Nitric oxide: delivery, measurement, and clinical application

Relationship between histopathological lesions and oxidative stress in mice infected with Angiostrongylus costaricensis

This study describes changes in oxidative stress (OS) parameters in mice experimentally infected with Angiostrongylus costaricensis, which causes abdominal angiostrongyliasis. For this, 28 Swiss mice were used, divided into two groups (G1 and G2), with 14 animals each. Of these, eight were infected with ten infective larvae each, by gavage, and six were used as a control group. Mice from G1 and G2 were euthanized at 14 days and 24 days post-infection, respectively. Tissue samples were used for histopathological analysis and blood (serum) samples were taken to assess the levels of proteins, non-protein thiols (NPTs) and nitric oxide (NO), from centrifugation and subsequent collection of aliquots of the supernatant. Among OS parameters, infected mice in both groups had higher NO levels than the control group, due to the presence of: eosinophil infiltrate in the liver and intestine; pancreatitis; and intestinal granuloma. However, the infected mice of both groups showed a reduction in the levels of NPTs, in relation to the control group, due to the presence of: eosinophilic infiltrate in the liver and intestine; and intestinal granuloma. Our results suggest that A. costaricensis infection has important effects on the intestine, liver and pancreas, and the analyses were performed from the tissue of these organs. The mechanisms for these changes are related to the decrease in the body's main antioxidant defences, as demonstrated by the reduction of NPTs, thus contributing to the development of more severe tissue damage. Thus, the objective of the present study was to evaluate the relationship between histopathological lesions and markers for OS.

Nitric oxide detection methods in vitro and in vivo

Initially being considered as an environmental pollutant, nitric oxide has gained the momentum of research since its discovery as endothelial derived growth factor in 1987. Extensive researches have revealed the various pathological and physiological roles of nitric oxide such as inflammation, vascular and neurological regulation functions. Hence, the development of methods for quantifying nitric oxide concentration and its metabolites will be beneficial to well know about its biological functions and effects. This review summaries various methods for in vitro and in vivo nitric oxide detection, and introduces their merits and demerits.

CCN1 suppresses pulmonary vascular smooth muscle contraction in response to hypoxia

Pulmonary vasoconstriction and increased vascular resistance are common features in pulmonary hypertension (PH). One of the contributing factors in the development of pulmonary vasoconstriction is increased pulmonary artery smooth muscle cell (PASMC) contraction. Here we report that CCN1, an extracellular matrix molecule, suppressed PASMC contraction in response to hypoxia. CCN1 (Cyr61), discovered in past decade, belongs to the Cyr61-CTGF-Nov (CCN) family. It carries a variety of cellular functions, including angiogenesis and cell adhesion, death, and proliferation. Hypoxia robustly upregulated the expression of CCN1 in the pulmonary vessels and lung parenchyma. Given that CCN1 is a secreted protein and functions in a paracine manner, we examined the potential effects of CCN1 on the adjacent smooth muscle cells. Interestingly, bioactive recombinant CCN1 significantly suppressed hypoxia-induced contraction in human PASMCs in vitro. Consistently, in the in vivo functional studies, administration of bioactive CCN1 protein significantly decreased right ventricular pressure in three different PH animal models. Mechanistically, protein kinase A-pathway inhibitors abolished the effects of CCN1 in suppressing PASMC contraction. Furthermore, CCN1-inhibited smooth muscle contraction was independent of the known vasodilators, such as nitric oxide. Taken together, our studies indicated a novel cellular function of CCN1, potentially regulating the pathogenesis of PH.

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.

Inhaled nitric oxide: technical aspects of administration and monitoring

OBJECTIVES

Clinical applications of inhaled nitric oxide (NO) therapy resulted in the development of delivery systems and monitoring devices applicable to routine clinical care. This article presents the various components necessary for an adequate clinical use of inhaled NO, and discusses the NO gas mixture cylinders, inhaled NO delivery techniques and specifications, monitoring devices, and ending with an exhaustive description of the scavengers of nitrogen oxides (NOx).

DATA SOURCES

Computerized search (CURRENT CONTENTS, MEDLINE) of published original research and review articles (approximately 200), conference abstracts and compendiums up to May 1997 (approximately 50), personal files, and contact with expert informants.

STUDY SELECTION

Technical, experimental, and clinical reports were selected from the recent English, French, German, and Spanish literature, if pertinent to the administration or monitoring of inhaled NO.

DATA EXTRACTION

The authors extracted all applicable data.

DATA SYNTHESIS

The production of NO gas mixture cylinders must be certified with respect to gas purity, stability, and concentration (limits between 100 and 1000 ppm), guaranteed calibration, and specific color. An ideal inhaled NO delivery device requires a synchronized delivery, a minimal production of nitrogen dioxide (NO2), and should be simple to use (verification, calibration, convenient flushing, cylinder change possible while in use and a simple alarm setting) with full information (high and low alarms and available precision monitoring of NO, NO2, and O2). Emergency and transport systems must be readily available. The choice of the monitoring device (chemiluminescence or electrochemistry) should be made based on the knowledge of their strength and weakness for a particular clinical application. Finally, scavengers of NOx should be used with caution until specific filters are proven safe and effective.

CONCLUSIONS

The great expectancies generated by inhaled NO action have led researchers to design personal inhaled NO delivery systems, but only with mitigated results. At present, medical companies are finding a financial interest in designing a delivery system which will suit the needs of clinicians and this, along with official governmental approval, will only then permit the use of inhaled NO safely and on a larger scale.

The Utility of Nitric Oxide in the Postoperative Period

Inhaled nitric oxide (iNO) is a pulmonary-selective vaso dilator with minimal bronchodilator activity in humans. NO also inhibits platelet and neutrophil activation and adhesion and inhibits ischemia-reperfusion injury. The pulmonary vasodilatory property of iNO causes a reduc tion in pulmonary vascular resistance and improvement in arterial oxygenation in a wide spectrum of diseases characterized by pulmonary hypertension and hypox emia. Promising examples of diseases for which NO may provide beneficial physiologic effects are primary and secondary pulmonary hypertension, right ventricu lar failure, cardiac transplantation, pulmonary embo lism, protamine reactions, acute respiratory distress syndrome, lung transplantation and, perhaps, chronic obstructive airways disease. The usefulness of iNO may be improved by concomitant therapy with pulmonary- selective intravenous vasoconstrictors (eg, Almitrine; Vectarian, Neuilly, France) and cGMP phosphodiester ase V inhibitors (eg, Zaprinast; Research Biochemicals International, Natick, MA). Almitrine improves oxygen ation, synergistically with iNO, and may be useful in disease states characterized primarily by hypoxemia. Zaprinast may be useful for weaning iNO and avoidance of rebound pulmonary hypertension.

Flow-proportional administration of nitric oxide with a new delivery system: inspiratory nitric oxide concentration fluctuation during different flow conditions

OBJECTIVE

To evaluate the accuracy of a flow-proportional delivery system and the pattern of inspiratory nitric oxide (NO) concentration during different flow conditions.

DESIGN

Laboratory study in a lung model.

SETTING

University experimental laboratory.

SUBJECT

With a new delivery system, NO was administered proportional to the inspiratory flow into the inspiratory circuit to deliver a NO concentration of 10 and 30 ppm to a test lung during different ventilatory modes (volume-controlled ventilation [VCV], pressure-controlled ventilation [PCV], and airway pressure release ventilation [APRV]) with a fraction of inspired oxygen (FIO2) of 1.0.

INTERVENTIONS

During VCV and PCV, the flow pattern was varied to achieve tidal volumes of 300, 600, and 900 mL, respectively, with inspiratory to expiratory time ratios of 1:3, 1:2, and 1:1. APRV was studied at a minute volume of 6, 12, and 18 L. Nitric oxides (NOx [NO+NO2]) and nitric dioxide (NO2) were monitored by chemiluminescence and electrochemical analysis. As the NO/N2 gas mixture is the only nitrogen source during ventilation with an FIO2 analyzer.

RESULTS

During all flow conditions, NOx concentration was stable but slightly higher than expected. Measured and expected mean concentrations differed <9% (mean, <4%). Inspiratory NOx concentration fluctuation derived from N2 concentration was significantly higher than expected at higher flow rates, but this difference was not detected by chemiluminescence or electrochemical analysis. The NO2 production was not affected by the flow rate and was always < or =0.2 ppm (NO, 10 ppm) and < or =1.9 ppm (NO, 30 ppm).

CONCLUSION

The tested NO delivery module administered stable mean inspiratory NO concentrations. Although inspiratory NO concentration fluctuates depending on the inspiratory flow rate, this delivery device allows stable NO administration without requiring adjustments when ventilator settings are changed.

Dose response to inhaled nitric oxide in pediatric patients with pulmonary hypertension and acute respiratory distress syndrome

OBJECTIVE

To determine the pulmonary vascular functional dose response to inhaled nitric oxide (NO) for infants and children with acute respiratory distress syndrome and pulmonary artery hypertension.

DESIGN

Prospective, clinical observational study.

SETTING

Thirteen-bed pediatric intensive care unit at a 168-bed children's hospital.

PATIENTS

Infants and children requiring mechanical ventilation with an oxygenation index greater than 10.

METHODS

Children with severe acute respiratory distress syndrome received inhalation therapy with NO after conventional mechanical ventilation failed to result in improvement. Inhaled NO was sequentially titrated from 10 parts per million to 20, 40, 60, and 80 ppm at 10-minute intervals. A reduction of at least 30% in the pulmonary vascular resistance index (PVRI), or a reduction in mean pulmonary artery pressure of at least 10%, or an increase in the hypoxemia score of at least 20%, or a decrease in the oxygenation index of at least 20% from pretreatment values was considered a therapeutic response. After sequential titration, children who responded received continuous inhaled NO at the lowest dose associated with a therapeutic response.

RESULTS

Fourteen children received 15 trials with inhaled NO (median age, 63.4 months; range, 0.4 to 201 months). One patient's condition deteriorated during the titration phase, unrelated to NO treatment, and the patient was withdrawn from the study protocol. The mean (+/- SD) pretreatment oxygenation index was 35 +/- 15, which decreased to 32 +/- 20 at 80 ppm of inhaled NO (p = 0.01). Ten children had pulmonary artery catheter measurements. The PVRI decreased by 30% or greater in seven children (70%). One child had a minimal decrease in PVRI during the titration phase but demonstrated an increase of more than 30% after NO therapy was discontinued. Mean pretreatment PVRI (270 +/- 106) decreased to 207 +/- 92 dynes/sec per cubic centimeter per square meter at 80 ppm of inhaled NO (p = 0.06). Pretreatment mean pulmonary artery pressure (31 +/- 7) decreased to 28 +/- 5 mm Hg at 80 ppm of inhaled NO (p = 0.04). Six trials (43%) showed an increase of 20% or greater in their hypoxemia score. Maximum improvement in the hypoxemia score and reduction in OI, PVRI, and mean pulmonary artery pressure occurred at 20 to 40 ppm of NO. Ten trials led to continuous inhaled NO therapy ranging from 7 to 661.5 hours, with a median of 47 hours. Systemic hypotension was not observed in any patient, and the maximum methemoglobin level was 5%.

CONCLUSION

Inhaled NO appears to be a safe, although variably effective, therapy for the treatment of infants and children with acute respiratory distress syndrome. The maximum dose response occurs between 20 and 40 ppm of inhaled NO. Systemic side effects did not occur in any child who received NO therapy.

Variation of nitric oxide concentration during inspiration

OBJECTIVE

To evaluate the pattern of inspiratory nitric oxide concentration in a simple, constant flow delivery system during the use of two phasic-flow ventilatory modes.

DESIGN

Laboratory study in a lung model.

SETTING

University experimental laboratory.

SUBJECT

Nitric oxide (800 ppm in nitrogen) was administered continuously into the inspiratory circuit to deliver a nitric oxide concentration of 10 and 40 ppm to a test lung during volume-controlled (constant flow) and pressure-controlled (decelerating flow) ventilation, with an FIO2 of 1.0.

INTERVENTIONS

In each mode, minute ventilation of 7, 14, and 21 L/min and installation of mixing chambers (none, 1-L, 2-L, and 3.2-L turbulence boxes) were studied, respectively. Nitric oxide and nitric dioxide were monitored by chemiluminescence. Since the nitric oxide/nitrogen gas is the only nitrogen source in the system during ventilation with an FIO2 of 1.0, we evaluated the fluctuation in the inspiratory nitric oxide (NOx) concentration by measuring nitrogen with a fast-response analyzer. To test the effect of the measurement site, we measured nitric oxide concentrations using chemiluminescence at different positions in the inspiratory and expiratory limbs, with and without the mixing chambers, with a minute ventilation of 14 L/min and a nitric oxide concentration of 40 ppm.

MEASUREMENTS AND MAIN RESULTS

Nitrogen dioxide production was not influenced by the flow pattern. During a nitric oxide concentration of 10 ppm, nitrogen dioxide was always < 0.6 ppm. During a nitric oxide concentration of 40 ppm, the highest nitrogen dioxide (4.47 ppm) concentration was found at the lowest minute ventilation and the largest inspiratory circuit volume. Nitric oxide values displayed by chemiluminescence indicated stable concentrations at all settings. However, without mixing chambers, NOx concentration calculated from nitrogen measurements demonstrated marked inspiratory fluctuations and was highest with a minute ventilation of 21 L/min and higher during pressure-controlled ventilation compared with volume-controlled ventilation (nitric oxide concentration of 40 ppm, pressure-controlled ventilation: 14.5 to 130.5 ppm; volume-controlled ventilation: 21.6 to 104.7 ppm; nitric oxide concentration of 10 ppm, pressure-controlled ventilation: 3.2 to 30.9 ppm; volume-controlled ventilation: 4.5 to 27.1 ppm). NOx concentration fluctuation decreased with an increasing mixing chamber, and was negligible at all settings with the 3.2-L turbulence box. Nitric oxide concentration fluctuation influenced chemiluminescence measurements. The displayed nitric oxide values varied, depending on the sampling site, and did not accurately reflect mean inspiratory nitric oxide concentration. Incorporation of a mixing chamber eradicated this sampling site influence.

CONCLUSIONS

Continuous flow delivery of nitric oxide into the circuit of a phasic-flow ventilator results in marked inspiratory nitric oxide concentration fluctuation that is not detected by a slow-response chemiluminescence analyzer. Moreover, nitric oxide concentration fluctuation can influence the accuracy of the chemiluminescence measurements. These effects can be diminished by using additional mixing chambers to facilitate a stable gas concentration. As these mixing volumes increase the contact time of nitric oxide with oxygen, an increase of nitrogen dioxide has to be taken into account.