Transient decrease of exhaled nitric oxide after acute exposure to passive smoke in healthy subjects

Assessing the Impact of Metalworking Exposures on Respiratory Health: The Role of Fractional Exhaled Nitric Oxide Levels

OBJECTIVE

The significance of measuring Fractional Exhaled Nitric Oxide (FeNO) has grown, particularly in monitoring respiratory diseases like asthma. FeNO levels indicate inflammation and a rise in response to respiratory irritants. This study investigates whether repeated exposure to irritants in metal casting and coating leads to respiratory inflammation and assesses the benefits of including FeNO measurement in periodic occupational health screenings.

METHODS

This cross-sectional study involved 99 workers aged 18-65 in the foundry and metal coating sectors in the İkitelli Organized Industrial Zone. The study group included 54 workers exposed to metal dust and fumes, while the control group comprised 45 workers in non-exposure roles (e.g., secretarial, assembly, packaging). Data were collected through face-to-face interviews, recording demographics, smoking habits, symptoms. FeNO levels were measured and analyzed with pulmonary function test parameters.

RESULTS

FeNO levels were significantly higher in the study group compared to the control group (p = 0.02). No significant relationships were found between FeNO levels and age, height, weight, BMI, waist circumference, years of work, or symptom presence, but a significant negative correlation was observed between FeNO levels and FEV1/FVC. Additionally, current smokers had significantly lower FeNO levels compared to those who had quit or never smoked (study, p = 0.014; control, p = 0.011).

CONCLUSION

Monitoring FeNO levels in occupational health assessments may facilitate early intervention and preventive measures, protecting worker health. Incorporating FeNO measurement into periodic screenings could enhance occupational health practices.

Fractional Exhaled Nitric Oxide (FeNO) in Patients with Stable Chronic Obstructive Pulmonary Disease: Short-Term Variability and Potential Clinical Implications

BACKGROUND

The use of fractional exhaled nitric oxide (FeNO) has been proposed for identifying and monitoring eosinophilic airway inflammation in chronic obstructive pulmonary disease (COPD). To explore the clinical utility of FeNO in COPD, we aimed to assess its short-term variability in a clinically stable COPD cohort.

METHODS

Consecutive COPD patients, formerly smokers, underwent FeNO assessment at the baseline and six time-points through serial sampling spaced 3 days apart.

RESULTS

A total of 41 patients (mean age 72.9, 87.8% males) showed a median baseline value of FeNO of 11.7 (8.0-16.8) ppb. A weak linear relationship was documented between baseline FeNO values and both eosinophil counts (r = 0.341, p = 0.029) and the percentage of eosinophils (r = 0.331, p = 0.034), confirmed in multiple linear regressions after adjusting for steroid use. The overall individual variability of FeNO between time-points was 3.90 (2.53-7.29) ppb, with no significant difference in the distribution of FeNO values measured at different time-points (p = 0.204). A total of 28 (68.3%) patients exhibited FeNO always below the 25 ppb cut-off at all determinations, while the remining 13 (31.7%) had at least one value above the established limit. Interestingly, none of these 13 participants had FeNO stably above 25 ppb, all showing at least one normal value during serial sampling. Compared to these patients with more fluctuating values, the 28 with stably normal FeNO only exhibited a significantly higher body weight (80.0 ± 18.2 kg vs. 69.0 ± 8.8 kg, p = 0.013) and body mass index (29.7 ± 6.5 kg/m2 vs. 25.9 ± 3.7 kg/m2, p = 0.026), confirmed in multiple logistic regressions after adjusting for major potential confounders.

CONCLUSIONS

A certain degree of FeNO variability, apparently unrelated to eosinophil counts but somehow influenced by body weight, must be considered in COPD patients. Further studies are needed to clarify whether this biomarker may be effectively used to plan more personalized pharmacological and rehabilitation strategies in this clinical setting.

Comparison of three different exhaled nitric oxide analyzers in chronic respiratory disorders

BACKGROUND

Fractional exhaled nitric oxide (FeNO) measurement is a simple and non-invasive method for monitoring eosinophilic airway inflammation. New portable analyzers for FeNO measurements are constantly being developed. The aim of our study was to evaluate the agreement of FeNO values measured by new portable analyzers.

MATERIALS AND METHODS

FeNO was measured in 20 healthy subjects, 20 asthmatic and 20 chronic obstructive pulmonary disease patients using the analyzers Niox-VERO, Vivatmo-PRO and HypAir-FeNO. A linear relationship was estimated with Pearson's coefficient (r), and absolute agreement by the intraclass correlation coefficient (ICC) and bias with the limits of agreement (95% of paired differences) were assessed according to the Bland-Altman method.

RESULTS

In the study population (58 ± 14 years, 20 females), mean values of FeNO with their 95% confidence interval were 24.0 (18.6-29.4) with the Niox-VERO, 19.6 (13.6-25.7) with the Vivatmo-PRO and 20.4 (15.7-25.1) with the HypAir-FeNO. FeNO measured with the Niox-VERO was higher than the Vivatmo-PRO (mean difference of paired values +4.3; limits -16.0 to 25.7 ppb) and the HypAir-FeNO (+3.6; -12.2 to 19.4 ppb); the Vivatmo-PRO and HypAir-FeNO showed large variability of paired differences (-0.7; -16.5 to 15.0 ppb). Measurements linearly correlated with an imperfect absolute agreement: Niox-VERO versus Vivatmo-PRO r = 0.90 and ICC = 0.87; Niox-VERO versus HypAir-FeNO r = 0.93 and ICC = 0.90, Vivatmo-PRO versus HypAir-FeNO r = 0.96 and ICC = 0.93. Most of the disagreement was greater in some asthmatic patients at high values of FeNO.

CONCLUSIONS

The present study indicates that absolute exhaled NO measurements may differ to a clinically relevant extent using the Niox-VERO, Vivatmo-PRO and HypAir-FeNO analyzers. The devices cannot be used interchangeably.

Recent Marijuana Use and Associations With Exhaled Nitric Oxide and Pulmonary Function in Adults in the United States

BACKGROUND

The medical and recreational use of marijuana is now legal in some parts of the United States; the health effects are unknown. We aimed to evaluate associations between recent marijuana use and exhaled nitric oxide (eNO) and pulmonary function.

METHODS

We performed a cross-sectional study of 10,327 US adults participating in the National Health and Nutrition Examination Survey in the years 2007 to 2012. We examined associations between marijuana use and eNO, FEV1, FVC, the FEV1/FVC ratio, and forced expiratory flow (midexpiratory phase) (FEF25%-75%) by weighted linear regression.

RESULTS

In the study population, there were 4,797 never users, 4,084 past marijuana users, 555 participants who used marijuana 5 to 30 days before the examination, and 891 participants who used marijuana 0 to 4 days before the examination. Current marijuana use in the past 4 days was associated with 13% lower eNO (95% CI, -18% to 8%). FVC was higher in past users (75 mL; 95% CI, 38-112) and current users in the past 5 to 30 days (159 mL; 95% CI, 80-237) and in users within 0 to 4 days of the examination (204 mL; 95% CI, 139-270) compared with never users. All associations remained unchanged and statistically significant in sensitivity analyses excluding current and past tobacco users.

CONCLUSIONS

Current marijuana use was associated with lower levels of eNO and higher FVC. The lower eNO in marijuana smokers suggests that short-term exposure to marijuana may, like tobacco, acutely affect the pulmonary vascular endothelium and impair airflow through the small airways.

Exposure to cigarette smoke impacts myeloid-derived regulatory cell function and exacerbates airway hyper-responsiveness

Cigarette smoking enhances oxidative stress and airway inflammation in asthma, the mechanisms of which are largely unknown. Myeloid-derived regulatory cells (MDRC) are free radical producing immature myeloid cells with immunoregulatory properties that have recently been demonstrated as critical regulators of allergic airway inflammation. NO (nitric oxide)-producing immunosuppressive MDRC suppress T-cell proliferation and airway-hyper responsiveness (AHR), while the O2(•-) (superoxide)-producing MDRC are proinflammatory. We hypothesized that cigarette smoke (CS) exposure may impact MDRC function and contribute to exacerbations in asthma. Exposure of bone marrow (BM)-derived NO-producing MDRC to CS reduced the production of NO and its metabolites and inhibited their potential to suppress T-cell proliferation. Production of immunoregulatory cytokine IL-10 was significantly inhibited, while proinflammatory cytokines IL-6, IL-1β, TNF-α and IL-33 were enhanced in CS-exposed BM-MDRC. Additionally, CS exposure increased NF-κB activation and induced BM-MDRC-mediated production of O2(•-), via NF-κB-dependent pathway. Intratracheal transfer of smoke-exposed MDRC-producing proinflammatory cytokines increased NF-κB activation, reactive oxygen species and mucin production in vivo and exacerbated AHR in C57BL/6 mice, mice deficient in Type I IFNR and MyD88, both with reduced numbers of endogenous MDRC. Thus CS exposure modulates MDRC function and contributes to asthma exacerbation and identifies MDRC as potential targets for asthma therapy.

Normal values and thresholds for the clinical interpretation of exhaled nitric oxide levels in the US general population: results from the National Health and Nutrition Examination Survey 2007-2010

BACKGROUND

Elevated fractional excretion of exhaled nitric oxide (FENO) reflects airway inflammation, but few studies have established its normal values. This study aims to establish the normal values and thresholds for the clinical interpretation of FENO in the US general population.

METHODS

Thirteen thousand two hundred seventy-five subjects aged 6 to 80 years sampled for the National Health and Nutrition Examination Survey (NHANES) 2007-2010 underwent interviews, physical examination, and FENO analysis at 50 mL/s using an online chemiluminescence device according to American Thoracic Society/European Respiratory Society guidelines. After excluding subjects with self-reported asthma and subjects with wheeze in the prior 12 months, prediction equations for the natural logarithm (ln) of FENO were constructed using age, sex, ethnicity, height, BMI, active/passive smoke exposure, and hay fever episodes as covariates.

RESULTS

The fifth to 95th percentile values of FENO were 3.5 to 36.5 parts per billion (ppb) for children < 12 years of age and 3.5 to 39 ppb for subjects 12 to 80 years of age. Using multiple linear regression, prediction equations explained only 10.3% to 15.7% of the variation in the general population. In the general population, 39% to 45% had ln(FENO) levels > 2 SD of the predicted means. When applied to the general population inclusive of subjects who reported asthma but who did not have attacks within the past year, nearly identical results were obtained.

CONCLUSIONS

Assuming 95% of the healthy US general population had no clinically significant airway inflammation as assessed by FENO, values exceeding the 95th percentiles indicated abnormality and a high risk of airway inflammation. A large variation of normal FENO values existed in the general population, which was poorly predicted by multiple linear regression models.

Screening by pulse CO-oximetry for environmental tobacco smoke exposure in preanesthetic children

OBJECTIVE

The purpose of this study was to evaluate the ability of multiple wavelength pulse CO-oximetry (SpCO) to screen for environmental tobacco smoke (ETS) exposure in children.

BACKGROUND

Exposure to ETS is associated with an increased risk of perioperative respiratory complications in children. It is often difficult to obtain an accurate history for ETS exposure, so a preoperative screening tool is desirable. Carbon monoxide is a measurable product of tobacco combustion. Multiple wavelength pulse CO-oximetry is a recently developed point-of-care monitor.

METHODS

Following IRB approval and parental consent, 220 children aged 1-16 years having outpatient surgical procedures were enrolled. SpCO was measured preoperatively three times with the Radical-7 Rainbow SET CO-oximeter (Masimo, Irvine, CA, USA). Immediately following induction of anesthesia, a blood sample for laboratory measurement of carboxyhemoglobin (COHb) and serum cotinine was obtained. Regression analysis determined the correlation of SpCO with serum cotinine values. Receiver operator characteristic (ROC) curves analyzed the discriminating ability of SpCO or COHb to predict ETS exposure based on cotinine cutoff values known to be present in children exposed to ETS. Agreement of SpCO and COHb values was assessed using Bland-Altman plots.

RESULTS

SpCO did not correlate with cotinine (R(2) = 0.005). Both SpCO and COHb had poor discriminating ability for ETS exposure (area under the ROC curve = 0.606 and 0.562, respectively). SpCO values had poor agreement with COHb values.

CONCLUSIONS

The point-of-care multiple wavelength pulse CO-oximeter does not appear to be a useful preoperative screening tool for ETS exposure in children.

Exhaled NO among inner-city children in New York City

BACKGROUND

Fractional exhaled nitric oxide (FeNO) has been proposed as a biomarker of airway inflammation for cohort studies of asthma.

OBJECTIVES

To assess the association between FeNO and asthma symptoms among 7-year-old children living in an inner-city community. To test the association between environmental tobacco smoke (ETS) exposure (previous and current) and FeNO among these children.

METHODS

As part of a longitudinal study of asthma, children recruited in Head Start centers at age 4 had offline FeNO and lung function testing at age 7. Children with allergen-specific immunoglobulin E (IgE) (≥0.35 IU/mL) at age 7 were considered seroatopic. ETS exposure at ages 4 and 7 was assessed by questionnaire.

RESULTS

Of 144 participating children, 89 had complete questionnaire data and achieved valid FeNO and lung function tests. Children with reported wheeze in the previous 12 months (n = 19) had higher FeNO than those without wheeze (n = 70) (geometric means 17.0 vs. 11.0 ppb, p = .005). FeNO remained significantly associated with wheeze (p = .031), after adjusting for seroatopy and forced expiratory volume in 1 second (FEV₁) in multivariable regression. FeNO at age 7 was positively associated with domestic ETS exposure at age 4 (29%) (β = 0.36, p = .015) but inversely associated with ETS exposure at age 7 (16%) (β = -0.74, p < .001).

CONCLUSIONS

Given its association with current wheeze, independent of seroatopy and lung function, FeNO provides a relevant outcome measure for studies in inner-city communities. While compelling, the positive association between ETS exposure at age 4 and a marker of airway inflammation at age 7 should be confirmed in a larger study.

Subclinical responses in healthy cyclists briefly exposed to traffic-related air pollution: an intervention study

BACKGROUND

Numerous epidemiological studies have demonstrated adverse health effects of a sedentary life style, on the one hand, and of acute and chronic exposure to traffic-related air pollution, on the other. Because physical exercise augments the amount of inhaled pollutants, it is not clear whether cycling to work in a polluted urban environment should be encouraged or not. To address this conundrum we investigated if a bicycle journey along a busy commuting road would induce changes in biomarkers of pulmonary and systematic inflammation in a group of healthy subjects.

METHODS

38 volunteers (mean age: 43 ± 8.6 years, 26% women) cycled for about 20 minutes in real traffic near a major bypass road (road test; mean UFP exposure: 28,867 particles per cm3) in Antwerp and in a laboratory with filtered air (clean room; mean UFP exposure: 496 particles per cm3). The exercise intensity (heart rate) and duration of cycling were similar for each volunteer in both experiments. Exhaled nitric oxide (NO), plasma interleukin-6 (IL-6), platelet function, Clara cell protein in serum and blood cell counts were measured before and 30 minutes after exercise.

RESULTS

Percentage of blood neutrophils increased significantly more (p = 0.004) after exercise in the road test (3.9%; 95% CI: 1.5 to 6.2%; p = 0.003) than after exercise in the clean room (0.2%; 95% CI: -1.8 to 2.2%, p = 0.83). The pre/post-cycling changes in exhaled NO, plasma IL-6, platelet function, serum levels of Clara cell protein and number of total blood leukocytes did not differ significantly between the two scenarios.

CONCLUSIONS

Traffic-related exposure to particles during exercise caused a small increase in the distribution of inflammatory blood cells in healthy subjects. The health significance of this isolated change is unclear.

Acute effects of passive smoking on endothelial function

Impairment of endothelial functions has been shown to occur after acute and chronic exposure to passive smoking (PS), as assessed by flow-mediated dilatation (FMD) of the brachial artery. A total of 61 participants, 30 male and 31 female, mean ages 26 (18-36) were enrolled in the study. All were clinically well and nonsmokers. All participants stayed for 30 minutes in the smoking room. Carbon monoxide (CO) level was 7.42 ± 0.98 ppm (4.71-10.50). Mean carboxyhemoglobin (COHb) levels of participants were significantly elevated after PS. Mean FMD was 18.6% ± 9% and decreased to 12.4% ± 7% after PS (P < .001). In the current study, with more number of participants at lower CO concentrations (7.42 ppm) and with smaller increase in COHb (51%) significant reduction (33%, P < .001) in FMD was observed.

Passive smoking is a major determinant of exhaled nitric oxide levels in allergic asthmatic children

BACKGROUND

Fraction of exhaled nitric oxide (FeNO) is considered, by some authors, to be a treatment follow-up parameter in allergic asthmatics. However, factors such as active smoking can influence NO production and must be taken into account in the interpretation of FeNO values. In children, the evidence in favour of an impact of passive smoking (PS) on FeNO values is controversial. The aim of this study was to evaluate the impact of chronic PS on FeNO in allergic asthmatic children.

METHODS

Seventy nontreated allergic asthmatic children over 5 years of age, exposed and unexposed to PS, underwent measurement of FeNO, spirometry, and allergic tests (skin prick tests, total and specific serum IgE, and blood eosinophilia). Children were considered to be exposed to PS when at least 1 cigarette per day was declared to be smoked at home.

RESULTS

Geometric mean FeNO value in 22 children exposed to PS was 26.3 +/- 1.5 ppb vs 56.3 +/- 1.7 ppb in 48 children unexposed (P < 0.001). After adjustment for age, blood eosinophilia, allergic sensitizations, total IgE, dust mite sensitization and asthma severity, multivariate analysis showed that PS exposure was negatively associated with FeNO values (P = 0.0001) and was the primary determinant of FeNO variations.

CONCLUSION

Passive smoking lowers FeNO, and might be a major determinant of FeNO levels in nontreated allergic asthmatic children.

Exhaled nitric oxide in the diagnosis and management of childhood asthma

The management of asthma in children and adolescents is currently guided by assessment of clinical symptoms, exacerbation risk and spirometric measure of lung function. The use of biomarkers, an objective measure which indicates normal or pathophysiologic processes and/or the response to a treatment intervention, could greatly enhance the efficacy and safety of current algorithms. Measurement of the fraction of expired nitric oxide in exhaled air (FeNO) has been suggested as a readily determined biomarker that can aid in the diagnosis and management of asthma. FeNO has been used to identify steroid responsive patients, adjust the dose of controller medications, most notably inhaled corticosteroids, and predict relapse during medication taper. In spite of early enthusiasm for the utility of this measure, more recent data suggest a more limited role for FeNO. This review will focus on the use of FeNO in the diagnosis and management of asthma in children and adolescents.

Cigarette smoke inhibits endometrial epithelial cell proliferation through a nitric oxide-mediated pathway

OBJECTIVE

To determine the direct effects of cigarette smoke (CS) on human endometrial surface epithelial cell line proliferation.

DESIGN

In vitro study using HES cells and primary human endometrial cells.

SETTING

University-based academic center.

PATIENT(S)

Premenopausal women in the proliferative phase of the cycle.

INTERVENTION(S)

The HES cells and primary human endometrial cells were exposed to cigarette smoke-saturated solution.

MAIN OUTCOME MEASURE(S)

Cell proliferation and expression of different isoforms of nitric oxide synthase.

RESULT(S)

Cigarette smoke inhibited HES cell proliferation in a dose- and time-dependant manner. The inhibitory effect of CS was blocked by hemoglobin and enhanced by L-arginine (L-Arg). Cigarette smoking and nicotine stimulated the expression of endothelial NO synthase (eNOS) and inducible NO synthase (iNOS) whereas benzo[a]pyrene (BP) only stimulated the expression of eNOS in HES cells. Cigarette smoke stimulated the expression of eNOS/iNOS in primary human endometrial cells, comprised of epithelial and stromal cells. The effect of CS on eNOS/iNOS expression in HES cells was blocked by ascorbic acid but not by glutathione.

CONCLUSION(S)

Cigarette smoke inhibits endometrial cell proliferation through a nitric oxide-mediated pathway.

Exhaled nitric oxide in childhood asthma: a review

As an 'inflammometer', the fraction of nitric oxide in exhaled air (Fe(NO)) is increasingly used in the management of paediatric asthma. Fe(NO) provides us with valuable, additional information regarding the nature of underlying airway inflammation, and complements lung function testing and measurement of airway hyper-reactivity. This review focuses on clinical applications of Fe(NO) in paediatric asthma. First, Fe(NO) provides us with a practical tool to aid in the diagnosis of asthma and distinguish patients who will benefit from inhaled corticosteroids from those who will not. Second, Fe(NO) is helpful in predicting exacerbations, and predicting successful steroid reduction or withdrawal. In atopic asthmatic children Fe(NO) is beneficial in adjusting steroid doses, discerning those patients who require additional therapy from those whose medication dose could feasibly be reduced. In pre-school children Fe(NO) may be of help in the differential diagnosis of respiratory symptoms, and may potentially allow for better targeting and monitoring of anti-inflammatory treatment.

Effects of erdosteine on smoking-induced lipid peroxidation in healthy smokers

AIM

Oxidative stress caused by smoking has been implicated in many pulmonary diseases. Smoking causes reductions in plasma nitrate plus nitrite (NOx) concentrations and increases in plasma malondialdehyde (MDA) concentrations, which indicate oxidative stress and lipid peroxidation, respectively. In this study, we investigated the acute effects of smoking a single cigarette on the plasma concentrations of NOx and thiobarbituric acid reactive substances (TBARS) including MDA, and whether administration of erdosteine, a mucolytic and antioxidant agent, affects these parameters.

METHODS

Thirty healthy smokers were included in the study. Subjects smoked a single cigarette in 10 minutes on the study day. For analysis of NOx, TBARS and cotinine, blood was drawn from each subject before and 5 and 30 minutes after smoking. The subjects were then randomly divided into two groups, one receiving placebo and the other erdosteine suspension 175mg/5mL twice daily for 1 month. After this treatment period, the same study protocol was carried out. Two subjects in the placebo and five subjects in the study group were excluded because of noncompliance.

RESULTS

Twenty-three (14 female, 9 male) subjects completed the study. Their mean age was 32 +/- 8 years and their smoking history was 14 +/- 9 pack-years. Baseline NOx, TBARS and cotinine concentrations were similar between the groups. NOx concentrations decreased significantly after smoke exposure. At the end of the treatment period there were no significant differences in NOx, TBARS or cotinine concentrations between the groups. The concentration of TBARS after smoking decreased significantly in the erdosteine-treated group (at 5 minutes: 2.8 +/- 0.5 micromol/L before treatment and 2.3 +/- 0.3 micromol/L after treatment, p < 0.05; at 30 minutes: 2.8 +/- 0.5 micromol/L before treatment and 1.8 +/- 0.7 micromol/L after treatment, p < 0.05). Smoking history was significantly correlated with cotinine concentrations.

CONCLUSION

Acute smoke exposure decreased plasma NOx concentrations in healthy smokers, and this was not changed with erdosteine treatment. However, significant decreases were noted in TBARS concentrations after smoke exposure in the group that received erdosteine, suggesting that short-term erdosteine administration might help prevent smoking-induced lipid peroxidation.

Possible association between passive smoking and lower exhaled nitric oxide in asthmatic children

In adults, both active and passive smoking reduce levels of exhaled nitric oxide (eNO); however, to date, passive exposure to environmental tobacco smoke (ETS) has not been shown to affect eNO in children. The authors recruited 174 asthmatic children (96 male, 78 female) and 79 nonasthmatic controls (46 male, 33 female) from a group of children aged 5 to 14 yr who attended a children's hospital for an outpatient visit or elective surgery. Each subject's exposure to ETS was ascertained by questionnaire, and their eNO levels were measured. Asthmatic children had higher eNO levels (ppb) than nonasthmatic children (p = 0.04), and asthmatic children exposed to ETS had significantly lower eNO levels than unexposed children (p = 0.005). Exposure to ETS did not alter eNO levels in nonasthmatic children (p = 0.4). Results of the study suggest that ETS exposure is associated with lower eNO levels among childhood asthmatics. Consequently, ETS exposure may need to be considered when physicians interpret eNO levels in asthmatic children. Further study of the effects of ETS on eNO levels is recommended.

Mid-infrared quantum cascade laser based off-axis integrated cavity output spectroscopy for biogenic nitric oxide detection

Tunable-laser absorption spectroscopy in the mid-IR spectral region is a sensitive analytical technique for trace-gas quantification. The detection of nitric oxide (NO) in exhaled breath is of particular interest in the diagnosis of lower-airway inflammation associated with a number of lung diseases and illnesses. A gas analyzer based on a continuous-wave mid-IR quantum cascade laser operating at approximately 5.2 microm and on off-axis integrated cavity output spectroscopy (ICOS) has been developed to measure NO concentrations in human breath. A compact sample cell, 5.3 cm in length and with a volume of < 80 cm3, that is suitable for on-line and off-line measurements during a single breath cycle, has been designed and tested. A noise-equivalent (signal-to-noise ratio of 1) sensitivity of 10 parts in 10(9) by volume (ppbv) of NO was achieved. The combination of ICOS with wavelength modulation resulted in a 2-ppbv noise-equivalent sensitivity. The total data acquisition and averaging time was 15 s in both cases. The feasibility of detecting NO in expired human breath as a potential noninvasive medical diagnostic tool is discussed.