Inhaled nitric oxide inhibits platelet aggregation after pulmonary embolism in pigs

Inhaled Nitric Oxide Treatment for Aneurysmal SAH Patients With Delayed Cerebral Ischemia

Background

We demonstrated experimentally that inhaled nitric oxide (iNO) dilates hypoperfused arterioles, increases tissue perfusion, and improves neurological outcome following subarachnoid hemorrhage (SAH) in mice. We performed a prospective pilot study to evaluate iNO in patients with delayed cerebral ischemia after SAH.

Methods

SAH patients with delayed cerebral ischemia and hypoperfusion despite conservative treatment were included. iNO was administered at a maximum dose of 40 ppm. The response to iNO was considered positive if: cerebral artery diameter increased by 10% in digital subtraction angiography (DSA), or tissue oxygen partial pressure (PtiO₂) increased by > 5 mmHg, or transcranial doppler (TCD) values decreased more than 30 cm/sec, or mean transit time (MTT) decreased below 6.5 secs in CT perfusion (CTP). Patient outcome was assessed at 6 months with the modified Rankin Scale (mRS).

Results

Seven patients were enrolled between February 2013 and September 2016. Median duration of iNO administration was 23 h. The primary endpoint was reached in all patients (five out of 17 DSA examinations, 19 out of 29 PtiO₂ time points, nine out of 26 TCD examinations, three out of five CTP examinations). No adverse events necessitating the cessation of iNO were observed. At 6 months, three patients presented with a mRS score of 0, one patient each with an mRS score of 2 and 3, and two patients had died.

Conclusion

Administration of iNO in SAH patients is safe. These results call for a larger prospective evaluation.

Platelet dysfunction in a large-animal model of endotoxic shock; effects of inhaled nitric oxide and low-dose steroid

OBJECTIVE

The role of inhaled nitric oxide in the treatment of shock remains controversial and further translational research is needed. Long-term observation studies using a model of endotoxin-induced shock to assess the effect of inhaled nitric oxide on platelet aggregation have not yet been reported.

APPROACH AND RESULTS

The tests were carried out in an animal model of shock in two 10-h periods. During the first 10 h, endotoxin was infused and the inhibition of platelet aggregation was evaluated; following the termination of endotoxin infusion, the restoration of platelet aggregation was assessed for 10 h. A total of 30 pigs were used (NO group, N = 14; control, N = 16). In the NO group, nitric oxide inhalation (30 ppm) was started 3 h after endotoxin infusion and continued until the end of the study. Treatment with NO selectively decreased pulmonary artery pressure at 4 (p = 0.002) and 8 h (p = 0.05) of the experiment as compared to the control. Endotoxin significantly reduced platelet aggregation, as indicated by the decreased activity of platelet receptors: ASPI, ADP, collagen, and TRAP during the experiment (p < 0.001). Endotoxin had no significant effect on changes in the response of the receptor after ristocetin stimulation. After stopping endotoxin infusion, a significant restoration of receptor activity was observed for collagen and TRAP, while ASPI and ADP remained partially depressed. Inhaled nitric oxide did not cause additional inhibition of platelet aggregation, either during or after endotoxin challenge.

CONCLUSIONS

A profound reduction in platelet aggregation was observed during endotoxic shock. After stopping endotoxin infusion a restoration of platelet receptor activity was seen. The inhibition of platelet aggregation induced by endotoxin infusion was not intensified by nitric oxide, indicating there was no harmful effect of inhaled nitric oxide on platelet aggregation.

Riociguat, sildenafil and inhaled nitric oxide reduces pulmonary vascular resistance and improves right ventricular function in a porcine model of acute pulmonary embolism

BACKGROUND

Pulmonary vasodilators as add-on to current treatment strategies in acute pulmonary embolism may improve right ventricular unloading and hence improve patient outcome. We aimed to investigate whether stimulation of the nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway with riociguat, sildenafil or inhaled NO causes pulmonary vasodilation and improves right ventricular function in a porcine model of acute intermediate risk pulmonary embolism.

METHODS

Two large autologous blood clots were administered to the pulmonary circulation of 28 pigs (60 kg). Animals were randomized to four increasing, clinically equivalent doses of riociguat (n=6), sildenafil (n=6), inhaled NO (n=6) or vehicle (n=6). Sham animals (n=4) did not receive pulmonary embolism or treatment. Haemodynamic responses were evaluated at baseline, after pulmonary embolism and after each dose using invasive pressure measurements, transoesophageal echocardiography, respiratory parameters and blood analysis.

RESULTS

Pulmonary embolism caused a three-fold increase in pulmonary vascular resistance compared with baseline (pulmonary embolism: 352±29 vs. baseline: 107±6 dynes, p<0.0001). All treatments lowered pulmonary vascular resistance compared with vehicle (riociguat: -158±35, sildenafil: -224±35, inhaled NO: -156±35 dynes, p<0.0001). Sildenafil, but neither inhaled NO nor riociguat, caused a decrease in systemic vascular resistance (sildenafil 678±41 vs. vehicle 1081±93 dynes, p=0.02) and increased cardiac output (sildenafil 8.8±0.8 vs. vehicle: 5.9±0.2 L/min, p<0.001). Systemic blood pressure was unaltered in all treatment groups.

CONCLUSION

Stimulation of the NO-sGC-cGMP pathway by riociguat, sildenafil and inhaled NO reduces pulmonary vascular resistance in a porcine model of acute pulmonary embolism without lowering systemic blood pressure.

Pulmonary vasodilation in acute pulmonary embolism - a systematic review

Acute pulmonary embolism is the third most common cause of cardiovascular death. Pulmonary embolism increases right ventricular afterload, which causes right ventricular failure, circulatory collapse and death. Most treatments focus on removal of the mechanical obstruction caused by the embolism, but pulmonary vasoconstriction is a significant contributor to the increased right ventricular afterload and is often left untreated. Pulmonary thromboembolism causes mechanical obstruction of the pulmonary vasculature coupled with a complex interaction between humoral factors from the activated platelets, endothelial effects, reflexes and hypoxia to cause pulmonary vasoconstriction that worsens right ventricular afterload. Vasoconstrictors include serotonin, thromboxane, prostaglandins and endothelins, counterbalanced by vasodilators such as nitric oxide and prostacyclins. Exogenous administration of pulmonary vasodilators in acute pulmonary embolism seems attractive but all come with a risk of systemic vasodilation or worsening of pulmonary ventilation-perfusion mismatch. In animal models of acute pulmonary embolism, modulators of the nitric oxide-cyclic guanosine monophosphate-protein kinase G pathway, endothelin pathway and prostaglandin pathway have been investigated. But only a small number of clinical case reports and prospective clinical trials exist. The aim of this review is to give an overview of the causes of pulmonary embolism-induced pulmonary vasoconstriction and of experimental and human investigations of pulmonary vasodilation in acute pulmonary embolism.

Effects of inhaled nitric oxide on hemostasis in healthy adults treated with heparin: a randomized, controlled, blinded crossover study

Background

Effects of nitric oxide (NO) on hemostasis have been studied in various investigational settings, but data regarding inhaled NO on bleeding and platelet function are conflicting. It is not known if inhaled NO has an effect when administered with drugs that influence hemostasis. This trial evaluated effects of inhaled NO on hemostasis in the presence of heparin using aspirin as a positive control.

Patients/Methods

Twelve healthy adult males were enrolled in a single-center, randomized, single-blind, four-way crossover trial. Subjects received 80 ppm NO or medical air (placebo) inhalation for 30 min with simultaneous injection of placebo or heparin. Aspirin capsules were used as a positive control. Parameters of hemostasis were measured before treatment and at post-treatment intervals.

Results

Activated clotting time (ACT), prothrombin time (PT) and activated partial thromboplastin time (aPTT) increased only in groups that received heparin. Areas under the curve for ACT in heparin groups receiving inhaled NO were judged to be equivalent to those receiving medical air for both 0- to 4-h (ratio: 1.00; 90% CI, 0.90-1.11) and 0- to 24-h time intervals (ratio: 1.01; 90% CI, 0.92-1.12). Changes in bleeding time and platelet aggregation were observed only in aspirin groups. No clinically significant changes in hemoglobin, red blood cell counts or haematocrit were observed in any group.

Conclusions

Inhaled NO, when administered with heparin, exhibited no significant additive effects on ACT, PT, aPTT, bleeding time or platelet aggregation.

Modulation of homocysteine toxicity by S-nitrosothiol formation: a mechanistic approach

The metabolic conversion of homocysteine (HCYSH) to homocysteine thiolactone (HTL) has been reported as the major cause of HCYSH pathogenesis. It was hypothesized that inhibition of the thiol group of HCYSH by S-nitrosation will prevent its metabolic conversion to HTL. The kinetics, reaction dynamics, and mechanism of reaction of HCYSH and nitrous acid to produce S-nitrosohomocysteine (HCYSNO) was studied in mildly to highly acidic pHs. Transnitrosation of this non-protein-forming amino acid by S-nitrosoglutathione (GSNO) was also studied at physiological pH 7.4 in phosphate buffer. In both cases, HCYSNO formed quantitatively. Copper ions were found to play dual roles, catalyzing the rate of formation of HCYSNO as well as its rate of decomposition. In the presence of a transition-metal ions chelator, HCYSNO was very stable with a half-life of 198 h at pH 7.4. Nitrosation by nitrous acid occurred via the formation of more powerful nitrosating agents, nitrosonium cation (NO(+)) and dinitrogen trioxide (N(2)O(3)). In highly acidic environments, NO(+) was found to be the most effective nitrosating agent with a first-order dependence on nitrous acid. N(2)O(3) was the most relevant nitrosating agent in a mildly acidic environment with a second-order dependence on nitrous acid. The bimolecular rate constants for the direct reactions of HCYSH and nitrous acid, N(2)O(3), and NO(+) were 9.0 x 10(-2), 9.50 x 10(3), and 6.57 x 10(10) M(-1) s(-1), respectively. These rate constant values agreed with the electrophilic order of these nitrosating agents: HNO(2) < N(2)O(3) < NO(+). Transnitrosation of HCYSH by GSNO produced HCYSNO and other products including glutathione (reduced and oxidized) and homocysteine-glutathione mixed disulfide. A computer modeling involving eight reactions gave a good fit to the observed formation kinetics of HCYSNO. This study has shown that it is possible to modulate homocysteine toxicity by preventing its conversion to a more toxic HTL by S-nitrosation.

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

OBJECTIVE

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

DATA SOURCE

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

RESULTS

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

CONCLUSIONS

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

Nitric oxide modulates air embolism-induced lung injury in rats with normotension and hypertension

1. Air embolism the in lungs induces microvascular obstruction, mediator release and acute lung injury (ALI). Nitrite oxide (NO) plays protective and pathological roles in ALI produced by various causes, but its role in air embolism-induced ALI has not been fully investigated. 2. The purpose of the present investigation was to elucidate the involvement of NO and pro-inflammatory cytokines in the pathogenesis of ALI following air infusion into isolated perfused lungs from spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. 3. The extent of ALI was evaluated by changes in lung weight, Evans blue dye leakage, the protein concentration in the bronchoalveolar lavage and pathological examination. We also measured nitrite/nitrate (NO(x)), tumour necrosis factor (TNF)-alpha and interleukin (IL)-1beta concentrations in lung perfusate and determined cGMP in lung tissue. 4. The NO synthase (NOS) inhibitors N(G)-nitro-l-arginine methyl ester (l-NAME) and l-N(6)-(1-iminoethyl)-lysine (l-Nil), as well as the NO donors sodium nitroprusside (SNP) and s-nitroso-N-acetylpenicillamine (SNAP), were administered 30 min before air embolism at a concentration of 10(-3) mol/L in the lung perfusate. 5. Air embolism-induced ALI was enhanced by pretreatment with l-NAME or l-Nil, but was alleviated by SNP or SNAP pretreatment, in both SHR and WKY rats. In both SHR and WKY rats, AE elevated levels of NO(x) (2.6 and 28.7%, respectively), TNF-alpha (52.7 and 158.6%, respectively) and IL-1beta (108.4 and 224.1%, respectively) in the lung perfusate and cGMP levels in lung tissues (35.8 and 111.2%, respectively). Pretreatment with l-LAME or l-Nil exacerbated, whereas SNP or SNAP abrogated, the increases in these factors, except in the case of NO(x) (levels were decreased by l-LAME or l-Nil pretreatment and increased by SNP or SNAP pretreatment). 6. Air embolism caused increases in the lung weight (LW)/bodyweight ratio, LW gain, protein concentration in bronchoalveolar lavage and Evans blue dye leakage. These AE-induced changes were less in lungs isolated from SHR compared with normotensive WKY rats. 7. The results suggest that ALI and associated changes following air embolism in lungs isolated from SHR are less than those in WKY rats. Nitric oxide production through inducible NOS isoforms reduces air embolism-induced lung injury and associated changes. Spontaneously hypertensive rats appear to be more resistant than WKY rats to air embolism challenge.

Formation and stability of a nitric oxide donor: S-nitroso-N-acetylpenicillamine

The formation, reaction dynamics, and detailed kinetics and mechanism of the reaction between nitrous acid and N-acetylpenicillamine (NAP) to produce S-nitroso-N-acetylpenicillamine (SNAP) was studied in acidic medium. The nitrous acid was prepared in situ by the rapid reaction between sodium nitrite and hydrochloric acid. The reaction is first order in nitrite and NAP. It is also first order in acid in pH conditions at or slightly higher than the pK(a) of nitrous acid. In lower pH conditions, the catalytic effect of acid quickly saturates. Higher acid concentrations also induce a faster decomposition rate of the SNAP, thus precluding the quantitative formation of SNAP from HNO2 and NAP. Both HPLC and quadrupole time-of-flight mass spectrometry techniques proved that SNAP was the sole product produced. No nitrosation occurred on the secondary amine center in NAP, and only the thiol group reacted to form the nitrosothiol. Cu(I) ions were found to be effective SNAP-decomposition catalysts. Cu(II) ions had no effect on the stability of SNAP. Ambient oxygen in reaction solutions was found to have no effect on initial rates of formation of SNAP, products obtained, and stability of SNAP. The formation of SNAP occurs through two distinct pathways. One involves the direct reaction of NAP and HNO2 to form SNAP and eliminate water, and the second pathway involved the initial formation of the nitrosyl cation, NO+, which then nitrosates the thiol. The bimolecular rate constant for the reaction of NAP and HNO2 was derived as 2.69 M(-1) s(-1), while that of direct nitrosation by the nitrosyl cation was 3.00 x 10(4) M(-1) s(-1). A simple reaction network made up of four reactions was found to be sufficient in simulating the formation kinetics and acid-induced decomposition of SNAP.

Endothelin receptor blockade does not improve hypoxemia following acute pulmonary thromboembolism

We studied the roles of endothelins in determining ventilation (V̇a) and perfusion (Q̇) mismatch in a porcine model of acute pulmonary thromboembolism (APTE), using a nonspecific endothelin antagonist, tezosentan. Nine anesthetized piglets (∼23 kg) received autologous clots (∼20 g) via a central venous catheter at time = 0 min. The distribution of V̇a and Q̇ at five different time points (−30, −5, 30, 60, 120 min) was mapped by fluorescent microspheres of 10 different colors. Five piglets ( group 1) received tezosentan (courtesy of Actelion) starting at time = 40 min for 2 h, and four piglets ( group 2) received only saline and served as control. Our results showed that, in all of the animals at 30 min following APTE but before tezosentan, the mean V̇a/Q̇ was increased, as was V̇a/Q̇ heterogeneity (log SD V̇a/Q̇), which represented a widening of its main peak. Afterwards, tezosentan attenuated the pulmonary hypertension in group 1 but also produced moderate systemic hypotension. However, it did not improve arterial Po2 or V̇a/Q̇ mismatch. We concluded that endothelin antagonism had minimal impact on gas exchange following APTE and confirmed our earlier observation that the main mechanism for hypoxemia in APTE was due to the mechanical redistribution of pulmonary regional blood flow away from the embolized vessels, resulting in the creation of many divergent low and high V̇a/Q̇ regions.

l-Arginine prevents air embolism-induced acute lung injury in rats

OBJECTIVE

Pulmonary air embolism, causing vessel obstruction and primary or secondary reactions of blood, can lead to acute lung injury. In addition, nitric oxide has been known to play a key role in various causes of lung injury. In this study we employed the isolated rat lung model to investigate the effects of l-arginine on air embolism-induced lung injury.

DESIGN

Randomized, controlled study.

SETTING

Animal-care facility procedure room.

SUBJECTS

Forty-two adult male Sprague-Dawley rats each weighing 250-350 g.

INTERVENTIONS

Infusion of air at the rate of 0.25 mL/min for 1 min into the pulmonary artery in isolated and perfused rat lung resulted in pulmonary hypertension and lung edema. Air embolism elicited a significant increase in microvascular permeability as measured by the capillary filtration coefficient, lung weight gain, lung weight-to-body weight ratio, pulmonary arterial pressure, and protein concentration of bronchoalveolar lavage fluid.

MEASUREMENTS AND MAIN RESULTS

Pretreatment with L-arginine (4 mmol/L) significantly attenuated the acute lung injury induced by air embolism as shown by a significant decrease in all of the assessed variables but did not alter the pulmonary arterial pressure (p < .05). The protective effect of l-arginine was blocked when N(G)-nitro-L-arginine methyl ester (5 mmol/L) was added. Pretreatment with N(G)-nitro-L-arginine methyl ester exacerbated air embolism-induced lung injury.

CONCLUSIONS

Our findings suggest that L-arginine can prevent air embolism-induced lung injury.

The Effect of a Combination of Inhaled Nitric Oxide and an EndothelinA-Receptor Antagonist onHemodynamic Dysfunction in Experimental AcutePulmonary Thromboembolism

Although either inhaled nitric oxide (NO) or endothelinA receptor antagonist has been tried in the treatment of various forms of pulmonary hypertension, the effects of combination therapy have not been reported. We evaluated the effects of inhaled NO alone or a combination of inhaled NO and ZD2574 (an endothelinA receptor antagonist) in an experimental canine acute pulmonary thromboembolism model. Forty parts per million of inhaled NO alone, or a combination of inhaled NO and 10 mg/kg of ZD2574 was administered 1 hour after embolization with an autologous blood clot. We compared the hemodynamic and gas exchange parameters between the two treatment groups. Two treatment regimens decreased mean pulmonary arterial pressure and pulmonary vascular resistance and attenuated decrease in cardiac output. Moreover, systemic arterial hypotension or worsening of hypoxemia did not occur in either of the treatment groups. In the combined group, more favorable hemodynamic outcomes were maintained than in the inhaled NO alone group. And hemodynamic deterioration shown after NO withdrawal was attenuated in the combined group. These findings suggest that when inhaled NO is concomitantly administered with an ETA receptor antagonist, more favorable hemodynamic outcomes can be expected during and after NO inhalation in acute pulmonary thromboembolism.

Is there a place for inhaled nitric oxide in the therapy of acute pulmonary embolism?

Acute pulmonary embolism (PE) is a serious complication resulting from the migration of emboli to the lungs. Although deep venous thrombi are the most common source of emboli to the lungs, other important sources include air, amniotic fluid, fat and bone marrow. Regardless of the specific source of the emboli, very little progress has been made in the pharmacological management of this high mortality condition. Because the prognosis is linked to the degree of elevation of pulmonary vascular resistance, any therapeutic intervention to improve the hemodynamics would probably increase the low survival rate of this critical condition. Inhaled nitric oxide (iNO) has been widely tested and used in cases of pulmonary hypertension of different causes. In the last few years some authors have described beneficial effects of iNO in animal models of acute PE and in anecdotal cases of massive PE. The primary cause of death in massive PE that is caused by deep venous thrombi, gas or amniotic fluid, is acute right heart failure and circulatory shock. Increased pulmonary vascular resistance following acute PE is the cumulative result of mechanical obstruction of pulmonary vessels and pulmonary arteriolar constriction (attributable to a neurogenic reflex and to the release of vasoconstrictors). As such, the vasodilator effects of iNO could actively oppose the pulmonary hypertension following PE. This hypothesis is consistently supported by experimental studies in different animal models of PE, which demonstrated that iNO decreased (by 10 to 20%) the pulmonary artery pressure without improving pulmonary gas exchange. Although maximal vasodilatory effects are probably achieved by less than 5 parts per million iNO, which is a relatively low concentration, no dose-response study has been published so far. In addition to the animal studies, a few anecdotal reports in the literature suggest that iNO may improve the hemodynamics during acute PE. However, no prospective, controlled, randomized clinical trial addressing this issue has been conducted to date. Future investigations addressing the effects of iNO combined with other drugs such as vasoconstrictors and inhibitors of phosphodiesterase III or V, may increase the responsiveness to iNO in acute PE.

Plasma levels of endothelin-1, big endothelin-1 and thromboxane following acute pulmonary air embolism

Acute pulmonary air embolism (APAE) was induced in nine piglets by repeated intravenous bolus injection of room air into a large bore central venous catheter at time=0 min so that the mean pulmonary artery pressure (MPAP) was maintained at two times the baseline value for 4 h. Another five animals served as controls. At time=0, 30, 60, 120, 240 min, circulating arterial plasma levels of endothelin-1 (ET-1), its precursor big ET-1, and thromboxane (Tx), were measured by RIA and EIA, respectively, along with hemodynamics and blood gases. The data showed that following APAE, there was a rapid increase in MPAP and a persistent decrease in Pa(O(2)), while the mean arterial blood pressure and cardiac output remained comparable. Plasma levels of ET-1, big ET-1 and Tx were also increased steadily in these first 4 h. These results showed that during APAE, the resulted changes in the pulmonary vascular and airway tones mediated by these potent mediators could explain the observed pulmonary hypertension and the deterioration of gas exchange.

Successful treatment of pulmonary hypertension with inhaled nitric oxide after pulmonary embolectomy

Inhaled nitric oxide is an agent known to reduce pulmonary vascular resistance and prevent right heart failure. Pulmonary embolism is frequently followed by right heart failure and cardiogenic shock. Although successful treatment of patients with right ventricular failure caused by pulmonary embolism has been reported, clinical use of inhaled nitric oxide as an adjunct to surgical treatment is not in widespread use. We present a case of a 69-year-old woman with massive pulmonary embolism followed by right ventricular failure. After emergency operation, weaning from ventilation was prolonged. Pulmonary hypertension was decreased with low-dose inhaled nitric oxide, although pulmonary gas exchange did not improve. The patient was weaned successfully from ventilation 52 hours after operation and recovered completely. In a follow-up examination after 9 months, the patient is in healthy constitution with good cardiopulmonary function.

Effects of oxygen and nitric oxide inhalation in a porcine model of recurrent microembolism

BACKGROUND

Inhalation of nitric oxide (iNO) has been proposed for the treatment of acute pulmonary embolism. The present study evaluates the effects of oxygen (O2) and nitric oxide inhalation in a porcine model of sustained pulmonary hypertension induced by recurrent pulmonary microembolism.

METHODS

Twelve pigs were embolized under general anesthesia with 300-microm microspheres intravenously three times over a period of seven weeks. Five pigs served as untreated controls. Hemodynamic and gas exchange responses to 100% oxygen and 40 ppm NO inhalation, and their combination (O2+iNO) were measured seven days after the last embolization.

RESULTS

Recurrent microembolism caused sustained pulmonary hypertension (pulmonary vascular resistance index; PVRI 408 +/- 57 dyn x s x cm(-5) x m(-2)) as compared to the control group (PVRI 143 +/- 20 dyn x s x cm(-5) m(-2); P<0.05). PVRI was significantly reduced by O2, iNO, and O2+iNO inhalation by 29 +/- 3, 28 +/- 4, and 32 +/- 3%, respectively.

CONCLUSION

We conclude that both O2 and iNO are selective pulmonary vasodilators in a porcine model of sustained pulmonary hypertension following recurrent pulmonary microembolism and, therefore, may be useful in the treatment not only in the acute phase of pulmonary embolism but also later in the time course of the disease.

Inhaled NO reduces leukocyte-endothelial cell interactions and myocardial dysfunction in endotoxemic rats

Inhaled nitric oxide (NO) has been shown to have some protective effect in the peripheral distal inflamed vasculature. The objective of the study was to determine whether inhaled NO would reduce endotoxin-induced leukocyte activation and myocardial contractile dysfunction. Rats were treated with either saline or endotoxin (10 mg/kg iv) and then allowed to breathe (4 h) either air or air plus NO (10 ppm). In endotoxemic rats, mesenteric venular endothelium leukocyte firm adhesion increased compared with control rats (1.15 +/- 0.32 vs. 4.08 +/- 0.96 leukocytes/100 microm; P < 0.05). Inhaled NO significantly attenuated endotoxin-induced venular endothelium leukocyte adhesion (4.08 +/- 0.96 vs. 1.86 +/- 0.76 leukocytes/100 microm; P < 0.05) and FITC-conjugated anti-intercellular adhesion molecule-1 fluorescence intensity. Endotoxin-induced myocardial dysfunction and leukocyte content increases were reduced in inhaled NO-treated rats. These observations suggest that inhaled NO reduces the degree of cardiovascular dysfunction and inflammation in endotoxemic rats.

Animal models for studies on cold-induced platelet activation in human beings

When human platelets are chilled below about 20 degrees C, they spontaneously activate, a phenomenon that limits their storage lifetime. We have previously shown that this activation in chilled human platelets is associated with passage through a lipid phase transition. Because animal models are necessary for Investigating methods for cold storage of platelets, it is essential to determine whether such phase transitions and chilling-induced activation are found in these models. In this study we examined platelets from some commonly used animal models-pigs, rhesus monkeys, mice, dogs, and rabbits. Using Fourier transform infrared spectroscopy (FTIR), we detected the thermotropic membrane phase transition in Intact platelets and assessed the morphologic response of the platelets to chilling. Statistical analysis of both FTIR and shape change show that of the animal models tested, pig platelets are most similar to human platelets. These studies suggest that pigs and pig platelets are the models of choice for the study of cold-induced platelet activation in human beings.

Nitric oxide successfully used to treat acute chest syndrome of sickle cell disease in a young adolescent

OBJECTIVES

To report a case of acute chest syndrome (ACS) of sickle cell disease treated successfully with nitric oxide and to review the physiologic effects of nitric oxide and its potential ability to improve outcome in ACS.

DESIGN

Descriptive case report.

SETTING

Eighteen-bed pediatric intensive care unit in a university children's hospital.

PATIENT

A 15-yr-old black male with sickle cell disease, bilateral pulmonary infiltrates, refractory hypoxemia, and unstable hemodynamics.

INTERVENTION

In addition to exchange transfusion, invasive hemodynamic monitoring, and aggressive ventilatory support, inhaled nitric oxide was administered in the gas mixture in a concentration of 20 ppm for 72 hrs.

MEASUREMENTS AND MAIN RESULTS

Cardiac output, pulmonary arterial pressure, pulmonary artery occlusion pressure, systemic vascular resistance, pulmonary vascular resistance, shunt fraction, and alveolar-arterial oxygen gradient were compared with and without inhaled nitric oxide. Marked reductions in pulmonary arterial pressure and pulmonary vascular resistance were noted. Cardiac output improved, and shunt fraction and alveolar-arterial oxygen gradient were markedly reduced. The patient required decreased ventilator and hemodynamic support and rapidly made a complete recovery.

CONCLUSIONS

Nitric oxide may be beneficial for patients with ACS because of its ability to ameliorate pulmonary hypertension and ventilation/perfusion mismatch. Nitric oxide may confer some protection against polymerization of sickle hemoglobin and exert a reversible antiplatelet effect that may be beneficial in ACS. Further study is necessary to determine the safety and efficacy of inhaled nitric oxide as a treatment for ACS.

Selective vasodilation by nitric oxide inhalation during sustained pulmonary hypertension following recurrent microembolism in pigs

PURPOSE

This study establishes a new model of sustained pulmonary hypertension induced by recurrent microembolism in pigs and evaluates the effects of nitric oxide (NO) inhalation in this model.

MATERIALS AND METHODS

Fourteen pigs were embolized under general anesthesia with 300-microm microspheres intravenously three times over a period of 7 weeks. Four pigs served as untreated controls. Hemodynamic and gas exchange measurements were performed on days 1 and 7 after the last embolization.

RESULTS

Recurrent microembolism caused sustained pulmonary hypertension (mean pulmonary artery pressure [MPAP] 26 +/- 2 and 18 +/- 1 mm Hg on days 1 and 7, respectively) compared with the control group (MPAP 13 +/- 1 mm Hg each for days 1 and 7; P < .05, respectively). Right heart hypertrophy was present at autopsy as indicated by an increase in minimal myocyte diameter. Inhaled NO (5 and 40 parts per million [ppm]) was administered on days 1 and 7. On both days, inhaled NO significantly reduced MPAP and pulmonary vascular resistance without affecting systemic hemodynamics. There were no differences in responses to 5 and 40 ppm inhaled NO.

CONCLUSION

We conclude that recurrent microembolization in pigs provides a reliable model of sustained pulmonary hypertension. In this model inhaled NO is a selective pulmonary vasodilator, indicating that active vasoconstriction significantly contributes to sustained pulmonary hypertension after recurrent microembolism.

Use of inhaled nitric oxide in pulmonary embolism

Acute massive pulmonary embolism carries a high mortality with the majority of deaths occurring during the early phase. We describe a case of massive pulmonary embolism resulting in severe cardiovascular collapse and cardiac arrest which was treated successfully with inhaled nitric oxide.

Small-dose inhaled nitric oxide attenuates hemodynamic changes after pulmonary air embolism in dogs

Inhaled nitric oxide (NO) has been used to treat pulmonary hypertension. Experimental studies have suggested therapeutic effects of NO after pulmonary microembolism. We evaluated the protective effects of NO in dogs during a pulmonary air embolism (PAE). NO (3 ppm) was administered to six anesthetized mongrel dogs (NO group) but not to the seven dogs in the control group. After 20 min, each dog received a venous air injection of 2.5 mL/kg. Hemodynamic evaluation was performed, and blood samples were drawn for blood gas analysis before and after NO inhalation and 5-60 min after the PAE. Both arterial blood pressure and cardiac output were decreased in the control group for >15 min after PAE, whereas NO-treated animals showed only transient hypotension. NO attenuated the pulmonary hypertension after PAE, as demonstrated by small (P < 0.05) increases in pulmonary artery pressure and pulmonary vascular resistance index in NO-treated animals (90% and 135%, respectively) compared with the controls (196% and 282%, respectively). These hemodynamic effects of NO were associated with higher mixed venous O2 tensions and saturations in the NO group compared with the controls. We conclude that small-dose NO (3 ppm) attenuated the hemodynamic changes induced by PAE in dogs. This protective effect of NO on hemodynamics is not accompanied by improvement in pulmonary oxygenation in this setting.

IMPLICATIONS

In this study, we evaluated the protective effects of inhaled nitric oxide in a pulmonary air embolism setting. Nitric oxide attenuated the hemodynamic changes induced by pulmonary air embolism without improving pulmonary oxygenation.

Inhaled nitric oxide does not affect adenosine 5'-diphosphate-dependent platelet activation in infants with persistent pulmonary hypertension of the newborn

OBJECTIVE

To investigate the effect of inhaled nitric oxide (NO) treatment in newborns with persistent pulmonary hypertension on adenosine 5'-diphosphate (ADP)-dependent platelet activation.

METHODS

After parental informed consent, infants with persistent pulmonary hypertension of the newborn were randomly assigned to receive conventional treatment (control group) or treatment with 40 parts per million of inhaled NO. Platelet activation was measured at time of entry and 30 minutes later by surface expression of P-selectin in response to increasing concentrations of the agonist ADP (0, 2, 5, 10, and 20 microM) using fluorescence-activated flow cytometry.

RESULTS

We examined 11 infants in the inhaled NO group and 13 in the control group. P-selectin expression, quantified as mean fluorescence, was not significantly different in the two groups of patients at baseline. Median percent change from baseline fluorescence was assessed using the Wilcoxon matched-pairs signed-rank test. At 30 minutes after enrollment there were no statistically significant changes from baseline fluorescence in either group of patients and at all ADP concentrations.

CONCLUSION

Thirty minutes of exposure to 40 ppm of inhaled NO does not inhibit ADP-dependent platelet activation as measured by surface expression of P-selectin in infants with persistent pulmonary hypertension of the newborn.

Impact of inhaled nitric oxide on platelet aggregation and fibrinolysis in rats with endotoxic lung injury. Role of cyclic guanosine 5'-monophosphate

As inhaled nitric oxide (iNO) may differently increase bleeding time (BT) and inhibit platelet aggregation in normal and lung-injured patients or experimental models, we studied the effects of iNO on hemostasis in presence and absence of an endotoxic lung injury in the rat. Eight hours after intratracheal administration of endotoxin (lipopolysaccharide [LPS]) or its solvent (phosphate-buffered solution [PBS]), four groups of rats were randomized according to the presence or absence of 15 ppm iNO added for an additional 10 h. We measured BT, ex vivo platelet aggregation, plasma fibrinogen, euglobulin clot lysis time (ECLT), and platelet and aortic cyclic guanosine 5'-monophosphate (cGMP) contents. Acute lung inflammation did not influence BT, but increased platelet aggregability, fibrinogen levels, and platelet and aortic cGMP. In control and endotoxic rats, iNO increased BT, reduced platelet aggregability, and increased platelet cGMP. iNO increased aortic cGMP only in healthy rats. ECLT was increased by LPS and unchanged with iNO. These results suggest that the extrapulmonary "systemic" effects induced by iNO on hemostasis were not strictly similar in healthy and LPS rats, inflammation inducing proper changes in coagulation parameters. However, iNO attenuated the procoagulant activity induced by acute lung inflammation, suggesting a potentially beneficial effect of this therapy.

Inhaled nitric oxide inhibits human platelet aggregation, P-selectin expression, and fibrinogen binding in vitro and in vivo

BACKGROUND

Recent data suggest that inhaled NO can inhibit platelet aggregation. This study investigates whether inhaled NO affects the expression level and avidity of platelet membrane receptors that mediate platelet adhesion and aggregation.

METHODS AND RESULTS

In 30 healthy volunteers, platelet-rich plasma was incubated with an air/5% CO2 mixture containing 0, 100, 450, and 884 ppm inhaled NO. ADP- and collagen-induced platelet aggregation, the membrane expression of P-selectin, and the binding of fibrinogen to the platelet glycoprotein (GP) IIb/IIIa receptor were determined before (t0) and during the 240 minutes of incubation. In addition, eight patients suffering from severe adult respiratory distress syndrome (ARDS) were investigated before and 120 minutes after the beginning of administration of 10 ppm inhaled NO. In vitro, NO led to a dose-dependent inhibition of both ADP-induced (3+/-3% at 884 ppm versus 70+/-6% at 0 ppm after 240 minutes; P<.001) and collagen-induced (13+/-5% versus 62+/-5%; P<.01) platelet aggregation. Furthermore, P-selectin expression (36+/-7% of t0 value; P<.01) and fibrinogen binding (33+/-11%; P<.01) were inhibited. In patients with ARDS, after two who did not respond to NO inhalation with an improvement in oxygenation had been excluded, an increase in plasma cGMP, prolongation of in vitro bleeding time, and inhibition of platelet aggregation and P-selectin expression were observed, and fibrinogen binding was also inhibited (19+/-7% versus 30+/-8%; P<.05).

CONCLUSIONS

NO-dependent inhibition of platelet aggregation may be caused by a decrease in fibrinogen binding to the platelet GP IIb/IIIa receptor.

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.