The development of the pediatric stroke neuroimaging platform (PEDSNIP)

Childhood stroke occurs from birth to 18 years of age, ranks among the top ten childhood causes of death, and leaves lifelong neurological impairments. Arterial ischemic stroke in infancy and childhood occurs due to arterial occlusion in the brain, resulting in a focal lesion. Our understanding of mechanisms of injury and repair associated with focal injury in the developing brain remains rudimentary. Neuroimaging can reveal important insights into these mechanisms. In adult stroke population, multi-center neuroimaging studies are common and have accelerated the translation process leading to improvements in treatment and outcome. These studies are centered on the growing evidence that neuroimaging measures and other biomarkers (e.g., from blood and cerebrospinal fluid) can enhance our understanding of mechanisms of risk and injury and be used as complementary outcome markers. These factors have yet to be studied in pediatric stroke because most neuroimaging studies in this population have been conducted in single-centred, small cohorts. By pooling neuroimaging data across multiple sites, larger cohorts of patients can significantly boost study feasibility and power in elucidating mechanisms of brain injury, repair and outcomes. These aims are particularly relevant in pediatric stroke because of the decreased incidence rates and the lack of mechanism-targeted trials. Toward these aims, we developed the Pediatric Stroke Neuroimaging Platform (PEDSNIP) in 2015, funded by The Brain Canada Platform Support Grant, to focus on three identified neuroimaging priorities. These were: developing and harmonizing multisite clinical protocols, creating the infrastructure and methods to import, store and organize the large clinical neuroimaging dataset from multiple sites through the International Pediatric Stroke Study (IPSS), and enabling central searchability. To do this, developed a two-pronged approach that included building 1) A Clinical-MRI Data Repository (standard of care imaging) linked to clinical data and longitudinal outcomes and 2) A Research-MRI neuroimaging data set acquired through our extensive collaborative, multi-center, multidisciplinary network. This dataset was collected prospectively in eight North American centers to test the feasibility and implementation of harmonized advanced Research-MRI, with the addition of clinical information, genetic and proteomic studies, in a cohort of children presenting with acute ischemic stroke. Here we describe the process that enabled the development of PEDSNIP built to provide the infrastructure to support neuroimaging research priorities in pediatric stroke. Having built this Platform, we are now able to utilize the largest neuroimaging and clinical data pool on pediatric stroke data worldwide to conduct hypothesis-driven research. We are actively working on a bioinformatics approach to develop predictive models of risk, injury and repair and accelerate breakthrough discoveries leading to mechanism-targeted treatments that improve outcomes and minimize the burden following childhood stroke. This unique transformational resource for scientists and researchers has the potential to result in a paradigm shift in the management, outcomes and quality of life in children with stroke and their families, with far-reaching benefits for other brain conditions of people across the lifespan.

Modeling severe functional impairment or death following ECPR in pediatric cardiac patients: Planning for an interventional trial

AIM

We aimed to characterize extracorporeal CPR (ECPR) outcomes in our center and to model prediction of severe functional impairment or death at discharge.

METHODS

All ECPR events between 2011 and 2019 were reviewed. The primary outcome measure was severe functional impairment or death at discharge (Functional Status Score [FSS] ≥ 16). Organ dysfunction was graded using the Pediatric Logistic Organ Dysfunction Score-2, neuroimaging using the modified Alberta Stroke Program Early Computed Tomography Score. Multivariable logistic regression was used to model FSS ≥ 16 at discharge.

RESULTS

Of the 214 patients who underwent ECPR, 182 (median age 148 days, IQR 14-827) had an in-hospital cardiac arrest and congenital heart disease and were included in the analysis. Of the 110 patients who underwent neuroimaging, 52 (47%) had hypoxic-ischemic injury and 45 (41%) had hemorrhage. In-hospital mortality was 52% at discharge. Of these, 87% died from the withdrawal of life-sustaining therapies; severe neurologic injury was a contributing factor in the decision to withdraw life-sustaining therapies in 50%. The median FSS among survivors was 8 (IQR 6-8), and only one survivor had severe functional impairment. At 6 months, mortality was 57%, and the median FSS among survivors was 6 (IQR 6-8, n = 79). Predictive models identified FSS at admission, single ventricle physiology, extracorporeal membrane oxygenation (ECMO) duration, mean PELOD-2, and worst mASPECTS (or DWI-ASPECTS) as independent predictors of FSS ≥ 16 (AUC = 0.931) and at 6 months (AUC = 0.924).

CONCLUSION

Mortality and functional impairment following ECPR in children remain high. It is possible to model severe functional impairment or death at discharge with high accuracy using daily post-ECPR data up to 28 days. This represents a prognostically valuable tool and may identify endpoints for future interventional trials.

Spectrum of cerebral arteriopathies in children with arterial ischemic stroke

OBJECTIVE

To determine that children with arterial ischemic stroke (AIS) due to an identifiable arteriopathy are distinct from those without arteriopathy and that each arteriopathy subtype has unique and recognizable clinical features.

METHODS

We report a large, observational, multicenter cohort of children with AIS, age 1 month to 18 years, enrolled in the International Pediatric Stroke Study from 2003 to 2014. Clinical and demographic differences were compared by use of the Fisher exact test, with linear step-up permutation min-p adjustment for multiple comparisons. Exploratory analyses were conducted to evaluate differences between cases of AIS with and without arteriopathy and between arteriopathy subtypes.

RESULTS

Of 2,127 children with AIS, 725 (34%) had arteriopathy (median age 7.45 years). Arteriopathy subtypes included dissection (27%), moyamoya (24.5%), focal cerebral arteriopathy-inflammatory subtype (FCA-i; 15%), diffuse cerebral vasculitis (15%), and nonspecific arteriopathy (18.5%). Children with arteriopathic AIS were more likely to present between 6 and 9 years of age (odds ratio [OR] 1.93, p = 0.029) with headache (OR 1.55, p = 0.023), multiple infarctions (OR 2.05, p < 0.001), sickle cell anemia (OR 2.9, p = 0.007), and head/neck trauma (OR 1.93, p = 0.018). Antithrombotic use and stroke recurrence were higher in children with arteriopathy. Among arteriopathy subtypes, dissection was associated with male sex, older age, headache, and anticoagulant use; FCA-i was associated with hemiparesis and single infarcts; moyamoya was associated with seizures and recurrent strokes; and vasculitis was associated with bilateral infarctions.

CONCLUSION

Specific clinical profiles are associated with cerebral arteriopathies in children with AIS. These observations may be helpful indicators in guiding early diagnosis and defining subgroups who may benefit most from future therapeutic trials.

Arterial Ischemic Stroke Secondary to Cardiac Disease in Neonates and Children

OBJECTIVE

We describe the risk factors for peri-procedural and spontaneous arterial ischemic stroke (AIS) in children with cardiac disease.

METHODS

We identified children with cardiac causes of AIS enrolled in the International Pediatric Stroke Study registry from January 2003 to July 2014. Isolated patent foramen ovale was excluded. Peri-procedural AIS (those occurring during or within 72 hours of cardiac surgery, cardiac catheterization, or mechanical circulatory support) and spontaneous AIS that occurred outside of these time periods were compared.

RESULTS

We identified 672 patients with congenital or acquired cardiac disease as the primary risk factor for AIS. Among these, 177 patients (26%) had peri-procedural AIS and 495 patients (74%) had spontaneous AIS. Among non-neonates, spontaneous AIS occurred at older ages (median 4.2 years, interquartile range 0.97 to 12.4) compared with peri-procedural AIS (median 2.4 years, interquartile range 0.35 to 6.1, P < 0.001). About a third of patients in both groups had a systemic illness at the time of AIS. Patients who had spontaneous AIS were more likely to have a preceding thrombotic event (16 % versus 9 %, P = 0.02) and to have a moderate or severe neurological deficit at discharge (67% versus 33%, P = 0.01) compared to those with peri-procedural AIS.

CONCLUSIONS

Children with cardiac disease are at risk for AIS at the time of cardiac procedures but also outside of the immediate 72 hours after procedures. Many have acute systemic illness or thrombotic event preceding AIS, suggesting that inflammatory or prothrombotic conditions could act as a stroke trigger in this susceptible population.

Abstract 19: Clinical and Neuroimaging Profile of Children With Arterial Ischemic Stroke Due to Cerebral Arteriopathy - Results From the International Pediatric Stroke Study (IPSS)

Introduction: Cerebral arteriopathies are frequently identified in children with arterial ischemic stroke (AIS), and are distinguished by high stroke recurrence. However, the clinical and neuroimaging profiles of AIS due to cerebral arteriopathy versus non- arteriopathy have not been compared.

Hypothesis: We hypothesized that children with AIS due to arteriopathy would differ in their demographic, clinical, and radiographic presentation from those without arteriopathy.

Methods: We report a large, prospective, multicentre cohort of children, 1 month - 17 years, with AIS, enrolled in the International Pediatric Stroke Study, 2003-2014. Those with arteriopathy including focal cerebral arteriopathy, dissection, moyamoya, vasculitis and non-specific arteriopathies, were compared to those with non-arteriopathic stroke etiologies.

Results: Of 2127 children with AIS, 725(34%) had arteriopathy (58% male, mean age 8.1years). The remaining 1402(66%) had non-arteriopathic AIS. Arteriopathy was associated with older age, but not a specific gender or ethnicity. Geographic differences were observed. Children with arteriopathy were likely to present with hemiparesis, dysarthria, ataxia, headache, preceding/concurrent thromboembolic events and without seizures. Risk factors associated with arteriopathy included sickle anemia, head/neck trauma and lack of acute systemic disease. Radiological associations with arteriopathy included right sided unilateral or bilateral stroke, multiple infarcts and relative reduction in occurrence of intracranial hemorrhage. On multivariate analysis, headache (p=0.006), additional thromboembolic events (p=0.007), multiple infarcts (p=0.002) and lack of seizures (p=0.001) were independently associated with arteriopathy.

Conclusions: Specific clinical profiles are associated with arteriopathy in children with AIS and may guide the clinician in early diagnostic evaluations and management.

Early-Term Birth in Single-Ventricle Congenital Heart Disease After the Fontan Procedure: Neurodevelopmental and Psychiatric Outcomes

OBJECTIVES

To investigate the long-term impact of early-term birth (37-38 weeks' gestation) relative to full-term birth (≥39 weeks' gestation) on neurodevelopmental and psychiatric outcomes in adolescents with single-ventricle congenital heart disease (CHD).

STUDY DESIGN

This cross-sectional cohort study analyzed retrospective medical records from full term adolescents with single-ventricle CHD who underwent the Fontan procedure. Participants underwent neurodevelopmental and psychiatric evaluations, as well as structural brain magnetic resonance imaging. Early-term born adolescents were compared with full-term born adolescents using regression models with adjustments for family social status, birth weight, and genetic abnormality status. Medical and demographic risk factors were examined as well.

RESULTS

Compared with the full-term group (n = 100), adolescents born early term (n = 33) scored significantly worse on daily-life executive functions, as measured by the Behavior Rating Inventory of Executive Function parent-report (mean scores: early term, 62.0 ± 10.9; full-term, 55.6 ± 12.2; P = .009) and self-report (P = .02) composites. Adolescents born early term were more likely than those born full term to have a lifetime attention-deficit/hyperactivity disorder (ADHD) diagnosis (early term, 55%; full term, 26%; P = .001). The early-term group also displayed greater psychiatric symptom severity, as indicated by the clinician-reported Brief Psychiatric Rating Scale (mean score: early term, 16.1 ± 8.6; full-term, 12.5 ± 8.2; P = .007).

CONCLUSION

Early-term birth is associated with greater prevalence of executive dysfunction, ADHD diagnosis, and psychiatric problems in adolescents with single-ventricle CHD. Early-term birth should be included as a potential risk factor in the algorithm for closer developmental surveillance in CHD.

Abstract WMP98: Thrombophilia Risk Factors in Perinatal Stroke: 213 Consecutive Cases

Introduction: Perinatal stroke, including neonatal and presumed perinatal presentation, is the most common type of pediatric stroke. No guidelines exist for evaluation after perinatal stroke and the roles of thrombophilia, arteriopathy and cardiac anomalies are unclear. We took a systematic approach to perinatal stroke evaluation to better understand these risk factors.

Hypothesis: Thrombophilia, arteriopathy and cardiac anomalies are more common in perinatal stroke and may predict recurrence.

Methods: After IRB-approval, we reviewed records of perinatal stroke patients from August 2008 to July 2015. Demographics, echocardiography, MRA and thrombophilia testing were collected. Statistical analysis is descriptive.

Results: Among 213 children with perinatal stroke, 92 (43.2%) were female and mean age at diagnosis was 1.56 years. Caucasians comprised 69.5%, African-Americans, 7.5%, Asians, 1.9%, other, 8% and undeclared, 13.1%. Presentation was neonatal (113, 53.1%) or presumed perinatal (100, 46.9%). Strokes were classified as arterial (140, 65.7%), venous (51, 23.9%), both (4, 1.9%) or uncertain (19, 8.5%) by imaging. Mean length of follow-up was 3.2 years. Of 213 patients, 10 (4.7%) experienced recurrent events (4 transient ischemic attack, 3 sinovenous thrombosis and 3 arterial ischemic stroke). Thrombophilia data are presented in Table 1. After excluding venous events, 162 patients were evaluated for arteriopathy, cardiac risk factors and recurrence. Of eight recurrences in this group, none had arteriopathy, 3 (37.5%) had patent foramen ovale and none had other cardiac risk factors, compared to 5/108 (4.6%), 52/102 (51%) and 7/102 (6.8%) in the non-recurrent cases.

Conclusions: Arteriopathy and cardiac anomalies were not associated with recurrence. Some thrombophilia tests appear enriched in perinatal stroke. With few cases of recurrence after perinatal stroke, it is unclear whether thrombophilia predicts recurrence.

X-linked creatine transporter defect: a report on two unrelated boys with a severe clinical phenotype

We report two unrelated boys with the X-linked creatine transporter defect (CRTR) and clinical features more severe than those previously described with this disorder. These two boys presented at ages 12 and 30 months with severe mental retardation, absent speech development, hypotonia, myopathy and extra-pyramidal movement disorder. One boy has seizures and some dysmorphic features; he also has evidence of an oxidative phosphorylation defect. They both had classical absence of creatine peak on brain magnetic resonance spectroscopy (MRS). In one, however, this critical finding was overlooked in the initial interpretation and was discovered upon subsequent review of the MRS. Molecular studies showed large genomic deletions of a large part of the 3' end of the complete open reading frame of the SLC6A8 gene. This report emphasizes the importance of MRS in evaluating neurological symptoms, broadens the phenotypic spectrum of CRTR and adds knowledge about the pathogenesis of creatine depletion in the brain and retina.

Practice parameter: neuroimaging of the neonate: report of the Quality Standards Subcommittee of the American Academy of Neurology and the Practice Committee of the Child Neurology Society

OBJECTIVE

The authors reviewed available evidence on neonatal neuroimaging strategies for evaluating both very low birth weight preterm infants and encephalopathic term neonates.

IMAGING FOR THE PRETERM NEONATE

Routine screening cranial ultrasonography (US) should be performed on all infants of <30 weeks' gestation once between 7 and 14 days of age and should be optimally repeated between 36 and 40 weeks' postmenstrual age. This strategy detects lesions such as intraventricular hemorrhage, which influences clinical care, and those such as periventricular leukomalacia and low-pressure ventriculomegaly, which provide information about long-term neurodevelopmental outcome. There is insufficient evidence for routine MRI of all very low birth weight preterm infants with abnormal results of cranial US.

IMAGING FOR THE TERM INFANT

Noncontrast CT should be performed to detect hemorrhagic lesions in the encephalopathic term infant with a history of birth trauma, low hematocrit, or coagulopathy. If CT findings are inconclusive, MRI should be performed between days 2 and 8 to assess the location and extent of injury. The pattern of injury identified with conventional MRI may provide diagnostic and prognostic information for term infants with evidence of encephalopathy. In particular, basal ganglia and thalamic lesions detected by conventional MRI are associated with poor neurodevelopmental outcome. Diffusion-weighted imaging may allow earlier detection of these cerebral injuries.

RECOMMENDATIONS

US plays an established role in the management of preterm neonates of <30 weeks' gestation. US also provides valuable prognostic information when the infant reaches 40 weeks' postmenstrual age. For encephalopathic term infants, early CT should be used to exclude hemorrhage; MRI should be performed later in the first postnatal week to establish the pattern of injury and predict neurologic outcome.

p27-p16 fusion gene inhibits angioplasty-induced neointimal hyperplasia and coronary artery occlusion

Inhibition of proliferative neointima formed by vascular smooth muscle cells is a potential target in preventing angioplasty-induced restenosis. We have created a potent antiproliferative by fusing the active regions of the p27 and p16 cell cycle inhibitors. Intravascular delivery of a replication-deficient adenoviral vector (AV) encoding this p27-p16 fusion protein, named W9, inhibited balloon injury-induced neointimal hyperplasia in rabbit carotid arteries. In a therapeutically more relevant model, AV-W9 was delivered to balloon-injured porcine coronary arteries in vivo using an infusion catheter. Of the three coronary arteries, two were injured with a 15-mm balloon catheter and either were left untreated or were treated with 10(12) viral particles of either AV-W9 or a control null virus. AV-W9 treatment significantly inhibited neointimal hyperplasia in this porcine arterial balloon injury model compared with untreated or control virus-treated vessels. The average intimal area of the AV-W9-treated group 10 days after balloon injury and treatment was 0.42+/-0.36 mm(2), whereas the AV-null group demonstrated an intimal area of 0.70+/-0.52 mm(2). At day 10 the average intimal thickness of the AV-W9-treated vessels was 9.1 microm (n=5, x 20 magnification) compared with 21.2 microm (n=5, x 20 magnification) in control virus-treated vessels. This trend was also observed at 28 days after balloon injury and gene transfer during which AV-W9-treated vessels demonstrated an average intimal thickness of 4.7 microm (n=8, x 20 magnification) compared with 13.3 microm (n=3, x 20 magnification) in control virus-treated vessels and 7.3 microm (n=5, x 20 magnification) in the sham-treated vessels. The AV-W9 treatment was safe and well tolerated. These data suggest that AV-W9 gene therapy may be useful in preventing angioplasty-induced intimal hyperplasia in the coronary artery.

Fos-related antigen 2: potential mediator of the transcriptional activation in rat adrenal medulla evoked by repeated immobilization stress

The precise mechanisms by which beneficial responses to acute stress are transformed into long-term pathological effects of chronic stress are largely unknown. Western blot analyses revealed that members of the AP1 transcription factor family are differentially regulated by single and repeated stress in the rat adrenal medulla, suggesting distinct roles in establishing stress-induced patterns of gene expression in this tissue. The induction of c-fos was transient, whereas marked elevation of long-lasting Fos-related antigens, including Fra2, was observed after repeated immobilization. We investigated DNA protein interactions at the AP1-like promoter elements of two stress-responsive genes, tyrosine hydroxylase and dopamine beta-hydroxylase. Increased DNA-binding activity was displayed in adrenomedullary extract from repeatedly stressed rats, which was predominantly composed of c-Jun- and Fra2-containing dimers. The induction of Fra2 and increased AP1-like binding activity was reflected in sustained transcriptional activation of tyrosine hydroxylase and dopamine beta-hydroxylase genes after repeated episodes of stress. The functional link between Fra2 and regulation of tyrosine hydroxylase and dopamine beta-hydroxylase transcription was confirmed in PC12 cells coexpressing this factor and the corresponding promoter-reporter gene constructs. These studies emphasize the potential importance of stress-evoked increases in the expression of the Fra2 gene for in vivo adaptations of the adrenal catecholamine producing system.

The p53-independent tumoricidal activity of an adenoviral vector encoding a p27-p16 fusion tumor suppressor gene

We describe here that DE1-adenovirus vectors (AV) expressing a p27-p16 fusion molecule, termed W9, induce tumor cell apoptosis when overexpressed in a wide range of tumor cell types. However, in primary human cells derived from a variety of normal tissues, AV-W9 induced minimal apoptosis. In tumor cells AV-W9 demonstrated 5- to 50-fold greater tumoricidal activity than either of the parental molecules p16 and p27. In these studies, AV-W9 elicited apoptosis independent of the p53 and Rb status of the tumor cells. In several murine tumor models AV-W9 demonstrated p53-independent antitumor activity. It completely prevented tumor formation in two ex vivo models, whereas the parental molecules resulted in partial protection. Furthermore, AV-W9 induced tumor regression or suppressed tumor growth when introduced intratumorally into preestablished tumors in mice. This effect may be mediated through tumor cell apoptosis or antiangiogenic activity of AV-W9. Thus, this novel chimeric molecule is more potent and capable of killing a broader spectrum of tumors than the parental p16 and p27 molecules independent of the tumor cell p53 and phenotype and represents a powerful new therapeutic agent for cancer gene therapy.

Mitochondrial neurogastrointestinal encephalomyopathy: diagnosis by rectal biopsy

A 14-year-old girl with the mitochondrial neurogastrointestinal encephalopathy syndrome had an 8-year history of intestinal pseudoobstruction with abdominal pain, persistent vomiting, gastric and duodenal dilatation, and duodenal diverticulosis. The child appeared chronically malnourished and had severe growth failure. Multisystem involvement was evident with the presence of ptosis, external ophthalmoplegia, muscle wasting, peripheral neuropathy, and diffuse white matter disease seen on magnetic resonance imaging. Lactic acidosis and increased cerebrospinal fluid protein were observed. Mitochondrial enzyme analysis of fresh-frozen skeletal muscle revealed a respiratory chain defect. Molecular genetic studies showed multiple mitochondrial DNA deletions. Pathologic findings in the intestine included atrophy of the external layer of the muscularis propria and an increased number of abnormal-appearing mitochondria in ganglion and smooth-muscle cells. Microvesicular steatosis was observed in liver, skeletal, and gastrointestinal smooth muscle, and Schwann cells of peripheral nerve. Brightly eosinophilic inclusions in the cytoplasm of gastrointestinal ganglion cells were visible by light microscopy, which were confirmed to be megamitochondria by ultrastructural studies. This is the first report of abnormal mitochondria observed in intestinal ganglion and smooth-muscle cells in this syndrome.

Glucocorticoids elevate GTP cyclohydrolase I mRNA levels in vivo and in PC12 cells

GTP cyclohydrolase I (GTPCH) is the rate-limiting enzyme in the formation of tetrahydrobiopterin, the cofactor for catecholamine, indolamine and nitric oxide biosynthesis. The effect of glucocorticoids on GTPCH gene expression was examined by direct infusion of cortisol to rats and by incubation of PC12 cells with glucocorticoids. Northern blot analysis revealed that infusion of cortisol for 1 or 7 days elevated levels of the 3.6 kb GTPCH mRNA species in rat adrenal medulla, while the 1.2 kb mRNA species were only increased by 1 day cortisol. Cortisol administration to hypophysectomized animals elicited a 4-5-fold elevation in both forms of GTPCH mRNA. These results indicate that glucocorticoids may be directly involved in the regulation of adrenomedullary GTPCH mRNA levels by physiological stress. Incubation of PC12 cells with plasma from immobilized, but not control, animals increased the level of the 3.6 kb mRNA. Treatment of PC12 cells with dexamethasone for 12-48 h elicited a 4-6-fold elevation in both GTPCH mRNAs. Using the nuclear run-on assay, increased transcription of the GTPCH gene was observed in the rat adrenal medulla with immobilization stress, or in PC12 cells treated with dexamethasone. This is the first report that glucocorticoids can alter GTPCH expression.

A syndrome of multiorgan hyperplasia with features of gigantism, tumorigenesis, and female sterility in p27(Kip1)-deficient mice

SUMMARY

Targeted disruption of the murine p27(Kip1) gene caused a gene dose-dependent increase in animal size without other gross morphologic abnormalities. All tissues were enlarged and contained more cells, although endocrine abnormalities were not evident. Thymic hyperplasia was associated with increased T lymphocyte proliferation, and T cells showed enhanced IL-2 responsiveness in vitro. Thus, p27 deficiency may cause a cell-autonomous defect resulting in enhanced proliferation in response to mitogens. In the spleen, the absence of p27 selectively enhanced proliferation of hematopoietic progenitor cells. p27 deletion, like deletion of the Rb gene, uniquely caused neoplastic growth of the pituitary pars intermedia, suggesting that p27 and Rb function in the same regulatory pathway. The absence of p27 also caused an ovulatory defect and female sterility. Maturation of secondary ovarian follicles into corpora lutea, which express high levels of p27, was markedly impaired.

Mechanical Seal with Elastomeric Rotating Element. Part 2: Experimental Study

An innovative flexible faced mechanical shaft seal using common elastomeric materials was designed and tested to determine its friction coefficient at a wide range of temperatures and speeds, its rate of heat generation, and its feasibility for use in the process industry. The new seal was constructed using an elastomeric rotating element stretched over the sleeve to at least 20 percent of its original length and an unlapped silicon carbide stationary annular ring. It was found that the main advantage of the elastomeric seal is its ability to maintain stable lubrication with a fluid film considerably thinner than that of traditional hard face seals, and consequently achieve negligible net leakage. This is particularly significant with respect to control of volatile organic carbon emissions. An experimental device was designed for precise measurement of the friction coefficient as well as the long term friction behavior of seal pairs in a wide range of liquid pressure and temperature. The original data were obtained for friction coefficient of EPDM, HNBR, FKM, and TFE/P type elastomers in contact with silicon carbide in the temperature range 15–110°C, linear speeds 0–12 m/s, water pressure 0.15–0.40 MPa, and effective contact pressure 0.8–1.2 MPa. Experiments showed that the friction coefficient constantly grows, typically from 0.05 to 0.15 at sliding speeds of 2–12 m/s, with temperature increases from 15 to 70°C. The temperature behavior of the friction coefficient above 70°C greatly depends on the elastomer. For high temperature elastomers, such as FKM, the friction coefficient may decrease slightly at 70°C; whereas, for EPDM, it continues to increase as temperature increases.

Mechanical Seal with Elastomeric Rotating Element. Part 1: Theory of Operation

This paper presents the results of fundamental research on flexible faced mechanical shaft seals. The effect of stretch and preload on the contact stress were investigated using a nonlinear finite element modeling package. The characteristics of the rubber materials including the stress-strain curves to elongation at break were required to complete the analysis. Pressure forces resulting from the static pressure in the pump stuffing box as well as the friction effects on all contacting surfaces were considered in the model. Stress distribution across the contact surface established the basis for the formation of multiple distinct lips: at least one on the outside or fluid side of the seal and the other on the inside or air side of the seal. This phenomenon is explained by the step change in magnitude of axial stress while traversing the contact in the radial direction allowing the formation of exterior lips and the development of an annular region trapping debris products and process fluid. Photomicrographic images of the wear track taken with a Scanning Probe Microscope show distinct wear tracks and the topology of each. Although the chemical composition of the debris in the annular spaces has not been determined quantitatively, increased levels of fluorine were present, suggesting fragments of the monomers in the elastomeric rotary or migration of Teflon fillers. Axial variations in the stretched rotary dimensions (waviness) affects seal performance. Statistics for a typical batch of rotary elements are presented and a method of factoring these variations into the seal design is presented. The formation of axial waves on the contact vertex affects the seal performance and is considered in the final design of the seal pair configuration. The results of this work were incorporated into a suite of mechanical face seals covering shaft sizes from 1.125 to 5.000 inches using seven pairs of seals, each pair consisting of a stretched rotary sliding against an unlapped silicon carbide annular ring. Each of these seal pairs were tested on an experimental test device to determine the heat generation and friction coefficients for a wide range of temperature, pressure, speed, and sealing fluid. Results of the experimental work are reported in a companion paper.

Identification of an antisense transcript from the IGF-II locus in mouse

We have identified a novel antisense RNA transcribed from the insulin-like growth factor-II (IGF-II) locus in mouse. This transcript was identified using probes derived from cloned genomic DNA lying between the insulin II locus and the IGF-II locus. S1 protection assays confirmed that this transcript is transcribed from the strand complementary to the stand encoding IGF-II. A 3.75 kb RNA was consistently detected on northern analysis of mouse tissue using different randomly primed DNA probes generated from this region. S1 nuclease protection analysis identified three exons contained in the transcript. Developmental northern analysis was performed using RNA from embryonic (E) and postnatal (P) tissues of E10, E13, E18, P1, P4, P10, and adult mice. The antisense RNA was most abundant in E13 and E18 mouse and was present in greatest amounts in skull, skeletal muscle, cardiac muscle, and placenta. No signal for this RNA was detected after the fourth day of life in any tissue studied.

ELISA determined IgM and IgA rheumatoid factors in seronegative rheumatoid and psoriatic arthritis

Previous studies have strongly suggested an association between rheumatoid factors (RF's), particularly IgA-RF, and the presence of erosions in rheumatoid arthritis (RA). The present study was aimed at studying this association in seronegative erosive arthritides. Forty-eight patients with seronegative arthritis were evaluated for the presence of IgM- and IgA-RFs using an enzyme linked immunosorbent assay (ELISA). Twenty-nine had seronegative RA and nineteen had psoriatic arthritis (PA). Twelve (41%) seronegative RA patients were found to be seropositive for IgM- or IgA-RF. Only 1 (7%) patient with PSA was positive for IgA-RF alone. Fifteen (51%) of the RA patients and eight (42%) of the PSA patients had erosive disease. A significant correlation between IgA-RF alone and erosive disease was found only in the seronegative RA patient (p less than 0.02). We conclude that in PSA patients there appears to be no need to define isotype specific RFs. On the other hand, our findings indicate that an early detection of IgA-RF can have clinical importance in seronegative rheumatoid arthritis, as it may constitute an indication for the timely institution of disease-modifying drugs in these patients.

Competitive ELISA for detection of native ras gene-related products in sera of cancer patients

A solid phase, enzyme-linked immunosorbent assay (ELISA) competition kit was developed to detect circulating native ras gene-related products in sera of 151 healthy volunteers and cancer patients. This assay uses monoclonal antibody (mAb) BST-6A generated against a yeast-derived, native ras-related polypeptide Yp20. Only 2% (1 of 58) of normal control sera showed strong competition, as compared to 15% (5 of 34) of patients with early stage or no evidence of disease, and 44% (26 of 59) of patients with advanced disease. These differences were statistically significant (x2, P less than 0.05-0.001). Eleven sera samples of cancer patients found to be strong competitors in the ELISA competition kit were tested for the presence of anti-ras antibodies by ELISA. None showed higher ELISA values as compared with pooled normal human serum and control sera. It is thus suggested that our procedure detected circulating ras-related onco-proteins in sera of cancer patients mainly with advanced disease.