Exhaled nitric oxide does not provide a marker of vascular endothelial function in healthy humans

Acute L-Citrulline Supplementation Increases Nitric Oxide Bioavailability but Not Inspiratory Muscle Oxygenation and Respiratory Performance

The present study aimed to investigate whether acute L-citrulline supplementation would affect inspiratory muscle oxygenation and respiratory performance. Twelve healthy males received 6 g of L-citrulline or placebo in a double-blind crossover design. Pulmonary function (i.e., forced expired volume in 1 s, forced vital capacity and their ratio), maximal inspiratory pressure (MIP), fractional exhaled nitric oxide (NO^•), and sternocleidomastoid muscle oxygenation were measured at baseline, one hour post supplementation, and after an incremental resistive breathing protocol to task failure of the respiratory muscles. The resistive breathing task consisted of 30 inspirations at 70% and 80% of MIP followed by continuous inspirations at 90% of MIP until task failure. Sternocleidomastoid muscle oxygenation was assessed using near-infrared spectroscopy. One-hour post-L-citrulline supplementation, exhaled NO^• was significantly increased (19.2%; p < 0.05), and this increase was preserved until the end of the resistive breathing (16.4%; p < 0.05). In contrast, no difference was observed in the placebo condition. Pulmonary function and MIP were not affected by the L-citrulline supplementation. During resistive breathing, sternocleidomastoid muscle oxygenation was significantly reduced, with no difference noted between the two supplementation conditions. In conclusion, a single ingestion of 6 g L-citrulline increased NO^• bioavailability but not the respiratory performance and inspiratory muscle oxygenation.

Novel Insights into Cardiovascular Regulation in Patients with Chronic Mountain Sickness

Studies of high-altitude populations, and in particular of maladapted subgroups, may provide important insight into underlying mechanisms involved in the pathogenesis of hypoxemia-related disease in general. Chronic mountain sickness (CMS) is a major public health problem in mountainous regions of the world affecting many millions of high-altitude dwellers. It is characterized by exaggerated chronic hypoxemia, erythrocytosis, and mild pulmonary hypertension. In later stages these patients often present with right heart failure and are predisposed to systemic cardiovascular disease, but the underlying mechanisms are poorly understood. Here, we present recent new data providing insight into underlying mechanisms that may cause these complications.

Pharmacokinetic-Pharmacodynamic Model for the Effect of l-Arginine on Endothelial Function in Patients with Moderately Severe Falciparum Malaria

Impaired organ perfusion in severe falciparum malaria arises from microvascular sequestration of parasitized cells and endothelial dysfunction. Endothelial dysfunction in malaria is secondary to impaired nitric oxide (NO) bioavailability, in part due to decreased plasma concentrations of l-arginine, the substrate for endothelial cell NO synthase. We quantified the time course of the effects of adjunctive l-arginine treatment on endothelial function in 73 patients with moderately severe falciparum malaria derived from previous studies. Three groups of 10 different patients received 3 g, 6 g, or 12 g of l-arginine as a half-hour infusion. The remaining 43 received saline placebo. A pharmacokinetic-pharmacodynamic (PKPD) model was developed to describe the time course of changes in exhaled NO concentrations and reactive hyperemia-peripheral arterial tonometry (RH-PAT) index values describing endothelial function and then used to explore optimal dosing regimens for l-arginine. A PK model describing arginine concentrations in patients with moderately severe malaria was extended with two pharmacodynamic biomeasures, the intermediary biochemical step (NO production) and endothelial function (RH-PAT index). A linear model described the relationship between arginine concentrations and exhaled NO. NO concentrations were linearly related to RH-PAT index. Simulations of dosing schedules using this PKPD model predicted that the time within therapeutic range would increase with increasing arginine dose. However, simulations demonstrated that regimens of continuous infusion over longer periods would prolong the time within the therapeutic range even more. The optimal dosing regimen for l-arginine is likely to be administration schedule dependent. Further studies are necessary to characterize the effects of such continuous infusions of l-arginine on NO and microvascular reactivity in severe malaria.

Airway gas exchange and exhaled biomarkers

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

No arguments for increased endothelial nitric oxide synthase activity in migraine based on peripheral biomarkers

OBJECTIVES

To assess whether migraine patients display a chronic nitric oxide synthase (NOS) hyperactivity by comparing the nitric oxide (NO) production before and following a loading dose of L-arginine between migraine patients (interictally) and matched healthy control subjects. In addition, we evaluated whether a loading dose of L-arginine triggers an acute migraine headache in migraineurs.

SUBJECTS AND METHODS

Twenty healthy subjects and 20 migraine patients participated in a 2-period, randomised, double-blind, placebo-controlled study. Each subject received a 30-min infusion, by peripheral vein, of 30 g L-arginine hydrochloride or placebo (i.e. an equal volume of 0.9% saline solution). Meanwhile, biomarkers associated with the L-arginine-NO pathway (i.e. exhaled NO/nasal NO), plasma citrulline and urinary excretion of nitrite/nitrate and cGMP were assessed before and for 6 h following the start of the infusion.

RESULTS

At baseline, exhaled NO and nasal NO were higher in migraineurs compared to healthy subjects (mean±95% confidence interval): 15.9 (8.8, 23.0) parts per billion (ppb) versus 10.8 (7.0, 14.5) ppb for exhaled NO (P=0.04) and 76.3 (61.2, 91.4) versus 61.6 (51.2, 72.0) ppb for nasal NO (P=0.03), respectively. The AUC0-6 in ppb for exhaled NO and nasal NO following L-arginine or saline infusion did not differ between both groups. The increase in L-citrulline, following L-arginine infusion, was smaller in migraine patients (15 (13, 18) µmol/l) compared to healthy volunteers (19 (16, 23) µmol/l; P=0.046). In healthy subjects, both nitrate and cGMP excretion were higher following L-arginine compared to placebo infusion: 132.63 (100.24, 165.02) versus 92.07 (66.33, 117.82) µmol/mmol creatinine for nitrate (P=0.014) and 50.53 (42.19, 58.87) versus 39.64 (33.94, 45.34) nmol/mmol creatinine for cGMP (P=0.0003), respectively. In migraineurs, excretion of these biomarkers was comparable following L-arginine or saline infusion.

CONCLUSIONS

The results of the present study do not support the idea of a generalised increase in NO synthase activity in migraine patients outside of a migraine attack. The smaller increase in plasma L-citrulline, urinary nitrate and cGMP excretion following L-arginine infusion in migraine patients might indicate dysfunction of endothelial NO synthase.

Partitioning of exhaled NO in ventilated patients undergoing cardiac surgery

The change in exhaled NO after cardio-pulmonary bypass remains controversial. The aims were to determine whether exhaled NO sources (alveolar or bronchial) are modified after bypass, and whether mechanical ventilation (MV) settings during bypass modify exhaled NO changes. Thirty-two patients were divided into three groups: without MV during bypass and positive end-expiratory pressure (PEEP) (n=12), dead space MV without PEEP (n=10) and dead space MV with PEEP (n=10). Alveolar NO concentration and bronchial NO flux were calculated before and 1h after surgery using a two-compartment model of NO exchange developed in spontaneous breathing patients. Whereas a significant decrease in bronchial NO was found after bypass in the two groups without PEEP during bypass, this decrease was not observed in patients with dead space ventilation with PEEP. Alveolar NO was not significantly modified whatever the ventilation settings. In conclusion, the impairment of bronchial NO seemed related to airway closure since dead space mechanical ventilation with PEEP prevented its decrease.

A single dose of Sildenafil does not enhance FeNO: a randomised, cross-over and placebo-controlled study

Monitoring of asthma control can be performed with different means including measurement of the concentration of nitric oxide (NO) in exhaled air. Due to its action on the NO-metabolism; we hypothesized that the intake of Sildenafil might augment and falsify the NO-values in exhaled air of subjects taking the drug to treat erectile dysfunction. This randomised, placebo-controlled cross-over study including 10 male non-asthmatic volunteers taking a single dose of 50 mg Sildenafil did not confirm this assumption in non-asthmatic subjects. We cannot think of any reason why asthmatics should behave differently. On the basis of these results, it does not seem necessary to ask asthma patients with elevated NO-values if they had taken any selective inhibitor of the cGMP-specific phosphodiesterase Type 5 as Sildenafil prior to the test.

Pulmonary-artery pressure and exhaled nitric oxide in Bolivian and Caucasian high altitude dwellers

There is evidence that high altitude populations may be better protected from hypoxic pulmonary hypertension than low altitude natives, but the underlying mechanism is incompletely understood. In Tibetans, increased pulmonary respiratory NO synthesis attenuates hypoxic pulmonary hypertension. It has been speculated that this mechanism may represent a generalized high altitude adaptation pattern, but direct evidence for this speculation is lacking. We therefore measured systolic pulmonary-artery pressure (Doppler chocardiography) and exhaled nitric oxide (NO) in 34 healthy, middle-aged Bolivian high altitude natives and in 34 age- and sex-matched, well-acclimatized Caucasian low altitude natives living at high altitude (3600 m). The mean+/-SD systolic right ventricular to right atrial pressure gradient (24.3+/-5.9 vs. 24.7+/-4.9 mmHg) and exhaled NO (19.2+/-7.2 vs. 22.5+/-9.5 ppb) were similar in Bolivians and Caucasians. There was no relationship between pulmonary-artery pressure and respiratory NO in the two groups. These findings provide no evidence that Bolivian high altitude natives are better protected from hypoxic pulmonary hypertension than Caucasian low altitude natives and suggest that attenuation of pulmonary hypertension by increased respiratory NO synthesis may not represent a universal adaptation pattern in highaltitude populations.

Exhaled nitric oxide and respiratory symptoms in a community sample of school aged children

OBJECTIVE

To test the association between reported allergy and allergic diseases, respiratory symptoms, and the fractional concentration of exhaled nitric oxide (FeNO), in a community sample of school aged children.

METHODOLOGY

We administered a respiratory questionnaire and measured FeNO in a cross-sectional study of 1,135 children.

RESULTS

FeNO was significantly greater in children with reported asthma (20.3 (standard deviation (SD) 21.3) parts per billion (ppb)) or allergies (18.1 (SD 18.0) ppb) than in healthy children (14.0 (SD 13.4) ppb). It was greater in children with asthma and reported allergies (22.8 (SD 23.6) ppb), than in children with asthma but no allergies (15.8 (SD 15.6) ppb) (overall P-value between disease groups = 0.002). FeNO was not related to respiratory symptoms in healthy children. Eczema was associated with an elevated FeNO concentration, even in the absence of respiratory symptoms. Some children with reported allergies but not asthma who had respiratory symptoms suggestive of asthma had elevated FeNO concentrations, and the proportion of healthy children with reported bronchitis or pneumonia in the past year who had an abnormally high FeNO concentration was significantly elevated.

CONCLUSIONS

In a community sample of children, FeNO concentrations appear to reflect allergic conditions, including allergic asthma, reported allergies, and eczema, rather than just asthma, particularly since asthma in children may be non-allergic. FeNO is similarly elevated in school aged children with reported asthma or reported allergies. FeNO is higher in children with asthma and allergies than in children with asthma alone. However, an elevated FeNO may help alert the clinician to the possibility of undiagnosed asthma.

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

OBJECTIVE

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

DATA SOURCE

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

RESULTS

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

CONCLUSIONS

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

Impaired nitric oxide bioavailability and L-arginine reversible endothelial dysfunction in adults with falciparum malaria

Severe falciparum malaria (SM) is associated with tissue ischemia related to cytoadherence of parasitized erythrocytes to microvascular endothelium and reduced levels of NO and its precursor, l-arginine. Endothelial function has not been characterized in SM but can be improved by l-arginine in cardiovascular disease. In an observational study in Indonesia, we measured endothelial function using reactive hyperemia-peripheral arterial tonometry (RH-PAT) in 51 adults with SM, 48 patients with moderately severe falciparum malaria (MSM), and 48 controls. The mean RH-PAT index was lower in SM (1.41; 95% confidence interval [CI] = 1.33-1.47) than in MSM (1.82; 95% CI = 1.7-2.02) and controls (1.93; 95% CI = 1.8-2.06; P < 0.0001). Endothelial dysfunction was associated with elevated blood lactate and measures of hemolysis. Exhaled NO was also lower in SM relative to MSM and controls. In an ascending dose study of intravenous l-arginine in 30 more patients with MSM, l-arginine increased the RH-PAT index by 19% (95% CI = 6-34; P = 0.006) and exhaled NO by 55% (95% CI = 32-73; P < 0.0001) without important side effects. Hypoargininemia and hemolysis likely reduce NO bioavailability. Endothelial dysfunction in malaria is nearly universal in severe disease, is reversible with l-arginine, and likely contributes to its pathogenesis. Clinical trials in SM of adjunctive agents to improve endothelial NO bioavailability, including l-arginine, are warranted.

Exhaled nitric oxide concentration is affected by age, height, and race in healthy 9- to 12-year-old children

BACKGROUND

The fractional concentration of exhaled nitric oxide (Feno) is a useful indicator of airway inflammation in children and adults with asthma.

METHODS

We determined the range of Feno concentrations and the factors affecting it in a large sample of healthy school children attending grades 4 through 6, in Windsor, ON, Canada.

RESULTS

Feno was measured in 657 children between 9.1 and 12.9 years of age. The range of Feno concentrations in healthy school children was 12.7 parts per billion (ppb) [95% confidence interval (CI), 11.8 to 13.7 ppb] in whites and 22.8 ppb [95% CI, 17.9 to 27.7 ppb] in Asian-Canadian children (p < 0.001). Feno values also appeared to be higher in African-Canadian children than in whites, although the CI was wide because of the small number of African-Canadian children sampled. Feno rose slightly but significantly with age (p = 0.007) and with height (p = 0.023). Body mass index and gender did not significantly alter the measured Feno. FVC had a nonsignificant effect on Feno. Participation in physical activity during the same day had a borderline-significant effect on measured Feno, but a reported history of a respiratory tract infection in the preceding 2 weeks did not.

CONCLUSIONS

Feno concentrations in healthy school-aged children appeared to be affected by race, and, to a lesser extent, by age and height. These factors should be taken into consideration when interpreting clinical results.

Pathogenesis of pulmonary edema: learning from high-altitude pulmonary edema

Pulmonary edema is a problem of major clinical importance resulting from a persistent imbalance between forces that drive water into the airspace of the lung and the biological mechanisms for its removal. Here, we will review the fundamental mechanisms implicated in the regulation of alveolar fluid homeostasis. We will then describe the perturbations of pulmonary fluid homeostasis implicated in the pathogenesis of pulmonary edema in conditions associated with increased pulmonary capillary pressure, namely cardiogenic pulmonary edema and high-altitude pulmonary edema (HAPE), with particular emphasis on the latter that has provided important new insight into underlying mechanisms of pulmonary edema. We will provide evidence that impaired pulmonary endothelial and epithelial nitric oxide synthesis and/or bioavailability may represent a central underlying defect predisposing to exaggerated hypoxic pulmonary vasoconstriction, and, in turn, capillary stress failure and alveolar fluid flooding. We will then demonstrate that exaggerated pulmonary hypertension, while possibly a prerequisite, may not always be sufficient to cause HAPE, and how defective alveolar fluid clearance may represent a second important pathogenic mechanism. Finally, we will outline, how this new insight gained from studies in HAPE, may be translated into the management of pulmonary edema and hypoxemia related disease states in general.

Heat shock protein 90 modulates endothelial nitric oxide synthase activity and vascular reactivity in the newborn piglet pulmonary circulation

Heat shock protein 90 (Hsp90) binding to endothelial nitric oxide synthase (eNOS) is an important step in eNOS activation. The conformational state of bound Hsp90 determines whether eNOS produces nitric oxide (NO) or superoxide (O(2)(*-)). We determined the effects of the Hsp90 antagonists geldanamycin (GA) and radicicol (RA) on basal and ACh-stimulated changes in vessel diameter, cGMP production, and Hsp90:eNOS coimmunoprecipitation in piglet resistance level pulmonary arteries (PRA). In perfused piglet lungs, we evaluated the effects of GA and RA on ACh-stimulated changes in pulmonary arterial pressure (Ppa) and perfusate accumulation of stable NO metabolites (NOx(-)). The effects of GA and RA on ACh-stimulated O(2)(*-) generation was investigated in cultured pulmonary microvascular endothelial cells (PMVEC) by dihydroethidine (DHE) oxidation and confocal microscopy. Hsp90 inhibition with GA or RA reduced ACh-mediated dilation, abolished the ACh-stimulated increase in cGMP, and reduced eNOS:Hsp90 coprecipitation. GA and RA also inhibited the ACh-mediated changes in Ppa and NOx(-) accumulation rates in perfused lungs. ACh increased the rate of DHE oxidation in PMVEC pretreated with GA and RA but not in untreated cells. The cell-permeable superoxide dismutase mimetic M40401 reversed GA-mediated inhibition of ACh-induced dilation in PRA. We conclude that Hsp90 is a modulator of eNOS activity and vascular reactivity in the newborn piglet pulmonary circulation. Uncoupling of eNOS with GA or RA inhibits ACh-mediated dilation by a mechanism that involves O(2)(*-) generation.

Pulmonary hypertension in high-altitude dwellers: novel mechanisms, unsuspected predisposing factors

Studies of high-altitude populations, and in particular of maladapted subgroups, may provide important insight into underlying mechanisms involved in the pathogenesis of hypoxemia-related disease states in general. Over the past decade, studies involving short-term hypoxic exposure have greatly advanced our knowledge regarding underlying mechanisms and predisposing events of hypoxic pulmonary hypertension. Studies in high altitude pulmonary edema (HAPE)-prone subjects, a condition characterized by exaggerated hypoxic pulmonary hypertension, have provided evidence for the central role of pulmonary vascular endothelial and respiratory epithelial nitric oxide (NO) for pulmonary artery pressure homeostasis. More recently, it has been shown that pathological events during the perinatal period (possibly by impairing pulmonary NO synthesis), predispose to exaggerated hypoxic pulmonary hypertension later in life. In an attempt to translate some of this new knowledge to the understanding of underlying mechanisms and predisposing events of chronic hypoxic pulmonary hypertension, we have recently initiated a series of studies among high-risk subpopulations (experiments of nature) of high-altitude dwellers. These studies have allowed to identify novel risk factors and underlying mechanisms that may predispose to sustained hypoxic pulmonary hypertension. The aim of this article is to briefly review this new data, and demonstrate that insufficient NO synthesis/bioavailability, possibly related in part to augmented oxidative stress, may represent an important underlying mechanism predisposing to pulmonary hypertension in high-altitude dwellers.

The biology of exhaled nitric oxide (NO) in ischemia–reperfusion-induced lung injury: A tale of dynamism of NO production and consumption

The main objective of this paper is to review the potential diagnostic roles of exhaled nitric oxide (NO) in evaluating ischemia-reperfusion-induced lung injury associated with cardiac surgery. We shall start by elaborating on current clinical practice of cardiac surgery and to arrive at the conclusion that clinically important ischemia-reperfusion injury is a common scenario of many forms of these surgical procedures. We shall conclude this part by establishing the clinical need for biomarkers of inflammation in cardiothoracic surgery and by proposing that exhaled NO could be an important new addition to our anaesthetic monitoring repertoire based on our expertise with exhaled breath monitoring. We shall then take a closer look at mechanisms of ischemia-reperfusion injury and will propose the role of reactive oxygen and nitrogen species as mediators and biomarkers of acute lung injury. This analysis will provide a good opportunity to highlight major potential mechanisms of altered NO production and bioactivity of NO. We shall conclude that multiple relevant mechanisms may either lead to increased production of NO or enhance consumption of NO, leaving us with the paradigm that NO maybe used either as a positive or negative biomarker of inflammation. In order to explore this dilemma further, we will investigate the predominant effect of oxidative stress on NO bioactivity in cell culture models of ischemia-reperfusion injury. We will then turn to animal models of ischemia-reperfusion injury to elucidate the ultimate effects of this condition on lung NO production and concentrations of NO in the lung. Finally, we shall complete this journey by highlighting the human relevance of these observations by reviewing our own experience at Harefield Hospital, UK, and that of others, regarding exhaled NO in ischemia-reperfusion injury associated with cardiac surgery and lung transplantation.

Correlation between pulmonary gas exchange and basal and nitroglycerin (GTN)-induced exhaled nitric oxide (eNO) in patients undergoing cardiac surgery

The relationship between eNO and events in the alveolar-capillary unit in acute lung injury remains to be established. Since endogenous eNO largely originates from the airway epithelium, but nitroglycerin (GTN)-induced eNO is due to microvascular/alveolar metabolism, we have proposed to use basal and GTN-induced eNO as metabolic markers of the airway--and microvascular/alveolar function, respectively. The current work investigates the relationship between basal and GTN-induced eNO and oxygenation parameters (PaO(2)/FiO(2) ratio) in patients undergoing cardiac surgery utilising cardiopulmonary bypass (CPB). Breath by breath eNO measurements were made in 10 patients before, and 1 and 3 h after CPB either under basal conditions or following intravenous administration of GTN (1, 2 and 3 microg/kg). Basal eNO remained unchanged, whereas GTN-induced eNO was reduced following CPB. Also, there was a transient reduction in PaO(2)/FiO(2) ratio 1 h after CPB (32+/-4 vs. 44+/-3 kPa). A negative correlation was found between oxygenation and basal eNO by Pearson's correlation test and linear regression analysis suggesting that decreased oxygenation was associated with increased basal eNO. In contrast, a decrease in GTN-induced eNO positively correlated with reduced oxygenation index (R=0.533, p=0.002). These data suggest that differential relationships exist between basal and nitrovasodilator-induced eNO and oxygenation indices during subclinical lung injury in patients following CPB and that GTN-induced eNO evolution may reflect better microvascular events and injury.

A prospective randomized study to evaluate the effect of leukodepletion on the rate of alveolar production of exhaled nitric oxide during cardiopulmonary bypass

BACKGROUND

Cardiopulmonary bypass is associated with a whole body inflammatory reaction. Exhaled nitric oxide increases in inflammatory lung conditions (eg, asthma) in proportion to the severity of inflammation, and has been proposed as a marker of pulmonary inflammation during cardiopulmonary bypass. This study evaluated the effect of arterial line leukocyte depletion during cardiopulmonary bypass on the rate of alveolar production of exhaled nitric oxide.

METHODS

One hundred and ten patients with normal respiratory function, undergoing first time coronary artery bypass grafting, were randomized to two groups. Fifty-five patients had an arterial line leukocyte-depleting filter and 55 controls had a standard arterial line filter. Nitric oxide was sampled through an endotracheal Teflon tube after median sternotomy, but before cardiopulmonary bypass and 30 minutes after cardiopulmonary bypass, using a real time chemiluminescence analyzer, during the phase of the alveolar plateau.

RESULTS

There were no significant differences in the precardiopulmonary bypass values of exhaled nitric oxide between the control (2.92 +/- 1.51 ppb/s) and the leukodepletion group (3.11 +/- 1.53 ppb/s) (p = 0.4). After cardiopulmonary bypass, the rate of alveolar production of exhaled nitric oxide increased in both groups, being, however, significantly higher in the control group (4.68 +/- 1.89 vs 3.72 +/- 1.33 ppb/s) (p = 0.02).

CONCLUSIONS

Continuous arterial line leukocyte-depletion significantly reduces the rate of alveolar production of exhaled nitric oxide after cardiopulmonary bypass. Changes in the rate of alveolar production of exhaled nitric oxide may be used as a marker of pulmonary inflammation in coronary artery surgery.

Decreased exhaled nitric oxide in pulmonary arterial hypertension: response to bosentan therapy

RATIONALE

Decreased nitric oxide (NO) is considered an important pathogenetic mechanism in pulmonary arterial hypertension (PAH), but clear evidence is lacking.

OBJECTIVES

We used multiple techniques to assess endogenous NO in 10 patients with untreated PAH (8 idiopathic and 2 anorexigen-associated PAH) and 12 control subjects.

METHODS

After a nitrite/nitrate-restricted diet, NO metabolites (NOx) were assayed in 24-hour urine collections and exhaled NO (FE(NO)) determined at multiple expiratory flows. Analysis of the relation between FE(NO) and flow allowed derivation of three flow-independent parameters: airway wall concentration (C(W)), diffusing capacity (D(NO)), and alveolar concentration (C(A)). Seven patients underwent follow-up testing after 3 months of bosentan treatment.

RESULTS

At baseline, FE(NO) was markedly decreased at the two lowest expiratory flows in PAH: 21 +/- 4 versus 36 +/- 4 ppb at 18 ml/second and 11 +/- 2 versus 17 +/- 2 ppb at 50 ml/second, for subjects with PAH and control subjects, respectively (p < 0.05). C(W) was 33 +/- 11 ppb in subjects with PAH versus 104 +/- 34 in control subjects (p = 0.04). Urinary NOx was also reduced in PAH (42 +/- 6 microM NOx/mM creatinine versus 62 +/- 7 in control subjects; p = 0.04). After bosentan, FE(NO), C(W), and urine NOx increased to control values (p < 0.05). Exclusion of the two anorexigen cases did not alter these results.

CONCLUSIONS

FE(NO) at low expiratory flows was decreased in PAH due to reduced C(W). Bosentan reversed these abnormalities, suggesting that suppression of NO in PAH may have been caused by endothelin.

Pulmonary transcription of CAT-2 and CAT-2B but not CAT-1 and CAT-2A were upregulated in hemorrhagic shock rats

Hemorrhagic shock stimulates nitric oxide (NO) biosynthesis through upregulation of inducible NO synthase (iNOS) expression. Trans-membrane l-arginine transportation mediated by the isozymes of cationic amino acid transporters (e.g. CAT-1, CAT-2, CAT-2A, and CAT-2B) is one crucial regulatory mechanism that regulates iNOS activity. We sought to assess the effects of hemorrhage and resuscitation on the expression of these regulatory enzymes in hemorrhage-stimulated rat lungs. Twenty-four rats were randomized to a sham-instrumented group, a sustained shock group, a shock with blood resuscitation group, or a shock with normal saline resuscitation group. Hemorrhagic shock was induced by withdrawing blood to maintain MAP between 40 and 45mmHg for 60min. Resuscitation by infusing blood/saline mixtures (blood resuscitation group) or saline alone (saline resuscitation group) was then performed. At the end of the experiment (300min after hemorrhage began), rats were sacrificed and enzymes expression as well as pulmonary NO biosynthesis and lung injuries were assayed. Our data revealed that hemorrhage-induced pulmonary iNOS, CAT-2, and CAT-2B transcription which was associated with pulmonary NO overproduction and subsequent lung injury. Resuscitation significantly attenuated the hemorrhage-induced enzyme upregulation, pulmonary NO overproduction, and lung injury. Blood/saline mixtures were superior to saline as a resuscitation solution in treating hemorrhage-induced pulmonary NO overproduction and lung injury. Hemorrhage and/or resuscitation, however, did not affect the expression of pulmonary CAT-1 and CAT-2A. It is, therefore, concluded that the expression of pulmonary iNOS, CAT-2, and CAT-2B is inducible and that of CAT-1 and CAT-2A is constitutive in hemorrhagic shock rat lungs.

Regulation of regional lung perfusion by nitric oxide

Improved oxygenation has previously been shown in patients with acute lung injury when ventilated in prone position. We hypothesized that this was due to higher regional production of nitric oxide in dorsocaudal lung regions. We measured nitric oxide synthase mRNA expression and nitric oxide production by citrulline assay in ventral and dorsal lung tissue from patients. In volunteers, regional lung perfusion in prone and supine postures was assessed by single photon emission computed tomography using (99m)Tc macroaggregated albumin before and after inhibition of nitric oxide synthase by N(G)-monomethyl-L-arginine infusion. Nitric oxide synthase mRNA expression and nitric oxide production were significantly higher in dorsal compared with ventral lung regions. In supine posture, lung perfusion was shifted to ventral parts during nitric oxide synthase inhibition, whereas in the prone posture lung perfusion remained unchanged. Our results suggest a role for endogenous nitric oxide in regulation of regional pulmonary perfusion.

Lack of evidence for association of high altitude pulmonary edema and polymorphisms of the NO pathway

One essential factor in the development of high altitude pulmonary edema (HAPE) is elevated pulmonary artery pressure, possibly due to a lack of nitric oxide (NO) in pulmonary vessels. NOS3 gene polymorphisms (G894T, T-786C, and CA-repeats > or =38) might be linked to decreased NO synthesis and increased susceptibility to HAPE, while the C242T polymorphism of the CYBA gene [encoding for the NAD(P)H oxidase subunit p22phox] may increase NO availability and thus convey resistance to HAPE. To test this hypothesis, we genotyped 51 mountaineers susceptible and 52 mountaineers not susceptible to HAPE. Genotyping revealed similar genotype frequencies of the G894T and the T-786C NOS3 polymorphism in both groups (G894T: susceptibles, 39.2% GG, 47.1% GT, 13.7% TT; nonsusceptibles, 48.0% GG, 44.0% GT, 8.0% TT; p = 0.54. T-786C: susceptibles, 45.1% TT, 39.2% TC, 15.7% CC; nonsusceptibles, 53.8% TT, 40.4% TC, 5.8% CC; p = 0.28). Genotype frequencies of the C242T CYBA polymorphism were 43.1% CC, 47.1 % CT, and 9.8% TT in HAPE susceptibles and 38.0% CC, 52.0 % CT, and 10.0% TT (p = 0.92) in nonsusceptibles. There was also no difference between the two groups in the number of CA repeats (p = 0.57), and individuals with > or =38 CA repeats were not more likely to develop HAPE (p = 1.0). Haplotype analysis for the NOS3 polymorphisms also revealed no association with HAPE. The results of this study suggest that none of these genetic variants plays a substantial role in the pathogenesis of HAPE in Caucasians, but does not exclude epistatic effects that might still involve the genetic systems studied here.

Contributions of nitric oxide synthase isozymes to exhaled nitric oxide and hypoxic pulmonary vasoconstriction in rabbit lungs

We investigated the source(s) for exhaled nitric oxide (NO) in isolated, perfused rabbits lungs by using isozyme-specific nitric oxide synthase (NOS) inhibitors and antibodies. Each inhibitor was studied under normoxia and hypoxia. Only nitro-L-arginine methyl ester (L-NAME, a nonselective NOS inhibitor) reduced exhaled NO and increased hypoxic pulmonary vasoconstriction (HPV), in contrast to 1400W, an inhibitor of inducible NOS (iNOS), and 7-nitroindazole, an inhibitor of neuronal NOS (nNOS). Acetylcholine-mediated stimulation of vascular endothelial NOS (eNOS) increased exhaled NO and could only be inhibited by L-NAME. Selective inhibition of airway and alveolar epithelial NO production by nebulized L-NAME decreased exhaled NO and increased hypoxic pulmonary artery pressure. Immunohistochemistry demonstrated extensive staining for eNOS in the epithelia, vasculature, and lymphatic tissue. There was no staining for iNOS but moderate staining for nNOS in the ciliated cells of the epithelia, lymphoid tissue, and cartilage cells. Our findings show virtually all exhaled NO in the rabbit lung is produced by eNOS, which is present throughout the airways, alveoli, and vessels. Both vascular and epithelial-derived NO modulate HPV.

Basal and nitroglycerin-induced exhaled nitric oxide before and after cardiac surgery with cardiopulmonary bypass

BACKGROUND

Exhaled nitric oxide (NO) may reflect NO production and consumption but the pulmonary origin of NO in exhaled gas is not clear. There are also conflicting data on exhaled NO after cardiopulmonary bypass (CPB). Because intravenous nitrovasodilators increase exhaled NO by conversion to NO in the lung, we measured basal and nitroglycerin (GTN)-induced exhaled NO in patients having low-risk coronary artery bypass graft (CABG) operations using routine CPB. We reasoned that GTN-induced exhaled NO would be a primarily vascular mechanism, which would contrast with the airway epithelial origin of basal exhaled NO, and that they might be differentially influenced by CPB.

METHODS

Breath-to-breath concentrations of gas phase NO were measured in 12 CABG patients before and 1, 3 and 6 h after CPB. After the baseline measurements, three increasing doses of 1, 2 and 3 micro g kg(-1) intravenous GTN were given by a central venous catheter and exhaled NO and haemodynamic responses were recorded.

RESULTS

Intravenous administration of 1, 2 and 3 micro g kg(-1) doses of GTN produced a dose-dependent increase in exhaled NO and a reduction in systemic blood pressure. Baseline exhaled NO remained unchanged. Exhaled NO but not blood pressure responses were reduced 1 and 3 h after CPB.

CONCLUSIONS

The capacity of the lungs to increase exhaled NO in response to intravenous GTN is reduced after CPB, suggesting microvascular injury and/or atelectasis after routine open-heart surgery.

Decreased exhaled nitric oxide in sickle cell disease: relationship with chronic lung involvement

A deficiency in airway nitric oxide (NO) could contribute to pulmonary vaso-occlusion in sickle cell disease (SCD). We measured the fractional expired concentration of NO (FE(NO)) by chemiluminescence during a slow vital capacity maneuver against a positive pressure of 16 cm H(2)O at an expiratory flow rate of 50 mL/sec in 44 stable ambulatory adults with SCD and 30 healthy controls. A history of acute chest syndrome was present in 29 patients, and 22 complained of dyspnea. Mean +/- SD FE(NO) was significantly reduced in the SCD group compared with controls (14.8 +/- 8.4 vs. 24.9 +/- 13.5 ppb, P < 0.001). SCD patients with dyspnea had lower FE(NO) than those without dyspnea (10.1 +/- 5.7 vs. 19.6 +/- 8 ppb, P < 0.001) and those with a history of ACS had lower values than those no episodes of ACS (13.0 +/- 8.3 vs. 18.4 +/- 7.6 ppb, P < 0.05). There was a weak correlation between FE(NO) and percent-predicted DLCO (r = 0.4, P = 0.02) among the SCD patients. We conclude that exhaled NO is reduced in adults with SCD, and this may play a role in the pathogenesis of acute chest syndrome and chronic sickle cell lung disease.

Resuscitation of hemorrhagic shock attenuates intrapulmonary nitric oxide formation

Hemorrhagic shock has been shown to upregulate intrapulmonary inducible nitric oxide (NO) synthase (iNOS) expression. Increased intrapulmonary iNOS expression is reflected by increases in concentrations of NO in the airways. The purpose of this study was to examine the effects of resuscitation on this induction of intrapulmonary NO formation caused by hemorrhage. Eighteen rats were randomized to one of three groups. One group of rats was simply sham-instrumented and monitored. Two other groups experienced hemorrhagic shock (mean systemic blood pressure of 40-45 mmHg) for 60 min. In one of the hemorrhagic shock groups, resuscitation was performed by re-infusing the shed blood and supplementing it with normal saline. Compared with sham-instrumented rats, those exposed to hemorrhagic shock without subsequent resuscitation exhibited a 10-fold increase in exhaled NO concentrations. Additionally, concentrations of both intrapulmonary iNOS protein and mRNA increased. Resuscitation attenuated the hemorrhage-induced upregulation of exhaled NO, iNOS protein and iNOS mRNA. This data suggests that resuscitation attenuates the hemorrhagic shock-induced formation of intrapulmonary NO by downregulating iNOS transcription. We believe that exhaled NO concentrations provide a useful, non-invasive method of monitoring the intrapulmonary inflammatory sequelae of hemorrhagic shock.

Effects of S-nitrosation and cross-linking of hemoglobin on hypoxic pulmonary vasoconstriction in isolated rat lungs

Free hemoglobin (Hb) and red blood cells augment hypoxic pulmonary vasoconstriction (HPV) by scavenging nitric oxide (NO). S-nitrosation of Hb (SNO-Hb) may confer vasodilatory properties by allowing release of NO during deoxygenation and/or by interaction with small-molecular weight thiols. Likewise, cross-linking of free Hb may limit its vasoconstrictive effect by preventing abluminal movement of the molecule. We compared the effects of free SNO-Hb and Hb intramolecularly cross-linked at the beta-cysteine 93 residue [Bis(maleidophenyl)-polyethylene glycol2000HbA (Bis-Mal-PEGHb)] to those of free oxyHb on pulmonary artery pressure (PAP), HPV, and exhaled NO (eNO) in isolated, perfused rat lungs. Ventilation of lungs with anoxic gas for 5 minutes reduced perfusate PO2 to 11+/-1.0 Torr. Addition of SNO-Hb or Bis-Mal-PEGHb (100 micromol/L) to buffer perfusate increased normoxic PAP and augmented HPV in similar magnitude as free oxyHb, but had no effect on eNO. Addition of the allosteric modulator inositol hexaphosphate to increase Hb P50 and the thiol glutathione (GSH) to allow removal of NO from Hb via transnitrosation to the perfusate did not reduce augmentation of HPV by SNO-Hb or increase eNO. GSH resulted in an approximately 50% reduction in perfusate [S-nitrosothiol], in association with an increase in perfusate [metHb]. Free SNO-Hb is a net NO scavenger and pulmonary vasoconstrictor in this model, although thiol-mediated release of NO from SNO-Hb does occur. However, release of NO from SNO-Hb was not influenced by deoxygenation-mediated allosteric changes in Hb across a broad range of oxyHb saturation. Cross-linking of Hb does not limit its pulmonary vasoconstrictor effects.

Exhaled nitric oxide: a marker of pulmonary hemodynamics in heart failure

OBJECTIVES

We sought to test the hypothesis that patients with decompensated heart failure (HF) lose a compensatory process whereby nitric oxide (NO) maintains pulmonary vascular tone.

BACKGROUND

Exhaled nitric oxide (eNO) partially reflects vascular endothelial NO release. Levels of eNO are elevated in patients with compensated HF and correlate inversely with pulmonary artery pressures (PAP), reflecting pulmonary vasodilatory activity.

METHODS

We measured the mean mixed expired NO content of a vital-capacity breath using chemiluminescence in patients with compensated HF (n = 30), decompensated HF (n = 7) and in normal control subjects (n = 90). Pulmonary artery pressures were also measured in patients with HF. The eNO and PAP were determined sequentially during therapy with intravenous vasodilators in patients with decompensated HF (n = 7) and in an additional group of patients with HF (n = 13) before and during administration of milrinone.

RESULTS

The eNO was higher in patients with HF than in control subjects (9.9 +/- 1.1 ppb vs. 6.2 +/- 0.4 ppb, p = 0.002) and inversely correlated with PAP (r = -0.81, p < 0.00001). In marked contrast, patients with decompensated HF exhibited even higher levels of eNO (20.4 +/- 6.2 ppb) and PAP, but there was a loss of the inverse relationship between these two variables. During therapy (7.3 +/- 6 days) with sodium nitroprusside and diuresis, hemodynamics improved, eNO concentrations fell (11.2 +/- 1.2 ppb vs. before treatment, p < 0.05), and the relationship between eNO and PAP was restored. After milrinone, eNO rose proportionally with decreased PAP (p < 0.05).

CONCLUSIONS

Elevated eNO may reflect a compensatory circulatory mechanism in HF that is lost in patients with clinically decompensated HF. The eNO may be an easily obtainable and quantifiable measure of the response to therapy in advanced HF.

Partitioning of alveolar and conducting airway nitric oxide in scleroderma lung disease

We partitioned exhaled nitric oxide (NO) into alveolar concentration (CA) and conducting airway flux (JNO(air,max)) in scleroderma (SSc) lung disease and hypothesized that CA would be elevated. Twenty patients with SSc, 15 with interstitial lung disease (SSc-ILD) alone, and 5 with pulmonary hypertension (SSc-PH) were compared with 20 control subjects. CA and JNO(air,max) were derived from the slope and y intercept, respectively, of the NO output versus expiratory flow rate ((V).exh) relationship obtained by measuring exhaled NO (FE(NO)) at multiple (V).exh values of 50-200 ml/second. There were no significant differences in FE(NO) at any (V).exh between the SSc group and control subjects. JNO(air,max) was reduced (0.6 +/- 0.1 versus 1.2 +/- 0.2 nl of NO per second; p = 0.01), whereas CA was increased (4.7 +/- 0.5 versus 1.8 +/- 0.2 ppb; p < 0.001) in the SSc group compared with control subjects. No differences were noted between SSc-ILD and SSc-PH. There was a negative correlation between CA and DL(CO) among the patients with SSc (R = -0.66, p = 0.002). We conclude that CA is increased whereas JNO(air,max) is decreased in SSc-ILD and SSc-PH. A reduced diffusing capacity of NO from the alveolar space into the blood could explain the observed increase in CA.

Transepithelial sodium and water transport in the lung. Major player and novel therapeutic target in pulmonary edema

Active transepithelial transport of sodium from the airspaces to the lung interstitium is a primary mechanism driving alveolar fluid clearance. This mechanism depends on sodium uptake by amiloride-sensitive sodium channels on the apical membrane of alveolar type II cells followed by extrusion of sodium on the basolateral surface by the Na-K-ATPase. Injury to the alveolar epithelium can disrupt the integrity of the alveolar barrier or downregulate ion transport pathways thus reducing net alveolar fluid reabsorption, and enhancing the extent of alveolar edema. Endogenous catecholamines upregulate alveolar fluid clearance in several experimental models of acute lung injury, but this upregulation is short-term and often not sufficient to counterbalance alveolar flooding. There is new evidence, however, that pharmacological treatment with beta-adrenergic agonists and/or epithelial growth factors may induce a more sustained stimulation of alveolar fluid reabsorption and in turn facilitate recovery from experimental pulmonary edema. Similar results have been achieved experimentally by gene transfer enhancing the abundance of sodium transporters in the alveolar epithelium. Clinical studies show that impaired alveolar fluid transport mechanisms contribute to the development, severity and outcome of pulmonary edema in humans. Very recent data suggest that mechanisms that augment transepithelial sodium transport and enhance the clearance of alveolar edema may lead to more effective prevention or treatment for pulmonary edema and acute lung injury.

Update: High altitude pulmonary edema

Recent high altitude studies with pulmonary artery (PA) catheterization and broncho-alveolar lavage (BAL) in early high altitude pulmonary edema(HAPE) have increased our understanding of the pathogenetic sequence in HAPE. High preceding PA and pulmonary capillary pressures lead to a non-inflammatory leak of the alveolar-capillary barrier with egress of red cells, plasma proteins and fluid into the alveolar space. The mechanisms accounting for an increased capillary pressure remain speculative. The concept that hypoxic pulmonary vasoconstriction (HPV) is uneven so that regions with less vasoconstriction are over-perfused and become edematous remains compelling but unproved. Also uncertain is the role and extent of pulmonary venoconstriction. With disruption of the normal alveolar-capillary barrier, some individuals may later develop a secondary inflammatory reaction. A high incidence of preceding or concurrent respiratory infection in children with HAPE has been used to support a causative role of inflammation in HAPE. However, alternatively even mild HPV may simply lower the threshold at which inflammation-mediated increases in alveolar capillary permeability cause significant fluid flux into the lung. Other major questions to be addressed in future research are: 1.) What is the mechanism of exaggerated hypoxic pulmonary vasoconstriction? Is there a link to primary pulmonary hypertension? Several observations suggest that susceptibility to HAPE is associated with endothelial dysfunction in pulmonary vessels. This has not yet been studied adequately. 2.) What is the nature of the leak? Is there structural damage, i. e. stress failure, or does stretch cause opening of pores? 3.) What is the pathophysiologic significance of a decreased sodium and water clearance across alveolar epithelial cells in hypoxia? 4.) What is the role of exercise? Do HAPE-susceptible individuals develop pulmonary edema when exposed to hypoxia without exercise? Answers to these questions will increase our understanding of the pathophysiology of HAPE and also better focus research on the genetic basis of susceptibility to HAPE.

Increased nitric oxide output from alveolar origin during liver cirrhosis versus bronchial source during asthma

The aim of this study was to assess the usefulness of nitric oxide (NO) output measurement at multiple expiratory flow rates during diseases characterized by increased exhaled NO (FE(NO)) that could come from alveolar (liver cirrhosis) or bronchial (asthma) sources. It has been proposed that NO output measurements expressed as a function of expiratory flow allow alveolar NO concentration (FA(NO)) and maximal bronchial NO output (Qbr,max (NO)) to be computed. In 36 healthy nonsmoking subjects, we found that maximal bronchial NO output (37 +/- 3 nl/min) was correlated with the height of the subjects (p = 0.02). Alveolar NO concentration was 5.1 +/- 0.3 (SEM) ppb, which represented 31 +/- 2% and 61 +/- 3% of FE(NO) at 50 and 200 ml/s expiratory flow rate, respectively. Nonsmoking subjects with asthma (n = 28) were characterized by an increase in Qbr,max (NO) (133 +/- 14 nl/min) as compared with healthy nonsmoking subjects (p < 0.0001). FE(NO)50, FE(NO)200, and Qbr,max (NO) were equally efficient in differentiating subjects with asthma from healthy subjects. Patients with liver cirrhosis (n = 26, 14 smokers and 12 nonsmokers) had an increased FA(NO) compared with healthy subjects (cirrhosis: 8.3 +/- 0.9 ppb, healthy nonsmokers [n = 36] and smokers [n = 20], n = 56: 4.7 +/- 0.3 ppb, p < 0.05), which was correlated with the alveolar-arterial oxygen difference (p = 0.007). FA(NO) and FE(NO)200, but not FE(NO)50 values, allowed patients with liver cirrhosis to be differentiated from healthy subjects. These results suggest that a two-compartment model for NO output allows the increase in FE(NO) from alveolar sources to be differentiated from the increase from bronchial sources.

Mechanisms of nitric oxide generation from nitroglycerin and endogenous sources during hypoxia in vivo

Nitroglycerin (GTN), often used in conditions of cardiovascular ischaemia, acts through the liberation of nitric oxide (NO) and the local concentration of NO in the tissue is responsible for any biological effect. However, little is known about the way in which the concentration of NO from GTN and other NO-donors is influenced by low oxygen tension in the target tissues. To evaluate the impact of changes in oxygen tension in the metabolism of NO-donors we measured exhaled NO in anaesthetized rabbits in vivo and expired NO and perfusate nitrite (NO(2)(-)) in buffer-perfused lungs in situ. The impact of acute hypoxia on NO formation from GTN, isosorbide-5-mononitrate (ISMN), dissolved authentic NO, NO(2)(-) and NO generated from endogenous NO-synthase (NOS) was studied in either model. Acute hypoxia drastically increased exhaled NO concentrations from all NO-donors studied, both in vivo and in the perfused lung. During similar conditions endogenous NO generation from NOS was strongly inhibited. The effects were most pronounced at less than 3% inspired oxygen. The mechanisms for the increased NO-formation during hypoxia seems to differ between GTN- and NO(2)(-)-derived NO. The former phenomenon is likely due to diminished breakdown of NO. In conclusion, hypoxic conditions preserve very high local NO concentrations generated from organic nitrates in vivo and we suggest that this might benefit preferential vasodilation in ischaemic tissue regions. Our findings point out the necessity to consider the influence of oxygen tension when studying the action of NO-donors.

Low exhaled nitric oxide and a polymorphism in the NOS I gene is associated with acute chest syndrome

Abnormalities of nitric oxide metabolism have been implicated in the pathogenesis of acute chest syndrome in subjects with sickle cell anemia. It is not known whether exhaled nitric oxide levels (FE(NO)) are abnormal in children with a history of the acute chest syndrome (ACS). We compared FE(NO), plasma nitric oxide metabolites (NO(x)), serum arginine and citrulline levels, and the number of AAT repeats in intron 20 of NOS I in subjects with sickle cell disease (SCD) and a history of at least one episode of ACS (ACS(+), n = 13), subjects with SCD and no prior history of ACS (ACS(-), n = 7), and healthy children (HC, n = 6). Mean +/- SD FE(NO) (ppb) was lower in ACS(+) than in ACS(-) and HC: (10.4 +/- 4.3 versus 23.4 +/- 6.1 p = 0.002] and 30.4 +/- 15.8 [p = 0.0001], respectively). Plasma NO(x) (microM) were similar in all three groups (37.3 +/- 19.4, 33.0 +/- 13.2, 44.7 +/- 7.8, respectively). Arginine and citrulline levels (microM) did not differ between ACS(+) and ACS(-) groups. Spirometric data revealed a mildly diminished FEV(1) and FVC in ACS(+) that was statistically different from HC but not ACS(-): (FEV(1) as % of predicted for ACS(+), ACS(-), and HC; 83 +/- 17 versus 87 +/- 16 versus 102 +/- 16, respectively, p < 0.05 between ACS(+) and HC). The level of FE(NO) was significantly associated with the sum of AAT repeats in intron 20 of NOS I gene alleles. The correlation coefficient (r) was 0.62 (p < 0.005). We conclude that FE(NO) levels are significantly reduced in subjects who have a history of ACS and that the FE(NO) levels are significantly correlated with the number of NOS I AAT repeats. FE(NO) is a sensitive marker and may be a predictor of ACS prone children.

Effect of pulmonary rehabilitation on exhaled nitric oxide in patients with chronic obstructive pulmonary disease

BACKGROUND

In patients with mild to moderate chronic obstructive pulmonary disease (COPD) the exercise induced increase in exhaled nitric oxide (eNO) parallels that observed in normal untrained subjects. There is no information on the effects of the level of exercise tolerance on eNO in these patients. The aim of this study was to evaluate the effect of a pulmonary rehabilitation programme including exercise training on eNO in patients with COPD.

METHODS

In 14 consecutive male patients with stable COPD of mean (SD) age 64 (9) years and forced expiratory volume in one second (FEV1) 55 (14)% predicted, fractional eNO concentration (FeNO), peak work rate (Wpeak) and oxygen uptake (VO2peak) were assessed at baseline (T-1), at the end of a 1 month run in period (T0), and after an 8 week outpatient multidisciplinary pulmonary rehabilitation programme (T1) including cycloergometer training.

RESULTS

FeNO did not significantly differ at T-1 and T0 (mean (SE) 4.3 (0.6) and 4.4 (0.6) ppb, respectively), whereas it rose significantly at T1 to 6.4 (0.7) ppb (p<0.02). Compared with T0, both Wpeak and VO2 were significantly (p<0.05) increased at T1 (mean (SE) Wpeak from 89 (5.6) W to 109 (6.9) W); VO2peak from 1.27 (0.1) l/min to 1.48 (0.1) l/min). A significant correlation was found between baseline FEV1 and the change in FeNO following the rehabilitation programme (r=-0.71; p<0.05) and between changes in FeNO and Wpeak from T0 to T1(r=0.60; p<0.05).

CONCLUSIONS

Pulmonary rehabilitation in patients with mild to moderate COPD is associated with an increase in exhaled nitric oxide.

Effect of pulmonary rehabilitation on exhaled nitric oxide in patients with chronic obstructive pulmonary disease

BACKGROUND

In patients with mild to moderate chronic obstructive pulmonary disease (COPD) the exercise induced increase in exhaled nitric oxide (eNO) parallels that observed in normal untrained subjects. There is no information on the effects of the level of exercise tolerance on eNO in these patients. The aim of this study was to evaluate the effect of a pulmonary rehabilitation programme including exercise training on eNO in patients with COPD.

METHODS

In 14 consecutive male patients with stable COPD of mean (SD) age 64 (9) years and forced expiratory volume in one second (FEV1) 55 (14)% predicted, fractional eNO concentration (Feno), peak work rate (Wpeak) and oxygen uptake (V˙o2peak) were assessed at baseline (T–1), at the end of a 1 month run in period (T0), and after an 8 week outpatient multidisciplinary pulmonary rehabilitation programme (T1) including cycloergometer training.

RESULTS

Fenodid not significantly differ at T–1 and T0 (mean (SE) 4.3 (0.6) and 4.4 (0.6) ppb, respectively), whereas it rose significantly at T1 to 6.4 (0.7) ppb (p<0.02). Compared with T0, both Wpeak andV˙o2 were significantly (p<0.05) increased at T1 (mean (SE) Wpeak from 89 (5.6) W to 109 (6.9) W);V˙o2peak from 1.27 (0.1) l/min to 1.48 (0.1) l/min). A significant correlation was found between baseline FEV1 and the change in Feno following the rehabilitation programme (r=–0.71; p<0.05) and between changes in Feno and Wpeak from T0 to T1(r=0.60; p<0.05).

CONCLUSIONS

Pulmonary rehabilitation in patients with mild to moderate COPD is associated with an increase in exhaled nitric oxide.

Hypoxia decreases exhaled nitric oxide in mountaineers susceptible to high-altitude pulmonary edema

An exaggerated hypoxic pulmonary vasoconstriction is essential for development of high-altitude pulmonary edema (HAPE). We hypothesized that susceptibility to HAPE may be related to decreased production of nitric oxide (NO), an endogenous modulator of pulmonary vascular resistance, and that a decrease in exhaled NO could be detected during hypoxic exposure. Therefore, we investigated respiratory tract NO excretion by chemiluminescence and pulmonary artery systolic pressure (Ppa,s) by echocardiography in nine HAPE-susceptible mountaineers and nine HAPE-resistant control subjects during normoxia and acute hypoxia (fraction of inspired oxygen [FI(O2)] = 0.12). The subjects performed oral breathing. Nasally excreted NO was separated from respiratory gas by suction via a nasal mask. In HAPE-susceptible subjects, NO excretion in expired gas significantly decreased (p < 0.05) during hypoxia of 2 h in comparison with normoxia (28 +/- 4 versus 21 +/- 2 nl/min, mean +/- SEM). In contrast, the NO excretion rate of control subjects remained unchanged (31 +/- 6 versus 33 +/- 6 nl/ min, NS). Nasal NO excretion did not differ significantly between groups during normoxia (HAPE-susceptible group, 183 +/- 16 nl/ min; control subjects, 297 +/- 55 nl/min, NS) and was not influenced by hypoxia. The changes in Ppa,s with hypoxia correlated with the percent changes in lower respiratory tract NO excretion (R = -0.49, p = 0.04). Our data provide the first evidence of decreased pulmonary NO production in HAPE-susceptible subjects during acute hypoxia that may contribute among other factors to their enhanced hypoxic pulmonary vascular response.

Hemoglobin and red blood cells alter the response of expired nitric oxide to mechanical forces

Expired nitric oxide (NO(e)) varies with hemodynamic or ventilatory perturbations, possibly due to shear stress- or stretch-stimulated NO production. Since hemoglobin (Hb) binds NO, NO(e) changes may reflect changes in blood volume and flow. To determine the role of blood and mechanical forces, we measured NO(e) in anesthetized rabbits, as well as rabbit lungs perfused with buffer, red blood cells (RBCs) or Hb following changes in flow, venous pressure (P(v)), and positive end-expiratory pressure (PEEP). In buffer-perfused lungs decreases in flow and P(v) reduced NO(e), but NO(e) rose when RBCs and Hb were present. These findings are consistent with changes in vascular NO production, whose detection is obscured in blood-perfused lungs by the more dominant effect of Hb NO scavenging. PEEP decreased NO(e) in all perfused lungs but increased NO(e) in live rabbits. The NO(e) fall with PEEP in isolated lungs is consistent with flow redistribution from alveolar septal capillaries to extra-alveolar vessels and decreased surface area or a direct, stretch-mediated depression of lung epithelial NO production. In live rabbits, increased NO(e) may reflect blood flow reduction and decreased Hb NO scavenging and/or autonomic responses that increase NO production. We conclude that blood and systemic responses render it difficult to use NO(e) changes as an accurate measure of lung tissue NO production.

Acetazolamide reduces hypoxic pulmonary vasoconstriction in isolated perfused rabbit lungs

Carbonic anhydrase (CA) may modulate regional blood flow by mediating changes in extra- and intracellular pH. We hypothesized that CA inhibition with acetazolamide would inhibit the kinetics and magnitude of hypoxic pulmonary vasoconstriction (HPV). Isolated rabbit lungs were ventilated and perfused in situ at constant flow, with buffer containing red blood cells. Preparations were sequentially challenged with hypoxic (FI(O(2)) 0.05) and/or hypercapnic (FI(CO(2)) 0.10) gas mixtures for 5 or 10 min. In the experimental groups, acetazolamide (33 microM) was added to the perfusate after establishing baseline responses, and gas challenges were repeated; control groups were studied without acetazolamide. Acetazolamide reduced the increase in pulmonary artery pressure (DeltaPAP) and the rate of pressure rise by approximately 30-50% during hypoxia and combined hypoxia/hypercapnia. The reduction in DeltaPAP occurred for both 5 and 10 min challenges. Acetazolamide did not affect expired nitric oxide concentrations. We conclude that acetazolamide reduces both the magnitude and kinetics of HPV by a mechanism that does not involve nitric oxide.

Exhaled nitric oxide in high-altitude pulmonary edema: role in the regulation of pulmonary vascular tone and evidence for a role against inflammation

High-altitude pulmonary edema (HAPE) is a life-threatening condition occurring in predisposed subjects at altitudes above 2,500 m. It is not clear whether, in addition to hemodynamic factors and defective alveolar fluid clearance, inflammation plays a pathogenic role in HAPE. We therefore made serial measurements of exhaled pulmonary nitric oxide (NO), a marker of airway inflammation, in 28 HAPE-prone and 24 control subjects during high-altitude exposure (4,559 m). To examine the relationship between pulmonary NO synthesis and pulmonary vascular tone, we also measured systolic pulmonary artery pressure (Ppa). In the 13 subjects who developed HAPE, exhaled NO did not show any tendency to increase during the development of lung edema. Throughout the entire sojourn at high altitude, pulmonary exhaled NO was roughly 30% lower in HAPE-prone than in control subjects, and there existed an inverse relationship between Ppa and exhaled NO (r = -0.51, p < 0.001). These findings suggest that HAPE is not preceded by airway inflammation. Reduced exhaled NO may be related to altered pulmonary NO synthesis and/or transport and clearance, and the data in our study could be consistent with the novel concept that in HAPE-prone subjects, a defect in pulmonary epithelial NO synthesis may contribute to exaggerated hypoxic pulmonary vasoconstriction and in turn to pulmonary edema.

Noninvasive measurement of airway inflammation using exhaled nitric oxide and induced sputum. Current status and future use

The recent use of IS and the analysis of exhaled mediators such as NO are important steps forward in our ability to noninvasively assess airway inflammation without the need to resort to bronchoscopy. Exhaled NO and IS are complementary techniques that provide different information (Table 1). Induced sputum can provide knowledge regarding the cells and mediators participating in the inflammatory response, but is time consuming and expensive. Exhaled NO measurement is performed simply and quickly, and is a nonspecific marker of an inflammatory process. The initial capital costs of equipment for NO analysis are high, however. Once the problems of standardized collection and oropharyngeal contamination have been dealt with, BC may also prove to be an additional tool for the assessment of airway inflammation. It is likely that the next 10 years will see the establishment of these noninvasive tools for the clinical assessment of airway inflammation and oxidative stress, and change the entire way we manage asthma.