0
Original Research: COPD |

Central and Peripheral Airway Sites of Nitric Oxide Gas Exchange in COPD FREE TO VIEW

Arthur F. Gelb, MD, FCCP; Colleen Flynn Taylor, MA; Anita Krishnan, MD; Christine Fraser, RCP, CPFT; Chris M. Shinar, PharmD; Mark J. Schein, MD; Kathryn Osann, PhD
Author and Funding Information

From the Pulmonary Division, Department of Medicine (Dr Gelb) and Department of Radiology (Dr Schein), Lakewood Regional Medical Center, Lakewood, CA; Geffen School of Medicine (Dr Gelb); University of California at Los Angeles, CA; the Department of Performance Improvement and Patient Safety (Dr Shinar), Orange Coast Memorial Medical Center, Fountain Valley, CA; and Department of Medicine, School of Medicine (Dr Osann), University of California at Irvine, CA. Ms Taylor, Dr Krishnan, and Ms Fraser are independent research contractors.

Correspondence to: Arthur F. Gelb, MD, 3650 E South St. Ste 308, Lakewood, CA 90712; e-mail: afgelb@msn.com


Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestpubs.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;137(3):575-584. doi:10.1378/chest.09-1522
Text Size: A A A
Published online

Background:  This study investigated sites of nitric oxide (NO) gas exchange and response to inhaled corticosteroids (ICS) in patients with COPD and varying extents of emphysema.

Methods:  This was a prospective, randomized, single-blind, crossover study in treated, stable, ex-smoking patients with COPD who were ICS and leukotriene receptor antagonists naive. Lung function, high-resolution thin-section CT scan of the lung, and exhaled NO were measured at 50, 100, 150, and 200 mL/s. Airway NO was adjusted for NO axial backdiffusion.

Results:  In 39 (18 women), clinically stable ex-smokers with COPD aged 73 ± 9 years (mean ± SD) on salmeterol 50 μg (S50) bid, after 180 μg aerosolized albuterol, FEV1 (L) was 52% ± 12% predicted and FEV1/FVC was 55% ± 6%. Compared with 20 (12 men) age-matched controls, 39 patients with COPD had normal large airway NO flux and small airway/alveolar NO. Subsequently, 19 patients with COPD (Group A) were randomized and continued on S50, and 20 (Group B) were randomized to fluticasone propionate 250 μg (F250)/S50 bid for 86 ± 16 days. Group A (S50) patients were then switched to F250/S50, and 12 of 19 completed 77 ± 15 days; there was significant (P < .001) reduction only in the exhaled fraction of NO (FENO) at 50 mL/s and large airway NO flux. In 20 patients with COPD initially randomized to F250/S50 (Group B), after 57 ± 22 days of S50 in 16 of 20 patients there was a significant (P = .04) increase only in (FENO) at 50 mL/s and large airway NO flux, which was not reduced after 60 ± 23 days of fluticasone propionate 100 μg (F100)/S50(P = .07). There was no correlation between NO gas exchange and CT-scored emphysema.

Conclusions:  In COPD, there was normal NO gas exchange in both large and small airways/alveoli and only large airway NO flux was suppressed with F250/S50 but not F100/S50, despite varying extents of emphysema. Peripheral NO must be corrected for axial NO backdiffusion to avoid spurious conclusions.

Trial registration:  NCT #00568347.

Figures in this Article

Measurement of exhaled nitric oxide (NO) is a relatively simple, reproducible, and noninvasive test for monitoring endogenous inflammatory airway signals in asthma and COPD and the response to inhaled corticosteroids (ICS).1-7 The accepted method8 of measuring the exhaled fraction of NO (FENO) at a single constant expiratory flow rate, usually at 50 mL/s, is unable to discriminate the individual contributions of large airway NO flux vs small airway/alveolar production sites. However, FENO at 50 mL/s predominantly reflects large airway NO flux. Therefore, more refined modeling to separate NO gas exchange between central and peripheral airways has been developed.9-14

Using a two-compartment model developed by Tsoukias et al,13,14 central airway NO flux and small airway/alveolar NO concentration can be estimated by measuring exhaled NO at multiple expiratory flow rates and plotting NO output vs expiratory flow rates. The slope of the linear regression line between NO output vs varying expiratory flow reflects small airway/alveolar NO concentration in parts per billion (ppb), whereas the y intercept reflects large airway NO flux in nanoliters per second (nL/s).13,14 We15,16 and others17-23 previously reported varying large airway NO flux and small airway/alveolar NO production in clinically stable patients with mild17,20-22 and moderate-to-severe persistent asthma10,15,16,18,19,22 using this model.13,14 Furthermore, using this model,13,14 Brindicci et al,24 Högman et al,10 Roy et al,25 and our group26 evaluated NO production in large and peripheral small airway/alveolar sites in stable patients with COPD, with varying results. However, in all previous studies in patients with asthma and COPD with abnormal expiratory airflow limitation, there was no correction for NO axial backdiffusion. Extensive experimental and theoretical evidence emphasized the importance of understanding and correcting for axial NO backdiffusion to avoid spurious conclusions.27 This avoids errors that may result from overestimating or underestimating NO contribution from peripheral sites by underestimating or overestimating central airway NO flux.27 Furthermore, previous studies did not evaluate the effect of the COPD emphysema phenotype on NO gas exchange.

Our prospective study measured exhaled NO using the two-compartment model13,14 in clinically stable, ex-smoking patients with COPD, moderate-to-severe expiratory airflow limitation, and varying extents of lung-CT-scored emphysema. Our goal was to evaluate (1) the contribution of large airway flux vs peripheral small airway/alveolar sites of NO production before and after correction for axial NO backdiffusion,27 (2) the effect of underlying lung-CT-scored emphysema, and (3) the response to ICS using both a moderate- and low-dose regimen, since the optimal dose is not known. Results in patients with COPD were compared with NO gas exchange data obtained in healthy, age-matched nonsmokers with normal lung function.

Patient Selection

We recruited potential study patients with moderate-to-severe COPD28 aged ≥ 40 years, with a past smoking history of more than 15 packs per year, who were currently nonsmokers for ≥ 5 years. All patients with COPD were regularly followed and treated in a tertiary referral outpatient clinic. Medical therapy in patients included short- and long-acting β2 agonists and short- and long-acting antimuscarinic agents, and all patients were ICS naive. Patients with COPD were clinically stable for 8 weeks or more, and were not on oral corticosteroids, antibiotics, leukotriene inhibitors, and/or receptor blockers within 8 weeks of entry into the study. No patient with COPD had a history of asthma or increased serum eosinophils. Sputa eosinophils, allergy skin tests, and serum IgE were not measured. In all enrolled patients with COPD, 15 min after receiving 270 μg albuterol sulfate by metered-dose inhaler (MDI), the FEV1 was < 80% predicted, and the ratio of FEV1/FVC < 70%.

Normal Controls

Normal values for exhaled NO were obtained from 20 normal subjects (12 men), aged 71 ± 7 years (mean ± SD), who were asymptomatic, healthy nonsmokers and age-matched with the COPD cohort. All patients and normal subjects studied gave informed consent for participation.

Measurement of FENO

All subjects abstained from food and coffee for 2 h and alcohol for 12 h prior to studies. FENO was measured prior to spirometry at four separate constant expiratory flow rates: 50, 100, 150, and 200 mL/s in triplicate, and the mean of three values obtained within 10% of each other was reported using a Sievers NOA 280 chemiluminescence analyzer with varying expiratory airflow resistors (GE Analytical Instruments, Inc; Boulder, CO), as previously described.15,16 Furthermore, to avoid nasal NO contamination, a mouth pressure of > 5 cm H2O was used, as previously recommended.29 The NO analyzer was calibrated daily with a known concentration (45 ppm) and before each patient and control subject with NO-free air. The technique of Tsoukias et al13,14 was used to calculate large airway NO maximal flux (y intercept) and steady-state small airway/alveolar NO concentration (CANO) (slope) using a linear regression. The investigators (C. F. T., C. F.) responsible for measuring exhaled NO gas exchange and lung function were blinded to the therapeutic intervention. NO gas exchange was measured at the initiation of the study and subsequently at the end of the run-in period, and at the end of each sequential randomization. Correction for axial diffusion of NO for the flow rate in this study was made using the method of Condorelli et al,27 by multiplying large airway NO flux × 1.7. Furthermore, initial uncorrected large airway flux was divided by 0.53 L/s and subtracted from initial uncorrected small airway/alveolar NO. This may yield trivial or zero values for peripheral NO in normal subjects27 Measurement of exhaled NO was always obtained prior to spirometry.

Lung CT Studies

High-resolution, thin-section scans of the lung were obtained using a helical, 64-slice, multidetector row CT scanner (Siemens Model Sensation 64; Siemens; Malverne, PA). Images were obtained at 5-mm collimation at intervals of 6 mm using 120 kVp and varying mA, dependent upon patient size. Reconstructured 1-mm slices were obtained every 9 mm using a window width of 850 HU and a level of −600 HU, with an edge-enhancing algorithm. Images were scored by a radiologist (M. J. S.), 0 to 100, no to worst emphysema, using picture templates that we previously validated using inflated whole lung specimens.30 This enabled us to correlate NO gas exchange in large and small airways/alveoli vs extent of emphysema.

Lung Function Studies

When clinically stable, patients with COPD were instructed to continue all their medications, except to withhold inhaled albuterol sulfate and/or ipratropium bromide for 6 h and long-acting β2-agonist and tiotropium bronchodilators for 24 h prior to testing. Our techniques for measuring spirometric data, thoracic gas volumes, and airway resistance using plethysmography and diffusing capacity were previously published.15,16

Protocol: Therapeutic Randomization with Intent to Treat

Once selected for this prospective, single-blind, randomized, crossover study, all patients with COPD were placed on salmeterol 50 μg (S50) bid (GlaxoSmithKline; Research Triangle Park, NC) during the 8-week run-in period (Fig 1). They were subsequently randomized into two parallel arms. This included Group A with 19 patients, who continued on S50 bid × 90 days, and Group B with 20 patients, who started fluticasone propionate 250 μg/salmeterol 50 μg bid (F250/S50) (Advair 250/50; GlaxoSmithKline) × 90 days. Subsequently, after 90 days, in Group A, all 19 patients were switched to F250/S50 bid × 90 days. In Group B, all 20 patients initially on F250/S50 were switched to S50 bid × 90 days, then switched to fluticasone propionate 100 μg (F100)/S50 bid × 90 days. This lower ICS dose was evaluated, because it is an acceptable alternative dose in asthma, and the optimal dose in COPD is unknown. Concurrent medications for patients with COPD included aerosolized and/or nebulized albuterol sulfate, ipratropium bromide, and tiotropium (Atrovent, Spiriva; Boehringer-Ingelheim Pharmaceuticals Inc; Ridgefield, CT). It was anticipated that 90 days would provide adequate time to avoid treatment carryover effects and allow for clinical stabilization on the new regimen.

Figure Jump LinkFigure 1. Diagram of 39 patients with COPD, ICS naive, on S50 bid × 60 days then subsequently randomized. Twelve of 19 patients in Group A (initially S50) and 16 of 20 patients in Group B (initially F250/S50) successfully completed the crossover. All 14 patients in Group B completed the switch from S50 to F100/S50. F100 5 fluticasone propionate 100 μg; F250 5 fluticasone propionate 250 μg; ICS 5 inhaled corticosteroids; S50 5 salmeterol 50 μg.Grahic Jump Location
Statistical Methods

Normal age-matched subjects were compared with patients with COPD who were off ICS using two-group t tests. A two-group t test comparing 20 normal controls to 39 patients with COPD has 80% power to detect an effect size of 0.78. Data for patients with COPD were analyzed using paired t tests to test for differences between prerandomized and postrandomized treatment measurements. For group A, paired differences reflect changes in treatment from S50 to F250/S50; for Group B, paired differences reflect changes after patients who were randomized to initial treatment with F250/S50 were returned to S50. A paired t test with a sample size of 12 to 16 subjects has 80% power to detect an effect size of 0.8 to 0.9. Because lung CT scan scores were not normally distributed (Shapiro-Wilk test), Spearman correlation coefficients were used to evaluate associations between NO gas exchange and extent of lung-CT-scan-scored emphysema. P values of < .05 were considered significant.

Patients With COPD

We enrolled 39 (21 men) patients with moderate to severe COPD,29 aged 73 ± 9 years (mean ± SD) with a former smoking history of 53 ± 31 pack-years (mean ± SD), all of whom were current nonsmokers for more than 5 years, and all ICS naive. In the 19 patients randomized to Group A, initially on S50 bid and then switched to F250/S50 bid, 12 of 19 patients successfully completed the crossover with a mean of 77 ± 15 treatment days. In the 20 patients randomized to Group B, initially on F250/S50 and then switched to S50 bid, 16 of 20 patients successfully completed the crossover with a mean of 57 ± 22 treatment days. Subsequently, 14 patients in group B agreed to be switched from S50 bid to F100/S50 bid, and all completed the cycle with a mean of 60 ± 23 treatment days. Patients who failed to successfully complete the prescribed treatment cycle had either exacerbations of COPD requiring oral corticosteroid, inability to technically cooperate for exhaled NO testing, or were poorly compliant with the protocol. During the study, no patient with COPD who successfully completed the treatment cycle had an exacerbation requiring oral corticosteroid.

Lung Function

Results of spirometry in age-matched normals and patients with COPD before and 15 min after receiving 180 μg albuterol by MDI with intent to treat are described in Table 1. At baseline (visit 1), there was a significant difference in lung function between normals and patients with COPD. There was no significant difference in lung function between Group A (19 patients), randomized to S50, and Group B (20 patients), randomized to F250/S50. There was no short-term difference in spirometry values in patients with COPD on S50 vs F250/50 and S50 vs F100/50.

Table Graphic Jump Location
Table 1 —Baseline (Visit 1) Lung Function in Normals and Patients With COPD, With Comparison of Group A (S50) vs Group B (F250/S50) After Randomization

Spirometric data obtained in COPD patients are before and after 180 mg albuterol by MDI and all other spirometric values obtained after bronchodilation. % pred = percent predicted, results are mean ± SD; DL/VA = diffusing capacity/alveolar volume; F250 = fluticasone propionate 250 μg; FRC = functional residual capacity; MDI = metered dose inhaler; RV = residual volume; S50 = salmeterol 50 μg; sGaw = specific airway conductance; TLC = total lung capacity.

NO Gas Exchange
Normals vs Patients With COPD ICS-Naive at Baseline:

There was no significant difference for NO gas exchange before and after correction for axial NO back diffusion in central (large airway NO maximal flux) and peripheral airways (CANO), comparing 20 age-matched older normals vs 39 enrolled patients with COPD on S50 at the end of run-in period, prior to randomization () At 50 mL/s, values for normals were 23 ± 10 ppb vs 28 ± 20 ppb for patients with COPD (P = .7) (Fig 2). For the two-group t tests for FENO at 50 mL/s and FENO at 100 mL/s, effect sizes were 0.29 and 0.21, respectively. The power to detect a difference of this size is limited and falls below the recommended 80%, thus a type 2 error cannot be ruled out. However, for large airway NO flux, the power was 86% (Fig 3) and for peripheral NO the power was 48% (Fig 4).

Figure Jump LinkFigure 2. Measurement of the total FENO at 50 mL/s in age-matched normals and patients with COPD in Group A and B on S50, F100/S50, and F250/S50. Values are in ppb, mean ± SD. In Group A, F250/S50 significantly decreased FENO in patients on S50. In Group B, FENO increased significantly when switching from F250/S50 to S50, but significantly decreased when switching from S50 to F100/S50. FENO 5 exhaled fraction of nitric oxide; NO 5 nitric oxide; ppb 5 parts per billion. See Figure 1 legend for expansion of other abbreviations.Grahic Jump Location
Figure Jump LinkFigure 3. Measurement of large airway NO flux in age-matched normals and patients with COPD in Group A and B on S50, F100/S50, and F250/S50. Values are in nL/s, mean ± SD. In Group A, F250/S50 significantly decreased NO flux in patients on S50. In Group B, NO flux increased significantly when switching from F250/S50 to S50, but there was no change when switching from S50 to F100/S50. Values are corrected for NO axial backdiffusion,27 and results are similar to uncorrected results. See Figures 1 and 2 legends for expansion of abbreviations.Grahic Jump Location
Figure Jump LinkFigure 4. Measurement of small airway/alveolar NO in age-matched normals and patients with COPD in Group A and B on S50, F100/S50, and F250/S50. Values are in ppb, mean ± SD. In Group A, F250/S50 insignificantly decreased peripheral NO in patients on S50. In Group B, peripheral NO increased insignificantly when switching from F250/S50 to S50, and there was no change when switching from S50 to F100/S50. Values are corrected for NO axial backdiffusion,27 and results are in contrast to uncorrected results. See Figures 1 and 2 legends for expansion of abbreviations.Grahic Jump Location
NO Gas Exchange in Patients With COPD in Group A on S50 vs F250/S50:

Comparison in 12 patients between S50 vs F250/S50 after a mean 77 ± 15 treatment days resulted in a significant decrease in FENO at 50 mL/s on S50: 32 ± 17 ppb vs F250/S50: 20 ± 11(P = .001) (Fig 2) and large airway NO flux (P < .001) (Fig 3), both before and after correction for NO axial backdiffusion,27 with a decrease in peripheral small airway/alveolar NO gas exchange (P = .03) only before correction for NO axial diffusion,27 reflecting a spurious result (Fig 4).

NO Gas Exchange in Patients With COPD in Group B on F250/S50 vs S50:

Comparison in 16 patients between F250/S50 vs S50 after a mean 57 ± 22 treatment days resulted in a significant increase in FENO at 50 mL/s on F250/S50: 10 ± 6 ppb vs S50: 23 ± 21 ppb (P = .01) (Fig 2) and large airway NO flux (P = .04), both before and after correction for NO axial diffusion27 (Fig 3), and an increase in peripheral small airway/alveolar NO gas exchange (P = .04) only before correction for NO axial diffusion,27 reflecting a spurious result (Fig 4).

NO Gas Exchange in Patients With COPD in Group B on S50 Vs F100/S50:

Pairwise comparison in 14 COPD patients on S50 vs F100/S50 after a mean 60 ± 23 treatment days resulted in a significant decrease only in FENO at 50 mL/s on S50: 24 ± 16 ppb vs F100/S50: 18 ± 10 ppb (P = .045) (Fig 2). There was no significant decrease in large airway NO flux (P = .07), both before and after correction for NO axial diffusion (see Fig 3). Peripheral small airway/alveolar NO gas exchange was similar (P = .5), both before and after correction for NO axial diffusion (Fig 4). Differences were small, and the power to detect differences of this magnitude with our sample was limited.

Lung CT Scan:

The high-resolution, thin-section lung CT scan emphysema score30 in 39 patients with COPD was 29 ± 26 (mean ± SD), and there was no difference between Group A and Group B (P = .6). There were no significant correlations between the lung CT scan emphysema score and NO gas exchange in patients with COPD on S50, F100/S50, and F250/S50. For patients on S50, correlations with lung CT scan were r = −0.1 (P = .7) for FENO at 50 mL/s, r = 0.04 (P = .6) for NO at 100 mL/s, r = −0.1 (P = .6) for large airway NO, and r = 0.3 (P = .1) for small airway/alveolar NO. Values were similar for F100/S50 and F250/S50.

As reported herein, we observed no significant difference for large airway NO flux and peripheral small airway/alveolar NO production in clinically stable, ex-smoking patients with moderate to severe COPD29 with varying extents of emphysema, compared with age-matched older, healthy, nonsmoking controls with normal lung function. Values were similar, both before and after correction for NO axial backdiffusion.27 These observations imply no increase in NO-mediated proinflammatory signals originating in proximal airways and/or distal bronchioles and alveoli in patients with COPD. Despite normal values, there was significant suppression of large airway NO flux in patients with COPD after F250/S50, before and after correction for axial NO backdiffusion,27 but not with F100/S50, compared with S50. Furthermore, after F250/S50, there was no significant suppression of peripheral NO production, after correction for NO axial backdiffusion.27 Moreover, there was no correlation between the extent of lung-CT-scored emphysema as a marker of COPD phenotype and any parameter of NO gas exchange in patients with COPD on S50, F100/S50, and F250/S50. To the best of our knowledge, these observations are novel and may have important clinical implications.

Peripheral Airway/Alveolar NO Production and ICS

The present observations expand our initial observations26 and contrast with previously published results by Högman et al10 and Brindicci et al.24 They both reported significantly increased small airway/alveolar NO production in their cohorts with COPD compared with controls, but did not correct for NO axial backdiffusion.27 Their cohorts with COPD had similar extents of expiratory airflow limitation as patients in the present study. However, in the Brindicci et al24 study, comparison healthy nonsmokers had a mean age of 45 years, whereas their symptomatic cohort with COPD had a mean age of 62 years. We noted that younger normals have significantly lower values for peripheral NO compared with older normals.15,16 Furthermore, Brindicci et al24 noted no effect of ICS on peripheral NO production. Alternatively, Högman et al10 used age-matched controls, but did not correct for axial NO back diffusion. If large airway NO flux in patients with COPD was either increased or decreased relative to controls, it would decrease or increase peripheral NO, respectively, after correction for axial NO diffusion.27 Our results are similar to those of Roy et al,25 who noted no increase in central NO flux and peripheral NO production in patients with COPD compared with age-matched, healthy, older, nonsmoking subjects. This would yield similar results with or without correction for axial NO diffusion.27 In the present study, despite normal values, F250/S50, but not F100/S50, was able to suppress central airway NO flux in the cohort with COPD.

The 20 older, healthy nonsmokers aged 71 ± 7 years (mean ± SD) in the present study with normal lung function had similar normal large airway NO flux, but unexpectedly had significantly elevated small airway/alveolar NO production: 5.5 ± 3.1 ppb (mean ± SD) vs 3.2 ± 2.0 ppb obtained in 34 younger controls aged 40 ± 17 years (P < .001) previously studied in our laboratory,15,16 both before and after correction for NO axial backdiffusion.27 This discrepancy is obviously not related to technical or equipment differences and probably is more reflective of aging, yet the mechanisms remain unexplained.

Potential Mechanisms for Spurious Increased Peripheral NO

Previously, Silkoff et al31 reported methacholine-induced bronchoconstriction in people with asthma, with reduction in epithelial surface area and decreased NO production by approximately 15%. We would have anticipated that the reduced small airway epithelial/alveolar surface area in COPD, especially with accompanying emphysema, would have reduced small airway/alveolar NO production (CANO). However, since partial pressure of NO in the small airway/alveolar area (PL) = production of NO by surrounding tissue (VNO) / diffusing capacity of NO (DNO) from air space into surrounding blood vessels, either an increase in NO tissue production as a signal of inflammation (increased inducible NO synthase and/or constitutive NO synthase) or reduced NO diffusion could increase CANO.32 Lehtimäki et al33 previously showed an inverse relationship between CANO and diffusing capacity in alveolitis. In histamine-induced bronchoconstriction in normals, Verbanck et al34 noted a spurious increase in convective NO flow, as reflected by increased FENO at 50 mL/s and reduced CANO that was attributed to a reduction in NO axial backdiffusion due to inhomogeneous airway bronchospasm. Moreover, studies by Kerckx et al,35,36 after correction for NO axial diffusion, reached similar conclusions as Condorelli et al27 that normals and people with asthma, without obstruction, had minimal NO contribution from peripheral airway sites. In the present study, after correction for NO axial backdiffusion, there was no difference in the peripheral contribution of NO in normals vs patients with COPD, and this correction avoids spurious overestimation of peripheral NO.

Large Airway NO Production and ICS and Potential Mechanisms

Large airway NO flux has been noted to be normal24,25 and increased10 in clinically stable patients with COPD. In the present study, despite normal values for large airway NO flux, F250/S50, but not F100/S50, significantly (P = .002) suppressed large airway NO flux compared with S50 in the cohort with COPD. Large airway NO flux is the product of NO production in the bronchial wall mucosa (Cw) and the bronchial NO diffusing capacity that reflects transfer of NO from the airway wall to the lumen of expired air and is proportional to the lumen surface area and the transfer coefficient.12 Despite similar values for large airway NO flux in patients with COPD vs age-matched and non-age-matched controls, patients with COPD may have disproportionately increased Cw and reduced DNO. This would explain the response of decreasing Cw and overall NO flux following ICS in patients with COPD. While we did not measure Cw and DNO, this could be estimated, as noted by Silkoff et al,12 using low exhaled flow rates (5-10 mL/s) and application of a nonlinear method. Results in the present study suggest that measuring NO gas exchange only at 50 mL/s may prove adequate as a reflection of predominantly central airway flux.

NO Gas Exchange at a Single Expiratory Flow Rate in Stable and Unstable Patients With COPD

COPD is an inflammatory disease of both large and small airways and alveoli that is predominantly mediated by cytokines and interleukins via neutrophilic cellular pathways.2,7,24,37-39 Exhaled NO, a presumed surrogate marker of eosinophilic-mediated proinflammatory pathways, is usually increased in symptomatic asthma.8,40 In stable patients with COPD, total exhaled NO measured at varying single expiratory flow rates has been previously reviewed.2,7,8,24,37 Delen et al41 and Rutgers et al42 reported exhaled NO to be normal; elevated exhaled NO was reported by Ansarin et al,43 Corradi et al,44 and Maziak et al.45 It may be increased with exacerbations, as noted by Bhowmik et al,46 Maskey-Warzechowska et al,47 Agustí et al,48 Montuschi et al,49 and Papi et al.50 Furthermore, Kunisaki et al51 reported that elevated NO in severe COPD may also be a signal for spirometric response to ICS. Siva et al52 reported that sputum eosinophils and exhaled NO were not good surrogates of eosinophilic airway inflammation in patients with COPD treated with ICS to control moderate exacerbations. Liu et al,53 using offline collection, reported that patients with COPD who were on or off ICS had significantly elevated exhaled NO compared with age-matched controls. However, suppression of large airway NO flux, as noted in the present study, may be an important mechanism that reflects potential benefit of ICS in COPD.54-56 The present results also support the clinical benefits of using F250/S50 in reducing exacerbations in COPD, as reported by Ferguson et al.55 Rennard et al57 also reported greater efficacy of higher-dose compared with lower-dose budesonide/formoterol per MDI for improvement in predose FEV1 in COPD.

Limitations of Study Design

The present randomization and crossover design with adequate therapeutic intervention time should limit potential errors related to multiple sequencing and incomplete washout with carryover effect, despite the small patient numbers. Moreover, results from the randomization demonstrated that F250/S50, but not F100/S50, can significantly (P < .001) suppress large airway NO flux compared with S50 alone (see Table 2). However, the current small patient numbers resulted in an underpowered study for F100/S50. A minimum of 160 patients with COPD per arm would be required to have 80% power to detect a difference of 0.4 nL/s in large airway NO flux in S50 (group B) vs F100/S50 (group B), assuming a common standard deviation of 1.3 nL/s using a two-group t test with a 0.05 two-sided significance level. However, using the observed standard deviation in each group, 115 patients with COPD in each group would be needed to achieve 80% power. The normal values for our 20 age-matched controls at 50 mL/s (ppb) are consistent with previous values obtained in normals aged < 65 years.58

Summary

Our current observations, using the two-compartment NO model13,14 with correction for NO axial backdiffusion,27 noted both normal large airway NO flux and peripheral small airway/alveolar NO production in clinically stable, ICS-naive, patients with COPD compared with age-matched older normals. Furthermore, large airway and small airway NO values were independent of the extent of lung-CT-scored emphysema. However, when compared with younger middle-aged normals,15,16 both older normals and patients with COPD had unexplained increased peripheral small airway/alveolar NO production. Moreover, moderate-dose ICS F250/S50, but not F100/S50, significantly suppressed large airway NO flux but not peripheral NO production in these patients with COPD. Correction for NO axial backdiffusion may avoid spurious values for peripheral NO production. Measurement of NO gas exchange at only 50 mL/s in clinically stable patients with COPD should prove adequate, since it reflects predominantly central airway NO flux and peripheral NO production is normal.

Table Graphic Jump Location
Table 2 —NO Gas Exchange in Normals and Patients With COPD, With Multiple Comparisons

In Group A, 19 patients were initially randomized to S50 then switched to F250/S50, and 12 patients completed FENO testing. In Group B, 20 patients were initially randomized to F250/S50 then switched to S50, and 16 patients completed FENO testing, then 14 patients switched to F100/S50, and all 14 completed FENO testing. Results are stated as mean ± SD. Measurements of NO gas exchange were obtained prior to spirometry. The NO gas exchange values in Table 2 are shown before and after correcting for NO axial backdiffusion.27 F100 = fluticasone propionate 100 μg; Grp= group; FENO = fraction expired nitric oxide; NO = nitric oxide; ppb = parts per billion.

Author contributions:Dr Gelb: was responsible for the development and completion of this study, was responsible for all patient care, and wrote this manuscript.

Ms Taylor: was responsible for data collection.

Dr Krishnan: was responsible for data collection, was responsible for data analysis, and had valuable input in this manuscript.

Ms Fraser: was responsible for data collection.

Dr Shinar: was responsible for data analysis and had valuable input in this manuscript.

Dr Schein: was responsible for interpretation of lung CT scans.

Dr Osann: was responsible for statistical analysis and also had valuable input in this manuscript.

Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Other contributions: We acknowledge Christy Kirkendall, Jomeka Beavers, and Michelle Curry for patient scheduling. The authors express their gratitude to Steven C. George MD, PhD, and Philip Silkoff, MD, for valuable input and discussion of the study and manuscript.

CANO

nitric oxide concentration

Cw

bronchial wall mucosa

DNO

diffusing capacity of nitric oxide

F100

fluticasone propionate 100 mg

F250

fluticasone propionate 250 mg

FENO

exhaled fraction of nitric oxide

ICS

inhaled corticosteroids

MDI

metered-dose inhaler

NO

nitric oxide

ppb

parts per billion

S50

salmeterol

Kharitonov SA, Gonio F, Kelly C, Meah S, Barnes PJ. Reproducibility of exhaled nitric oxide measurements in healthy and asthmatic adults and children. Eur Respir J. 2003;213:433-438. [CrossRef] [PubMed]
 
Barnes PJ, Chowdhury B, Kharitonov SA, et al. Pulmonary biomarkers in chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2006;1741:6-14. [CrossRef] [PubMed]
 
Kharitonov SA, Yates DH, Barnes PJ. Inhaled glucocorticoids decrease nitric oxide in exhaled air of asthmatic patients. Am J Respir Crit Care Med. 1996;1531:454-457. [PubMed]
 
Green RH, Brightling CE, McKenna S, et al. Asthma exacerbations and sputum eosinophil counts: a randomised controlled trial. Lancet. 2002;3609347:1715-1721. [CrossRef] [PubMed]
 
Taylor DR, Pijnenburg MW, Smith AD, De Jongste JC. Exhaled nitric oxide measurements: clinical application and interpretation. Thorax. 2006;619:817-827. [CrossRef] [PubMed]
 
Ricciardolo FL, Sterk PJ, Gaston B, Folkerts G. Nitric oxide in health and disease of the respiratory system. Physiol Rev. 2004;843:731-765. [CrossRef] [PubMed]
 
Kharitonov SA, Barnes PJ. Exhaled biomarkers. Chest. 2006;1305:1541-1546. [CrossRef] [PubMed]
 
American Thoracic Society, European Respiratory SocietyAmerican Thoracic Society, European Respiratory Society ATS/ERS recommendations for standardized procedures for the online and offline measurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005. Am J Respir Crit Care Med. 2005;1718:912-930. [CrossRef] [PubMed]
 
George SC, Hogman M, Permutt S, Silkoff PE. Modeling pulmonary nitric oxide exchange. J Appl Physiol. 2004;963:831-839. [CrossRef] [PubMed]
 
Högman M, Holmkvist T, Wegener T, et al. Extended NO analysis applied to patients with COPD, allergic asthma and allergic rhinitis. Respir Med. 2002;961:24-30. [CrossRef] [PubMed]
 
Pietropaoli AP, Perillo IB, Torres A, et al. Simultaneous measurement of nitric oxide production by conducting and alveolar airways of humans. J Appl Physiol. 1999;874:1532-1542. [PubMed]
 
Silkoff PE, Sylvester JT, Zamel N, Permutt S. Airway nitric oxide diffusion in asthma: role in pulmonary function and bronchial responsiveness. Am J Respir Crit Care Med. 2000;1614 Pt 1:1218-1228. [PubMed]
 
Tsoukias NM, George SC. A two-compartment model of pulmonary nitric oxide exchange dynamics. J Appl Physiol. 1998;852:653-666. [PubMed]
 
Tsoukias NM, Shin HW, Wilson AF, George SC. A single-breath technique with variable flow rate to characterize nitric oxide exchange dynamics in the lungs. J Appl Physiol. 2001;911:477-487. [PubMed]
 
Gelb AF, Flynn-Taylor C, Nussbaum E, et al. Alveolar and airway sites of nitric oxide inflammation in treated asthma. J Respir Crit Care Med. 2004;1707:737-741. [CrossRef]
 
Gelb AF, Flynn Taylor C, Shinar CM, Gutierrez C, Zamel N. Role of spirometry and exhaled nitric oxide to predict exacerbations in treated asthmatics. Chest. 2006;1296:1492-1499. [CrossRef] [PubMed]
 
Lehtimäki L, Kankaanranta H, Saarelainen S, Turjanmaa V, Moilanen E. Inhaled fluticasone decreases bronchial but not alveolar nitric oxide output in asthma. Eur Respir J. 2001;184:635-639. [CrossRef] [PubMed]
 
van Veen IH, Sterk PJ, Schot R, Gauw SA, Rabe KF, Bel EH. Alveolar nitric oxide versus measures of peripheral airway dysfunction in severe asthma. Eur Respir J. 2006;275:951-956. [PubMed]
 
Berry M, Hargadon B, Morgan A, et al. Alveolar nitric oxide in adults with asthma: evidence of distal lung inflammation in refractory asthma. Eur Respir J. 2005;256:986-991. [CrossRef] [PubMed]
 
Mahut B, Delacourt C, Zerah-Lancner F, De Blic J, Harf A, Delclaux C. Increase in alveolar nitric oxide in the presence of symptoms in childhood asthma. Chest. 2004;1253:1012-1018. [CrossRef] [PubMed]
 
Paraskakis E, Brindicci C, Fleming L, et al. Measurement of bronchial and alveolar nitric oxide production in normal children and children with asthma. AJRCCM. 2006;1743:260-267
 
Brindicci C, Ito K, Barnes PJ, Kharitonov SA. Differential flow analysis of exhaled nitric oxide in patients with asthma of differing severity. Chest. 2007;1315:1353-1362. [CrossRef] [PubMed]
 
Shin HW, Rose-Gottron CM, Cooper DM, et al. Airway diffusing capacity of nitric oxide and steroid therapy in asthma. J Appl Physiol. 2004; Jan961:65-75. [CrossRef] [PubMed]
 
Brindicci C, Ito K, Resta O, Pride NB, Barnes PJ, Kharitonov SA. Exhaled nitric oxide from lung periphery is increased in COPD. Eur Respir J. 2005;261:52-59. [CrossRef] [PubMed]
 
Roy K, Borrill ZL, Starkey C, et al. Use of different exhaled nitric oxide multiple flow rate models in COPD. Eur Respir J. 2007;294:651-659. [CrossRef] [PubMed]
 
Gelb AF, Taylor CF, Shinar C, et al. Nitric oxide gas exchange in COPD. Am J Respir Crit Care Med. 2007;174X:A630
 
Condorelli P, Shin HW, Aledia AS, Silkoff PE, George SC. A simple technique to characterize proximal and peripheral nitric oxide exchange using constant flow exhalations and an axial diffusion model. J Appl Physiol. 2007;1021:417-425. [CrossRef] [PubMed]
 
Silkoff PE, McClean PA, Slutsky AS, et al. Marked flow-dependence of exhaled nitric oxide using a new technique to exclude nasal nitric oxide. Am J Respir Crit Care Med. 1997;1551:260-267. [PubMed]
 
Rabe KF, Hurd S, Anzueto A, et al. Global strategy for the diagnosis, management, and prevention of COPD: GOLD Executive Summary. Am J Respir Crit Care Med. 2007;1766:532-555. [CrossRef] [PubMed]
 
Gelb AF, Hogg JC, Müller NL, et al. Contribution of emphysema and small airways in COPD. Chest. 1996;1092:353-359. [CrossRef] [PubMed]
 
Silkoff PE, McClean PA, Slutsky AS, et al. Exhaled nitric oxide and bronchial reactivity during and after inhaled beclomethasone in mild asthma. J Asthma. 1998;356:473-479. [CrossRef] [PubMed]
 
Hyde RW, Geigel EJ, Olszowka AJ, et al. Determination of production of nitric oxide by lower airways of humans—theory. J Appl Physiol. 1997;824:1290-1296. [PubMed]
 
Lehtimäki L, Kankaanranta H, Saarelainen S, et al. Extended exhaled NO measurement differentiates between alveolar and bronchial inflammation. Am J Respir Crit Care Med. 2001;1637:1557-1561. [PubMed]
 
Verbanck S, Kerckx Y, Schuermans D, et al. How accurately should we estimate the anatomical source of exhaled nitric oxide? J Appl Physiol. 2008;1044:909-911. [CrossRef] [PubMed]
 
Kerckx Y, Michils A, Van Muylem A. Airway contribution to alveolar nitric oxide in healthy subjects and stable asthma patients. J Appl Physiol. 2008;1044:918-924. [CrossRef] [PubMed]
 
Kerckx Y, Van Muylem A. Axial distribution heterogeneity of nitric oxide airway production in healthy adults. J Appl Physiol. 2009;1066:1832-1839. [CrossRef] [PubMed]
 
Celli BR, Barnes PJ. Exacerbations of chronic obstructive pulmonary disease. Eur Respir J. 2007;296:1224-1238. [CrossRef] [PubMed]
 
Barnes PJ. The cytokine network in asthma and chronic obstructive pulmonary disease. J Clin Invest. 2008;11811:3546-3556. [CrossRef] [PubMed]
 
Barnes PJ. Immunology of asthma and chronic obstructive pulmonary disease. Nat Rev Immunol. 2008;83:183-192. [CrossRef] [PubMed]
 
Silkoff PE, Lent AM, Busacker AA, et al. Exhaled nitric oxide identifies the persistent eosinophilic phenotype in severe refractory asthma. J Allergy Clin Immunol. 2005;1166:1249-1255. [CrossRef] [PubMed]
 
Delen FM, Sippel JM, Osborne ML, Law S, Thukkani N, Holden WE. Increased exhaled nitric oxide in chronic bronchitis: comparison with asthma and COPD. Chest. 2000;1173:695-701. [CrossRef] [PubMed]
 
Rutgers SR, van der Mark TW, Coers W, et al. Markers of nitric oxide metabolism in sputum and exhaled air are not increased in chronic obstructive pulmonary disease. Thorax. 1999;547:576-580. [CrossRef] [PubMed]
 
Ansarin K, Chatkin JM, Ferreira IM, Gutierrez CA, Zamel N, Chapman KR. Exhaled nitric oxide in chronic obstructive pulmonary disease: relationship to pulmonary function. Eur Respir J. 2001;175:934-938. [CrossRef] [PubMed]
 
Corradi M, Majori M, Cacciani GC, et al. Exhaled nitric oxide in COPD: glancing through a smoke screen. Thorax. 1999;547:565-567. [CrossRef] [PubMed]
 
Maziak W, Loukides S, Culpitt S, Sullivan P, Kharitonov SA, Barnes PJ. Exhaled nitric oxide in chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 1998;1573 Pt 1:998-1002. [PubMed]
 
Bhowmik A, Seemungal TA, Donaldson GC, et al. Effects of exacerbations and seasonality on exhaled nitric oxide in COPD. Eur Respir J. 2005;266:1009-1015. [CrossRef] [PubMed]
 
Maskey-Warzechowska M, Przybyłowski T, Hildebrand K, et al. [The effect of asthma and COPD exacerbation on exhaled nitric oxide (FE(NO))]. Pneumonol Alergol Pol. 2004;725-6:181-186. [PubMed]
 
Agustí AG, Villaverde JM, Togores B, Bosch M. Serial measurements of exhaled nitric oxide during exacerbations of chronic obstructive pulmonary disease. Eur Respir J. 1999;143:523-528. [CrossRef] [PubMed]
 
Montuschi P, Kharitonov SA, Barnes PJ. Exhaled carbon monoxide and nitric oxide in COPD. Chest. 2001;1202:496-501. [CrossRef] [PubMed]
 
Papi A, Romagnoli M, Baraldo S, et al. Partial reversibility of airflow limitation and increased exhaled NO and sputum eosinophilia in chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2000;1625:1773-1777. [PubMed]
 
Kunisaki KM, Rice KL, Janoff EN, et al. Exhaled nitric oxide, systemic inflammation, and the spirometric response to inhaled fluticasone propionate in severe chronic obstructive pulmonary disease: a prospective study. Ther Adv Respir Dis. 2008;22:55-64. [CrossRef] [PubMed]
 
Siva R, Green RH, Brightling CE, et al. Eosinophilic airway inflammation and exacerbations of COPD: a randomised controlled trial. Eur Respir J. 2007;295:906-913. [CrossRef] [PubMed]
 
Liu J, Sandrini A, Thurston MC, Yates DH, Thomas PS. Nitric oxide and exhaled breath nitrite/nitrates in chronic obstructive pulmonary disease patients. Respiration. 2007;746:617-623. [CrossRef] [PubMed]
 
Drummond MB, Dasenbrook EC, Pitz MW, Murphy DJ, Fan E. Inhaled corticosteroids in patients with stable chronic obstructive pulmonary disease: a systematic review and meta-analysis. JAMA. 2008;30020:2407-2416. [CrossRef] [PubMed]
 
Ferguson GT, Anzueto A, Fei R, Emmett A, Knobil K, Kalberg C. Effect of fluticasone propionate/salmeterol (250/50 microg) or salmeterol (50 microg) on COPD exacerbations. Respir Med. 2008;1028:1099-1108. [CrossRef] [PubMed]
 
Calverley PMA, Anderson JA, Celli B, et al; TORCH investigators TORCH investigators Salmeterol and fluticasone propionate and survival in chronic obstructive pulmonary disease. N Engl J Med. 2007;3568:775-789. [CrossRef] [PubMed]
 
Rennard SI, Tashkin DP, McElhattan J, et al. Efficacy and tolerability of budesonide/formoterol in one hydrofluoroalkane pressurized metered-dose inhaler in patients with chronic obstructive pulmonary disease: results from a 1-year randomized controlled clinical trial. Drugs. 2009;695:549-565. [CrossRef] [PubMed]
 
Olin AC, Bake B, Toren K. Fraction of exhaled nitric oxide at 50 mL/s: reference values for adult lifelong never-smokers. Chest. 2007;1316:1852-1856. [CrossRef] [PubMed]
 

Figures

Figure Jump LinkFigure 1. Diagram of 39 patients with COPD, ICS naive, on S50 bid × 60 days then subsequently randomized. Twelve of 19 patients in Group A (initially S50) and 16 of 20 patients in Group B (initially F250/S50) successfully completed the crossover. All 14 patients in Group B completed the switch from S50 to F100/S50. F100 5 fluticasone propionate 100 μg; F250 5 fluticasone propionate 250 μg; ICS 5 inhaled corticosteroids; S50 5 salmeterol 50 μg.Grahic Jump Location
Figure Jump LinkFigure 2. Measurement of the total FENO at 50 mL/s in age-matched normals and patients with COPD in Group A and B on S50, F100/S50, and F250/S50. Values are in ppb, mean ± SD. In Group A, F250/S50 significantly decreased FENO in patients on S50. In Group B, FENO increased significantly when switching from F250/S50 to S50, but significantly decreased when switching from S50 to F100/S50. FENO 5 exhaled fraction of nitric oxide; NO 5 nitric oxide; ppb 5 parts per billion. See Figure 1 legend for expansion of other abbreviations.Grahic Jump Location
Figure Jump LinkFigure 3. Measurement of large airway NO flux in age-matched normals and patients with COPD in Group A and B on S50, F100/S50, and F250/S50. Values are in nL/s, mean ± SD. In Group A, F250/S50 significantly decreased NO flux in patients on S50. In Group B, NO flux increased significantly when switching from F250/S50 to S50, but there was no change when switching from S50 to F100/S50. Values are corrected for NO axial backdiffusion,27 and results are similar to uncorrected results. See Figures 1 and 2 legends for expansion of abbreviations.Grahic Jump Location
Figure Jump LinkFigure 4. Measurement of small airway/alveolar NO in age-matched normals and patients with COPD in Group A and B on S50, F100/S50, and F250/S50. Values are in ppb, mean ± SD. In Group A, F250/S50 insignificantly decreased peripheral NO in patients on S50. In Group B, peripheral NO increased insignificantly when switching from F250/S50 to S50, and there was no change when switching from S50 to F100/S50. Values are corrected for NO axial backdiffusion,27 and results are in contrast to uncorrected results. See Figures 1 and 2 legends for expansion of abbreviations.Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1 —Baseline (Visit 1) Lung Function in Normals and Patients With COPD, With Comparison of Group A (S50) vs Group B (F250/S50) After Randomization

Spirometric data obtained in COPD patients are before and after 180 mg albuterol by MDI and all other spirometric values obtained after bronchodilation. % pred = percent predicted, results are mean ± SD; DL/VA = diffusing capacity/alveolar volume; F250 = fluticasone propionate 250 μg; FRC = functional residual capacity; MDI = metered dose inhaler; RV = residual volume; S50 = salmeterol 50 μg; sGaw = specific airway conductance; TLC = total lung capacity.

Table Graphic Jump Location
Table 2 —NO Gas Exchange in Normals and Patients With COPD, With Multiple Comparisons

In Group A, 19 patients were initially randomized to S50 then switched to F250/S50, and 12 patients completed FENO testing. In Group B, 20 patients were initially randomized to F250/S50 then switched to S50, and 16 patients completed FENO testing, then 14 patients switched to F100/S50, and all 14 completed FENO testing. Results are stated as mean ± SD. Measurements of NO gas exchange were obtained prior to spirometry. The NO gas exchange values in Table 2 are shown before and after correcting for NO axial backdiffusion.27 F100 = fluticasone propionate 100 μg; Grp= group; FENO = fraction expired nitric oxide; NO = nitric oxide; ppb = parts per billion.

References

Kharitonov SA, Gonio F, Kelly C, Meah S, Barnes PJ. Reproducibility of exhaled nitric oxide measurements in healthy and asthmatic adults and children. Eur Respir J. 2003;213:433-438. [CrossRef] [PubMed]
 
Barnes PJ, Chowdhury B, Kharitonov SA, et al. Pulmonary biomarkers in chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2006;1741:6-14. [CrossRef] [PubMed]
 
Kharitonov SA, Yates DH, Barnes PJ. Inhaled glucocorticoids decrease nitric oxide in exhaled air of asthmatic patients. Am J Respir Crit Care Med. 1996;1531:454-457. [PubMed]
 
Green RH, Brightling CE, McKenna S, et al. Asthma exacerbations and sputum eosinophil counts: a randomised controlled trial. Lancet. 2002;3609347:1715-1721. [CrossRef] [PubMed]
 
Taylor DR, Pijnenburg MW, Smith AD, De Jongste JC. Exhaled nitric oxide measurements: clinical application and interpretation. Thorax. 2006;619:817-827. [CrossRef] [PubMed]
 
Ricciardolo FL, Sterk PJ, Gaston B, Folkerts G. Nitric oxide in health and disease of the respiratory system. Physiol Rev. 2004;843:731-765. [CrossRef] [PubMed]
 
Kharitonov SA, Barnes PJ. Exhaled biomarkers. Chest. 2006;1305:1541-1546. [CrossRef] [PubMed]
 
American Thoracic Society, European Respiratory SocietyAmerican Thoracic Society, European Respiratory Society ATS/ERS recommendations for standardized procedures for the online and offline measurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005. Am J Respir Crit Care Med. 2005;1718:912-930. [CrossRef] [PubMed]
 
George SC, Hogman M, Permutt S, Silkoff PE. Modeling pulmonary nitric oxide exchange. J Appl Physiol. 2004;963:831-839. [CrossRef] [PubMed]
 
Högman M, Holmkvist T, Wegener T, et al. Extended NO analysis applied to patients with COPD, allergic asthma and allergic rhinitis. Respir Med. 2002;961:24-30. [CrossRef] [PubMed]
 
Pietropaoli AP, Perillo IB, Torres A, et al. Simultaneous measurement of nitric oxide production by conducting and alveolar airways of humans. J Appl Physiol. 1999;874:1532-1542. [PubMed]
 
Silkoff PE, Sylvester JT, Zamel N, Permutt S. Airway nitric oxide diffusion in asthma: role in pulmonary function and bronchial responsiveness. Am J Respir Crit Care Med. 2000;1614 Pt 1:1218-1228. [PubMed]
 
Tsoukias NM, George SC. A two-compartment model of pulmonary nitric oxide exchange dynamics. J Appl Physiol. 1998;852:653-666. [PubMed]
 
Tsoukias NM, Shin HW, Wilson AF, George SC. A single-breath technique with variable flow rate to characterize nitric oxide exchange dynamics in the lungs. J Appl Physiol. 2001;911:477-487. [PubMed]
 
Gelb AF, Flynn-Taylor C, Nussbaum E, et al. Alveolar and airway sites of nitric oxide inflammation in treated asthma. J Respir Crit Care Med. 2004;1707:737-741. [CrossRef]
 
Gelb AF, Flynn Taylor C, Shinar CM, Gutierrez C, Zamel N. Role of spirometry and exhaled nitric oxide to predict exacerbations in treated asthmatics. Chest. 2006;1296:1492-1499. [CrossRef] [PubMed]
 
Lehtimäki L, Kankaanranta H, Saarelainen S, Turjanmaa V, Moilanen E. Inhaled fluticasone decreases bronchial but not alveolar nitric oxide output in asthma. Eur Respir J. 2001;184:635-639. [CrossRef] [PubMed]
 
van Veen IH, Sterk PJ, Schot R, Gauw SA, Rabe KF, Bel EH. Alveolar nitric oxide versus measures of peripheral airway dysfunction in severe asthma. Eur Respir J. 2006;275:951-956. [PubMed]
 
Berry M, Hargadon B, Morgan A, et al. Alveolar nitric oxide in adults with asthma: evidence of distal lung inflammation in refractory asthma. Eur Respir J. 2005;256:986-991. [CrossRef] [PubMed]
 
Mahut B, Delacourt C, Zerah-Lancner F, De Blic J, Harf A, Delclaux C. Increase in alveolar nitric oxide in the presence of symptoms in childhood asthma. Chest. 2004;1253:1012-1018. [CrossRef] [PubMed]
 
Paraskakis E, Brindicci C, Fleming L, et al. Measurement of bronchial and alveolar nitric oxide production in normal children and children with asthma. AJRCCM. 2006;1743:260-267
 
Brindicci C, Ito K, Barnes PJ, Kharitonov SA. Differential flow analysis of exhaled nitric oxide in patients with asthma of differing severity. Chest. 2007;1315:1353-1362. [CrossRef] [PubMed]
 
Shin HW, Rose-Gottron CM, Cooper DM, et al. Airway diffusing capacity of nitric oxide and steroid therapy in asthma. J Appl Physiol. 2004; Jan961:65-75. [CrossRef] [PubMed]
 
Brindicci C, Ito K, Resta O, Pride NB, Barnes PJ, Kharitonov SA. Exhaled nitric oxide from lung periphery is increased in COPD. Eur Respir J. 2005;261:52-59. [CrossRef] [PubMed]
 
Roy K, Borrill ZL, Starkey C, et al. Use of different exhaled nitric oxide multiple flow rate models in COPD. Eur Respir J. 2007;294:651-659. [CrossRef] [PubMed]
 
Gelb AF, Taylor CF, Shinar C, et al. Nitric oxide gas exchange in COPD. Am J Respir Crit Care Med. 2007;174X:A630
 
Condorelli P, Shin HW, Aledia AS, Silkoff PE, George SC. A simple technique to characterize proximal and peripheral nitric oxide exchange using constant flow exhalations and an axial diffusion model. J Appl Physiol. 2007;1021:417-425. [CrossRef] [PubMed]
 
Silkoff PE, McClean PA, Slutsky AS, et al. Marked flow-dependence of exhaled nitric oxide using a new technique to exclude nasal nitric oxide. Am J Respir Crit Care Med. 1997;1551:260-267. [PubMed]
 
Rabe KF, Hurd S, Anzueto A, et al. Global strategy for the diagnosis, management, and prevention of COPD: GOLD Executive Summary. Am J Respir Crit Care Med. 2007;1766:532-555. [CrossRef] [PubMed]
 
Gelb AF, Hogg JC, Müller NL, et al. Contribution of emphysema and small airways in COPD. Chest. 1996;1092:353-359. [CrossRef] [PubMed]
 
Silkoff PE, McClean PA, Slutsky AS, et al. Exhaled nitric oxide and bronchial reactivity during and after inhaled beclomethasone in mild asthma. J Asthma. 1998;356:473-479. [CrossRef] [PubMed]
 
Hyde RW, Geigel EJ, Olszowka AJ, et al. Determination of production of nitric oxide by lower airways of humans—theory. J Appl Physiol. 1997;824:1290-1296. [PubMed]
 
Lehtimäki L, Kankaanranta H, Saarelainen S, et al. Extended exhaled NO measurement differentiates between alveolar and bronchial inflammation. Am J Respir Crit Care Med. 2001;1637:1557-1561. [PubMed]
 
Verbanck S, Kerckx Y, Schuermans D, et al. How accurately should we estimate the anatomical source of exhaled nitric oxide? J Appl Physiol. 2008;1044:909-911. [CrossRef] [PubMed]
 
Kerckx Y, Michils A, Van Muylem A. Airway contribution to alveolar nitric oxide in healthy subjects and stable asthma patients. J Appl Physiol. 2008;1044:918-924. [CrossRef] [PubMed]
 
Kerckx Y, Van Muylem A. Axial distribution heterogeneity of nitric oxide airway production in healthy adults. J Appl Physiol. 2009;1066:1832-1839. [CrossRef] [PubMed]
 
Celli BR, Barnes PJ. Exacerbations of chronic obstructive pulmonary disease. Eur Respir J. 2007;296:1224-1238. [CrossRef] [PubMed]
 
Barnes PJ. The cytokine network in asthma and chronic obstructive pulmonary disease. J Clin Invest. 2008;11811:3546-3556. [CrossRef] [PubMed]
 
Barnes PJ. Immunology of asthma and chronic obstructive pulmonary disease. Nat Rev Immunol. 2008;83:183-192. [CrossRef] [PubMed]
 
Silkoff PE, Lent AM, Busacker AA, et al. Exhaled nitric oxide identifies the persistent eosinophilic phenotype in severe refractory asthma. J Allergy Clin Immunol. 2005;1166:1249-1255. [CrossRef] [PubMed]
 
Delen FM, Sippel JM, Osborne ML, Law S, Thukkani N, Holden WE. Increased exhaled nitric oxide in chronic bronchitis: comparison with asthma and COPD. Chest. 2000;1173:695-701. [CrossRef] [PubMed]
 
Rutgers SR, van der Mark TW, Coers W, et al. Markers of nitric oxide metabolism in sputum and exhaled air are not increased in chronic obstructive pulmonary disease. Thorax. 1999;547:576-580. [CrossRef] [PubMed]
 
Ansarin K, Chatkin JM, Ferreira IM, Gutierrez CA, Zamel N, Chapman KR. Exhaled nitric oxide in chronic obstructive pulmonary disease: relationship to pulmonary function. Eur Respir J. 2001;175:934-938. [CrossRef] [PubMed]
 
Corradi M, Majori M, Cacciani GC, et al. Exhaled nitric oxide in COPD: glancing through a smoke screen. Thorax. 1999;547:565-567. [CrossRef] [PubMed]
 
Maziak W, Loukides S, Culpitt S, Sullivan P, Kharitonov SA, Barnes PJ. Exhaled nitric oxide in chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 1998;1573 Pt 1:998-1002. [PubMed]
 
Bhowmik A, Seemungal TA, Donaldson GC, et al. Effects of exacerbations and seasonality on exhaled nitric oxide in COPD. Eur Respir J. 2005;266:1009-1015. [CrossRef] [PubMed]
 
Maskey-Warzechowska M, Przybyłowski T, Hildebrand K, et al. [The effect of asthma and COPD exacerbation on exhaled nitric oxide (FE(NO))]. Pneumonol Alergol Pol. 2004;725-6:181-186. [PubMed]
 
Agustí AG, Villaverde JM, Togores B, Bosch M. Serial measurements of exhaled nitric oxide during exacerbations of chronic obstructive pulmonary disease. Eur Respir J. 1999;143:523-528. [CrossRef] [PubMed]
 
Montuschi P, Kharitonov SA, Barnes PJ. Exhaled carbon monoxide and nitric oxide in COPD. Chest. 2001;1202:496-501. [CrossRef] [PubMed]
 
Papi A, Romagnoli M, Baraldo S, et al. Partial reversibility of airflow limitation and increased exhaled NO and sputum eosinophilia in chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2000;1625:1773-1777. [PubMed]
 
Kunisaki KM, Rice KL, Janoff EN, et al. Exhaled nitric oxide, systemic inflammation, and the spirometric response to inhaled fluticasone propionate in severe chronic obstructive pulmonary disease: a prospective study. Ther Adv Respir Dis. 2008;22:55-64. [CrossRef] [PubMed]
 
Siva R, Green RH, Brightling CE, et al. Eosinophilic airway inflammation and exacerbations of COPD: a randomised controlled trial. Eur Respir J. 2007;295:906-913. [CrossRef] [PubMed]
 
Liu J, Sandrini A, Thurston MC, Yates DH, Thomas PS. Nitric oxide and exhaled breath nitrite/nitrates in chronic obstructive pulmonary disease patients. Respiration. 2007;746:617-623. [CrossRef] [PubMed]
 
Drummond MB, Dasenbrook EC, Pitz MW, Murphy DJ, Fan E. Inhaled corticosteroids in patients with stable chronic obstructive pulmonary disease: a systematic review and meta-analysis. JAMA. 2008;30020:2407-2416. [CrossRef] [PubMed]
 
Ferguson GT, Anzueto A, Fei R, Emmett A, Knobil K, Kalberg C. Effect of fluticasone propionate/salmeterol (250/50 microg) or salmeterol (50 microg) on COPD exacerbations. Respir Med. 2008;1028:1099-1108. [CrossRef] [PubMed]
 
Calverley PMA, Anderson JA, Celli B, et al; TORCH investigators TORCH investigators Salmeterol and fluticasone propionate and survival in chronic obstructive pulmonary disease. N Engl J Med. 2007;3568:775-789. [CrossRef] [PubMed]
 
Rennard SI, Tashkin DP, McElhattan J, et al. Efficacy and tolerability of budesonide/formoterol in one hydrofluoroalkane pressurized metered-dose inhaler in patients with chronic obstructive pulmonary disease: results from a 1-year randomized controlled clinical trial. Drugs. 2009;695:549-565. [CrossRef] [PubMed]
 
Olin AC, Bake B, Toren K. Fraction of exhaled nitric oxide at 50 mL/s: reference values for adult lifelong never-smokers. Chest. 2007;1316:1852-1856. [CrossRef] [PubMed]
 
NOTE:
Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging & repositioning the boxes below.

Find Similar Articles
CHEST Journal Articles
  • CHEST Journal
    Print ISSN: 0012-3692
    Online ISSN: 1931-3543