Superoxide dismutase improves oxygenation and reduces oxidation in neonatal pulmonary hypertension

RATIONALE: Hyperoxic ventilation in the management of persistent pulmonary hypertension of the newborn (PPHN) can result in the formation of reactive oxygen species, such as superoxide anions, which can inactivate nitric oxide (NO) and cause vasoconstriction and oxidation. OBJECTIVE: To compare the effect of intratracheal recombinant human superoxide dismutase (rhSOD) and/or inhaled NO (iNO) on systemic oxygenation, contractility of pulmonary arteries (PAs), and lung reactive oxygen species (isoprostane, 3-nitrotyrosine) levels in neonatal lambs with PPHN. METHODS: Six newborn lambs with PPHN (induced by antenatal ductal ligation) were killed at birth. Twenty-six PPHN lambs were ventilated for 24 h with 100% O(2) alone (n = 6) or O(2) combined with rhSOD (5 mg/kg intratracheally) at birth (n = 4), rhSOD at 4 h of age (n = 5), iNO (20 ppm, n = 5), or rhSOD + iNO (n = 6). Contraction responses of fifth-generation PAs to norepinephrine and KCl, lung isoprostane levels, and 3-nitrotyrosine fluorescent intensity were measured. RESULTS: Systemic oxygenation was impaired in PPHN lambs and significantly improved (up to threefold) in both rhSOD groups with or without iNO. Oxygenation improved more rapidly with the combination of rhSOD + iNO compared with either intervention alone. Norepinephrine- and KCl-induced contractions and lung isoprostane levels were significantly increased by 100% O(2) compared with nonventilated newborn lambs with PPHN. Both rhSOD and iNO mitigated the increased PA contraction response and lung isoprostane levels. Intratracheal rhSOD decreased the enhanced lung 3-nitrotyrosine fluorescence observed with iNO therapy. CONCLUSION: Intratracheal rhSOD and/or iNO rapidly increase oxygenation and reduce both vasoconstriction and oxidation in newborn lambs with PPHN. This has important implications for clinical trials of rhSOD and iNO in newborn infants with PPHN.     

Superoxide dismutase improves gas exchange and pulmonary hemodynamics in premature lambs

RATIONALE: Oxidant stress may increase the severity of respiratory distress syndrome (RDS) after premature birth by altering vasoreactivity and increasing lung edema, but the acute effects of superoxide dismutase (SOD) treatment on gas exchange, lung compliance (CL), and pulmonary vascular resistance in premature animals with RDS are unknown. OBJECTIVE: We studied the effects of intratracheal recombinant human SOD treatment (rhSOD) on gas exchange, CL, and pulmonary hemodynamics in 46 premature lambs with RDS. Methods: After C-section delivery, lambs were randomly assigned to treatment with SOD (2.5-10 mg/kg) with or without inhaled nitric oxide (iNO, 5 ppm), and mechanically ventilated for 4 hours. At the end of the study, pressure-volume curves and wet-dry lung weights were measured to assess CL and edema, respectively. MAIN RESULTS: Despite an initial rise in Pa(O(2)), Pa(O(2)) in control animals progressively declined over the 4-hour treatment period (Pa(O(2)) = 25.0 +/- 7.5 mm Hg at 4 hours). In comparison with control animals, early treatment with SOD at 5 and 10 mg/kg improved Pa(O(2)) at 4 hours (167 +/- 44 and 269 +/- 33 mm Hg, respectively; p < 0.05 vs. control), but did not decrease lung edema or improve CL. In contrast, late treatment with SOD did not improve Pa(O(2)). Treatment with iNO increased Pa(O(2)) (196 +/- 22 vs. 25 +/- 8 mm Hg, control animals; p < 0.01), but the response to iNO was not augmented by combined therapy (SOD + iNO). After 4 hours of ventilation with FI(O(2)) = 1.00, rhSOD treatment lowered pulmonary vascular resistance compared with control animals. CONCLUSIONS: Early intratracheal rhSOD treatment improves oxygenation in premature lambs with RDS and prevents the development of pulmonary hypertension.     

The cGMP-specific phosphodiesterase inhibitor E4021 dilates the pulmonary circulation.

We investigated the pulmonary vascular effects of E4021, a potent inhibitor of cGMP-specific phosphodiesterase, in control late-gestation fetal lambs, and in newborn lambs with persistent pulmonary hypertension (PPHN) after prenatal ligation of the ductus arteriosus. E4021 alone significantly relaxed fifth-generation pulmonary arteries isolated from control fetal lambs, an effect completely blocked after inhibition of nitric oxide synthase (NOS). In contrast, E4021 did not relax pulmonary arteries isolated from hypertensive lambs. Pretreatment with E4021 (10(-7) M) significantly enhanced relaxations to the NO donor S-nitrosyl-acetyl-penicilamine (SNAP) in arteries from both control and hypertensive lambs. In control, fully instrumented fetal lambs, infusions of E4021 (31 microgram/min) selectively dilated the pulmonary circulation, an effect again blocked after inhibition of NO synthase. Further studies were performed in newborn lambs with PPHN to study the vascular effects of E4021 alone, and in combination with inhaled NO. E4021 alone (1 to 100 microgram/kg/min) decreased pulmonary artery pressure (Ppa) in a dose-dependent fashion, and had minimal effect on systemic pressure. At the highest dose (100 microgram/kg/min), the dilation was selective for the pulmonary circulation. In subsequent protocols, E4021 (10 microgram/kg/min) significantly decreased Ppa and pulmonary vascular resistance (PVR), but these pulmonary vascular effects were not enhanced after NO inhalation at 0.5 or 5 ppm. We speculate that the lack of enhancement was due to the dramatic effects of E4021 alone. Potent, specific phosphodiesterase inhibitors such as E4021 may prove to be useful in the treatment of PPHN.     

Inhaled nitric oxide and methemoglobin in full-term infants with persistent pulmonary hypertension of the newborn

Inhaled nitric oxide (iNO), a potent pulmonary vasodilator, has become a mainstay therapy for neonates with persistent pulmonary hypertension of the newborn (PPHN). However, it also oxidizes hemoglobin to methemoglobin (metHgb), thereby reducing the delivery of oxygen to tissues. Studies have suggested that elevated levels of metHgb may be avoided by limiting iNO concentration to less than 40 parts per million (ppm). However, the relationship between iNO exposure and elevated levels of metHgb (greater than 4%) has not been examined. Therefore, we studied this relationship in full term newborns with PPHN.We reviewed the charts of twenty-eight neonates with a diagnosis of PPHN admitted to our Intensive Care Nursery between 1/92 and 10/97. Our retrospective analysis demonstrated that: (1) high metHgb levels can occur with exposure to low iNO concentration (three of eight newborns with maximum metHgb levels >4% had been exposed to no more than 40 ppm of iNO concentration); and (2) cumulative iNO ( summation operatoriNO) exposure was the best predictor of elevated metHgb levels (seven of nine newborns receiving summation operatoriNO>2000 ppm x hour had maximum metHgb levels >4%).     

Inhaled nitric oxide effects on lung structure and function in chronically ventilated preterm lambs

RATIONALE: Inhaled nitric oxide (iNO) can reverse neonatal pulmonary hypertension and bronchoconstriction and reduce proliferation of cultured arterial and airway smooth muscle cells. OBJECTIVES: To see if continuous iNO from birth might reduce pulmonary vascular and respiratory tract resistance (PVR, RE) and attenuate growth of arterial and airway smooth muscle in preterm lambs with chronic lung disease. METHODS: Eight premature lambs received mechanical ventilation for 3 weeks, four with and four without iNO (5-15 ppm). Four term lambs, mechanically ventilated without iNO for 3 weeks, served as additional control animals. MEASUREMENTS: PVR and RE were measured weekly. After 3 weeks, lung tissue was processed for quantitative image analysis of smooth muscle abundance around small arteries (SMart) and terminal bronchioles (SMtb). Radial alveolar counts were done to assess alveolar number. Endothelial NO synthase (eNOS) protein in arteries and airways was measured by immunoblot analysis. MAIN RESULTS: At study's end, PVR was similar in iNO-treated and untreated preterm lambs; PVR was less in iNO-treated preterm lambs compared with term control animals. RE in iNO-treated lambs was less than 40% of RE measured in preterm control animals. SMart was similar in iNO-treated and both groups of control lambs; SMtb in lambs given iNO was significantly less (approximately 50%) than in preterm control animals. Radial alveolar counts of iNO-treated lambs were more than twice that of preterm control animals. eNOS was similar in arteries and airways of iNO-treated preterm lambs compared with control term lambs. CONCLUSIONS: iNO preserves structure and function of airway smooth muscle and enhances alveolar development in preterm lambs with chronic lung disease.     

Pulmonary hypertension alters soluble guanylate cyclase activity and expression in pulmonary arteries isolated from fetal lambs

The nitric oxide (NO)-guanosine 3',5'-cyclic monophosphate (cGMP) signaling pathway plays an important role in the pulmonary vascular transition at birth. We studied pulmonary arteries and veins isolated from normal late-gestation fetal lambs and from fetal lambs with persistent pulmonary hypertension (PPHN) following prenatal ligation of the ductus arteriosus. We additionally used double immunolabeling and immunoblot analysis to determine relative vascular contents of endothelial nitric oxide synthase (NOS-III) and soluble guanylate cyclase (sGC). Cyclic GMP content and sGC activity were significantly lower in arteries from hypertensive lambs than controls. A rank order for contents of both soluble guanylate cyclase and NOS-III was observed by both immunolabeling and immunoblotting: Control vein = Hypertensive vein > Control artery > Hypertensive artery. Our data demonstrate that the relative expression of sGC correlates well with the relative expression of NOS-III, and indicate the potential importance of soluble guanylate cyclase in the regulation of the perinatal pulmonary circulation. These data may help us understand vascular mechanisms producing PPHN, as well as patterns of response to exogenous NO.     

Maturational changes in ovine pulmonary vascular responses to inhaled nitric oxide

Developmental changes in modulation of pulmonary vasomotor tone by endothelium-derived nitric oxide (EDNO) may reflect maturational differences in endothelial synthesis of and/or vascular smooth muscle response to nitric oxide. This study sought to determine whether pulmonary vascular sensitivity and responsiveness to nitric oxide change during newborn development, and whether this is related to changes in guanylate cyclase activity. Pulmonary artery dose-responses to inhaled nitric oxide (iNO, 0.25-100 parts per million) were measured in hypoxic, indomethacin-treated, isolated lungs from 1-day (1-d)- and 1-month (1-m)-old lambs. The lungs of 1-m-old lambs were ventilated with 4% (oxygen) O2, and lungs of 1-d-old lambs were ventilated with either 4% or 7% O2 in order to achieve similar stimuli or vasomotor tone. Cyclic guanosine monophosphate (cGMP) concentrations in the perfusate were measured at iNO concentrations of 0, 5, and 100 parts per million (ppm). Basal and stimulated pulmonary guanylate cyclase activity was also measured in lung extracts in vitro. The effects of iNO were similar in both 1-d groups, even though baseline hypoxic tone was significantly higher in 1-d lungs ventilated with 4% O2 than with 7% O2. Furthermore, both the 1-d 7% O2 and 1-d 4% O2 lungs exhibited greater responsiveness and sensitivity to iNO than 1-m lungs. Perfusate cGMP concentrations and soluble guanylate cyclase activity were higher under stimulated than basal conditions, but neither differed statistically between 1 d and 1 m. These data suggest that pulmonary vascular responsiveness and sensitivity to nitric oxide decrease with age, but the mechanisms underlying these maturational changes require further investigation.     

Type I nitric oxide synthase is decreased in the fetal pulmonary circulation of hypertensive lambs

The nitric oxide (NO)/guanosine 3',5'-cyclic monophosphate (cGMP) pathway plays an essential role in mediating pulmonary vasodilatation during transition of the pulmonary circulation at birth. We used immunoblot analysis (Western) and semiquantitative immunohistochemistry to study the presence, distribution, and relative amounts of type I nitric oxide synthase (NOS-I). Immunoblots were performed on normal fetal sheep lungs, whereas immunohistochemistry for NOS-I was compared between lungs from normal fetal lambs vs. fetal lambs with persistent pulmonary hypertension of the newborn (PPHN) induced by ligation of the ductus arteriosus.Western blot analysis using a polyclonal antibody detected NOS-I protein in homogenates of normal fetal sheep lungs. Abundant NOS-I immunoreactivity was observed exclusively in the precapillary resistance vessels, i.e., terminal bronchiole-associated arteries (TA) and respiratory bronchiole-associated arteries (RA) in normal fetal lung. In marked contrast, immunoreactivity for NOS-I was significantly reduced in the TA and RA of hypertensive lungs.We conclude that there is a heterogeneous distribution of NOS-I in the normal fetal sheep lung, but that NOS-I staining is significantly reduced in lambs with PPHN.     

Hemodynamic effects of inhaled nitric oxide and phosphodiesterase inhibitor (dipyridamole) on secondary pulmonary hypertension following heart valve surgery in adults

BACKGROUND: Inhaled nitric oxide (iNO) is proposed in the management of pulmonary hypertension (PH) in patients undergoing cardiac surgery. Secondary PH related to a long-standing heart valve disease however may be refractory to iNO. Aim of this prospective study was to determine whether the combination of iNO plus dipyridamole (DP), a cyclic guanosine monophosphate-specific phosphodiesterase inhibitor (PDE5), may enhance and/or prolong the response to iNO in adult patients with secondary valve-related PH undergoing cardiac surgery, and attenuate rebound events related to its discontinuation. METHODS: Responses in 27 patients, 11 male, mean age 72+/-11 years, with PH due to mitral and/or aortic valve disease, were studied in the Intensive Care Unit after cardiac surgery, during sedation and stable hemodynamic conditions. The effect of isolated iNO administration (40 ppm), iNO combined with DP (0.2 mg/kg i.v.), and DP alone (1 mg/kg/24 h) on pulmonary vascular resistance, mean pulmonary artery pressure, cardiac index, mixed venous O2Sat%, and mean arterial pressure were determined. RESULTS: All patients showed at least a 10% decrease in pulmonary vascular resistance vs. baseline after administration of iNO [responders]. Inhaled NO and the combination of iNO/DP produced a reduction of pulmonary vascular resistance and mean pulmonary artery pressure (p<0.05). Cardiac index improved with a significant difference between iNO and the association iNO/DP versus baseline (p<0.05). This significant hemodynamic improvement versus baseline was maintained during isolated DP administration (p<0.05), but not during isolated iNO discontinuation. Mixed venous oxygen saturation showed an overall improvement of 17% (p<0.05). CONCLUSIONS: Inhaled NO and DP infusion might represent a valuable association in the management of PH secondary to a heart valve disease in patients undergoing cardiac surgery. Their beneficial hemodynamic effects might be particularly valuable in the management of patients with associated right ventricular dysfunction.     

Phosphodiesterase inhibitors for persistent pulmonary hypertension of the newborn: a review

Persistent pulmonary hypertension of the newborn (PPHN) is a complex syndrome with multiple causes, with an incidence of 0.43-6.8/1,000 live births and a mortality of 10-20%. Survivors have high morbidity in the forms of neurodevelopmental and audiological impairment, cognitive delays, hearing loss, and a high rate of rehospitalization. The optimal approach to the management of PPHN remains controversial. Inhaled nitric oxide (iNO) is currently regarded as the gold standard therapy, but with as many as 30% of cases failing to respond, has not proven to be the single magic bullet. Given the complex pathophysiology of the disease, any such magic bullet is unlikely. A number of recent studies have suggested a role for specific phosphodiesterase (PDE) inhibitors in the management of PPHN. Sildenafil, a specific PDE5 inhibitor, appears the most promising of such agents. We aim to review the current status and limitations of iNO and the potential of PDE inhibitors in the management of PPHN. The reasons why caution is warranted before specific PDE5 inhibitors like sildenafil are labelled as potential magic bullets for PPHN will be discussed. The need for randomized-controlled trials to determine the safety, efficacy, and long-term outcome following treatment with sildenafil in PPHN is emphasized.     

Infant lung function after inhaled nitric oxide therapy for persistent pulmonary hypertension of the newborn.

Our objectives were to determine whether the use of inhaled nitric oxide (iNO) for severe persistent pulmonary hypertension of the newborn (PPHN) causes impaired lung function during infancy. We therefore performed a prospective study of lung function in 22 infants after neonatal intensive care unit (NICU) discharge who had been treated for severe persistent pulmonary hypertension of the newborn (PPHN) with (n = 15) or without (n = 7) iNO, and compared these findings in lung function to those of healthy control infants (n = 18). Five infants with interstitial lung disease (ILD) were included to assure that the pulmonary function tests (PFT) were sensitive enough to detect abnormalities of lung function in this age group. We measured passive respiratory mechanics and functional residual capacity (FRC) using a commercially available system. All data were expressed as means and standard deviation. Statistical analysis was performed by analysis of variance (ANOVA). A Bonferroni multiple comparisons test was used for variables that showed overall group differences. Twenty-two infants were studied during follow-up 4-12 months after NICU discharge. None of the infants were actuely ill, and only one infant was on 0.25 L of oxygen per minute at the time of study. We found no differences in lung function between the treatment groups (iNO + mechanical ventilation (MV), or MV alone), or between either treatment group and healthy control infants of the same age. We were able to detect significant differences in functional residual capacity adjusted for weight or height, and compliance of the respiratory system adjusted for weight or lung volume in the ILD infants compared to the healthy controls or infants who had PPHN, indicating that these PFTs were sensitive enough to determine abnormal lung function in this age group. We conclude that inhaled nitric oxide therapy for the treatment of severe PPHN does not alter lung function as determined by lung volume and passive respiratory mechanics measurements during early infancy.     

Long-term inhaled nitric oxide plus dipyridamole for pulmonary arterial hypertension

Inhaled nitric oxide (iNO) has been shown to be a potent and selective vasodilator in pulmonary arterial hypertension (PAH). However, the clinical experience in prolonged treatment is limited. We assess the safety and effectiveness of long-term administration of iNO in severe PAH. Two female patients were admitted to our hospital because of severe dyspnea (World Health Organization functional class IV) and hypoxemia. They were diagnosed with PAH (primary and secondary to congenital heart disease) and treated with iNO for 2 years. The delivery system consisted of an NO tank of 800 ppm, a modified gas-pulsing device, and nasal cannulas. On iNO treatment the patients showed remarkable improvement of symptoms, oxygenation and 6-min walk distance. After 16 months the patients began to experience a progressive rebound of symptoms. A phosphodiesterase type 5 inhibitor (dipyridamole) was added to iNO. This intervention proved useful in improving clinical deterioration and hemodynamics. This is the first study reporting 2-year iNO therapy in 2 patients with primary and secondary pulmonary hypertension. The combination of dipyridamole with iNO augments the pulmonary vasodilatation and may be useful in managing PAH.     

Hyperoxia increases phosphodiesterase 5 expression and activity in ovine fetal pulmonary artery smooth muscle cells

In the pulmonary vasculature, cGMP concentrations are regulated in part by a cGMP-dependent phosphodiesterase (PDE), PDE5. Infants with persistent pulmonary hypertension of the newborn (PPHN) are often mechanically ventilated with high oxygen concentrations. The effects of hyperoxia on the developing pulmonary vasculature and PDE5 are largely unknown. Here, we demonstrate that exposure of fetal pulmonary artery smooth muscle cells (FPASMCs) to high levels of oxygen for 24 hours leads to decreased responsiveness to exogenous NO, as determined by a decreased intracellular cGMP response, increased PDE5 mRNA and protein expression, as well as increased PDE5 cGMP hydrolytic activity. We demonstrate that inhibition of PDE5 activity with sildenafil partially rescues cGMP responsiveness to exogenous NO. In FPASMCs, hyperoxia leads to increased oxidative stress without increasing cell death. Treatment of normoxic FPASMCs with H2O2 is sufficient to induce PDE5 expression and activity, suggesting that reactive oxygen species mediate the effects of hyperoxia in FPASMCs. In support of this mechanism, a chemical antioxidant, N-acetyl-cysteine, is sufficient to block the hyperoxia-mediated increase in PDE5 expression and activity and rescue cGMP responsiveness to exogenous NO. Finally, ventilation of healthy neonatal sheep with 100% O2 for 24 hours leads to increased PDE5 protein expression in the resistance pulmonary arteries and increased PDE5 activity in whole lung extracts. These data suggest that PDE5 expression and activity play a critical role in modulating neonatal pulmonary vascular tone in response to common clinical treatments for PPHN, such as oxygen and inhaled NO.     

Lung physiology and histopathology during cumulated exposure to nitric oxide in combination with assisted ventilation in healthy piglets

Inhaled nitric oxide (iNO) is routinely used for hypoxic respiratory failure and persistent pulmonary hypertension of the newborn, and investigation of its new indications requiring various levels of iNO is underway. Cumulated exposure of high level of iNO may exert adverse effects on lung function and morphology, which may be confounded with ventilator-associated lung injury. Sixteen healthy piglets (5.5-11 kg) were anaesthetised, intubated and mechanically ventilated at low FiO(2) on continuous positive airway pressure and pressure support mode. The animals were randomly allocated to receive 40 ppm iNO (NO group, n=8) or no iNO (Control group, n=8). In both groups at 24 and 48 h, mild to moderate lung injury was observed, with mean values of PaO(2)/FiO(2)<300 mmHg. Compared to the Control, iNO at 40 ppm for 24-48 h did not adversely affect dynamic compliance or resistance of respiratory system, oxygenation, pulmonary and systemic hemodynamics. Neither did it affect composition and surface activity of surfactant phospholipids and white cell counts in bronchoalveolar lavage fluid. Inhaled NO resulted in elevated total serum nitrite/nitrate to 352+/-90 micromol/l and methemoglobin (MetHb) to 5.0+/-3.4%, in contrast to 88+/-38 micromol/l and 0.88+/-0.52% in the Control; 50% of the iNO animals having MetHb>3%. The lung injury scores as well as alveolar expansion were similar between the two groups at 24 h. At 48 h, low wet/dry lung weight ratio and lung injury score were found in the NO group. We conclude that no significant adverse effects on lung physiology and structure were found in the piglets receiving 40 ppm iNO for 24 or 48 h, on the contrary lung injury was moderately alleviated. The significantly impaired gas exchange over time associated with discrete morphological changes suggests adverse effects of prolonged positive pressure breathing and not necessarily exposure to oxides of nitrogen.     

Residual pulmonary vasoreactivity to inhaled nitric oxide in patients with severe obstructive pulmonary hypertension and Eisenmenger syndrome

OBJECTIVE—To determine whether inhaled NO (iNO) can reduce pulmonary vascular resistance in adults with congenital heart disease and obstructive pulmonary hypertension or Eisenmenger syndrome.
DESIGN—23 patients received graded doses of iNO. Pulmonary and systemic haemodynamic variables and circulating cyclic guanosine monophosphate (cGMP) concentrations were measured at baseline and after 20 and 80 ppm iNO. Patients were considered responders when total pulmonary resistance was reduced by at least 20%, and rebound was defined as a greater than 10% increase in total pulmonary resistance upon withdrawal from iNO.
RESULTS—In response to 20 ppm iNO, total pulmonary resistance decreased in four patients (18%, 95% confidence interval (CI), 2% to 34%), while in response to 80 ppm iNO it decreased in six patients (29%, 95% CI 10% to 38%). Systemic blood pressure did not change. Withdrawal resulted in rebound in three patients (16%, 95% CI 0% to 32%) after cessation of 20 ppm iNO, and in six patients (35%, 95% CI 12% to 58%) after cessation of 80 ppm iNO. Patients with predominant right to left shunting did not respond. In all patients cGMP increased from (mean (SD)) 28 (13) µmol/l at baseline to 55 (30) and 78 (44) µmol/l after 20 and 80 ppm iNO (p < 0.05 v baseline).
CONCLUSIONS—NO inhalation is safe and is associated with a dose dependent increase in circulating cGMP concentrations. Pulmonary vasodilatation in response to iNO was observed in 29% of patients and was influenced by baseline pulmonary haemodynamics. Responsiveness to acute iNO may identify patients with advanced obstructive pulmonary hypertension and Eisenmenger syndrome who could benefit from sustained vasodilator treatment.


Keywords: nitric oxide; pulmonary hypertension; Eisenmenger syndrome     

Inhaled nitric oxide,oxygen, and alkalosis: Dose‐response interactions in a lamb model of pulmonary hypertension

Inhaled nitric oxide (NO) is currently used as an adjuvant therapy for a variety of pulmonary hypertensive disorders. In both animal and human studies, inhaled NO induces selective, dose‐dependent pulmonary vasodilation. However, its potential interactions with other simultaneously used pulmonary vasodilator therapies have not been studied. Therefore, the objective of this study was to determine the potential dose‐response interactions of inhaled NO, oxygen, and alkalosis therapies. Fourteen newborn lambs (age 1–6 days) were instrumented to measure vascular pressures and left pulmonary artery blood flow. After recovery, the lambs were sedated and mechanically ventilated. During steady‐state pulmonary hypertension induced by U46619 (a thromboxane A₂ mimic), the lambs were exposed to the following conditions: Protocol A, inhaled NO (0, 5, 40, and 80 ppm) and inspired oxygen concentrations (FiO₂) of 0.21, 0.50, and 1.00; and Protocol B, inhaled NO (0, 5, 40, and 80 ppm) and arterial pH levels of 7.30, 7.40, 7.50, and 7.60. Each condition (in randomly chosen order) was maintained for 10 min, and all variables were allowed to return to baseline between conditions. Inhaled NO, oxygen, and alkalosis produced dose‐dependent decreases in mean pulmonary arterial pressures (P < 0.05). Systemic arterial pressure remained unchanged. At 5 ppm of inhaled NO, alkalosis and oxygen induced further dose‐dependent decreases in mean pulmonary arterial pressures (P<0.05). At inhaled NO doses >5 ppm, alkalosis induced further dose‐independent decreases in mean pulmonary arterial pressure, while oxygen did not. We conclude that in this animal model, oxygen, alkalosis, and inhaled NO induced selective, dose‐dependent pulmonary vasodilation. However, when combined, a systemic arterial pH >7.40 augmented inhaled NO‐induced pulmonary vasodilation, while an FiO₂ >0.5 did not. Therefore, weaning high FiO₂ during inhaled NO therapy should be considered, since it may not diminish the pulmonary vasodilating effects. Further studies are warranted to guide the clinical weaning strategies of these pulmonary vasodilator therapies. Pediatr Pulmonol. 1999; 28:3–11. © 1999 Wiley‐Liss, Inc.     

Eine Standortbestimmung zum Einsatz von inhalativem Stickstoffmonoxid

Summary Since the first clinical use of inhaled nitric oxide (iNO) as a selective pulmonary vasodilator, the concept of NO inhalation has been investigated for various indications. Used in the therapy of acute respiratory distress syndrome (ARDS), it has shown positive effects on intrapulmonary shunting and oxygenation, but no change on ARDS mortality has been demonstrated so far. Perhaps the combination of iNO with other therapeutic interventions, such as the increase of the hypoxic pulmonary vasoconstriction response through almitrine, will lead to a reduction in the mortality of the ARDS. In the treatment of persistent pulmonary hypertension of the newborn, iNO has been shown to be advantageous. Although the influence on the mortality rate has not yet been proven, a reduced need for extracorporeal membrane oxygenation (ecmo) through the use of iNO has been demonstrated. In addition, NO inhalation has been successful in the postoperative care of children after repair of congenital heart defects. There may be a special role for inhalation of NO in the prophylaxis of early complications after heart or lung transplantation if right heart failure after heart transplant or edema due to reperfusion injury after lung transplant becomes the main problem. Due to the different effects of NO, e.g., in clotting and the immunsystem, further investigations will be needed to complete our knowledge on the clinical use of NO inhalation. Zusammenfassung Seit Beginn der klinischen Nutzung von inhalativem NO (iNO) als selektivem pulmonalem Vasodilatator wird dieses Therapiekonzept für verschiedene Indikationen untersucht. Während im Rahmen der Behandlung des akuten Lungenversagens (ARDS) die günstigen Effekte auf den intrapulmonalen Shunt und damit auf die Oxygenierung belegt sind, konnte ein Einfluß auf die Letalität des ARDS bisher nicht gezeigt werden. Möglicherweise kann jedoch eine Kombination von iNO mit anderen therapeutischen Maßnahmen wie gleichzeitige Verstärkung der hypoxisch-pulmonalen Vasokonstriktion durch Almitrine zu einer verbesserten Überlebensrate des ARDS führen. Bei der Behandlung der persistierenden pulmonalen Hypertonie des Neugeborenen (PPHN) erscheint iNO einer intravenösen Vasodilatatorgabe eindeutig überlegen zu sein. Auch hier ist ein Einfluß auf die Überlebensrate zwar nicht bewiesen, es konnte jedoch gezeigt werden, daß die Notwendigkeit zur extrakorporalen Membranoxygenation (ECMO) bei diesem Krankheitsbild durch iNO reduziert wird. In der postoperativen Therapie der pulmonalen Hypertension nach Korrektur kongenitaler Vitien bei Kindern findet iNO ebenfalls häufig eine Anwendung. Einen besonderen Stellenwert könnte die NO-Inhalation in der Verhütung früher Komplikationen nach Herz- oder Lungentransplantation erlangen, wenn nach der Herztransplantation eine Rechtsherzbelastung bzw. nach der Lungentransplantation ein Ödem als Folge eines Reperfusionsschadens im Vordergrund stehen. Wegen der vielfältigen Wirkungen des NO, z.B. auch auf Gerinnungs- und Immunsystem, bedarf es noch zahlreicher Untersuchungen, um die Kenntnisse über die klinischen Effekte der NO-Inhalation zu vervollständigen.     

Effects of variable concentrations of inhaled nitric oxide and oxygen on the lungs of newborn piglets

We previously demonstrated that inhalation of high concentrations of nitric oxide (iNO) and oxygen for 48 hr causes significant lung injury in newborn piglets. To determine if these effects persist at lower concentrations, groups of newborn piglets were mechanically ventilated for 48 hr with (study 1) constant O(2) (90-100%) and decreasing iNO (100-2 ppm) or (study 2) constant iNO (50 ppm) and decreasing O(2) (95-30%). Bronchoalveolar lavage (BAL) fluid was assayed for surfactant function, and markers of lung inflammation and physiologic parameters were monitored.Neutrophil chemotactic activity (NCA), % neutrophils, and total protein (TP) concentrations decreased significantly in BAL fluid of study 1 piglets as iNO was reduced and inhaled oxygen fraction remained constant, indicating less pulmonary injury at low iNO levels. Low-dose iNO (2 ppm) did not have antiinflammatory effects. However, surfactant function was minimally affected by lowering iNO, and was abnormal in all groups. In contrast, in study 2, pulmonary inflammation and injury were lower when O(2) was decreased to 70% or less, with iNO constant at 50 ppm. Surfactant function normalized and oxygenation improved in study 2 piglets when the inhaled oxygen fraction was decreased and iNO remained constant.These data suggest that iNO- and O(2)-induced lung injury may be minimized by weaning O(2) or iNO, although better physiologic function may be obtained when iNO concentrations are constant and O(2) is reduced. This has important implications in the clinical management of critically ill newborns treated with O(2) and iNO for pulmonary disorders.     

Ghrelin ameliorates hypoxia-induced pulmonary hypertension via phospho-GSK3 β/β-catenin signaling in neonatal rats

Effective treatment and/or prevention strategies for neonatal persistent pulmonary hypertension of the newborn (PPHN) have been an important topic in neonatal medicine. However, mechanisms of impaired pulmonary vascular structure in hypoxia-induced PPHN are poorly understood and consequently limit the development of effective treatment. In this study, we aimed to explore the molecular signaling cascades in the lungs of a PPHN animal model and used primary cultured rat pulmonary microvascular endothelial cells to analyze the physiological benefits of ghrelin during the pathogenesis of PPHN. Randomly selected newborn rats were exposed to hypoxia (10-12%) or room air and received daily s.c. injections of ghrelin (150 μg/kg) or saline. After 2 weeks, pulmonary hemodynamics and morphometry were assessed in the rats. Compared with the control, hypoxia increased pulmonary arterial pressure, right ventricle (RV) hypertrophy, and arteriolar wall thickness. Ghrelin treatment reduced both the magnitude of PH and the RV/(left ventricle+septum (Sep)) weight ratio. Ghrelin protected neonatal rats from hypoxia-induced PH via the upregulation of phosphorylation of glycogen synthase kinase 3β (p-GSK3β)/β-catenin signaling and associated with β-catenin translocation to the nucleus in the presence of growth hormone secretagogue receptor-1a. Our findings suggest that s.c. administration of ghrelin improved PH and attenuated pulmonary vascular remodeling after PPHN. These beneficial effects may be mediated by the regulation of p-GSK3β/β-catenin expression. We propose ghrelin as a novel potential therapeutic agent for PPHN.     

Responsiveness to inhaled nitric oxide is a predictor for mid-term survival in adult patients with congenital heart defects and pulmonary arterial hypertension.

BACKGROUND: It was previously demonstrated that in adults with congenital heart disease and pulmonary arterial hypertension and/or the Eisenmenger syndrome, the pulmonary circulation remained responsive to inhaled nitric oxide (iNO). We wanted to evaluate whether the responsiveness to iNO was related to mid-term outcome in these patients. METHODS: In 21 consecutive patients, total pulmonary vascular resistance (TPR) was measured at baseline, after 5 min iNO (80 ppm), and after NO withdrawal. Patients were considered responders when TPR was reduced by at least 20% during NO inhalation or when TPR increased by more than 10% after NO withdrawal. Responders and non-responders were followed prospectively and the primary endpoint of the study was cardiopulmonary death, the secondary endpoint the combination of death, need for treatment with prostacyclin or heart-lung transplantation. Kaplan-Meier survival curves for both groups were plotted and compared using log rank testing. RESULTS: Ten patients were considered responders (four male, median age 25 years, Q1 19 and Q3 66 years), while 11 patients did not respond (two male, median age 27 years, Q1 18 and Q3 40 years). The median follow-up time of the total group was 5.0 years (Q1 3.2 and Q3 5.7 years). Four of the non-responders died a cardiovascular death; none of the responders died. The difference in survival between responders and non-responders was statistically significant. For the secondary endpoint, no significant differences were found between both groups. CONCLUSIONS: The responsiveness to inhaled NO in adult patients with pulmonary arterial hypertension and/or the Eisenmenger syndrome is related to mid-term outcome. These findings might be important for risk stratification and the choice of treatment in this specific patient population.