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. 2016 Dec;6(4):545–550. doi: 10.1086/688768

Exhaled nitric oxide in pulmonary arterial hypertension associated with systemic sclerosis

Zeling Cao 1,✉, Stephen C Mathai 1, Laura K Hummers 2, Ami A Shah 2, Fredrick M Wigley 2, Noah Lechtzin 1, Paul M Hassoun 1, Reda E Girgis 3
PMCID: PMC5210065  PMID: 28090297

Abstract Abstract

The fractional exhaled concentration of nitric oxide (FENO) has been shown to be reduced in idiopathic pulmonary arterial hypertension (PAH) but has not been adequately studied in PAH associated with systemic sclerosis (SSc). We measured FENO at an expiratory flow rate of 50 mL/s in 21 treatment-naive patients with SSc-associated PAH (SSc-PAH), 94 subjects with SSc without pulmonary involvement, and 84 healthy volunteers. Measurements of FENO at additional flow rates of 100, 150, and 250 mL/s were obtained to derive the flow-independent nitric oxide exchange parameters of maximal airway flux (J′awNO) and steady-state alveolar concentration (CANO). FENO at 50 mL/s was similar (P = 0.22) in the SSc-PAH group (19 ± 12 parts per billion [ppb]) compared with the SSc group (17 ± 12 ppb) and healthy control group (21 ± 11 ppb). No change was observed after 4 months of targeted PAH therapy in 14 SSc-PAH group patients (P = 0.9). J′awNO was modestly reduced in SSc group subjects without lung disease (1.2 ± 0.5 nl/s) compared with healthy controls (1.64 ± 0.9; P < 0.05) but was similar to that in the SSc-PAH group. CANO was elevated in individuals with SSc-PAH (4.8 ± 2.6 ppb) compared with controls with SSc (3.3 ± 1.4 ppb) and healthy subjects (2.6 ± 1.5 ppb; P < 0.001 for both). However, after adjustment for the diffusing capacity of CO, there was no significant difference in CANO between individuals with SSc-PAH and controls with SSc. We conclude that FENO is not useful for the diagnosis of PAH in SSc. Increased alveolar nitric oxide in SSc-PAH likely represents impaired diffusion into pulmonary capillary blood.

Keywords: exhaled nitric oxide, pulmonary arterial hypertension, scleroderma, systemic sclerosis

Pulmonary arterial hypertension (PAH) is a leading cause of morbidity and mortality in scleroderma or systemic sclerosis (SSc).1 Despite therapy with currently available agents, prognosis remains poor with a 3-year survival of 51%–56%.1-3 The early detection of SSc-associated PAH (SSc-PAH) 4 is critical, because initiating therapy in patients with milder stages of disease may improve long-term outcomes.5 There is an urgent need to develop reliable and simple biomarkers for the early diagnosis of SSc-PAH and monitoring response to therapy.

A deficiency in nitric oxide (NO) signaling is felt to play an important role in the pathogenesis of PAH,6 and several studies have described reductions in the fractional NO concentration in exhaled breath (FENO) in PAH, particularly the idiopathic variety (IPAH), where FENO has been correlated with hemodynamic severity of disease and prognosis and has been shown to increase in response to therapy.7 However, there are scarce data on FENO in SSc-PAH. Earlier studies have been hampered by small patient numbers, variable methodology, and absence of hemodynamic confirmation of PAH.8-10 Moreover, these studies all used a single expiratory flow rate that cannot distinguish conducting airway versus alveolar source of NO. An increased alveolar concentration of NO has been reported to be of diagnostic value in SSc-associated interstitial lung disease (SSc-ILD) but has not been adequately investigated in SSc-PAH.11

We sought to assess FENO at the conventional expiratory flow rate of 50 mL/s as a potential biomarker in patients with SSc who had confirmed PAH. In addition, we measured FENO at multiple expiratory flow rates to allow partitioning into conducting airway and alveolar sources.12 Our hypothesis was that FENO would be reduced in patients with SSc-PAH compared with patients with SSc without lung disease because of decreased conducting airway NO generation.

Methods

Subjects

This prospective study was approved by the local institutional review board, and all participants provided written, informed consent. Twenty-four consecutive, treatment-naive patients with SSc-PAH without significant interstitial or obstructive lung disease, as previously described, were enrolled.13 Fourteen of these patients were evaluated again 4 months after initiation of targeted PAH therapy. A randomly selected cohort of 103 control subjects with SSc without evidence of pulmonary involvement was studied for comparison. The absence of lung disease was defined as (1) no respiratory complaints; (2) pulmonary function testing performed within the previous year showing a forced vital capacity (FVC) and total lung capacity ≥70% of predicted and a forced expiratory volume in 1 s (FEV1)/FVC ratio ≥0.7; (3) echocardiogram within the past year with normal right heart chamber size and function and estimated right ventricular systolic pressure of <40 mmHg and no evidence of significant left heart disease; (4) if performed, chest radiograph or computed tomography of chest with no significant parenchymal lung disease; and (5) no PAH-specific therapies given within the preceding month, including those used for non-PAH indications. Eighty-four healthy volunteers served as a control group. Exclusion criteria for all groups included smoking within the preceding 6 months, respiratory tract infection within the preceding 2 weeks, history of hyperreactive airways disease, pregnancy, corticosteroid use of >10 mg prednisone daily or equivalent and use of L-arginine, nitrates, or phosphodiesterase inhibitors. Another group of 38 patients with SSc-PAH who were receiving various PAH-specific therapies were also included and provided FENO only at the expiratory flow rate of 50 mL/s.

FENO measurements

Online recording of FENO was performed according to the recommendations of the American Thoracic Society at expiratory flow rates of 50, 100, 150, and 250 mL/s with a chemiluminescent analyzer (NIOX Flex, Aerocrine, Morrisville, NC).14 For each flow rate, the average of 2 measurements within 10% of each other was taken. To derive the flow-independent NO exchange parameters of maximum airway flux (J′awNO) and steady-state alveolar concentration (CANO), the 2-compartment model was applied.12 The Y-intercept and slope of the linear relationship between NO output (FENO × flow) and flow rate correspond to J′awNO and CANO, respectively, after adjustment for the trumpet shape of the airway tree and axial diffusion (model TMAD).15

Because CANO is determined by the uptake of NO by pulmonary capillary blood as well as by production by alveolar wall lining cells,16 we calculated the diffusing capacity of NO (DLNO) from the measured diffusing capacity of CO (DLCO) on the most recent pulmonary function test, assuming a DLNO/DLCO ratio of 4.3, as described elsewhere.17 For the healthy controls, a DLCO of 100% predicted (Knudson) was assumed. Subsequently, the alveolar production of NO (VLNO) was derived as the product of CANO and DLNO.18

Statistical analysis

Data are presented as mean ± standard deviation (SD). Comparisons between groups were performed with one-way analysis of variance, followed by Tukey multiple comparison test or Kruskal-Wallis test, followed by Dunn post hoc test, as appropriate. Multivariate linear regression was used to compare CANO by patient group while adjusting for DLCO. Serial measurements in the SSc-PAH group were analyzed with paired t test. P value <0.05 was considered significant. Analyses were performed with GraphPad Prism (La Jolla, CA) and Stata (College Station, TX).

Results

Subject characteristics

Nine controls with SSc, 3 treatment-naive patients with PAH, and 1 subject with PAH who was receiving treatment were unable to generate an adequate FENO recording at 50 mL/s. The demographic and clinical characteristics of the remaining 94 controls with SSc, 21 treatment-naive patients with SSc-PAH, 37 patients with SSc-PAH who were receiving therapy, and 84 healthy controls are presented in Table 1. An additional 2 controls with SSc could not generate a reliable FENO measurement at the highest expiratory flow rate of 250 mL/s, thereby precluding derivation of the flow-independent parameters.

Table 1.

Demographic and clinical characteristics

Variable SSc controls
(N = 94)		 Patients with SSc-PAH
(N = 21)		 Patients with SSc-PAH receiving therapy
(N = 37)		 Healthy controls
(N = 84)
Age, years 52 (10) 66 (10) 63 (12) 50 (13)
Sex, F/M 87/7 20/1 29/8 43/41
Race, white/black/other 86/5/3 18/2/1 29/8/0 58/15/11
Height, cm 166 (9) 160 (6) 165 (9) 169 (10)
Skin involvement, limited/diffuse 53/41 17/4 30/7 …
Immunosuppressive therapy, % 30 14 16 …
Six-minute walk distance, m … 292 (158) 335 (128) …
Pulmonary function:
 FVC, % predicted 97 (14) 88 (13) 73 (19) …
 FEV1/FVC ratio 0.79 (0.05) 0.77 (0.05) 0.75 (0.09) …
 TLC, % predicted 98 (15) 91 (11) 82 (20) …
 DLCO, % predicted 90 (19) 58 (17) 47 (17) …
Hemodynamic characteristic
 Mean PAP, mmHg … 38 (13) 40 (14) …
 RAP, mmHg … 7 (4) 9 (5) …
 PAWP, mmHg … 11 (4) 12 (4) …
 Cardiac index, L/min/m2 … 2.7 (0.9) 2.6 (0.6) …
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Note

Data are presented as mean value (± standard deviation), unless otherwise indicated. DLCO: diffusing capacity of CO; FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; PAH: pulmonary arterial hypertension; PAP: pulmonary artery pressure; PAWP: pulmonary artery wedge pressure; RAP: right atrial pressure; SSc: systemic sclerosis; TLC: total lung capacity.

FENO measurements

Table 2 summarizes the FENO results at the different expiratory flow rates in the controls with SSc, treatment-naive patients with SSc-PAH, and healthy control groups. There were no significant differences observed for any flow rate. Within the SSc control group, there were no differences between those with limited versus diffuse skin involvement or among patients receiving immunosuppressive therapy versus those who were not receiving such therapy (P values for FENO at 50 mL/s: 0.49 and 0.98, respectively). FENO at 50 mL/s in the SSc-PAH patients receiving therapy (17.6 ± 13 parts per billion [ppb]) was comparable to the SSc-PAH treatment-naive group (19.2 ± 12 ppb; P = 0.64). Combining the two SSc-PAH groups, we had >95% power to detect a 33% difference in FENO at 50 mL/s compared with controls with SSc at a two-sided α of 0.05. Within the SSc-PAH treatment-naive group, there was no relationship between FENO at 50 mL/s and mean pulmonary artery pressure or pulmonary vascular resistance index (data not shown).

Table 2.

Fractional exhaled concentration of nitric oxide (FENO) measurements

Variable SSc controls
(N = 94)a 		SSc-PAH
(N = 21)		 Healthy controls
(N = 84)		 P value
FENO 50 mL/s, ppb 17 (6) 19 (12) 21 (11) 0.22
FENO 100 mL/s, ppb 11 (4) 13 (6) 13 (6) 0.53
FENO 150 mL/s, ppb 8 (3) 10 (5) 9 (4) 0.58
FENO 250 mL/s, ppb 6 (2) 7 (4) 6 (3) 0.41
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Note

PAH: pulmonary arterial hypertension; ppb: parts per billion.

a

Two control subjects with systemic sclerosis (SSc) could not generate an adequate FENO recording at the highest flow rate of 250 mL/s.

Two-compartment model and VLNO calculation

Maximal airway flux of NO (J′awNO) in patients with SSc without pulmonary involvement was similar to that in subjects with SSc-PAH but significantly less than that in healthy volunteers (Fig. 1). In contrast, CANO was considerably increased in the SSc-PAH group compared with both the SSc control group and healthy volunteers (Fig. 2A). CANO was also significantly higher in patients with SSc without pulmonary involvement than in healthy controls. However, after adjusting for DLCO, there was no longer a significant difference in CANO between the SSc control group and SSc-PAH group (P = 0.08). The alveolar production of NO (VLNO) calculation also showed no difference between controls with SSc and the SSc-PAH group. Both SSc groups had reduced VLNO values compared with healthy controls (Fig. 2B).

Figure 1.

Figure 1

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Maximal airway flux of nitric oxide (J′awNO) in patients with systemic sclerosis (SSc) without lung involvement (N = 92), treatment-naive subjects with SSc and pulmonary arterial hypertension (PAH; N = 21), and healthy control subjects (N = 84). Error bars represent standard deviation. Single asterisk indicates P < 0.05 compared with healthy controls.

Figure 2.

Figure 2

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Steady-state alveolar concentration of nitric oxide (CANO; A) and calculated alveolar production of nitric oxide (VLNO; B) in patients with systemic sclerosis (SSc) without lung involvement (N = 92), treatment-naive subjects with SSc and pulmonary arterial hypertension (PAH; N = 21), and healthy control subjects (N = 84). Error bars represent standard deviation. One asterisk indicates P < 0.01 compared with healthy controls. Number sign indicates P < 0.05 compared with controls with SSc. Two asterisks indicate P < 0.05 versus controls with SSc and the SSc-PAH group.

Changes in response to specific PAH therapy

As shown in Figure 3, no change was noted in FENO at 50 mL/s (P = 0.9) in 14 patients with SSc-PAH after 4 months of treatment. Specific PAH therapies were a combination of tadalafil and ambrisentan as part of an open-label clinical trial13 (N = 5) and monotherapy with tadalafil (3), sildenafil (3), ambrisentan (1), bosentan (1), and inhaled treprostinil (1). Similar findings were observed for J′awNO and CANO (data not shown). As a group, this small cohort did not demonstrate a significant clinical response to therapy in terms of 6-minute walk distance.

Figure 3.

Figure 3

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The fractional exhaled concentration of nitric oxide (FENO) at 50 mL/s in parts per billion (ppb) at baseline and after 4 months of targeted pulmonary arterial hypertension (PAH) therapy in 14 patients with systemic sclerosis and PAH. Mean values at each time point are shown.

Discussion

The main findings of this study are (1) FENO at 50 mL/s in patients with SSc-PAH is similar to that in subjects with SSc without lung involvement and healthy control subjects; (2) J′awNO is modestly lower in individuals with SSc without lung disease relative to healthy controls but is similar to that in individuals with SSc-PAH; (3) unadjusted steady-state alveolar concentration (CANO) is higher in individuals with SSc-PAH than in those with SSc without pulmonary involvement but not after correcting for DLCO, and calculated alveolar production of NO (VLNO) is similar; and (4) no change in any exhaled NO variable was observed in subjects with SSc-PAH after 4 months of specific PAH therapy.

These observations are in contrast to those reported in IPAH. Lower airway NO sampled bronchoscopically as well as NO oxidative reaction products were found to be decreased in patients with IPAH relative to healthy controls.19 Our group has also shown a reduction in FENO at 50 mL/s in this population,20 along with a low airway wall concentration of NO using the 3-compartment model.12 Moreover, these abnormalities reversed after 3 months of therapy with the dual endothelin-receptor antagonist bosentan. In a mixed population of individuals with PAH (mainly IPAH), Machado et al.21 found an inverse correlation between FENO and pulmonary artery pressure and better survival among those with an increase in FENO on serial testing.

Our results indicate that FENO is not a useful diagnostic biomarker for PAH in patients with SSc. Despite the relatively small sample size, we had adequate power to demonstrate a biologically or clinically meaningful difference between SSc subjects without pulmonary involvement and SSc-PAH, particularly when combined with a group of patients receiving specific PAH therapy. Combining these 2 groups was justified, because their FENO values were similar, and the latter did not change in response to therapy in treatment-naive patients with SSc-PAH. As expected, there was considerable individual variability among all groups, but our sample size precluded the ability to investigate any potential association between FENO, severity of disease, prognosis, or response to therapy.

Earlier studies of exhaled NO in SSc-PAH were limited by variable methodology, small sample size, and inadequate patient characterization. Kharitonov and coworkers8 and Rolla and colleagues10 reported significantly reduced FENO compared with subjects with SSc without lung disease. However, expiratory flow rate, which dramatically influences FENO,14 was not adequately controlled. Malerba et al.9 assessed FENO at 50 mL/s and found significantly reduced values among patients with SSc with ILD alone or isolated PAH compared with those without lung involvement, roughly 11 versus 20 ppb. Those with combined ILD and PH had the lowest values, ∼6 ppb. Both this study and that of Rolla’s described an inverse correlation between FENO and Doppler estimated pulmonary artery systolic pressure.9,10 All 3 studies lacked hemodynamic confirmation of PH by right heart catheterization.

The basis for the absence of reduced FENO in SSc-PAH compared with our previous findings in treatment-naive IPAH is not clear.20 Although the hemodynamic severity of disease was less in the current study, as is typical for SSc compared with IPAH,22 there was no suggestion that FENO was lower in those with higher pulmonary artery pressure or vascular resistance. Immune activation leads to increased expression of inducible NO synthase (iNOS) in a variety of cell types,23,24 and circulating NO metabolites are consistently elevated in SSc,25,26 even among subjects with pulmonary hypertension.27,28 Thus, inflammatory mechanisms may overshadow reduced NO production by the constitutive endothelial and neuronal NOS isoforms.24,29

Our finding of a modestly lower J′awNO in patients with SSc without pulmonary involvement relative to healthy controls mirrors earlier results of a study involving subjects with SSc-ILD.17 The difference was larger in the latter study, which found a mean value in patients with SSc-ILD that was half that observed in healthy subjects. Tiev et al.30 also found significantly lower J′awNO in SSc-ILD compared with SSc without ILD, although others reported normal values.31 The determinants of maximal bronchial NO flux include its production by airway wall relative to catabolism.16 The presence of reactive oxygen species, which play a central role in the pathogenesis of systemic sclerosis,32 would enhance the degradation of NO and could contribute to reduced J′awNO.

Elevated alveolar concentrations of NO have been a consistent finding in SSc.17,30,31 Tiev et al.30 reported median CANO values of 7.5, 4.9, and 2.0 ppb in SSc-ILD, SSc without ILD, and healthy controls, respectively. These investigators also showed an association with subsequent decrease in pulmonary function,33 the presence of alveolitis defined by bronchoalveolar lavage fluid cellular differential,34 and the clinical response to cyclophosphamide therapy,35 suggesting that CANO reflects alveolar inflammation. Wuttge et al.31 found a weak correlation between CANO and the extent of ground-glass opacities and reticulations on high-resolution chest CT but not with pulmonary function variables.

Steady-state alveolar NO concentration reflects the balance between production by alveolar lining cells (VLNO) and the diffusion capacity into pulmonary capillary blood (DLNO). Because the avidity of hemoglobin for NO is extremely high, DLNO is largely determined by the membrane component of gas transfer rather than pulmonary capillary blood volume.36 In the absence of a direct measurement, we calculated DLNO using an assumed DLNO/DLCO ratio. The average ratio of 4.3, derived from healthy volunteers,36 closely approximates the value of 4.41 in a group of patients with SSc without lung disease and 4.29 in a small number of subjects with SSc-PAH.37 In this study, although CANO in the SSc-PAH group was significantly higher than in both the SSc group and healthy controls, the VLNO calculation did not suggest increased alveolar NO production relative to either group. These findings are similar to an earlier report involving SSc-ILD.17 The basis for the statistically lower VLNO in the SSc group compared with the healthy control group is unclear, but it could be partly explained by a higher proportion of male subjects and younger mean age in the latter, with a consequently higher predicted DLNO. The alveolar compartment in the model includes the most distal airways,38 where subtle abnormalities are common in SSc,39,40 which could contribute to reduced NO production.17 Enhanced oxidative catabolism, as invoked for the reduced bronchial flux, may also be a factor. The loss of a significant difference in CANO between the SSc-PAH group and the control group with SSc after adjusting for DLCO provides additional support for the absence of increased NO production in the alveolar compartment.

In summary, we have demonstrated that FENO in patients with SSc-PAH is similar to that in subjects with SSc without pulmonary involvement and healthy controls. Furthermore, we found no change in FENO after 4 months of specific PAH therapy. Elucidation of the basis for and significance of the observed elevation in alveolar NO concentrations in SSc lung disease will require concomitant measurements of DLNO. Additional studies including direct comparison with IPAH are needed to clarify differences between these subtypes.

Acknowledgments

We thank Traci Housten and Audrey Perkins in the Division of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, for their assistance with this study.

Source of Support: This study was supported by the National Institutes of Health/National Heart, Lung, and Blood Institute (NIH/NHLBI; R01 HL092831 to REG and P50 HL084946 to PMH) and the Scleroderma Research Foundation (FMW).

Conflict of Interest: SCM serves as a consultant for Actelion, Bayer, and United Therapeutics; receives research funding from NIH/NHLBI and the Scleroderma Research Foundation; and is on the speakers bureau for the Pulmonary Hypertension Association. PMH is on the advisory board for scientific affairs of Gilead Sciences. REG serves on the speakers bureau of Gilead Sciences and Bayer Pharmaceuticals and participates in clinical research trials sponsored by Pfizer and United Therapeutics. All other authors: none declared.

References

  • 1.Lefevre G, Dauchet L, Hachulla E, Montani D, Sobanski V, Lambert M, Hatron PY, Humbert M, Launay D. Survival and prognostic factors in systemic sclerosis-associated pulmonary hypertension: a systematic review and meta-analysis. Arthritis Rheum 2013;65(9):2412–2423. [DOI] [PubMed]
  • 2.Launay D, Sitbon O, Hachulla E, Mouthon L, Gressin V, Rottat L, Clerson P, Cordier JF, Simonneau G, Humbert M. Survival in systemic sclerosis-associated pulmonary arterial hypertension in the modern management era. Ann Rheum Dis 2013;72(12):1940–1946. [DOI] [PMC free article] [PubMed]
  • 3.Chung L, Farber HW, Benza R, Miller DP, Parsons L, Hassoun PM, McGoon M, Nicolls MR, Zamanian RT. Unique predictors of mortality in patients with pulmonary arterial hypertension associated with systemic sclerosis in the REVEAL registry. Chest 2014;146(6):1494–1504. [DOI] [PMC free article] [PubMed]
  • 4.Coghlan JG, Denton CP, Grunig E, Bonderman D, Distler O, Khanna D, Müller-Ladner U, et al. Evidence-based detection of pulmonary arterial hypertension in systemic sclerosis: the DETECT study. Ann Rheum Dis 2014;73(7):1340–1349. [DOI] [PMC free article] [PubMed]
  • 5.Humbert M, Yaici A, de Groote P, Montani D, Sitbon O, Launay D, Gressin V, et al. Screening for pulmonary arterial hypertension in patients with systemic sclerosis: clinical characteristics at diagnosis and long-term survival. Arthritis Rheum 2011;63(11):3522–3530. [DOI] [PubMed]
  • 6.Klinger JR. The nitric oxide/cGMP signaling pathway in pulmonary hypertension. Clin Chest Med 2007;28(1):143–167. [DOI] [PubMed]
  • 7.Malinovschi A, Ludviksdottir D, Tufvesson E, Rolla G, Bjermer L, Alving K, Diamant Z, et al. Application of nitric oxide measurements in clinical conditions beyond asthma. Eur Clin Respir J 2015;2:28517. [DOI] [PMC free article] [PubMed]
  • 8.Kharitonov SA, Cailes JB, Black CM, du Bois RM, Barnes PJ. Decreased nitric oxide in the exhaled air of patients with systemic sclerosis with pulmonary hypertension. Thorax 1997;52(12):1051–1055. [DOI] [PMC free article] [PubMed]
  • 9.Malerba M, Radaeli A, Ragnoli B, Airo' P, Corradi M, Ponticiello A, Zambruni A, Grassi V. Exhaled nitric oxide levels in systemic sclerosis with and without pulmonary involvement. Chest 2007;132(2):575–580. [DOI] [PubMed]
  • 10.Rolla G, Colagrande P, Scappaticci E, Chiavassa G, Dutto L, Cannizzo S, Bucca C, et al. Exhaled nitric oxide in systemic sclerosis: relationships with lung involvement and pulmonary hypertension. J Rheumatol 2000;27(7):1693–1698. [PubMed]
  • 11.Tiev KP, Coste J, Ziani M, Aubourg F, Cabane J, Dinh-Xuan AT. Diagnostic value of exhaled nitric oxide to detect interstitial lung disease in systemic sclerosis. Sarcoidosis Vasc Diffuse Lung Dis 2009;26(1):32–38. [PubMed]
  • 12.George SC, Hogman M, Permutt S, Silkoff PE. Modeling pulmonary nitric oxide exchange. J Appl Physiol 2004;96(3):831–839. [DOI] [PubMed]
  • 13.Hassoun PM, Zamanian RT, Damico R, Lechtzin N, Khair R, Kolb TM, Tedford RJ, et al. Ambrisentan and tadalafil up-front combination therapy in scleroderma-associated pulmonary arterial hypertension. Am J Respir Crit Care Med 2015;192(9):1102–1110. [DOI] [PMC free article] [PubMed]
  • 14.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;171(8):912–930. [DOI] [PubMed]
  • 15.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 (1985) 2007;102(1):417–425. [DOI] [PubMed]
  • 16.Tsoukias NM, George SC. A two-compartment model of pulmonary nitric oxide exchange dynamics. J Appl Physiol 1998;85(2):653–666. [DOI] [PubMed]
  • 17.Girgis RE, Gugnani MK, Abrams J, Mayes MD. Partitioning of alveolar and conducting airway nitric oxide in scleroderma lung disease. Am J Respir Crit Care Med 2002;165(12):1587–1591. [DOI] [PubMed]
  • 18.Perillo IB, Hyde RW, Olszowka AJ, Pietropaoli AP, Frasier LM, Torres A, Perkins PT, Forster RE 2nd, Utell MJ, Frampton MW. Chemiluminescent measurements of nitric oxide pulmonary diffusing capacity and alveolar production in humans. J Appl Physiol (1985) 2001;91(5):1931–1940. [DOI] [PubMed]
  • 19.Kaneko FT, Arroliga AC, Dweik RA, Comhair SA, Laskowski D, Oppedisano R, Thomassen MJ, Erzurum SC. Biochemical reaction products of nitric oxide as quantitative markers of primary pulmonary hypertension. Am J Respir Crit Care Med 1998;158(3):917–923. [DOI] [PubMed]
  • 20.Girgis RE, Champion HC, Diette GB, Johns RA, Permutt S, Sylvester JT. Decreased exhaled nitric oxide in pulmonary arterial hypertension: response to bosentan therapy. Am J Respir Crit Care Med 2005;172(3):352–357. [DOI] [PubMed]
  • 21.Machado RF, Londhe Nerkar MV, Dweik RA, Hammel J, Janocha A, Pyle J, Laskowski D, Jennings C, Arroliga AC, Erzurum SC. Nitric oxide and pulmonary arterial pressures in pulmonary hypertension. Free Radic Biol Med 2004;37(7):1010–1017. [DOI] [PubMed]
  • 22.Fisher MR, Mathai SC, Champion HC, Girgis RE, Housten-Harris T, Hummers L, Krishnan JA, Wigley F, Hassoun PM. Clinical differences between idiopathic and scleroderma-related pulmonary hypertension. Arthritis Rheum 2006;54(9):3043–3050. [DOI] [PubMed]
  • 23.Chen K, Popel AS. Vascular and perivascular nitric oxide release and transport: biochemical pathways of neuronal nitric oxide synthase (NOS1) and endothelial nitric oxide synthase (NOS3). Free Radic Biol Med 2007;42(6):811–822. [DOI] [PMC free article] [PubMed]
  • 24.Cotton SA, Herrick AL, Jayson MI, Freemont AJ. Endothelial expression of nitric oxide synthases and nitrotyrosine in systemic sclerosis skin. J Pathol 1999;189(2):273–278. [DOI] [PubMed]
  • 25.Dooley A, Gao B, Bradley N, Abraham DJ, Black CM, Jacobs M, Bruckdorfer KR. Abnormal nitric oxide metabolism in systemic sclerosis: increased levels of nitrated proteins and asymmetric dimethylarginine. Rheumatology (Oxford) 2006;45(6):676–684. [DOI] [PubMed]
  • 26.Mok MY, Fung PC, Ooi C, Tse HF, Wong Y, Lam YM, Wong WS, Lau CS. Serum nitric oxide metabolites and disease activity in patients with systemic sclerosis. Clin Rheumatol 2008;27(3):315–322. [DOI] [PubMed]
  • 27.Tiev KP, Le-Dong NN, Duong-Quy S, Hua-Huy T, Cabane J, Dinh-Xuan AT. Exhaled nitric oxide, but not serum nitrite and nitrate, is a marker of interstitial lung disease in systemic sclerosis. Nitric Oxide 2009;20(3):200–206. [DOI] [PubMed]
  • 28.Kawashiri SY, Ueki Y, Terada K, Yamasaki S, Aoyagi K, Kawakami A. Improvement of plasma endothelin-1 and nitric oxide in patients with systemic sclerosis by bosentan therapy. Rheumatol Int 2014;34(2):221–225. [DOI] [PubMed]
  • 29.Ibba-Manneschi L, Niissalo S, Milia AF, Allanore Y, Del Rosso A, Pacini A, Manetti M, et al. Variations of neuronal nitric oxide synthase in systemic sclerosis skin. Arthritis Rheum 2006;54(1):202–213. [DOI] [PubMed]
  • 30.Tiev KP, Cabane J, Aubourg F, Kettaneh A, Ziani M, Mouthon L, Duong-Quy S, Fajac I, Guillevin L, Dinh-Xuan AT. Severity of scleroderma lung disease is related to alveolar concentration of nitric oxide. Eur Respir J 2007;30(1):26–30. [DOI] [PubMed]
  • 31.Wuttge DM, Bozovic G, Hesselstrand R, Aronsson D, Bjermer L, Scheja A, Tufvesson E. Increased alveolar nitric oxide in early systemic sclerosis. Clin Exp Rheumatol 2010;28(5 suppl 62):S5–S9. [PubMed]
  • 32.Gabrielli A, Avvedimento EV, Krieg T. Scleroderma. N Engl J Med 2009;360(19):1989–2003. [DOI] [PubMed]
  • 33.Tiev KP, Hua-Huy T, Kettaneh A, Allanore Y, Le-Dong NN, Duong-Quy S, Cabane J, Dinh-Xuan AT. Alveolar concentration of nitric oxide predicts pulmonary function deterioration in scleroderma. Thorax 2012;67(2):157–163. [DOI] [PubMed]
  • 34.Tiev KP, Hua-Huy T, Rivière S, Le-Dong NN, Febvre M, Cabane J, Dinh-Xuan AT. High alveolar concentration of nitric oxide is associated with alveolitis in scleroderma. Nitric Oxide 2013;28:65–70. [DOI] [PubMed]
  • 35.Tiev KP, Rivière S, Hua-Huy T, Cabane J, Dinh-Xuan AT. Exhaled NO predicts cyclophosphamide response in scleroderma-related lung disease. Nitric Oxide 2014;40:17–21. [DOI] [PubMed]
  • 36.Borland CD, Higenbottam TW. A simultaneous single breath measurement of pulmonary diffusing capacity with nitric oxide and carbon monoxide. Eur Respir J 1989;2(1):56–63. [PubMed]
  • 37.Sivova N, Launay D, Wemeau-Stervinou L, De Groote P, Remy-Jardin M, Denis G, Lambert M. Relevance of partitioning DLCO to detect pulmonary hypertension in systemic sclerosis. PLoS One 2013;8(10):e78001. [DOI] [PMC free article] [PubMed]
  • 38.Puckett JL, Taylor RW, Leu SY, Guijon OL, Aledia AS, Galant SP, George SC, et al. Clinical patterns in asthma based on proximal and distal airway nitric oxide categories. Respir Res 2010;11:47. [DOI] [PMC free article] [PubMed]
  • 39.Yousem SA. The pulmonary pathologic manifestations of the CREST syndrome. Hum Pathol 1990;21(5):467–474. [DOI] [PubMed]
  • 40.Guttadauria M, Ellman H, Emmanuel G, Kaplan D, Diamond H. Pulmonary function in scleroderma. Arthritis Rheum 1977;20(5):1071–1079. [DOI] [PubMed]

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