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      Pulmonary vascular effects of pulsed inhaled nitric oxide in COPD patients with pulmonary hypertension

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          Abstract

          Introduction

          Severe chronic obstructive pulmonary disease (COPD) is often associated with secondary pulmonary hypertension (PH), which worsens prognosis. PH can be lowered by oxygen, but also by inhaled nitric oxide (NO), which has the potential to improve the health status of these patients. NO is an important mediator in vascular reactions in the pulmonary circulation. Oral compounds can act through NO-mediated pathways, but delivering pulsed inhaled NO (iNO) directly to the airways and pulmonary vasculature could equally benefit patients. Therefore, a proof-of-concept study was performed to quantify pulmonary blood vessel caliber changes after iNO administration using computed tomography (CT)-based functional respiratory imaging (FRI).

          Methods

          Six patients with secondary PH due to COPD received “pulsed” iNO in combination with oxygen for 20 minutes via a nasal cannula. Patients underwent a high-resolution CT scan with contrast before and after iNO. Using FRI, changes in volumes of blood vessels and associated lobes were quantified. Oxygen saturation and blood pressure were monitored and patients were asked about their subjective feelings.

          Results

          Pulmonary blood vessel volume increased by 7.06%±5.37% after iNO. A strong correlation (Ω 2 0=0.32, P=0.002) was obtained between ventilation and observed vasodilation, suggesting that using the pulsed system, iNO is directed toward the ventilated zones, which consequently experience more vasodilation. Patients did not develop oxygen desaturation, remained normotensive, and perceived an improvement in their dyspnea sensation.

          Conclusion

          Inhalation of pulsed NO with oxygen causes vasodilation in the pulmonary circulation of COPD patients, mainly in the well-ventilated areas. A high degree of heterogeneity was found in the level of vasodilation. Patients tend to feel better after the treatment. Chronic use trials are warranted.

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          Most cited references 34

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          Reduced expression of endothelial nitric oxide synthase in the lungs of patients with pulmonary hypertension.

          Pulmonary hypertension is characterized by abnormal thickening of the pulmonary arteries and increased pulmonary vascular resistance. Nitric oxide is a potent endothelium-derived vasorelaxant substance and an inhibitor of smooth-muscle-cell growth. Nitric oxide is produced in various cell types by the action of an enzyme, nitric oxide synthase. We compared the expression of endothelial nitric oxide synthase in the lungs of control subjects with that in the lungs of patients with pulmonary hypertension. We investigated the expression of endothelial nitric oxide synthase by histochemical and immunohistochemical analysis, in situ hybridization, and Northern blot analysis in the lungs of 22 patients with plexogenic pulmonary arteriopathy (arteriopathy of grades 4 through 6), 24 patients with secondary pulmonary hypertension (arteriopathy of grades 1 through 3), and 23 control subjects. In the lungs of the control subjects, nitric oxide synthase was expressed at a high level in the vascular endothelium of all types of vessels and in the pulmonary epithelium. In contrast, little or no expression of the enzyme was found in the vascular endothelium of pulmonary arteries with severe histologic abnormalities (i.e., plexiform lesions) in patients with pulmonary hypertension. The intensity of the enzyme immunoreactivity correlated inversely with the severity of histologic changes. There was an inverse correlation between the arterial expression of the enzyme and total pulmonary resistance in patients with plexogenic pulmonary arteriopathy (r = -0.766, P = 0.004). Pulmonary hypertension is associated with diminished expression of endothelial nitric oxide synthase. It is possible that decreased expression of nitric oxide synthase may contribute to pulmonary vasoconstriction and to the excessive growth of the tunica media observed in this disease.
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            Long term domiciliary oxygen therapy in chronic hypoxic cor pulmonale complicating chronic bronchitis and emphysema. Report of the Medical Research Council Working Party.

             Research Medical (corresponding) (1981)
            A controlled trial of long term domiciliary oxygen therapy has been carried out in three centres in the U.K. The 87 patients, all under 70 years of age, who took part had chronic bronchitis or emphysema with irreversible airways obstruction, severe arterial hypoxaemia, carbon dioxide retention, and a history of congestive heart failure. The patients were randomised to oxygen therapy (treated) or no oxygen (controls). Oxygen was given by nasal prongs for at least 15 h daily, usually at 2 1/min. The two groups were well matched, both clinically and in terms of lung function and other laboratory findings. 19 of the 42 oxygen treated patients died in the five years of survival follow-up compared with 30 out of 45 controls: in the 66 men in this trial the survival advantage of oxygen did not emerge until 500 days had elapsed. Survival for the 12 female controls was surprisingly poor, 8 of them being dead at 3 years. Mortality was not easy to predict, though a summation of arterial carbon dioxide tension and red cell mass was helpful. Neither time spent in hospital because of exacerbations of respiratory failure nor work attendance were affected by oxygen therapy, but these patients were very ill at the start of the trial and many had already retired on grounds of age or ill-health. Physiological measurements suggested that oxygen did not slow the progress of respiratory failure in those who died early. However, in longer term survivors on oxygen, arterial oxygenation did seem to stop deterioration.
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              Pulmonary vascular involvement in COPD.

              Alterations in pulmonary vessel structure and function are highly prevalent in patients with COPD. Vascular abnormalities impair gas exchange and may result in pulmonary hypertension, which is one of the principal factors associated with reduced survival in COPD patients. Changes in pulmonary circulation have been identified at initial disease stages, providing new insight into their pathogenesis. Endothelial cell damage and dysfunction produced by the effects of cigarette smoke products or inflammatory elements is now considered to be the primary alteration that initiates the sequence of events resulting in pulmonary hypertension. Cellular and molecular mechanisms involved in this process are being extensively investigated. Progress in the understanding of the pathobiology of pulmonary hypertension associated with COPD may provide the basis for a new therapeutic approach addressed to correct the imbalance between endothelium-derived vasoactive agents. The safety and efficacy of endothelium-targeted therapy in COPD-associated pulmonary hypertension warrants further investigation in randomized clinical trials.
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                Author and article information

                Journal
                Int J Chron Obstruct Pulmon Dis
                Int J Chron Obstruct Pulmon Dis
                International Journal of COPD
                International Journal of Chronic Obstructive Pulmonary Disease
                Dove Medical Press
                1176-9106
                1178-2005
                2016
                05 July 2016
                : 11
                : 1533-1541
                Affiliations
                [1 ]Department of Respiratory Medicine, University Hospital Antwerp, Edegem
                [2 ]FluidDA nv, Antwerp, Belgium
                [3 ]Bellerophon Therapeutics, Warren, NJ, USA
                Author notes
                Correspondence: Bita Hajian, Department of Respiratory Medicine, University Hospital Antwerp, Wilrijkstraat 10, Edegem 2650, Belgium, Tel +32 3 821 30 00, Email bita.hajian@ 123456uza.be
                Article
                copd-11-1533
                10.2147/COPD.S106480
                4940019
                27462149
                © 2016 Hajian et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

                Categories
                Clinical Trial Report

                Respiratory medicine

                fri, pulsed inhaled nitric oxide, copd, pulmonary hypertension

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