Exhaled NO during graded changes in inhaled oxygen in man

Exhaled Nitric Oxide and Pulmonary Oxygen Toxicity Susceptibility

Individual susceptibility to pulmonary oxygen toxicity (PO2tox) is highly variable and currently lacks a reliable biomarker for predicting pulmonary hyperoxic stress. As nitric oxide (NO) is involved in many respiratory system processes and functions, we aimed to determine if expired nitric oxide (FENO) levels can provide an indication of PO2tox susceptibility in humans. Eight U.S. Navy-trained divers volunteered as subjects. The hyperoxic exposures consisted of six- and eight-hour hyperbaric chamber dives conducted on consecutive days in which subjects breathed 100% oxygen at 202.65 kPa. Subjects' individual variability in pulmonary function and FENO was measured twice daily over five days and compared with their post-dive values to assess susceptibility to PO2tox. Only subjects who showed no decrements in pulmonary function following the six-hour exposure conducted the eight-hour dive. FENO decreased by 55% immediately following the six-hour oxygen exposure (n = 8, p < 0.0001) and by 63% following the eight-hour exposure (n = 4, p < 0.0001). Four subjects showed significant decreases in pulmonary function immediately following the six-hour exposure. These subjects had the lowest baseline FENO, had the lowest post-dive FENO, and had clinical symptoms of PO2tox. Individuals with low FENO were the first to develop PO2tox symptoms and deficits in pulmonary function from the hyperoxic exposures. These data suggest that endogenous levels of NO in the lungs may protect against the development of PO2tox.

Monitoring of endogenous nitric oxide exhaled by pig lungs during ex-vivo lung perfusion

In the context of organ shortage for transplantation, new criteria for better organ evaluation should be investigated. Ex-Vivo Lung Perfusion (EVLP) allows extra-corporal lung re-conditioning and evaluation, under controlled parameters of the organ reperfusion and mechanical ventilation. This work reports on the interest of exhaled gas analysis during the EVLP procedure. After a one-hour cold ischemia, the endogenous gas production by an isolated lung of nitric oxide and carbon monoxide is simultaneously monitored in real time. The exhaled gas is analysed with two very sensitive and selective laser spectrometers developed upon the technique of optical-feedback cavity-enhanced absorption spectroscopy. Exhaled gas concentration measured for an ex-vivo lung is compared to the corresponding production by the whole living pig, measured before euthanasia. On-line measurements of the fraction of nitric oxide in exhaled gas (FENO) in isolated lungs are reported here for the first time, allowing to resolve the respiratory cycles. In this study, performed on 9 animals, FENO by isolated lungs range from 3.3 to 10.6 ppb with a median value of 4.4 ppb. Pairing ex-vivo lung and pig measurements allows to demonstrate a systematic increase of FENO in the ex-vivo lung as compared to the living animal, by a factor of 3 ± 1.2. Measurements of the fraction of carbon monoxide in exhaled gas (FECO) confirm levels recorded during previous studies driven to evaluate FECO as a potential marker of ischemia reperfusion injuries. FECO production by ex-vivo lungs ranges from 0.31 to 2.3 ppm with a median value of 0.8 ppm. As expected, these FECO values are lower than the production by the corresponding whole pig body, by a factor of 6.9 ± 2.7.

Fractional exhaled nitric oxide in adult congenital heart disease

BACKGROUND

Fractional exhaled nitric oxide levels are related to various clinical diseases. This study investigated the associations between the clinical characteristics and the level of fractional exhaled nitric oxide in patients with adult congenital heart disease.

METHODS AND RESULTS

Fractional exhaled nitric oxide values were measured in 30 adult patients with stable congenital heart disease who had undergone right heart catheterization and 17 healthy individuals (controls). There was no significant difference in fractional exhaled nitric oxide values between patients with congenital heart disease and healthy controls. Depending on whether their fractional exhaled nitric oxide values were above or below the median value, patients with congenital heart disease were divided into two groups (low vs. high fractional exhaled nitric oxide groups). The relationship between fractional exhaled nitric oxide values and clinical characteristics was investigated. There was a higher percentage of patients with cyanosis in the low fractional exhaled nitric oxide group (50%) than in the high fractional exhaled nitric oxide group (7.1%). There was no significant difference in right heart catheterization data between the low and high fractional exhaled nitric oxide groups. The fractional exhaled nitric oxide value was correlated to the number of neutrophils in patients with cyanosis (r = 0.84 (N = 8), p = 0.005).

CONCLUSIONS

In this cohort of patients with adult congenital heart disease, lower levels of fractional exhaled nitric oxide corresponded to the presence of cyanosis.

Fraction of Exhaled Nitric Oxide Is Elevated in Patients With Stable Chronic Obstructive Pulmonary Disease: A Meta-analysis

BACKGROUND

Fraction of exhaled nitric oxide (FeNO) is a noninvasive indicator of eosinophilic airway inflammation and has been used for the diagnosis and treatment of asthma. The levels of FeNO are controversial in patients with stable chronic obstructive pulmonary disease (COPD). Accordingly, this study aimed to assess FeNO levels in patients with stable COPD.

MATERIALS AND METHODS

A search of the Medline, Embase, Web of Science, ClinicalTrials.gov and The Cochrane Library databases was performed in August 2019. The literature search was restricted to articles published in English. Studies were included if they reported data addressing FeNO levels in patients with stable COPD and healthy controls. Review Manager version 5.3 (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark) was used for meta-analysis.

RESULTS

A total of 19 studies were included. Analysis revealed that FeNO levels in patients with stable COPD were higher than those in the healthy control group (mean difference [MD] 2.49 [95% confidence interval {CI} 0.99-4.00]; P < 0.05), those in nonsmoking patients with stable COPD were higher than those in the healthy control group (MD 5.04 [95% CI 2.19-7.89]; P < 0.05) and those in smoking patients with stable COPD were not higher than those in the healthy control group (MD 0.30 [95% CI -2.81 to 3.41]; P = 0.85). FeNO measured using a chemiluminescence analyzer in nonsmoking patients with stable COPD was higher than those in the healthy control group (MD 4.84 [95% CI 1.83-7.86]; P < 0.05).

CONCLUSIONS

Findings suggested that FeNO levels in patients with stable COPD were elevated, and that smokers exhibited decreased levels.

Perioperative Hyperoxyphobia: Justified or Not? Benefits and Harms of Hyperoxia during Surgery

The use of an inspiratory oxygen fraction of 0.80 during surgery is a topic of ongoing debate. Opponents claim that increased oxidative stress, atelectasis, and impaired oxygen delivery due to hyperoxic vasoconstriction are detrimental. Proponents point to the beneficial effects on the incidence of surgical site infections and postoperative nausea and vomiting. Also, hyperoxygenation is thought to extend the safety margin in case of acute intraoperative emergencies. This review provides a comprehensive risk-benefit analysis for the use of perioperative hyperoxia in noncritically ill adults based on clinical evidence and supported by physiological deduction where needed. Data from the field of hyperbaric medicine, as a model of extreme hyperoxygenation, are extrapolated to the perioperative setting. We ultimately conclude that current evidence is in favour of hyperoxia in noncritically ill intubated adult surgical patients.

Is a 12-h Nitrox dive hazardous for pulmonary function?

PURPOSE

Prolonged exposure to a high partial pressure of oxygen leads to inflammation of pulmonary tissue [pulmonary oxygen toxicity (POT)], which is associated with tracheobronchial irritation, retrosternal pain and coughing, and decreases in vital capacity (V_C). The nitric oxide (NO) concentration in exhaled gas (FeNO) has been used as an indicator of POT, but the effect of SCUBA diving on FeNO has rarely been studied. The study presented here aimed to assess alterations to pulmonary function and FeNO following a 12-h dive using breathing apparatus with a relatively high partial pressure of oxygen.

METHODS

Six healthy, male, non-smoking military SCUBA divers were recruited (age 31.8 ± 2.7 years, height 179 ± 0.09 cm, and body weight 84.6 ± 14 kg). Each diver completed a 12-h dive using a demand-controlled semi-closed-circuit rebreather. During the 12 h of immersion, divers were subjected to 672 oxygen toxicity units (OTU). A complete pulmonary function test (PFT) was completed the day before and immediately after immersion. FeNO was measured using a Nobreath™ Quark (COSMED™, Rome, Italy), three times for each diver. The first datapoint was collected before the dive to establish the "basal state", a second was collected immediately after divers emerged from the water, and the final measurement was taken 24 h after the dive.

RESULT

Despite prolonged inhalation of a hyperoxic hyperbaric gas mixture, no clinical pulmonary symptoms were observed, and no major changes in pulmonary function were detected. However, a major decrease in FeNO values was observed immediately after emersion [0-12 ppb (median, 3.8 ppb)], with a return to baseline [2-60 ppb (median, 26 ppb) 24 h later (3-73 ppb (median, 24.7 ppb)].

CONCLUSION

These results suggest that if the OTU remain below the recommended limit values, but does alter FeNO, this type of dive does not persistently impair lung function.

Oxygen, the lung and the diver: friends and foes?

Worldwide, the number of professional and sports divers is increasing. Most of them breathe diving gases with a raised partial pressure of oxygen (P_O2). However, if the P_O2 is between 50 and 300 kPa (375–2250 mmHg) (hyperoxia), pathological pulmonary changes can develop, known as pulmonary oxygen toxicity (POT). Although in its acute phase, POT is reversible, it can ultimately lead to non-reversible pathological changes. Therefore, it is important to monitor these divers to prevent them from sustaining irreversible lesions.

This review summarises the pulmonary pathophysiological effects when breathing oxygen with a P_O2 of 50–300 kPa (375–2250 mmHg). We describe the role and the limitations of lung function testing in monitoring the onset and development of POT, and discuss new techniques in respiratory medicine as potential markers in the early development of POT in divers.

To prevent the early development of pulmonary oxygen toxicity divers must be properly monitoredhttp://ow.ly/RVJL301fySb

The Influence of 17 Hours of Normobaric Hypoxia on Parallel Adjustments in Exhaled Nitric Oxide and Airway Function in Lowland Healthy Adults

Van Iterson, Erik H., Eric M. Snyder, and Bruce D. Johnson. The influence of 17 hours of normobaric hypoxia on parallel adjustments in exhaled nitric oxide and airway function in lowland healthy adults. High Alt Med Biol. 18:1-10, 2017.-Currently, there is a disparate understanding of the role that normobaric hypoxia plays in affecting nitric oxide (NO) measured in exhaled air (eNO) and airway function in lowland healthy adults. Compared to normobaric normoxia, this study aimed to test the effect of 17 hours of normobaric hypoxia on relationships between eNO and airway function in healthy adults. In a crossover study including 2 separate visits, 26 lowland healthy Caucasian adults performed eNO and pulmonary function tests on visit 1 in normobaric normoxia, while repeating all tests on visit 2 following 17 hours of normobaric hypoxia (12.5% O₂). Compared to normobaric normoxia, eNO (29 ± 24 vs. 36 ± 28 ppb), forced expiratory volume in one second (FEV₁) (4.1 ± 0.7 vs. 4.3 ± 0.8 L), mean forced expiratory flow between 25% and 75% FVC (FEF_25-75) (3.9 ± 1.0 vs. 4.2 ± 1.2 L/s), and forced expiratory flow at 75% FVC (FEF₇₅) (2.0 ± 0.7 vs. 2.3 ± 0.8 L/s) increased in normobaric hypoxia, respectively (all p < 0.05). Correlations at normoxia between eNO and FEV₁ (r = 0.39 vs. 0.44), FEF_25-75 (r = 0.51 vs. 0.51), and FEF₇₅ (r = 0.53 vs. 0.55) persisted as both parameters increased in hypoxia, respectively. For the first time, these data suggest that 17 hours of hypoxic breathing in the absence of low ambient pressure contribute to increased eNO and airway function in lowland healthy adults.

Antenatal hypoxia and pulmonary vascular function and remodeling

This review provides evidence that antenatal hypoxia, which represents a significant and worldwide problem, causes prenatal programming of the lung. A general overview of lung development is provided along with some background regarding transcriptional and signaling systems of the lung. The review illustrates that antenatal hypoxic stress can induce a continuum of responses depending on the species examined. Fetuses and newborns of certain species and specific human populations are well acclimated to antenatal hypoxia. However, antenatal hypoxia causes pulmonary vascular disease in fetuses and newborns of most mammalian species and humans. Disease can range from mild pulmonary hypertension, to severe vascular remodeling and dangerous elevations in pressure. The timing, length, and magnitude of the intrauterine hypoxic stress are important to disease development, however there is also a genetic-environmental relationship that is not yet completely understood. Determining the origins of pulmonary vascular remodeling and pulmonary hypertension and their associated effects is a challenging task, but is necessary in order to develop targeted therapies for pulmonary hypertension in the newborn due to antenatal hypoxia that can both treat the symptoms and curtail or reverse disease progression.

Assessment of pulmonary oxygen toxicity: relevance to professional diving; a review

When breathing oxygen with partial oxygen pressures PO₂ of between 50 and 300 kPa pathological pulmonary changes develop after 3-24h depending on the PO₂. This kind of injury (known as pulmonary oxygen toxicity) is not only observed in ventilated patients but is also considered an occupational hazard in oxygen divers or mixed gas divers. To prevent these latter groups from sustaining irreversible lesions adequate prevention is required. This review summarizes the pathophysiological effects on the respiratory tract when breathing oxygen with PO₂ of 50-300 kPa (hyperoxia). We discuss to what extent the most commonly used lung function parameters change after exposure to hyperoxia and its role in monitoring the onset and development of pulmonary oxygen toxicity in daily practice. Finally, new techniques in respiratory medicine are discussed with regard to their usefulness in monitoring pulmonary oxygen toxicity in divers.

Lung oxidative damage by hypoxia

One of the most important functions of lungs is to maintain an adequate oxygenation in the organism. This organ can be affected by hypoxia facing both physiological and pathological situations. Exposure to this condition favors the increase of reactive oxygen species from mitochondria, as from NADPH oxidase, xanthine oxidase/reductase, and nitric oxide synthase enzymes, as well as establishing an inflammatory process. In lungs, hypoxia also modifies the levels of antioxidant substances causing pulmonary oxidative damage. Imbalance of redox state in lungs induced by hypoxia has been suggested as a participant in the changes observed in lung function in the hypoxic context, such as hypoxic vasoconstriction and pulmonary edema, in addition to vascular remodeling and chronic pulmonary hypertension. In this work, experimental evidence that shows the implied mechanisms in pulmonary redox state by hypoxia is reviewed. Herein, studies of cultures of different lung cells and complete isolated lung and tests conducted in vivo in the different forms of hypoxia, conducted in both animal models and humans, are described.

Hypoxic pulmonary vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Enhancement of myofilament calcium sensitivity by acute hypoxia in rat distal pulmonary arteries

Hypoxic contraction of pulmonary arterial smooth muscle is thought to require increases in both intracellular Ca(2+) concentration ([Ca(2+)](i)) and myofilament Ca(2+) sensitivity, which may or may not be endothelium-dependent. To examine the effects of hypoxia and endothelium on Ca(2+) sensitivity in pulmonary arterial smooth muscle, we measured the relation between [Ca(2+)](i) and isometric force at 37°C during normoxia (21% O(2)-5% CO(2)) and after 30 min of hypoxia (1% O(2)-5% CO(2)) in endothelium-intact (E+) and -denuded (E-) rat distal intrapulmonary arteries (IPA) permeabilized with staphylococcal α-toxin. Endothelial denudation enhanced Ca(2+) sensitivity during normoxia but did not alter the effects of hypoxia, which shifted the [Ca(2+)](i)-force relation to higher force in E+ and E- IPA. Neither hypoxia nor endothelial denudation altered Ca(2+) sensitivity in mesenteric arteries. In E+ and E- IPA, hypoxic enhancement of Ca(2+) sensitivity was abolished by the nitric oxide synthase inhibitor N(ω)-nitro-l-arginine methyl ester (30 μM), which shifted normoxic [Ca(2+)](i)-force relations to higher force. In E- IPA, the Rho kinase antagonist Y-27632 (10 μM) shifted the normoxic [Ca(2+)](i)-force relation to lower force but did not alter the effects of hypoxia. These results suggest that acute hypoxia enhanced myofilament Ca(2+) sensitivity in rat IPA by decreasing nitric oxide production and/or activity in smooth muscle, thereby revealing a high basal level of Ca(2+) sensitivity, due in part to Rho kinase, which otherwise did not contribute to Ca(2+) sensitization by hypoxia.

Protective effect of total flavones of rhododendra on ischemic myocardial injury in rabbits

This study was to investigate the effect of total flavones of rhododendra (TFR) on ischemic myocardial injury in rabbits. Rabbit ischemic myocardial injury was induced by occluding the anterior descent of the left artery (LAD). The ECG was recorded; the plasma creatine kinase (CK), nitric oxide (NO) and endothelin-1 (ET-1) levels were measured using spectrophotometry, Griess method and radioimmunoassay, respectively. The myocardial ischemic size and infarction size were determined by dual staining with Evan's blue and Nitroblue tetrazolium reductionest (N-BT). A typical ECG S-T segment elevation and an increase of plasma CK activity were observed 6 and 24 hours after the induction of ischemia. These changes were inhibited in rabbits treated with either TFR (30, 60 mg/kg) or ginkgo biloba extract (EGB) for 7 days, indicating a protective effect of TFR on ischemic myocardial injury. The myocardial ischemic size and infarction size were 40.7 +/- 3.6% and 36.8 +/- 3.6% respectively in the control group, while TFR (60 mg/kg) pretreatment for 7 days significantly reduced both myocardial ischemic size (32.40 +/- 5.38%, p < 0.05) and infarction size (28.7 +/- 5.8%, p < 0.05). In addition, the occlusion of LAD resulted in an increase of ET-1 and a decrease of NO levels in the plasma, effects that were inhibited by TFR treatment, suggesting a possible mechanism for the protective effect of TFR against myocardial ischemic injury.

Exhaled nitric oxide during normoxic and hypoxic exercise in endurance athletes

AIM

Endogenous nitric oxide (NO) through its relaxing effect on smooth muscle cells may be involved in pulmonary gas exchange as well as in the modulation of the hypoxic pulmonary vasoconstriction. As athletes with exercise-induced hypoxaemia (EIH) present pulmonary gas exchange abnormalities in normoxia that could be even greater in hypoxia, we hypothesized that pulmonary NO may be lower in such athletes with EIH.

METHODS

Eleven athletes with EIH [decrease in arterial oxygen blood partial pressure (PaO2) > 12 mmHg] and 9 without EIH (NEIH) exercised at 40%, 60% (10 min) and 90% (5 min) of normoxic maximal power output (Pmax) in normoxia, and at 40% and 60% (10 min) of Pmax in hypoxia (FiO2 = 15%). Exhaled NO concentration during a constant flow exhalation (FENO(0.170)) and arterialized blood gases were measured at every power output.

RESULTS

FENO(0.170) decreased from rest to exercise both in normoxia (-27.8 +/- 22.8% at 90% Pmax, P < 0.001) and hypoxia (-23.8 +/- 17.5% at 60% Pmax, P < 0.001). At 90% Pmax in normoxia, EIH athletes showed lower PaO2 (76.7 +/- 5.4 vs. 82.8 +/- 4.4 mmHg, P = 0.013) and greater FENO(0.170) decrement (-37.0 +/- 24.7% vs. -16.6 +/- 14.6%, P = 0.042) than NEIH athletes. During hypoxic exercise, P(a)O(2) and FENO(0.170) decreases were similar in both groups (P > 0.05).

CONCLUSION

The present study shows lower pulmonary NO in athletes with gas exchange abnormalities during intense exercise in normoxia, while EIH and NEIH athletes have similar decreases in blood gases and pulmonary NO during hypoxic exercise. Decreased pulmonary NO in such conditions may contribute to ventilation-perfusion inequality and/or increase pulmonary vascular tone in athletes.

Influence of different therapeutic strategies on exhaled NO and lung inflammation in asthma and COPD

Nitric oxide (NO), a simple free radical gas, elicits a diverse range of physiological and pathophysiological effects, and plays an important role in pulmonary diseases. Nitrosative stress and nitration of proteins in airway epithelium maybe responsible for steroid resistance in asthma and their ineffectiveness in chronic obstructive pulmonary disease (COPD), supporting the potential role of future therapeutic strategies aimed at regulating NO synthesis in asthma and COPD. Here, we have reviewed the potential role of NO modulators (NO synthase inhibitors and NO donors), which if given on a regular basis may have clinical benefit in asthma and COPD.

Endothelial nitric oxide synthase/soluble guanylate cyclase system in human nasal polyps

The aim of our study was to analyze the level of expression of the endothelial nitric oxide synthase (eNOS)/soluble guanylate cyclase (sGC) system in nasal polyps and control nasal mucosae. The study was performed in polyps from 15 patients and nasal mucosae from 11 subjects operated on the nasal septum (control group). The expression of endothelial nitric oxide synthase (eNOS) and soluble guanylate cyclase (sGC) was determined in nasal mucosae. Western blot analysis demonstrated that eNOS protein was overexpressed in the nasal polyps with respect to control nasal mucosae. Immunohistochemistry also demonstrated that the vascular endothelium of nasal polyps contained higher amounts of eNOS protein than control nasal mucosae. Moreover, the beta(1) subunit of sGC was also overexpressed in the nasal polyps, which was associated with an increased content of cyclic GMP in the nasal polyps with respect to nasal control mucosae. In human nasal polyposis, there is an overexpression of the eNOS/sGC system. Further studies are needed to assess whether this overexpression is involved in the genesis of nasal polyposis.

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.

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

Nitric oxide (NO) is produced and detected in the exhalate from the respiratory tract where it plays important regulatory functions. Exhaled nitric oxide (eNO) concentrations are reduced in active cigarette smokers between cigarettes and in nonsmoking subjects during short-term exposure to environmental tobacco smoke. In this study, the authors evaluated eNO before and after an acute exposure to environmental tobacco smoke in healthy, nonsmoking subjects (n = 12). Baseline eNO levels were measured by chemiluminescence at baseline (1 hr before exposure), shortly after the end of exposure, and 10 and 30 min after the end of exposure. Mean room air NO concentration increased from 3 ppb to 4 ppm (range, 560 ppb-8.5 ppm) during the exposure period. Carboxyhemoglobin levels were assessed before and after the exposure with spectrophotometry. All subjects had decreased eNO with exposure to environmental tobacco smoke (mean +/- standard error of the mean: 16.65 +/- 1.35 ppb to 13.86 +/- 1.33 ppb; p < .001). These concentrations remained significantly decreased at 10 min and recovered within 30 min. No modifications in airway resistance or increase in carboxyhemoglobin levels were observed. Exposure to environmental tobacco smoke transiently--but consistently--decreased eNO concentration in healthy, nonsmoking subjects, suggesting that second-hand smoke can directly affect NO in the airway environment.

Exchange dynamics of nitric oxide in the human nose

Nasal nitric oxide (NO) exchange dynamics are poorly understood but potentially are of importance, inasmuch as they may provide insight into the NO-related physiology of the bronchial tree. In healthy human volunteers, NO output was assessed by isolating the nasal cavity through elevation of the soft palate and application of tight-fitting nasal olives. Mean NO output was 334 nl/min and was a positive function of gas flow. With the use of a mathematical model and the introduction of nonzero concentrations of NO, the diffusing capacity for NO in the nose (DNO) and the mucosal NO concentration (Cw) were determined. DNO ranged from 0.52 to 2.98 x 10(-3) nl x s(-1) x ppb(-1) and Cw from 1,236 to 8,947 ppb. Cw declined with increasing gas flow, while DNO was constant. NO output declined with luminal hypoxia, particularly at oxygen tensions <10%. Measurement of nasal DNO and Cw is easy using this method, and the range of intersubject values of Cw raises the possibility of interindividual differences in NO-dependent nasal physiology.

Nitric oxide production in the hypoxic lung

Nitric oxide (NO) is a potent vasodilator and inhibitor of vascular remodeling. Reduced NO production has been implicated in the pathophysiology of pulmonary hypertension, with endothelial NO synthase (NOS) knockout mice showing an increased risk for pulmonary hypertension. Because molecular oxygen (O2) is an essential substrate for NO synthesis by the NOSs and biochemical studies using purified NOS isoforms have estimated the Michaelis-Menten constant values for O2 to be in the physiological range, it has been suggested that O2 substrate limitation may limit NO production in various pathophysiological conditions including hypoxia. This review summarizes numerous studies of the effects of acute and chronic hypoxia on NO production in the lungs of humans and animals as well as in cultured vascular cells. In addition, the effects of hypoxia on NOS expression and posttranslational regulation of NOS activity by other proteins are also discussed. Most studies found that hypoxia limits NO synthesis even when NOS expression is increased.

Differential induction of extracellular glutathione peroxidase and nitric oxide synthase 2 in airways of healthy individuals exposed to 100% O(2) or cigarette smoke

Reactive oxygen species (ROS) is increased in the airway during the inhalation of 100% O(2) or cigarette smoke and participates in the development of tracheobronchitis. We hypothesized that inhaled ROS upregulates local extracellular ROS scavenging systems or reactive molecules, e.g., nitric oxide (NO). Extracellular glutathione peroxidase (eGPx) is synthesized by airway epithelium and alveolar macrophages, secreted into the surface epithelial lining fluid, and functions as a first-line defense against inhaled ROS. NO, produced by NO synthase 2 (NOS2), combines rapidly with ROS to form reactive nitrogen species (RNS). In this study, human airway epithelial cells and alveolar macrophages from healthy individuals before and after exposure to 100% O(2) for 12 h, or from cigarette-smoking individuals, were evaluated for eGPx and NOS2 messenger RNA (mRNA) expression. Hyperoxia increased NOS2 mRNA in airway epithelial cells by 2.5-fold but did not increase eGPx mRNA. In contrast, cigarette smoke upregulated eGPx mRNA over 2-fold in airway epithelial cells and alveolar macrophages but did not affect NOS2 expression. In vitro exposure of respiratory epithelial cells to ROS or RNS also increased eGPx expression. These findings define distinct molecular responses in the airway to different inhaled ROS, which likely influences the susceptibility of the airway to oxidative injury.

Hypoxia depresses nitric oxide output in the human nasal airways

OBJECTIVES

The role of oxygen in the nasal air on nasal nitric oxide (NO) output was studied in 13 adult volunteers.

METHODS

Nasal NO was measured while air containing oxygen (0%-100% in nitrogen) was aspirated through the nasal airway before and after the topical application of xylometazoline.

RESULTS

The mean nasal NO output of the untreated nose was 507.8 +/- 161.9 nL/min (mean +/- SD) when 21% oxygen was aspirated through the nasal cavities in series and remained unaltered by 100% O2 (P = .79). Below 10% oxygen the reduction in nasal NO output correlated positively and significantly with the decrease in oxygen concentration (r2 = 0.14). NO output was 245.2 +/- 153.4 nL/min at 0% oxygen, a significant decline from 21% oxygen (P < .0001). Nasal vasoconstriction induced by xylometazoline and alterations in the blood oxygen content by a maximal breath-holding or breathing 100% oxygen did not alter nasal NO in hypoxia (P = .41).

CONCLUSIONS

Nasal NO output is markedly depressed in hypoxia and is oxygen dependent at concentrations of less than 10%. Approximately 50% of nasally generated NO is produced from oxygen in nasal air or regulated by it.

Pharmacokinetic-pharmacodynamic profile of systemic nitric oxide-synthase inhibition with L-NMMA in humans

AIMS

It has been demonstrated that inhibition of endothelium derived nitric oxide with NG-monomethyl-L-arginine (L-NMMA) results in a different cardiac and peripheral vascular response. The purpose of this study was to investigate the pharmacokinetic-pharmacodynamic profile of L-NMMA and pharmacokinetic interactions with L-arginine in healthy subjects.

METHODS

Plasma pharmacokinetics were analysed from two different studies: In study 1, 3 mg kg-1 L-NMMA was administered i.v. over 5 min and systemic haemodynamics, cardiac output (CO), fundus pulsation amplitude (FPA), and NO-exhalation (exhNO) were measured at baseline and 15, 65, 95, 155, and 305 min after start of drug administration (n=7). In study 2, 17 mg kg-1 min-1 of the physiologic substrate for nitric oxide synthase, L-arginine, was coinfused i.v. over 30 min with a primed constant infusion of 50 microg kg-1 min-1 L-NMMA (n=8).

RESULTS

Bolus infusion of L-NMMA resulted in a maximum plasma concentration of 12. 9+/-3.4 microg ml-1 (mean+/-s.d.) with elimination half-life of 63. 5+/-14.5 min and clearance of 12.2+/-3.5 ml min-1 kg-1 and caused a small hypertensive response, decreased CO by 13%, FPA by 26%, exhNO by 46% and increased systemic vascular resistance by 16% (P<0.05 each) 15 min after start of drug administration. Although only limited data points were available in the L-NMMA plasma concentration range between 0 and 4 microg ml-1, drug effects over time were in good agreement with an Emax model (r2>0.98 each), which also suggested that concentrations producing half-maximum effects were higher for FPA than for CO and exhNO. The coinfusion with L-arginine caused a nearly two-fold increase in plasma L-NMMA levels, indicating a pharmacokinetic interaction.

CONCLUSIONS

In the absence of a systemic hypertensive response, L-NMMA significantly decreased CO, exhNO, and FPA. The concentration calculated to produce a half maximal effect was equivalent for exhNO and CO, but markedly higher for FPA. Furthermore, measurement of FPA is susceptible to changes in L-NMMA levels at small plasma concentrations.

Renal hemodynamic effects of L-arginine and sodium nitroprusside in heart transplant recipients

BACKGROUND

Long-term treatment with cyclosporine A (CsA) induces vasoconstriction in the kidney and causes renal impairment. An altered L-arginine (L-Arg)/nitric oxide (NO) pathway may play a key role in CsA nephrotoxicity.

METHODS

We studied the effect of L-Arg (dosage, 17 mg/kg/min over 30 min), the precursor of NO synthesis, and sodium nitroprusside (SNP; dosage, 1.0 microgram/kg/min over 30 min) on renal hemodynamics in a double-blind, placebo-controlled, randomized, three-way cross-over study comprising 12 stable cardiac transplant recipients on long-term CsA treatment, 10 patients with chronic nephropathy not receiving CsA, and 13 healthy controls. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were measured by paraaminohippurate (PAH) and the inulin clearance method, respectively.

RESULTS

In healthy subjects, L-Arg induced an increase in RPF (P = 0.009) and GFR (P = 0.001). By contrast, L-Arg did not induce renal hemodynamic effects in heart transplant patients or patients with chronic nephropathy. SNP reduced RPF (P = 0.050) and GFR (P = 0.005) in patients with chronic nephropathy but did not affect renal hemodynamics in heart transplant recipients or in healthy subjects.

CONCLUSIONS

These data indicate that L-Arg cannot be used to reverse CsA-induced renal vasoconstriction in heart transplant recipients under long-term CsA treatment, although these patients have a normal renal response to SNP.