Combined inhaled nitric oxide and inhaled prostacyclin during experimental chronic pulmonary hypertension

Inhaled Pulmonary Vasodilators for the Treatment of Right Ventricular Failure in Cardio-Thoracic Surgery: Is One Better than the Others?

Right ventricular failure (RFV) is a potential complication following cardio-thoracic surgery, with an incidence ranging from 0.1% to 30%. The increase in pulmonary vascular resistance (PVR) is one of the main triggers of perioperative RVF. Inhaled pulmonary vasodilators (IPVs) can reduce PVR and improve right ventricular function with minimal systemic effects. This narrative review aims to assess the efficacy of inhaled nitric oxide and inhaled prostacyclins for the treatment of perioperative RVF. The literature, although statistically limited, supports the clinical similarity between them. However, it failed to demonstrate a clear benefit from the pre-emptive use of inhaled nitric oxide in patients undergoing left ventricular assist device implantation or early administration during heart-lung transplants. Additional concerns are related to cost safety and IPV use in pathologies associated with pulmonary venous congestion. The largest ongoing randomized controlled trial on adults (INSPIRE-FLO) is addressing whether inhaled Epoprostenol and inhaled nitric oxide are similar in preventing RVF after heart transplants and left ventricular assist device placement, and whether they are similar in preventing primary graft dysfunction after lung transplants. The preliminary analysis supports their equivalence. Several key points may be achieved by the present narrative review. When RVF occurs in the setting of elevated PVR, IPV should be the preferred initial treatment and they should be preventively used in patients at high risk of postoperative RVF. If severe refractory postoperative RVF occurs, IPVs should be combined with complementary pharmacology (inotropes and inodilators). If unsuccessful, right ventricular mechanical support should be established.

Mechanisms of pulmonary vascular dysfunction in pulmonary hypertension and implications for novel therapies

Pulmonary hypertension (PH) is a serious disease characterized by various degrees of pulmonary vasoconstriction and progressive fibroproliferative remodeling and inflammation of the pulmonary arterioles that lead to increased pulmonary vascular resistance, right ventricular hypertrophy, and failure. Pulmonary vascular tone is regulated by a balance between vasoconstrictor and vasodilator mediators, and a shift in this balance to vasoconstriction is an important component of PH pathology, Therefore, the mainstay of current pharmacological therapies centers on pulmonary vasodilation methodologies that either enhance vasodilator mechanisms such as the NO-cGMP and prostacyclin-cAMP pathways and/or inhibit vasoconstrictor mechanisms such as the endothelin-1, cytosolic Ca2+, and Rho-kinase pathways. However, in addition to the increased vascular tone, many patients have a "fixed" component in their disease that involves altered biology of various cells in the pulmonary vascular wall, excessive pulmonary artery remodeling, and perivascular fibrosis and inflammation. Pulmonary arterial smooth muscle cell (PASMC) phenotypic switch from a contractile to a synthetic and proliferative phenotype is an important factor in pulmonary artery remodeling. Although current vasodilator therapies also have some antiproliferative effects on PASMCs, they are not universally successful in halting PH progression and increasing survival. Mild acidification and other novel approaches that aim to reverse the resident pulmonary vascular pathology and structural remodeling and restore a contractile PASMC phenotype could ameliorate vascular remodeling and enhance the responsiveness of PH to vasodilator therapies.

Persistent pulmonary hypertension of the newborn

Failure of the normal circulatory adaptation to extrauterine life results in persistent pulmonary hypertension of the newborn (PPHN). Although this condition is most often secondary to parenchymal lung disease or lung hypoplasia, it may also be idiopathic. PPHN is characterized by elevated pulmonary vascular resistance with resultant right-to-left shunting of blood and hypoxemia. Although the preliminary diagnosis of PPHN is often based on differential cyanosis and labile hypoxemia, the diagnosis is confirmed by echocardiography. Management strategies include optimal lung recruitment and use of surfactant in patients with parenchymal lung disease, maintaining optimal oxygenation and stable blood pressures, avoidance of respiratory and metabolic acidosis and alkalosis, and pulmonary vasodilator therapy. Extracorporeal membrane oxygenation is considered when medical management fails. Although mortality associated with PPHN has decreased significantly with improvements in medical care, there remains the potential risk for neurodevelopmental disability which warrants close follow-up of affected infants after discharge.

Pharmacologic strategies in neonatal pulmonary hypertension other than nitric oxide

Inhaled nitric oxide (iNO) is approved for use in persistent pulmonary hypertension of the newborn (PPHN) but does not lead to sustained improvement in oxygenation in one-third of patients with PPHN. Inhaled NO is less effective in the management of PPHN secondary to congenital diaphragmatic hernia (CDH), extreme prematurity, and bronchopulmonary dysplasia (BPD). Intravenous pulmonary vasodilators such as prostacyclin, alprostadil, sildenafil, and milrinone have been successfully used in PPHN resistant to iNO. Oral pulmonary vasodilators such as endothelin receptor antagonist bosentan and phosphodiesterase-5 inhibitors such as sildenafil and tadalafil are used both during acute and chronic phases of PPHN. In the absence of infection, glucocorticoids may also be effective in PPHN. Many of these pharmacologic agents are not approved for use in PPHN and our knowledge is based on case reports and small trials. Large multicenter randomized controlled trials with long-term follow-up are required to evaluate alternate pharmacologic strategies in PPHN.

Inhaled nitric oxide plus iloprost in the setting of post-left assist device right heart dysfunction

BACKGROUND

Pulmonary hypertension and right ventricular (RV) dysfunction may complicate the implantation of a left ventricular assist device (LVAD). We examined whether inhaled vasodilators can sufficiently reduce RV afterload, avoiding the need for temporary RV mechanical support.

METHODS

The study includes 7 patients with RV dysfunction after LVAD insertion. Treatment consisted of inotropes, inhaled nitric oxide (10 ppm), and iloprost (10 μg) in repeated doses. Full hemodynamic profile was obtained before inhalation, during administration of inhaled NO alone (before and after iloprost), as well as after the first two doses of inhaled iloprost. Tricuspid annular velocity was estimated at baseline and before and after adding iloprost.

RESULTS

There was a statistically significant reduction in pulmonary vascular resistance (PVR), mean pulmonary artery pressure (MPAP), RV systolic pressure, and pulmonary capillary wedge pressure, and a considerable increase in LVAD flow, LV flow rate index, and tricuspid annular velocity at all points of evaluation versus baseline. By the end of the protocol, MPAP/mean systemic arterial pressure, and PVR/systemic vascular resistance ratios were reduced by 0.17±0.03 (95% confidence interval, 0.10 to 0.25, p=0.001) and 0.12±0.025 (95% confidence interval, 0.06 to 0.18; p=0.003), respectively. The tricuspid annular velocity increased by 2.3±0.18 cm/s (95% confidence interval, 1.83 to 2.73 cm/s; p<0.001). Pairwise comparisons before and after iloprost showed an important decrease in PVR (p=0.022), MPAP (p=0.001), pulmonary capillary wedge pressure (p=0.002), and RV systolic pressure (p<0.001), and a rise in tricuspid annular velocity (p=0.008).

CONCLUSIONS

Inhaled vasodilators mainly affected the pulmonary vasculature. Combination treatment with inhaled NO and iloprost sufficiently decreased PVR and MPAP on the basis of an additive effect, improved RV function, and avoided the need for RV assist device.

Endurance training increases exercise-induced prostacyclin release in young, healthy men--relationship with VO2max

In the present study, we evaluated the effect of 5 weeks of moderate-intensity endurance training on the basal and exercise-induced systemic release of prostacyclin (PGI(2)), as assessed by plasma 6-keto-PGF(1 alpha) concentration. Twelve physically active young men with the following characteristics participated in this study (the mean +/- SD): age, 22.7 +/- 2.0 years; body mass, 76.8 +/- 8.9 kg; BMI, 23.48 +/- 2.17 kg x m(-2); and maximal oxygen uptake (VO(2 max)), 46.1 +/- 4.0 ml x kg(-1) x min(-1). Plasma 6-keto-PGF(1 alpha) concentrations were measured in venous blood samples taken prior to the exercise and at exhaustion (at VO(2 max)) before and after completing the training protocol. On average, the training resulted in a significant increase in VO(2 max) (p = 0.03), power output at VO(2 max) (p = 0.001) and a significant increase (p = 0.05) in the net-exercise-induced increase in plasma 6-keto-PGF(1 alpha) concentration (Delta 6-keto-PGF(1 alpha) i.e., the difference between the end-exercise and pre-exercise 6-keto-PGF(1 alpha) concentrations). No effect of training on the basal PGI(2) concentration was found. Interestingly, within the study sample (n = 12), two subgroups could be defined with a differential pattern of response with respect to Delta 6-keto-PGF(1 alpha) concentrations. In one subgroup (n = 7), a significant increase in Delta 6-keto-PGF(1 alpha) concentration after training was found (p < 0.02) (responders). This enhancement in the exercise-induced PGI(2) release was accompanied by a significant (p < 0.05) increase in VO(2 max) after training. In contrast, in another subgroup (n = 5), there was no observed effect of training on the Delta 6-keto-PGF(1 alpha) concentration and the VO(2 max) after training (non-responders). In both of these subgroups, training did not influence the basal PGI(2) concentration. In conclusion, the endurance training resulted in the adaptive augmentation of the systemic release of PGI(2) in response to exercise, which plays a role in the training-induced increase in VO(2 max) in young, healthy men. The impairment of the training-induced augmentation of PGI(2) release in response to exercise demonstrated in the non-responders subgroup may predispose them to increased cardiovascular risk during vigorous exercise.

Prostanoids and phosphodiesterase inhibitors in experimental pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease with a poor prognosis, characterized by intimal lesions, medial hypertrophy, and adventitial thickening of precapillary pulmonary arteries. Several approved therapies are currently available for the treatment of PAH, of which intravenous epoprostenol is the best explored over the past decade. Newly available oral endothelin receptor antagonists, although clinically efficacious, bear the risk of liver toxicity in a significant portion of patients. Substances that stimulate the formation of the second messengers cyclic adenosine monophosphate (cAMP) or guanosine monophosphate (cGMP) have proved useful in the treatment of various forms of pre-capillary pulmonary hypertension. These second messengers of the endogenous vasodilator mediators that include prostacyclin and nitric oxide (NO) are hydrolyzed by cyclic nucleotide phosphodiesterases (PDEs), a class of enzymes from which 11 isoforms have been characterized. This chapter highlights developments in the treatment of experimental pulmonary hypertension with special attention to prostanoids and PDE inhibitors. We summarize findings for the acute vasodilatory as well as chronic effects of prostanoids, PDE inhibitors, or combinations of both, in animal models of pulmonary hypertension.

Golgi, trafficking, and mitosis dysfunctions in pulmonary arterial endothelial cells exposed to monocrotaline pyrrole and NO scavenging

Although the administration of monocrotaline (MCT) into experimental animals is in widespread use today in investigations of pulmonary arterial hypertension (PAH), the underlying cellular and subcellular mechanisms that culminate in vascular remodeling are incompletely understood. Bovine pulmonary arterial endothelial cells (PAECs) in culture exposed to monocrotaline pyrrole (MCTP) develop "megalocytosis" 18-24 h later characterized by enlarged hyperploid cells with enlarged Golgi, mislocalization of endothelial nitric oxide synthase away from the plasma membrane, decreased cell-surface/caveolar nitric oxide (NO), and hypo-S-nitrosylation of caveolin-1, clathrin heavy chain, and N-ethylmaleimide-sensitive factor. We investigated whether MCTP did in fact affect functional intracellular trafficking. The NO scavenger (4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) and the NO donor diethylamine NONOate were used for comparison. Both MCTP and c-PTIO produced distinctive four- to fivefold enlarged PAECs within 24-48 h with markedly enlarged/dispersed Golgi, as visualized by immunostaining for the Golgi tethers/matrix proteins giantin, GM130, and p115. Live-cell uptake of the Golgi marker C(5) ceramide revealed a compact juxtanuclear Golgi in untreated PAECs, brightly labeled enlarged circumnuclear Golgi after MCTP, but minimally labeled Golgi elements after c-PTIO. These Golgi changes were reduced by NONOate. After an initial inhibition during the first day, both MCTP and c-PTIO markedly enhanced anterograde secretion of soluble cargo (exogenous vector-expressed recombinant horseradish peroxidase) over the next 4 days. Live-cell internalization assays using fluorescently tagged ligands showed that both MCTP and c-PTIO inhibited the retrograde uptake of acetylated low-density lipoprotein, transferrin, and cholera toxin B. Moreover, MCTP, and to a variable extent c-PTIO, reduced the cell-surface density of all receptors assayed (LDLR, TfnR, BMPR, Tie-2, and PECAM-1/CD31). In an important distinction, c-PTIO enhanced mitosis in PAECs but MCTP inhibited mitosis, even that due to c-PTIO, despite markedly exaggerated Golgi dispersal. Taken together, these data define a broad-spectrum Golgi and subcellular trafficking dysfunction syndrome in endothelial cells exposed to MCTP or NO scavenging.

Treatment of refractory pulmonary arterial hypertension with inhaled epoprostenol in an infant with congenital heart disease

Epoprostenol is a potent arterial vasodilator, and its administration by inhalation localizes its effects to the pulmonary circulation. In this case report, we describe a 3-month-old male patient with significant refractory pulmonary hypertension after pulmonary artery banding and placement of a Blalock-Taussig shunt. This patient continued to have significant hypoxic episodes despite maximal therapy with sedation, alkalinization, sildenafil, and inhaled nitric oxide. After the addition of inhaled epoprostenol, improvements in both clinical response and echocardiography-based hemodynamics were observed. The case supports a synergistic role among the agents in the treatment of pulmonary arterial hypertension from congenital heart disease.

Inhaled nitric oxide combined with prostacyclin and adrenomedullin in acute respiratory failure with pulmonary hypertension in piglets

Our aim was to evaluate if the combined inhalation of both nitric oxide (iNO) and aerosolized prostacyclin or iNO and adrenomedullin (ADM) is more effective in lowering pulmonary arterial pressure (PAP) and improving oxygenation than nitric oxide alone in an animal model with pulmonary hypertension (PH). Moreover, we studied the effect on pulmonary mechanics, surfactant activity, and pulmonary oxidative stress of the different treatments. Twenty-eight piglets with acute lung injury induced by lung lavages with saline were randomized to receive nitric oxide, nitric oxide plus prostacyclin, nitric oxide plus ADM or saline, after. Dynamic compliance, tidal volume, and airway resistance were measured. Lung tissue oxidation was evaluated by measuring total hydroperoxide and advanced oxidation protein products in bronchial aspirate samples. Surface surfactant activity was studied using Capillary Surfactometer. Inhaled nitric oxide combined with prostacyclin or ADM was more effective than nitric oxide alone in lowering PAP and improving oxygenation. Nitric oxide alone or combined increased lung compliance and tidal volume, and decreased airway resistance. No effects on surfactant surface activity and lung tissue oxidation were observed. The treatment with nitric oxide alone or combined with prostacyclin or ADM were effective in decreasing mean PAP and improving oxygenation in a piglet model of PH. However, nitric oxide plus prostacyclin and nitric oxide plus ADM were more effective than nitric oxide alone. The combination of aerosolized prostacyclin and ADM with nitric oxide might have a role in the treatment of infants with PH refractory to nitric oxide alone.

Intravenous vasoactive intestinal polypeptide lowers pulmonary-to-systemic vascular resistance ratio in a neonatal piglet model of pulmonary arterial hypertension

BACKGROUND

Several studies of vasoactive intestinal polypeptide (VIP) demonstrated its potent vasodilative effects on pulmonary and systemic circulation. However, no hemodynamic studies were performed to depict the effects of VIP in an in vivo model of pulmonary arterial hypertension (PAH), thereby limiting a complete understanding of the overall hemodynamic effects of VIP in PAH.

METHODS AND RESULTS

The pulmonary and systemic hemodynamic effects of intravenous infusion of 100 ng/kg per minute of VIP in control and pulmonary hypertensive piglets at 6 to 8 weeks of age were assessed. Pulmonary arterial hypertension was induced after the instillation of meconium solution in the subjects' trachea and was characterized by the establishment of a persistently elevated pulmonary arterial pressure, diminished cardiac output, and elevated pulmonary-to-systemic vascular resistance (PVR/SVR) ratio.

CONCLUSIONS

Continuous intravenous infusion of VIP markedly decreased PVR/SVR ratio in pulmonary hypertensive subjects; however, it lowered blood pressure without causing any significant changes in PVR/SVR ratio in control subjects. Collectively, these results suggest an overall pulmonary vasodilative effect of VIP in PAH.

The effect of inhaled nitric oxide and inhaled iloprost on hypoxaemia in a patient with pulmonary hypertension after pulmonary thrombarterectomy

Acute pulmonary hypertension with life-threatening right heart failure may complicate the postoperative course following cardiothoracic surgery. Both inhaled nitric oxide and inhaled iloprost, a stable analogue of prostacyclin, have been used frequently for this purpose in acute pulmonary hypertension of various origins. We present a case of a patient with acute pulmonary hypertension and severely impaired gas exchange following pulmonary thrombo-endarterectomy. Therapy with one inhaled vasodilator alone did not satisfactorily abort a postoperative pulmonary hypertensive crisis and low-output syndrome due to right heart failure. Combined inhaled nitric oxide and inhaled iloprost, however, showed additive effects. Hence, the combination of both drugs may be reasonable in cases where the standard therapy fails. The effect has been demonstrated by means of continuous blood gas monitoring.

Nitric oxide and prostaglandins potentiate the liver regeneration cascade

The liver has the remarkable ability to regenerate following damage or surgical resection. Although this feature of the liver has been studied for over 100 years, the trigger of the liver regeneration cascade remains controversial. Recent experimental evidence supports the hypothesis that nitric oxide (NO) and prostaglandins (PGs), released secondary to an increase in the blood flow-to-liver mass ratio following two-thirds partial hepatectomy (PHx), work synergistically to trigger liver regeneration. To extend this research, the hypothesis that NO and PGs are potential therapeutic targets to potentiate the liver regeneration cascade is tested. The NO donor s-nitroso-n-acetylpenicillamine, the phosphodiesterase V antagonist zaprinast (ZAP) and PGI2 each potentiated c-fos messenger RNA expression, an index of initiation of the liver regeneration cascade, following PHx. Also, the triple combination of s-nitroso-n-acetylpenicillamine, ZAP and PGI2 potentiated c-fos messenger RNA expression. These results support the hypothesis that NO and PGs can potentiate initiation of the regeneration cascade. An additional index of liver weight restoration 48 h after PHx was also used to test the hypothesis, because this index encompasses the entire liver regeneration cascade. ZAP and 6-keto-PGF1alpha, a stable metabolite of PGI2, and the combination of ZAP and 6-keto-PGF1alpha, each potentiated liver weight restoration 48 h after PHx. These results also provide support for the hypothesis that NO and PGs are possible therapeutic targets to potentiate liver regeneration following surgical resection.

Nitric oxide blunts the endothelin-mediated pulmonary vasoconstriction in exercising swine

We have previously shown that vasodilators and vasoconstrictors that are produced by the vascular endothelium, including nitric oxide (NO), prostanoids and endothelin (ET), contribute to the regulation of systemic and pulmonary vascular tone in swine, in particular during treadmill exercise. Since NO and prostanoids can modulate the release of ET, and vice versa, we investigated the integrated endothelial control of pulmonary vascular resistance in exercising swine. Specifically, we tested the hypothesis that increased NO and prostanoid production during exercise limits the vasoconstrictor influence of ET, so that loss of these vasodilators results in exaggerated ET-mediated vasoconstriction during exercise. Fifteen instrumented swine were exercised on a treadmill at 0-5 km h(-1) before and during ET(A)/ET(B) receptor blockade (tezosentan, 3 mg kg(-1) I.V.) in the presence and absence of inhibition of NO synthase (N(omega)-nitro-L-arginine, 20 mg kg(-1) I.V.) and/or cyclo-oxygenase (indometacin, 10 mg kg(-1) I.V.). In the systemic circulation, ET receptor blockade decreased vascular resistance at rest, which waned with increasing exercise intensity. Prior inhibition of either NO or prostanoid production augmented the vasodilator effect of ET receptor blockade, and these effects were additive. In contrast, in the pulmonary bed, ET receptor blockade had no effect under resting conditions, but decreased pulmonary vascular resistance during exercise. Prior inhibition of NO synthase enhanced the pulmonary vasodilator effect of ET receptor blockade, particularly during exercise, whereas inhibition of prostanoids had no effect, even after prior NO synthase inhibition. In conclusion, endogenous endothelin limits pulmonary vasodilatation in response to treadmill exercise. This vasoconstrictor influence is blunted by NO but not by prostanoids.

Inhaled alternatives to nitric oxide

OBJECTIVE

Inhaled nitric oxide has gained an established place in the management of pulmonary hypertension. However, cost, potential toxicity, and the lack of positive outcome data with inhaled nitric oxide therapy has generated interest in alternative inhaled, selective pulmonary vasodilators. This article describes those alternatives that have been studied to date.

DESIGN

Literature review of inhaled, selective pulmonary vasodilators other than nitric oxide.

METHODS

A review of the molecular mechanisms, potential side effects, and the studies to date in both animal models and clinical studies describing the physiologic effects of alternative agents to inhaled nitric oxide.

CONCLUSION

There are a number of available agents that have comparable physiologic effects as inhaled nitric oxide. The best studied of these are the inhaled prostanoids (prostacyclin and iloprost), and there is growing interest in novel therapies such as phosphodiesterase inhibitors and neuropeptides.

New approaches for persistent pulmonary hypertension of newborn

The management of PPHN entered a new era with the development of inhaled NO therapy for the relief of pulmonary hypertension. The wider application of INO therapy and improved ventilation strategies led to a decrease in the need for invasive life-sustaining therapies such as ECMO. The remarkable advances in the understanding and treatment of PPHN were made possible by the extensive investigations in the laboratory using animal models. Further decreases in morbidity and mortality are possible with specific strategies targeted to correct the alterations in NO and prostacyclin biology and strategies to reduce lung injury. Further research is needed to understand the basis for the biologic susceptibility of some infants to environmental insults such as intra-uterine stressor exposure to NSAIDs in utero.

Inhaled prostacyclin is safe, effective, and affordable in patients with pulmonary hypertension, right heart dysfunction, and refractory hypoxemia after cardiothoracic surgery

BACKGROUND

The purpose of this study was to describe our institutional experience in using inhaled prostacyclin as a selective pulmonary vasodilator in patients with pulmonary hypertension, refractory hypoxemia, and right heart dysfunction after cardiothoracic surgery.

METHODS

Between February 2001 and March 2003, cardiothoracic surgical patients with pulmonary hypertension (mean pulmonary artery pressure >30 mm Hg or systolic pulmonary artery pressure >40 mm Hg), hypoxemia (PaO(2)/fraction of inspired oxygen <150 mm Hg), or right heart dysfunction (central venous pressure >16 mm Hg and cardiac index <2.2 L.min(-1).m(-2)) were prospectively administered inhaled prostacyclin at an initial concentration of 20,000 ng/mL and then weaned per protocol. Hemodynamic variables were measured before the initiation of inhaled prostacyclin, 30 to 60 minutes after initiation, and again 4 to 6 hours later.

RESULTS

One hundred twenty-six patients were enrolled during the study period. At both time points, inhaled prostacyclin significantly decreased the mean pulmonary artery pressure without altering the mean arterial pressure. The average length of time on inhaled prostacyclin was 45.6 hours. There were no adverse events attributable to inhaled prostacyclin. The average cost for inhaled prostacyclin was 150 US dollars per day. Compared with nitric oxide, which costs 3000 US dollars per day, the potential cost savings over this period were 681,686 US dollars.

CONCLUSIONS

Inhaled prostacyclin seems to be a safe and effective pulmonary vasodilator for cardiothoracic surgical patients with pulmonary hypertension, refractory hypoxemia, or right heart dysfunction. Overall, inhaled prostacyclin significantly decreases mean pulmonary artery pressures without altering the mean arterial pressure. Compared with nitric oxide, there is no special equipment required for administration or toxicity monitoring, and the cost savings are substantial.

Inhaled nitric oxide in 2003: a review of its mechanisms of action

PURPOSE

To review the pulmonary and systemic effects of endogenous nitric oxide and inhaled nitric oxide administered to patients.

SOURCE

A systematic search for experimental data, human case reports, and randomized clinical trials since 1980, the year of discovery of endothelium-derived relaxing factor.

PRINCIPAL FINDINGS

Nitric oxide has pulmonary and systemic effects. Inhaled nitric oxide not only causes selective pulmonary vasodilation but also results in pulmonary vasoconstriction of the vessels perfusing non-ventilated alveolae. The systemic effects of inhaled nitric oxide, which include modulation of the distribution of systemic blood flow, increase in renal output, interaction with coagulation, fibrinolysis and platelet functions, alteration of the inflammatory response, are described and the mechanisms of nitric oxide transport are explained. The possible toxicity of inhaled nitric oxide is also discussed.

CONCLUSION

The multiple effects of inhaled nitric oxide support its role as a pulmonary and extra-pulmonary medication.

Alternatives to nitric oxide

Inhaled nitric oxide (INO) is a selective pulmonary vasodilator that has the ability to produce vasodilation in the pulmonary vascular bed without causing it in the systemic circulation. This property of INO has made it a useful therapy in the management of both adult and paediatric patients with a variety of conditions associated with pulmonary hypertension (PH), with or without hypoxia. Toxicity, cost and negative-outcome studies have prompted a search for alternative agents. These include inhaled prostacyclin and alternative prostaglandin preparations such as inhaled iloprost, treprostinol and beraprost. The phospodiesterase inhibitors show real potential in the management of both acute and chronic forms of PH, and antagonists of endogenous pulmonary vasoconstrictors, such as endothelin and thromboxane, are being evaluated for the long-term treatment of conditions such as primary pulmonary hypertension.

Inhaled prostacyclin for term infants with persistent pulmonary hypertension refractory to inhaled nitric oxide

We report the use of inhaled prostacyclin (PGI(2)) in 4 neonates with persistent pulmonary hypertension and hypoxemia refractory to inhaled nitric oxide. Oxygenation rapidly improved after inhalation of PGI(2) in all infants. The condition of one infant subsequently deteriorated, and alveolar capillary dysplasia was found at autopsy. The surviving infants were discharged with normal oxygen saturations in room air.

Gene transfer of human prostacyclin synthase into the liver is effective for the treatment of pulmonary hypertension in rats

BACKGROUND

As one of the future strategies of advanced pulmonary hypertension, intrinsic prostacyclin drug delivery using gene therapy may be useful. We investigated whether transfer of the prostacyclin synthase gene into the liver could ameliorate monocrotaline-induced pulmonary hypertension in rats.

METHODS

The human prostacyclin synthase gene was transfected into the liver of rats with monocrotaline-induced pulmonary hypertension. Hemodynamic indices, blood samples, lung tissues, and survival curves were evaluated between rats receiving the gene and control rats.

RESULTS

High levels of prostacyclin synthase gene expression were found in the hepatocytes of the prostacyclin synthase group. The level of 6-keto-prostaglandin F(1alpha) was significantly higher in the prostacyclin synthase group (prostacyclin synthase, 35.4 +/- 4.4 ng/mL; control, 22.3 +/- 3.3 ng/mL; P =.0436). The right ventricular/femoral artery pressure ratio was significantly lower in the prostacyclin synthase group than in the control group (prostacyclin synthase, 0.60 +/- 0.039; control, 0.88 +/- 0.051; P =.0036). The endothelin-1 levels in the lung tissues were significantly lower in the prostacyclin synthase group than in the control group (prostacyclin synthase, 10.42 +/- 2.01 pg/mg protein; control, 19.94 +/- 2.82 pg/mg protein; P =.0176). The survival ratio was significantly higher in the prostacyclin synthase group than the control group (P =.0375).

CONCLUSION

This drug delivery system using gene transfer can be considered as an alternative for continuous intravenous prostacyclin infusion for pulmonary hypertension.

Intra-operative use of inhaled vasodilators: are there indications?

The US Food and Drug Administration and European authorities have recently approved inhaled nitric oxide for the treatment of neonates with hypoxic respiratory failure associated with pulmonary hypertension. In addition to this highly specific condition, there is an increasing 'off-label' use of inhaled nitric oxide and other inhaled vasodilators in the perioperative setting. Potential indications include right heart failure as a result of acute pulmonary hypertension in cardiac and non-cardiac surgery, the prevention of reperfusion injury in lung transplantation, the treatment of hypoxaemia during single-lung ventilation, and more recently, the treatment of sickle cell crisis.

Inhaled prostacyclin (PGI2) is an effective addition to the treatment of pulmonary hypertension and hypoxia in the operating room and intensive care unit

PURPOSE

There is a growing interest in the intraoperative and intensive care use of inhaled epoprostenol (PGI2) for the treatment of pulmonary hypertension (PHT) and hypoxia of cardiac or non-cardiac origin. We report our experience with this form of therapy.

METHODS

A retrospective chart review of all patients who received inhaled PGI2 over a one-year period was undertaken. Demographic, hemodynamic, oxygenation status, mode of administration, side effects, duration of hospital stay, and mortality were noted.

RESULTS

Thirty-five patients, of which 33 (92%) were in the intensive care unit, received inhaled PGI2. Of the 27 patients whose pulmonary artery pressure (PAP) was monitored, a significant decrease in mean PAP from 34.8 +/- 11.8 mmHg to 32.1 +/- 11.8 mmHg was observed within one hour after the start of therapy (P=0.0017). Selective pulmonary vasodilatation occurred in 77.8% of the patients. Thirty-three patients had arterial blood gases before and after therapy. There was an improvement in the PaO2/FIO2 ratio in 88% of these with a 175% improvement on average. The ratio of PaO2/FIO2 improved from 108 +/- 8 to 138 +/- 105 (P=0.001). Six patients (17%) presented hypotension, two had subsequent pneumothorax, one had bronchospasm and in one patient PGI2 inhalation was stopped because of increasing peak pulmonary pressures from the secondary flow coming from the nebulizer. Mortality of the cohort was 54%.

CONCLUSION

Inhaled PGI2 can be useful in the treatment of patients with PHT and severe hypoxia. It can however be associated with systemic side effects.

Hemodynamic and oxygenation changes of combined therapy with inhaled nitric oxide and inhaled aerosolized prostacyclin

OBJECTIVE

To evaluate hemodynamic and oxygenation changes of combined therapy with inhaled nitric oxide (iNO) and inhaled aerosolized prostcyclin (IAP) during lung transplantation.

DESIGN

Prospective study.

SETTING

University hospital.

PARTICIPANTS

Ten patients scheduled for lung transplantation.

INTERVENTIONS

Ten patients, with a mean age of 38 years (range, 24 to 56 years), were scheduled for lung transplantation (2 single-lung transplantations and 8 double-lung transplantations). During first lung implantation with single-lung perfusion and ventilation, hemodynamic and oxygenation data were analyzed in 3 phases: (1) baseline, 5 minutes after pulmonary artery clamping; (2) inhaled NO phase, 15 minutes after inhaled NO administration (20 ppm) in 100% oxygen; and (3) IAP-inhaled NO phase, 15 minutes after combined administration of inhaled NO (20 ppm) and IAP (10 ng/kg/min) in 100% oxygen.

MEASUREMENTS AND MAIN RESULTS

During the inhaled NO phase, reductions of mean pulmonary arterial pressure (p < 0.05) and intrapulmonary shunt (p < 0.05) were noted. After the start of prostacyclin inhalation, a further decrease in mean pulmonary arterial pressure (p < 0.05) was observed. PaO2/FIO2 increased during the IAP-inhaled NO phase (p < 0.05), whereas intrapulmonary shunt decreased (p < 0.05).

CONCLUSION

This study confirms the action of inhaled NO as a selective pulmonary vasodilator during lung transplantation. Combined therapy with IAP and inhaled NO increases the effects on pulmonary arterial pressure and oxygenation compared with inhaled NO administered alone without any systemic changes.

Effects of inhaled prostacyclin analogue on chronic hypoxic pulmonary hypertension

Inhaled PGI2 has been reported to elicit pulmonary vasodilation, but whether it is also effective in treating chronic hypoxic pulmonary hypertension is still uncertain. We designed this study to address the in vivo effectiveness of inhaled Beraprost, a stable PGI2 analogue, on pulmonary vascular tone during hypoxic exposure in normoxic (N) and chronically hypoxic (CH) rats. Pulmonary vasodilation was observed by low-dose inhaled Beraprost in N rats, but not in CH rats. It was not until higher doses of Beraprost were given that pulmonary vasodilation was obtained in CH rats. When the agent was continuously administered by an intravascular route at the inhaled dose, it elicited no vasodilation in N rats. On the contrary, it elicited profound vasodilation in CH rats, although a concomitant systemic hypotension was observed. The PGI2 receptor mRNA expression was unchanged in the lungs of CH rats compared with that of N rats. We conclude that low doses of aerosolized Beraprost may reduce pulmonary vascular tone in rats without preexisting lung diseases. In contrast, when hypoxic pulmonary hypertension is present, the threshold of Beraprost inhalation was elevated to provoke pulmonary vasodilation.

40-O-(2-hydroxyethyl)-rapamycin attenuates pulmonary arterial hypertension and neointimal formation in rats

Pneumonectomized rats develop pulmonary hypertension (PH) and pulmonary vascular neointimal formation 4 wk after monocrotaline (MCT) administration. Male Sprague-Dawley rats were injected with MCT (60 mg/kg) on Day 7 after left pneumonectomy. Three groups (n = 5) received 40-O-(2-hydroxyethyl)-rapamycin (RAD, 2.5 mg/kg/d, by gavage): Group PMR(5-35) from Day 5 to Day 35, Group PMR5-14 from Day 5 to Day 14, and Group PMR15-35 from Day 15 to Day 35. By Day 35, rats that received vehicle had higher mean pulmonary arterial pressures (Ppa = 41 +/- 3 mm Hg) (p < 0.001), right ventricular systolic pressures (Prv,s = 45 +/- 2 mm Hg) (p < 0.01), and right ventricle/(left ventricle plus septum) (0.55 +/- 0.05) (p = 0.028) than rats in Groups PMR5-35 (Ppa = 25 +/- 3 mm Hg, Prv,s = 32 +/- 7 mm Hg, RV/LV&S = 0.42 +/- 0.06) and PMR5-14 (Ppa = 29 +/- 4 mm Hg, Prv,s = 30 +/- 5 mm Hg, RV/LV&S = 0.43 +/- 0.07). Pulmonary arterial neointimal formation (quantified by a vascular occlusion score) was more severe in vehicle-treated rats (1.93 +/- 0.03) than in Groups PMR5-14 (1.56 +/- 0.27) and PMR(5-35) (1.57 +/- 0.1) (p < 0.01). RAD attenuates the development of MCT-induced pulmonary arterial hypertension in the pneumonectomized rat.

Inhaled nitric oxide versus aerosolized iloprost in secondary pulmonary hypertension in children with congenital heart disease: vasodilator capacity and cellular mechanisms

BACKGROUND

Inhaled nitric oxide (iNO) has been used to assess the vasodilator capacity of the pulmonary vascular bed in children with congenital heart disease and elevated pulmonary vascular resistance. Inhaled iloprost is a pulmonary vasodilator for the long-term treatment of pulmonary hypertension (PHT). Because these 2 vasodilators act through different pathways (release of cGMP or cAMP, respectively), we compared the pulmonary vasodilator capacity of each.

METHODS AND RESULTS

A total of 15 children with congenital heart disease and PHT who had elevated pulmonary vascular resistance (preoperative, n=10; immediately postoperative, n=5) were first given 20 ppm of iNO for 10 minutes; then, after baseline values were reached again, they were given aerosolized iloprost at 25 ng. kg(-1). min(-1) for another 10 minutes. Finally, iNO and iloprost were given simultaneously for 10 minutes. With iNO, the pulmonary vascular resistance and systemic vascular resistance ratio decreased from 0.48+/-0.38 to 0.27+/-0.16 (P:<0.001). Similarly, iloprost decreased the ratio from 0.49+/-0.38 to 0.26+/-0.11 (P:<0.05). The combination had no additional effect on the resistance ratio. Plasma cGMP increased from 17.6+/-11.9 to 34.7+/-21.4 nmol/L during iNO (P:<0.01), and plasma cAMP increased from 55.7+/-22.9 to 65.1+/-21.2 nmol/L during iloprost inhalation (P:<0.05).

CONCLUSIONS

In children with PHT and congenital heart disease, both iNO and aerosolized iloprost are equally effective in selectively lowering pulmonary vascular resistance through an increase in cGMP or cAMP, respectively. However, the combination of both vasodilators failed to prove more potent than either substance alone. Aerosolized iloprost might be an alternative to iNO for early testing of vascular reactivity and for the postoperative treatment of acute PHT.

Aerosolized iloprost therapy could not replace long-term IV epoprostenol (prostacyclin) administration in severe pulmonary hypertension

OBJECTIVES

To switch patients with severe pulmonary hypertension and previous life-threatening catheter-related complications from long-term IV epoprostenol therapy to aerosolized iloprost therapy.

DESIGN

Open, uncontrolled trial.

SETTING

Medical ICU of a university hospital.

PATIENTS

Two patients with primary pulmonary hypertension and one patient with pulmonary hypertension after surgical closure of atrial septal defect (mean pulmonary artery pressure > or =50 mm Hg). All were classified as New York Heart Association class II under treatment with continuous IV epoprostenol for 4 years.

INTERVENTIONS

Stepwise reduction of IV epoprostenol (1 ng/kg/min steps every 3 to 10 h) during repeated inhalations of aerosolized iloprost (150 to 300 microg/d with 6 to 18 inhalations/d). Continuous pulmonary and systemic arterial monitoring were performed.

RESULTS

Aerosolized iloprost reduced pulmonary artery pressure by 49%, 49%, and 45%, respectively, and increased cardiac output by 70%, 75%, and 41% in the three patients. The effect lasted for 20 min and was similar at different doses of IV epoprostenol. Persistent treatment change to inhaled iloprost could not be achieved because all patients developed signs of right heart failure. After termination of iloprost inhalations, return to standard epoprostenol therapy led to clinical and hemodynamic restoration.

CONCLUSIONS

Although aerosolized iloprost demonstrated short-term hemodynamic effects, it could not be utilized as alternative chronic vasodilator in patients with severe pulmonary hypertension.

Triptolide attenuates pulmonary arterial hypertension and neointimal formation in rats

This paper reports the effect of triptolide (a diterpenoid triepoxide) on the development of monocrotaline (MCT)-induced pulmonary hypertension in pneumonectomized rats. Male Sprague- Dawley rats were injected with MCT (60 mg/kg) on Day 7 after left pneumonectomy. Rats received therapy from Day 5 to 35 with triptolide (0.25 mg/kg intraperitoneally, every other day, n = 10), or vehicle (0.1 ml of ethanol/cremophor intraperitoneally, every other day, n = 10). By Day 35, triptolide-treated rats demonstrated lower mean pulmonary arterial pressure (mPAP) than vehicle-treated rats (mPAP 21 +/- 3 versus 42 +/- 5 mm Hg, p < 0.001). Triptolide-treated rats also had significantly less right ventricular hypertrophy (RVH) and pulmonary arterial neointimal formation. In a rescue experiment, rats initiated therapy on Day 21. At Day 35, vehicle-treated rats (n = 4) had higher mPAP (40 +/- 9 mm Hg), greater RVH, and more severe pulmonary arterial neointimal formation than rats that received triptolide (0.25 mg/kg every other day, n = 7, mPAP 30 +/- 4 mm Hg) and rats that received triptolide (0.2 mg/kg daily, n = 7, mPAP 25 +/- 5 mm Hg, p < 0.01). In pneumonectomized rats that receive MCT, triptolide attenuates the development of pulmonary hypertension and RVH, and promotes regression of pulmonary arterial neointimal formation.

Use of aerosolized inhaled epoprostenol in the treatment of portopulmonary hypertension

BACKGROUND

Portopulmonary hypertension is a known complication in the liver transplant candidate. Intravenous epoprostenol has been demonstrated to decrease pulmonary artery pressures and possibly remodel right ventricle geometry.

METHODS

In this report, we document the efficacy of inhaled aerosolized epoprostenol in a patient with portopulmonary hypertension. The effect was of rapid onset and offset.

RESULTS

After 10 min of delivery, mean pulmonary artery pressure decreased 26%; cardiac output increased by 22%; pulmonary vascular resistance decreased by 42%; and the transpulmonary gradient decreased by 29%. There were no untoward side effects.

CONCLUSION

The inhaled route of delivery of epoprostenol is potential alternative for the acute therapy of portpulmonary hypertension.

Intraoperative use of inhaled PGI(2) for acute pulmonary hypertension and right ventricular failure

Inhaled prostacyclin (PGI(2)) can be used as an effective pulmonary vasodilator intraoperatively to treat pulmonary hypertension and impending right ventricular failure.

Combined therapy with inhaled nitric oxide and intravenous vasodilators during acute and chronic experimental pulmonary hypertension

Both inhaled nitric oxide (NO) and IV vasodilators decrease pulmonary hypertension, but the effects of combination therapy are unknown. We studied the response to inhaled NO (100 ppm) alone, IV vasodilator alone, and combined therapy during acute (U46619-induced) and chronic (monocrotaline-induced) pulmonary hypertension in the pentobarbital-anesthetized rat. Vasodilator doses were 1.0, 3.2, 10, and 32 microg x kg(-1) x min(-1) sodium nitroprusside (SNP); 50, 100, 150, 200, and 300 microg x kg(-1) x min(-1) adenosine; or 25, 50, 150, 200, and 300 ng x kg(-1) x min(-1) prostacyclin. In the absence of IV vasodilator therapy, inhaled NO decreased mean pulmonary artery pressure without decreasing mean systemic arterial pressure. In both acute and chronic pulmonary hypertension, the addition of inhaled NO to the largest dose of adenosine or prostacyclin, but not of SNP, decreased pulmonary artery pressure. Because inhaled NO and SNP activate guanylyl cyclase and adenosine and prostacyclin activate adenylyl cyclase, the results suggest that adding inhaled NO to a vasodilator not dependent on guanylyl cyclase may produce additional selective pulmonary vasodilation.

IMPLICATIONS

In therapy of pulmonary hypertension, inhaled nitric oxide should produce additional selective pulmonary vasodilation when combined with a vasodilator whose mechanism of action is not dependent on cyclic guanosine 3',5'-monophosphate.