Supraventricular Tachycardia in Infants With Congenital Diaphragmatic Hernia: Prevalence, Associations, and Outcomes.

OBJECTIVES: To characterize the prevalence, associations, management, and outcomes of supraventricular tachycardia (SVT) in neonates with congenital diaphragmatic hernia (CDH). DESIGN: Retrospective chart and cardiology code review within a cohort of patients with CDH was used to define a subpopulation with atrial arrhythmia. SVT mechanisms were confirmed by electrocardiogram analysis. Cox proportional hazard regression identified risk factors for SVT and association with clinical outcomes. SETTING: Medical Surgical ICU in a single, tertiary center, Boston Children's Hospital. PATIENTS: Eligible patients included neonates presenting with classic Bochdalek posterolateral CDH between 2005 and 2017, excluding newborns with Morgagni hernia or late diagnoses of CDH (>28 d). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: SVT arose in 25 of 232 neonates with CDH, (11%); 14 of 25 infants (56%) had recurrent SVT; atrioventricular node-dependent tachycardia was the most frequent mechanism (32%). The majority (71%) of SVT episodes received intervention. Nine patients (36%) received preventative antiarrhythmic medications. SVT was associated with lower Apgar score at 1 min, structural heart disease, larger defect size, extracorporeal membrane oxygenation (ECMO) support, and prostaglandin therapy for ductal patency as well as hospital stay greater than or equal to 8 weeks and use of supplemental oxygen at discharge. CONCLUSIONS: SVT can occur in neonates with CDH and frequently requires treatment. Odds of occurrence are increased with greater CDH disease severity, ECMO, and prostaglandin use. In unadjusted logistic regression analysis, SVT was associated with adverse hospital outcomes, underscoring the importance of recognition and management in this vulnerable population.

Clinical Characteristics and Outcomes of Children with Acute Catastrophic Brain Injury: A 13-Year Retrospective Cohort Study.

BACKGROUND: The purpose of this study was to describe and analyze clinical characteristics and outcomes in children with acute catastrophic brain injury (CBI). METHODS: This was a single-center, 13-year (2008-2020) retrospective cohort study of children in the pediatric and cardiac intensive care units with CBI, defined as (1) acute neurologic injury based on clinical and/or imaging findings, (2) the need for life-sustaining intensive care unit therapies, and (3) death or survival with a Glasgow Coma Scale score < 13 at discharge. Patients were excluded if they were discharged directly to home < 14 days from admission or had a chronic neurologic condition with a baseline Glasgow Coma Scale score < 13. The association between the primary outcome of death and clinical variables was analyzed by using Kaplan-Meier estimates and multivariable Cox proportional hazard models. Outcomes assessed after discharge were technology dependence, neurologic deficits, and Functional Status Score. Improved functional status was defined as a change in total Functional Status Score [Formula: see text] 2. RESULTS: Of 106 patients (58% boys, median age 3.9 years) with CBI, 86 (81%) died. Withdrawal of life-sustaining therapies was the most common cause of death (60 of 86, 70%). In our multivariable analysis, each unit increase in admission pediatric sequential organ failure assessment score was associated with 10% greater hazard of death (hazard ratio 1.10, 95% confidence interval 1.04-1.17, p < .01). After controlling for admission pediatric sequential organ failure assessment scores, compared with those of patients with traumatic brain injury, all other etiologies of CBI were associated with a greater hazard of death (p = .02; hazard ratio 3.76-10). The median survival time for the cohort was 22 days (95% confidence interval 14-37 days). Of 23 survivors to hospital discharge, 20 were still alive after a median of 2 years (interquartile range 1-3 years), 6 of 20 (30%) did not have any technology dependence, 12 of 20 (60%) regained normal levels of alertness and responsiveness, and 15 of 20 (75%) had improved functional status. CONCLUSIONS: Most children with acute CBI died within 1 month of hospitalization. Having traumatic brain injury as the etiology of CBI was associated with greater survival, whereas increased organ dysfunction score on admission was associated with a higher hazard of mortality. Of the survivors, some recovered consciousness and functional status and did not require permanent technology dependence. Larger prospective studies are needed to improve prediction of CBI among critically ill children, understand factors guiding clinician and family decisions on the continuation or withdrawal of life-sustaining treatments, and characterize the natural history and long-term outcomes among CBI survivors.

A Novel Protective Role for Matrix Metalloproteinase-8 in the Pulmonary Vasculature.

Rationale: Mechanical signaling through cell-matrix interactions plays a major role in progressive vascular remodeling in pulmonary arterial hypertension (PAH). MMP-8 (matrix metalloproteinase-8) is an interstitial collagenase involved in regulating inflammation and fibrosis of the lung and systemic vasculature, but its role in PAH pathogenesis remains unexplored. Objectives: To evaluate MMP-8 as a modulator of pathogenic mechanical signaling in PAH. Methods: MMP-8 levels were measured in plasma from patients with pulmonary hypertension (PH) and controls by ELISA. MMP-8 vascular expression was examined in lung tissue from patients with PAH and rodent models of PH. MMP-8-/- and MMP-8+/+ mice were exposed to normobaric hypoxia or normoxia for 4-8 weeks. PH severity was evaluated by right ventricular systolic pressure, echocardiography, pulmonary artery morphometry, and immunostaining. Proliferation, migration, matrix component expression, and mechanical signaling were assessed in MMP-8-/- and MMP-8+/+ pulmonary artery smooth muscle cells (PASMCs). Measurements and Main Results: MMP-8 expression was significantly increased in plasma and pulmonary arteries of patients with PH compared with controls and induced in the pulmonary vasculature in rodent PH models. Hypoxia-exposed MMP-8-/- mice had significant mortality, increased right ventricular systolic pressure, severe right ventricular dysfunction, and exaggerated vascular remodeling compared with MMP-8+/+ mice. MMP-8-/- PASMCs demonstrated exaggerated proliferation and migration mediated by altered matrix protein expression, elevated integrin-ß3 levels, and induction of FAK (focal adhesion kinase) and downstream YAP (Yes-associated protein)/TAZ (transcriptional coactivator with PDZ-binding motif) activity. Conclusions: MMP-8 is a novel protective factor upregulated in the pulmonary vasculature during PAH pathogenesis. MMP-8 opposes pathologic mechanobiological feedback by altering matrix composition and disrupting integrin-ß3/FAK and YAP/TAZ-dependent mechanical signaling in PASMCs.

Echocardiographic markers of pulmonary hemodynamics and right ventricular hypertrophy in rat models of pulmonary hypertension.

Echocardiography is the gold standard non-invasive technique to diagnose pulmonary hypertension. It is also an important modality used to monitor disease progression and response to treatment in patients with pulmonary hypertension. Surprisingly, only few studies have been conducted to validate and standardize echocardiographic parameters in experimental animal models of pulmonary hypertension. We sought to define cut-off values for both invasive and non-invasive measures of pulmonary hemodynamics and right ventricular hypertrophy that would reliably diagnose pulmonary hypertension in three different rat models. The study was designed in two phases: (1) a derivation phase to establish the cut-off values for invasive measures of right ventricular systolic pressure, Fulton's index (right ventricular weight/left ventricle + septum weight), right ventricular to body weight ratio, and non-invasive echocardiographic measures of pulmonary arterial acceleration time, pulmonary arterial acceleration time to ejection time ratio and right ventricular wall thickness in diastole in the hypoxic and monocrotaline rat models of pulmonary hypertension and (2) a validation phase to test the performance of the cut-off values in predicting pulmonary hypertension in an independent cohort of rats with Sugen/hypoxia-induced pulmonary hypertension. Our study demonstrates that right ventricular systolic pressure ≥35.5 mmHg and Fulton's Index ≥0.34 are highly sensitive (>94%) and specific (>91%) cut-offs to distinguish animals with pulmonary hypertension from controls. When pulmonary arterial acceleration time/ejection time and right ventricular wall thickness in diastole were both measured, a result of either pulmonary arterial acceleration time/ejection time ≤0.25 or right ventricular wall thickness in diastole ≥1.03 mm detected right ventricular systolic pressure ≥35.5 mmHg or Fulton's Index ≥0.34 with a sensitivity of 88% and specificity of 100%. With properly validated non-invasive echocardiography measures of right ventricular performance in rats that accurately predict invasive measures of pulmonary hemodynamics, future studies can now utilize these markers to test the efficacy of different treatments with preclinical therapeutic modeling.

Heme oxygenase-1 dampens the macrophage sterile inflammasome response and regulates its components in the hypoxic lung.

Exposure to hypoxia causes an inflammatory reaction in the mouse lung, and this response can be modulated by overexpressing the hypoxia-inducible stress-response enzyme, heme oxygenase-1 (HO-1). We hypothesized that the inflammasome activity may be a central pathway by which HO-1 controls pulmonary inflammation following alveolar hypoxia. Therefore, we investigated whether HO-1 controls inflammasome activation by altering its expression in macrophages primed with classic NOD-like receptor containing a pyrin domain 3 (NLRP3) inducers, and in murine lungs lacking HO-1 and exposed to acute hypoxia. We found that lack of HO-1 activated lipopolysaccharide (LPS) and ATP-treated bone marrow-derived macrophages, causing an increase in secreted levels of cleaved interleukin (IL)-1B, IL-18, and caspase-1, markers of increased inflammasome activity, whereas HO-1 overexpression suppressed IL-1B, NLRP3, and IL-18. The production of cleaved IL-1B and the activation of caspase-1 in LPS- and ATP-primed macrophages were inhibited by hemin, an HO-1 inducer, and two HO-1 enzymatic products [bilirubin and carbon monoxide (CO)]. Exposure of mice to hypoxia induced the expression of several inflammasome mRNA components (IL-1B, Nlrp3, and caspase-1), and this was further augmented by HO-1 deficiency. This pronounced inflammasome activation was detected as increased protein levels of apoptosis-associated speck-like protein containing a COOH-terminal caspase recruitment domain, IL-18, procaspase-1, and cleaved caspase-1 in the lungs of hypoxic mice. Systemically, Hmox1-deficient mice showed increased basal levels of IL-18 that were further increased after 48 h of hypoxic exposure. Taken together, these finding point to a pivotal role for HO-1 in the control of baseline and hypoxic inflammasome signaling, perhaps through the antioxidant properties of bilirubin and CO's pleiotropic effects.

Mesenchymal Stromal Cell Exosomes Ameliorate Experimental Bronchopulmonary Dysplasia and Restore Lung Function through Macrophage Immunomodulation.

RATIONALE: Mesenchymal stem/stromal cell (MSC) therapies have shown promise in preclinical models of pathologies relevant to newborn medicine, such as bronchopulmonary dysplasia (BPD). We have reported that the therapeutic capacity of MSCs is comprised in their secretome, and demonstrated that the therapeutic vectors are exosomes produced by MSCs (MSC-exos). OBJECTIVES: To assess efficacy of MSC-exo treatment in a preclinical model of BPD and to investigate mechanisms underlying MSC-exo therapeutic action. METHODS: Exosomes were isolated from media conditioned by human MSC cultures. Newborn mice were exposed to hyperoxia (HYRX; 75% O2), treated with exosomes on Postnatal Day (PN) 4 and returned to room air on PN7. Treated animals and appropriate controls were harvested on PN7, -14, or -42 for assessment of pulmonary parameters. MEASUREMENTS AND MAIN RESULTS: HYRX-exposed mice presented with pronounced alveolar simplification, fibrosis, and pulmonary vascular remodeling, which was effectively ameliorated by MSC-exo treatment. Pulmonary function tests and assessment of pulmonary hypertension showed functional improvements after MSC-exo treatment. Lung mRNA sequencing demonstrated that MSC-exo treatment induced pleiotropic effects on gene expression associated with HYRX-induced inflammation and immune responses. MSC-exos modulate the macrophage phenotype fulcrum, suppressing the proinflammatory "M1" state and augmenting an antiinflammatory "M2-like" state, both in vitro and in vivo. CONCLUSIONS: MSC-exo treatment blunts HYRX-associated inflammation and alters the hyperoxic lung transcriptome. This results in alleviation of HYRX-induced BPD, improvement of lung function, decrease in fibrosis and pulmonary vascular remodeling, and amelioration of pulmonary hypertension. The MSC-exo mechanism of action is associated with modulation of lung macrophage phenotype.

Continuous infusion, general anesthesia and other intensive care treatment for uncontrolled status epilepticus.

PURPOSE OF REVIEW: To discuss the use of continuous infusions, general anesthesia, hypothermia, and ketogenic diet as treatment for uncontrolled status epilepticus in pediatric patients. RECENT FINDINGS: Recent studies demonstrate that clinical practitioners have a hierarchy in approach in controlling refractory status epilepticus (RSE) and super-refractory status epilepticus in children. In the acute setting of RSE, midazolam achieves clinical seizure control at a mean of 41 min after starting an infusion. When midazolam has failed to control RSE, the evidence points to barbiturate anesthesia as the next frequently used option. When both midazolam and barbiturates have failed, use of isoflurane or ketamine anesthesia has been tried at a mean of 10 days after RSE onset, although the studies are largely anecdotal. Increasingly, the use of therapeutic hypothermia or ketogenic diet is described as a strategy for super-refractory status epilepticus, and better evidence for their use may become available from ongoing randomized studies. SUMMARY: Uncontrolled episodes of status epilepticus require intensive care treatment and the literature describes a common pathway of care used by many. However, cases of truly refractory and super-refractory status epilepticus are seen infrequently at any given institution. One strategy to improve the quality of evidence is to develop prospective, national and multinational case registries to determine the range of presentations and causes, efficacy of treatments, and clinical outcomes.

The Sugen 5416/hypoxia mouse model of pulmonary hypertension revisited: long-term follow-up.

The combination of a vascular endothelial growth factor receptor antagonist, Sugen 5416 (SU5416), and chronic hypoxia is known to cause pronounced pulmonary hypertension (PH) with angioobliterative lesions in rats and leads to exaggerated PH in mice as well. We sought to determine whether weekly SU5416 injections during 3 weeks of hypoxia leads to long-term development of angioobliterative lesions and sustained or progressive PH in mice. Male C57BL/6J mice were injected with SU5416 (SuHx) or vehicle (VehHx) weekly during 3 weeks of exposure to 10% oxygen. Echocardiographic and invasive measures of hemodynamics and pulmonary vascular morphometry were performed after the 3-week hypoxic exposure and after 10 weeks of recovery in normoxia. SuHx led to higher right ventricular (RV) systolic pressure and RV hypertrophy than VehHx after 3 weeks of hypoxia. Ten weeks after hypoxic exposure, RV systolic pressure decreased but remained elevated in SuHx mice compared with VehHx or normoxic control mice, but RV hypertrophy had resolved. After 3 weeks of hypoxia and 10 weeks of follow-up in normoxia, tricuspid annular plane systolic excursion was significantly decreased, indicating decreased systolic RV function. Very few angioobliterative lesions were found at the 10-week follow-up time point in SuHx mouse lungs. In conclusion, SU5416 combined with 3 weeks of hypoxia causes a more profound PH phenotype in mice than hypoxia alone. PH persists over 10 weeks of normoxic follow-up in SuHx mice, but significant angioobliterative lesions do not occur, and neither PH nor RV dysfunction worsens. The SuHx mouse model is a useful adjunct to other PH models, but the search will continue for a mouse model that better recapitulates the human phenotype.

Mechanical ventilation guided by electrical impedance tomography in experimental acute lung injury.

OBJECTIVE: To utilize real-time electrical impedance tomography to guide lung protective ventilation in an animal model of acute respiratory distress syndrome. DESIGN: Prospective animal study. SETTING: Animal research center. SUBJECTS: Twelve Yorkshire swine (15 kg). INTERVENTIONS: Lung injury was induced with saline lavage and augmented using large tidal volumes. The control group (n = 6) was ventilated using ARDSnet guidelines, and the electrical impedance tomography-guided group (n = 6) was ventilated using guidance with real-time electrical impedance tomography lung imaging. Regional electrical impedance tomography-derived compliance was used to maximize the recruitment of dependent lung and minimize overdistension of nondependent lung areas. Tidal volume was 6 mL/kg in both groups. Computed tomography was performed in a subset of animals to define the anatomic correlates of electrical impedance tomography imaging (n = 5). Interleukin-8 was quantified in serum and bronchoalveolar lavage samples. Sections of dependent and nondependent regions of the lung were fixed in formalin for histopathologic analysis. MEASUREMENTS AND MAIN RESULTS: Positive end-expiratory pressure levels were higher in the electrical impedance tomography-guided group (14.3 cm H2O vs. 8.6 cm H2O; p < 0.0001), whereas plateau pressures did not differ. Global respiratory system compliance was improved in the electrical impedance tomography-guided group (6.9 mL/cm H2O vs. 4.7 mL/cm H2O; p = 0.013). Regional electrical impedance tomography-derived compliance of the most dependent lung region was increased in the electrical impedance tomography group (1.78 mL/cm H2O vs. 0.99 mL/cm H2O; p = 0.001). Pao2/FIO2 ratio was higher and oxygenation index was lower in the electrical impedance tomography-guided group (Pao2/FIO2: 388 mm Hg vs. 113 mm Hg, p < 0.0001; oxygentation index, 6.4 vs. 15.7; p = 0.02) (all averages over the 6-hr time course). The presence of hyaline membranes (HM) and airway fibrin (AF) was significantly reduced in the electrical impedance tomography-guided group (HMEIT 42% samples vs. HMCONTROL 67% samples, p < 0.01; AFEIT 75% samples vs. AFCONTROL 100% samples, p < 0.01). Interleukin-8 level (bronchoalveolar lavage) did not differ between the groups. The upper and lower 95% limits of agreement between electrical impedance tomography and computed tomography were ± 16%. CONCLUSIONS: Electrical impedance tomography-guided ventilation resulted in improved respiratory mechanics, improved gas exchange, and reduced histologic evidence of ventilator-induced lung injury in an animal model. This is the first prospective use of electrical impedance tomography-derived variables to improve outcomes in the setting of acute lung injury.

Exosomes mediate the cytoprotective action of mesenchymal stromal cells on hypoxia-induced pulmonary hypertension.

BACKGROUND: Hypoxia induces an inflammatory response in the lung manifested by alternative activation of macrophages with elevation of proinflammatory mediators that are critical for the later development of hypoxic pulmonary hypertension. Mesenchymal stromal cell transplantation inhibits lung inflammation, vascular remodeling, and right heart failure and reverses hypoxic pulmonary hypertension in experimental models of disease. In this study, we aimed to investigate the paracrine mechanisms by which mesenchymal stromal cells are protective in hypoxic pulmonary hypertension. METHODS AND RESULTS: We fractionated mouse mesenchymal stromal cell-conditioned media to identify the biologically active component affecting in vivo hypoxic signaling and determined that exosomes, secreted membrane microvesicles, suppressed the hypoxic pulmonary influx of macrophages and the induction of proinflammatory and proproliferative mediators, including monocyte chemoattractant protein-1 and hypoxia-inducible mitogenic factor, in the murine model of hypoxic pulmonary hypertension. Intravenous delivery of mesenchymal stromal cell-derived exosomes (MEX) inhibited vascular remodeling and hypoxic pulmonary hypertension, whereas MEX-depleted media or fibroblast-derived exosomes had no effect. MEX suppressed the hypoxic activation of signal transducer and activator of transcription 3 (STAT3) and the upregulation of the miR-17 superfamily of microRNA clusters, whereas it increased lung levels of miR-204, a key microRNA, the expression of which is decreased in human pulmonary hypertension. MEX produced by human umbilical cord mesenchymal stromal cells inhibited STAT3 signaling in isolated human pulmonary artery endothelial cells, demonstrating a direct effect of MEX on hypoxic vascular cells. CONCLUSION: This study indicates that MEX exert a pleiotropic protective effect on the lung and inhibit pulmonary hypertension through suppression of hyperproliferative pathways, including STAT3-mediated signaling induced by hypoxia.

Mesenchymal stem cell-mediated reversal of bronchopulmonary dysplasia and associated pulmonary hypertension.

Clinical trials have failed to demonstrate an effective preventative or therapeutic strategy for bronchopulmonary dysplasia (BPD), a multifactorial chronic lung disease in preterm infants frequently complicated by pulmonary hypertension (PH). Mesenchymal stem cells (MSCs) and their secreted components have been shown to prevent BPD and pulmonary fibrosis in rodent models. We hypothesized that treatment with conditioned media (CM) from cultured mouse bone marrow-derived MSCs could reverse hyperoxia-induced BPD and PH. Newborn mice were exposed to hyperoxia (FiO(2)=0.75) for two weeks, were then treated with one intravenous dose of CM from either MSCs or primary mouse lung fibroblasts (MLFs), and placed in room air for two to four weeks. Histological analysis of lungs harvested at four weeks of age was performed to determine the degree of alveolar injury, blood vessel number, and vascular remodeling. At age six weeks, pulmonary artery pressure (PA acceleration time) and right ventricular hypertrophy (RVH; RV wall thickness) were assessed by echocardiography, and pulmonary function tests were conducted. When compared to MLF-CM, a single dose of MSC-CM-treatment (1) reversed the hyperoxia-induced parenchymal fibrosis and peripheral PA devascularization (pruning), (2) partially reversed alveolar injury, (3) normalized lung function (airway resistance, dynamic lung compliance), (4) fully reversed the moderate PH and RVH, and (5) attenuated peripheral PA muscularization associated with hyperoxia-induced BPD. Reversal of key features of hyperoxia-induced BPD and its long-term adverse effects on lung function can be achieved by a single intravenous dose of MSC-CM, thereby pointing toward a new therapeutic intervention for chronic lung diseases.

Improved pulmonary vascular reactivity and decreased hypertrophic remodeling during nonhypercapnic acidosis in experimental pulmonary hypertension.

Pulmonary hypertension (PH) is characterized by pulmonary arteriolar remodeling with excessive pulmonary vascular smooth muscle cell (VSMC) proliferation. This results in decreased responsiveness of pulmonary circulation to vasodilator therapies. We have shown that extracellular acidosis inhibits VSMC proliferation and migration in vitro. Here we tested whether induction of nonhypercapnic acidosis in vivo ameliorates PH and the underlying pulmonary vascular remodeling and dysfunction. Adult male Sprague-Dawley rats were exposed to hypoxia (8.5% O(2)) for 2 wk, or injected subcutaneously with monocrotaline (MCT, 60 mg/kg) to develop PH. Acidosis was induced with NH(4)Cl (1.5%) in the drinking water 5 days prior to and during the 2 wk of hypoxic exposure (prevention protocol), or after MCT injection from day 21 to 28 (reversal protocol). Right ventricular systolic pressure (RVSP) and Fulton's index were measured, and pulmonary arteriolar remodeling was analyzed. Pulmonary and mesenteric artery contraction to phenylephrine (Phe) and high KCl, and relaxation to acetylcholine (ACh) and sodium nitroprusside (SNP) were examined ex vivo. Hypoxic and MCT-treated rats demonstrated increased RVSP, Fulton's index, and pulmonary arteriolar thickening. In pulmonary arteries of hypoxic and MCT rats there was reduced contraction to Phe and KCl and reduced vasodilation to ACh and SNP. Acidosis prevented hypoxia-induced PH, reversed MCT-induced PH, and resulted in reduction in all indexes of PH including RVSP, Fulton's index, and pulmonary arteriolar remodeling. Pulmonary artery contraction to Phe and KCl was preserved or improved, and relaxation to ACh and SNP was enhanced in NH(4)Cl-treated PH animals. Acidosis alone did not affect the hemodynamics or pulmonary vascular function. Phe and KCl contraction and ACh and SNP relaxation were not different in mesenteric arteries of all groups. Thus nonhypercapnic acidosis ameliorates experimental PH, attenuates pulmonary arteriolar thickening, and enhances pulmonary vascular responsiveness to vasoconstrictor and vasodilator stimuli. Together with our finding that acidosis decreases VSMC proliferation, the results are consistent with the possibility that nonhypercapnic acidosis promotes differentiation of pulmonary VSMCs to a more contractile phenotype, which may enhance the effectiveness of vasodilator therapies in PH.

Impaired vasoconstriction and nitric oxide-mediated relaxation in pulmonary arteries of hypoxia- and monocrotaline-induced pulmonary hypertensive rats.

Pulmonary hypertension (PH) is a life-threatening disease with unclear vascular mechanisms. We tested whether PH involves abnormal pulmonary vasoconstriction and impaired vasodilation. Male Sprague-Dawley rats were exposed to hypoxia (9% O(2)) for 2 weeks or injected with single dose of monocrotaline (MCT, 60 mg/kg s.c.). Control rats were normoxic or injected with saline. After the hemodynamic measurements were performed, pulmonary and mesenteric arteries were isolated for measurement of vascular function. Hematocrit was elevated in hypoxic rats. Right ventricular systolic pressure and Fulton's Index [right/(left + septum) ventricular weight] were greater in hypoxic and MCT-treated rats than in normoxic rats. Pulmonary artery contraction by phenylephrine and 96 mM KCl was less in hypoxic and MCT-treated rats than in normoxic rats. Acetylcholine-induced relaxation was less in the pulmonary arteries of hypoxic and MCT-treated rats than of normoxic rats, suggesting reduced effects of endothelium-derived vasodilators. The nitric oxide synthase inhibitor, N(omega)-nitro-l-arginine methyl ester, and the guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, inhibited acetylcholine relaxation, suggesting that it was mediated by nitric oxide (NO)-cGMP. The NO donor sodium nitroprusside caused less relaxation in the pulmonary arteries of hypoxic and MCT-treated than of normoxic rats, suggesting decreased responsiveness of vascular smooth muscle cells (VSMCs) to vasodilators. Phenylephrine and KCl contraction and acetylcholine and sodium nitroprusside relaxation were not different in the mesenteric arteries from all groups. In lung tissue sections, the wall thickness of pulmonary arterioles was greater in hypoxic and MCT-treated rats than in normoxic rats. The specific reductions in pulmonary, but not systemic, arterial vasoconstriction and vasodilation in hypoxia- and MCT-induced PH are consistent with the possibility of de-differentiation of pulmonary VSMCs to a more proliferative/synthetic and less contractile phenotype in PH.

Divergent cardiopulmonary actions of heme oxygenase enzymatic products in chronic hypoxia.

BACKGROUND: Hypoxia and pressure-overload induce heme oxygenase-1 (HO-1) in cardiomyocytes and vascular smooth muscle cells (VSMCs). HO-1(-/-) mice exposed to chronic hypoxia develop pulmonary arterial hypertension (PAH) with exaggerated right ventricular (RV) injury consisting of dilation, fibrosis, and mural thrombi. Our objective was to identify the HO-1 product(s) mediating RV protection from hypoxic injury in HO-1(-/-) mice. METHODOLOGY/PRINCIPAL FINDINGS: HO-1(-/-) mice were exposed to seven weeks of hypoxia and treated with inhaled CO or biliverdin injections. CO reduced right ventricular systolic pressure (RVSP) and prevented hypoxic pulmonary arteriolar remodeling in both HO-1(-/-) and control mice. Biliverdin had no significant effect on arteriolar remodeling or RVSP in either genotype. Despite this, biliverdin prevented RV failure in the hypoxic HO-1(-/-) mice (0/14 manifested RV wall fibrosis or thrombus), while CO-treated HO-1(-/-) mice developed RV insults similar to untreated controls. In vitro, CO inhibited hypoxic VSMC proliferation and migration but did not prevent cardiomyocyte death from anoxia-reoxygenation (A-R). In contrast, bilirubin limited A-R-induced cardiomyocyte death but did not inhibit VSMC proliferation and migration. CONCLUSIONS/SIGNIFICANCE: CO and bilirubin have distinct protective actions in the heart and pulmonary vasculature during chronic hypoxia. Moreover, reducing pulmonary vascular resistance may not prevent RV injury in hypoxia-induced PAH; supporting RV adaptation to hypoxia and preventing RV failure must be a therapeutic goal.

Assessing the quality of case-control association studies on the genetic basis of sepsis.

OBJECTIVE: To define methodological standards that would improve the quality and reproducibility of case-control genetic association studies in sepsis. DESIGN: Summary of the published standards. RESULTS: Twelve main criteria and measures for evaluation of those criteria were developed from a variety of reviews and editorials on the subject. CONCLUSIONS: Case-control candidate gene association studies represent an important tool for understanding the role that genes play in the pathogenesis of sepsis. It is important, however, to understand the limitations of these studies and the need for replication.