impulse oscillometry. Rhinitic patients with asthma demonstrate an increase in both proximal and peripheral NO compared to those with rhinitis alone or those with BHR. There is a trend of increased peripheral NO from patients with rhinitis only, rhinitis and BHR, to rhinitis with asthma. The increase in peripheral NO correlated with an increased peripheral obstruction in response to methacholine. Patients with seasonal allergic rhinitis demonstrated a decrease in both proximal and peripheral NO in the off-season. The results support our hypothesis that rhinitic patients with asthma have more peripheral lung inflammation and small airway involvement compared to rhinitic patients with BHR alone.

Measurement of IL-13-induced iNOS-derived gas phase nitric oxide in human bronchial epithelial cells

Exhaled nitric oxide (NO) is altered in numerous diseases including asthma, and is thought broadly to be a noninvasive marker of inflammation. However, the precise source of exhaled NO has yet to be identified, and the interpretation is further hampered by significant inter-subject variation. Using fully differentiated normal human bronchial epithelial (NHBE) cells, we sought to determine (1) the rate of NO release (flux, pl.s(-1.)cm(-2)) into the gas; (2) the effect of IL-13, a prominent mediator of allergic inflammation, on NO release; and (3) inter-subject/donor variability in NO release. NHBE cells from three different donors were cultured at an air-liquid interface and stimulated with different concentrations of IL-13 (0, 1, and 10 ng/ml) for 48 h. Gas phase NO concentrations in the headspace over the cells were measured using a chemiluminescence analyzer. The basal NO flux from the three donors (0.05 +/- 0.03) is similar in magnitude to that estimated from exhaled NO concentrations, and was significantly increased by IL-13 in a donor-specific fashion. The increase in NO release was strongly correlated with inducible nitric oxide synthase (iNOS) gene and protein expression. There was a trend toward enhanced production of nitrate relative to nitrite as an end product of NO metabolism in IL-13-stimulated cells. NO release from airway epithelial cells can be directly measured. The rate of release in response to IL-13 is strongly dependent on the individual donor, but is primarily due to the expression of iNOS.

Airway nitric oxide output is reduced in bronchiectasis

BACKGROUND

Increased concentrations of exhaled nitric oxide (NO) have been detected in inflammatory lung diseases including asthma and have been attributed to increased expression and activity of inducible nitric oxide synthase (iNOS) within the airways. However, previous studies of exhaled NO in patients with bronchiectasis have yielded conflicting results, with reports of both increased and normal NO values. Recent evidence from animal models suggests that chronic airway infection reduces NO production within the lung, despite causing increased iNOS expression. We tested the hypothesis that, in human subjects with bronchiectasis, chronic airway infection reduces NO output from the conducting airways.

METHODS

Using a recently described two-compartment model, we measured separately the contributions of the conducting airways and the alveoli to exhaled NO in nine patients with stable bronchiectasis and eight control subjects before and after inhaled glucocorticoid therapy.

RESULTS

We found that airway NO output was significantly lower in bronchiectasis than in normal airways whereas NO output from the alveoli was similar to that of control subjects. High-dose inhaled glucocorticoid therapy did not alter airway or alveolar NO production.

CONCLUSIONS

These findings demonstrate that, in patients with bronchiectasis, airway NO output is reduced and that iNOS does not contribute significantly to airway NO production.