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Biomedical subjects

A Leviton

Publications and source records attributed to A Leviton.

At least 91 records · Page 5Linked to original sources
PubMed1992

Pre-natal blood lead levels and learning difficulties in children: an analysis of non-randomly missing categorical data.

This paper presents an analysis of categorical variables subject to non-response. We incorporate the incomplete data into the analysis by modelling the distribution of the variables of interest and the non-response mechanism. We discuss issues of model selection and interpretation and the effect of discarding incomplete observations. In addition, we describe how to perform all of the computations with standard statistical software. We discuss the problem of incomplete categorical data within the context of a study of the effect of lead exposure on learning difficulties in children. In this study, many of the children are not observed on some of the variables of interest. It is particularly important in this study to incorporate the incomplete data, since there is evidence that non-response is related to the variables of interest. We reach different conclusions when we incorporate the incomplete data into the analysis than we reach when we discard the incomplete data. We also examine the sensitivity of our conclusions to the choice of a model for the non-response mechanism.

Algorithms↗
PubMed1992

Childhood brain tumors that occupy more than one compartment at presentation. Multiple compartment tumors.

Children whose brain tumor involves two or more compartments at presentation differ clinically and pathologically from children whose brain tumor is confined to one compartment. In this study of 3,291 children with a brain tumor, at least 10% had a tumor that occupied two or three compartments at first hospitalization. Infratentorial tumors occupying multiple compartments were 1.7 times more likely to involve the cervicomedullary junction than the mesodiencephalic junction. Younger children (1-3 years) were more likely to have had multiple compartment tumors than older children. Children whose tumor was limited to the infratentorial compartment had a longer survival than children whose tumor also occupied other compartments. Ependymoma, anaplastic ependymoma, and astrocytoma (nos) were over represented among infratentorial multiple compartment tumors. Pilocytic astrocytoma, primitive neuroectodermal tumor (medulloblastoma), and desmoplastic medulloblastoma were less likely to have occupied multiple compartments at the time of the first surgical exploration. The distributions of histologic features in tumors at the cervicomedullary junction differed from those in tumors limited to the posterior fossa or to the spinal canal. Seizures were more likely if the tumor was confined to the supratentorial compartment, whereas nausea or vomiting and headache were more likely if the tumor was confined to the infratentorial compartment. Children whose tumor was confined to the spinal canal were significantly more likely to have bladder symptoms and back and/or abdominal pain than those whose tumor also involved compartments above the foramen magnum. We conclude that brain tumors apparently confined to one compartment at presentation are biologically and structurally different from tumors evident in two or more compartments.

Adolescent↗
PubMed1992

Epidemiology of seizures in children with brain tumors. The Childhood Brain Tumor Consortium.

We examined potential clinical and pathologic correlates of seizures among the 3,291 children in the Childhood Brain Tumor Consortium database. Fourteen percent had seizures prior to their hospitalization for a brain tumor. Among children who had a supratentorial tumor, seizures occurred in 22% of those less than 14 years of age. The prevalence of seizures increased to 68% of older teenagers. Among children with an infratentorial tumor, the prevalence of seizures was relatively constant at 6% over all age groups. The onset of seizures began more than one year prior to surgical tumor removal in over half of the children aged five or more with supratentorial tumors, significantly longer than for those of the same age with infratentorial tumors. Almost all children (98.9%) with an infratentorial tumor and seizures had at least one other symptom and more than three-fourths of them had at least three. Eighty-nine percent of children with a supratentorial tumor and seizures had at least one other symptom and more than one-half had at least three symptoms. Regardless of whether the tumor was above or below the tentorium, confusion or stupor and coma were more common in children with seizures than in children without seizures. Among children with supratentorial tumors, symptoms of a declining academic performance or an abnormality of personality, speech, walking, or sensation were significantly more frequent in children with seizures, while visual symptoms (other than visual loss or diplopia) and nausea or vomiting were less frequent. Among children with supratentorial tumors, those who had seizures were more likely to have paralysis of an arm, hand, or face, confusion or stupor, or coma and less likely to exhibit irritability, papilledema, optic atrophy, decreased visual acuity, pupillary abnormalities, or abducens paresis. Among children with infratentorial tumors, those with seizures were significantly less likely to have truncal ataxia, but more likely to experience confusion, stupor, or coma. In the supratentorial compartment, astrocytoma (nos), protoplasmic astrocytoma, anaplastic astrocytoma, and ependymoma were more frequently associated with seizures than was craniopharyngioma. No infratentorial tumor type was more or less likely to be associated with seizures. All common tumor types that were represented in both the supratentorial and the infratentorial compartment except astrocytoma (nos) were associated with significantly greater rates of seizures when located in the supratentorial compartment. The tumor location with the highest incidence of seizures was, as expected, the superficial cerebrum. More than 40% of the children with such tumors had seizures.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1992

Temporal trends among childhood brain tumor biopsies. The Childhood Brain Tumor Consortium.

We sought temporal trends in the demographic, clinical, histologic feature, diagnostic class, and quality of life data over the interval 1930-1979 in the Childhood Brain Tumor Consortium database. The proportion of children younger than eight years old declined from 72% to 55% and the proportion of those older than ten more than doubled from 12% to 27%. The relative frequency of tumors in the supratentorial compartment increased significantly, while infratentorial tumors decreased. We found significant declines in supratentorial ependymomas and pilocytic astrocytomas. Similarly, some infratentorial tumors, especially ependymomas, decreased and brain stem tumors increased. Infratentorial medulloblastoma (primitive neuroectodermal tumor) increased significantly. Some individual histologic features which are markers of anaplasia increased in frequency in both supratentorial and infratentorial tumors. There was a significant increase in biopsies that contained nonneoplastic neural tissue in addition to tumor for both compartments and among supratentorial tumors there was a marked increase in the proportion of cases containing an indistinct neural tissue boundary. The probability of postoperative death declined, but the probability of survival five or ten years after surgery did not improve significantly for children who had tumors in either compartment. Among children who survived five years after the initial craniotomy, the proportion who had significant long term deficits increased. Most of this increase occurred in the last decade (1970-79). In this decade, the proportion of children for whom no deficits were reported five years following operation was 4% if they had a supratentorial tumor and 27% if they had an infratentorial tumor. The proportions of children alive five years following first surgery who had arachnoidal metastases increased significantly for infratentorial tumors.

Adolescent↗
PubMed1992

Rate of bronchopulmonary dysplasia as a function of neonatal intensive care practices.

Some differences among neonatal intensive care units (NICUs) in incidence of bronchopulmonary dysplasia may reflect variations in medical care practices. After adjusting for differences in the inherent risk of bronchopulmonary dysplasia among 223 infants of less than 1751 gm birth weight who were admitted to three Harvard-affiliated NICUs, we used multivariate analysis to explore the extent to which medical care practices during the first days of life varied with the rate of bronchopulmonary dysplasia. In our analyses, variables were grouped by three major hypotheses: oxygen toxicity, barotrauma, and fluid overload. The NICU designated 1 (the one with the highest rate of bronchopulmonary dysplasia) used much higher than expected colloidal volumes during the first 4 days of life; in contrast, in the NICU designated 3 (the one with the lowest rate of bronchopulmonary dysplasia), infants consistently received lower than expected amounts of colloidal solution. Signs of patent ductus arteriosus were also much more frequent than expected during this time at NICU 1; rates were much lower than predicted at NICU 2 and were near predicted values at NICU 3. Maximum inspired oxygen fraction during the first 4 days varied significantly in a direction inconsistent with the oxygen toxicity hypothesis. Maximum arterial oxygen tension was significantly less than expected at the hospital with the lowest rate of bronchopulmonary dysplasia (NICU 3). None of six medical care practices indicating potential for barotrauma varied with NICU expect for positive end-expiratory pressure, which varied in a direction suggesting a protective effect against bronchopulmonary dysplasia. These findings agree best with the hypothesis that differences in hydration during the first days of life account for some of the difference among NICUs in bronchopulmonary dysplasia occurrence.

Bronchopulmonary Dysplasia↗
PubMed1992

Maternal toxemia is associated with reduced incidence of germinal matrix hemorrhage in premature babies.

To evaluate prenatal and perinatal risk factors for development of germinal matrix hemorrhage-intraventricular hemorrhage (GMH-IVH), we conducted a prospective epidemiologic study of 449 babies whose birth weight was less than 1501 grams. This study permitted us to test our previously generated hypothesis that babies born to mothers with preeclampsia were at substantially reduced risk of developing GMH-IVH. Seventy-two (16%) of the babies in this population developed GMH-IVH. One (2.5%) of the 40 mothers with a diagnosis of preeclampsia and 71 (17.4%) of 409 mothers without preeclampsia gave birth to babies who developed GMH-IVH. GMH-IVH was seen in 6/107 (5.6%) of babies born to women with hypertension including 4/69 (5.8%) of babies born to women with pregnancy-induced hypertension, compared to 66/352 (18.8%) of babies born to mothers who did not have hypertension. Only 7.3% (8/108) of babies born to women who had proteinuria had GMH-IVH, compared to 18.3% (64/350) of babies whose mothers did not have proteinuria. GMH-IVH was seen in 5/89 (5.6%) of babies whose mothers had both hypertension and proteinuria, whereas 63/332 (19%) of babies born to mothers who lacked both factors, developed GMH-IVH. In stepwise logistic regression analysis, these significant findings were not explained by the presence of labor, postnatal acidemia, need for intubation, antenatal administration of steroids, birth weight, or gestational age. In addition, we found that maternal receipt of magnesium sulfate was associated with diminished risk of GMH-IVH even in those babies born to mothers who apparently did not have preeclampsia.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral Hemorrhage↗
PubMed1991

How much of neonatal encephalopathy is due to birth asphyxia?

In the literature on neonatal encephalopathy, the pervasive assumption is that once infants with major malformations or infections have been excluded, most of the remaining cases are due to birth asphyxia. Assessing the proportion of neonatal encephalopathy that is due to asphyxia during birth is difficult because of problems in defining asphyxia and neonatal encephalopathy and in recognizing the cause of neonatal neurologic illness. Available evidence indicates that neonatal neurologic signs are not strongly related to obstetric complications, signs of fetal distress, or biochemical markers usually considered to indicate perinatal asphyxia. Most studies that have sought positive evidence of independent markers of intrapartum asphyxia have found them to be absent in a large majority of neurologically symptomatic neonates. We conclude that the proportion of neonatal encephalopathy that is asphyxial in origin is not known but warrants examination, especially in view of the probable need in the near future to identify, on the basis of evidence available in the first hour or so of life, suitable candidates for clinical trials of powerful but risky treatments of birth asphyxia.

Asphyxia Neonatorum↗
PubMed1991

Weight gain and maturity in fetuses exposed to low levels of lead.

The relationship between prenatal low-level lead exposure and fetal growth was evaluated in a sample of 4354 pregnancies in which the mean umbilical cord blood lead level was 7.0 micrograms/dl (SD = 3.3; 10th percentile, 3.4 micrograms/dl, 90th percentile, 10.9 micrograms/dl). Higher cord blood lead levels were significantly associated with gestations of slightly longer duration. Comparing infants with cord blood lead levels greater than or equal to 15 micrograms/dl to those with levels less than 5 micrograms/dl, adjusted risk ratios of 1.5 to 2.5 were observed for low birth weight (less than 2500 g) and for fetal growth indices that express birth weight as a function of length of gestation (e.g., small-for-gestational age, intrauterine growth retardation). The 95% confidence intervals of these risk ratios included 1, however, precluding rejection of the null hypothesis of no association. We conclude that the risk of adverse fetal growth is not increased at cord blood lead levels less than 15 micrograms/dl but that modest increases in risk may be associated with levels greater than or equal to 15 micrograms/dl.

Body Weight↗
PubMed1991

The epidemiology of germinal matrix hemorrhage during the first half-day of life.

The personal and maternal characteristics of 27 babies with early-onset germinal matrix hemorrhage (EGMH) were compared with those of 280 babies with normal cranial ultrasonograms, studied in a separate clinical trial. None of the mothers of the babies with EGMH had high blood pressure or pre-eclampsia during pregnancy. Gestational age less than 30 weeks and initial pH less than 7.2 indicated increased risks of EGMH, and maternal receipt of steroids indicated reduced risk of EGMH. Thus prenatal and immediately perinatal factors appear to convey much of the information about the risk of EGMH.

Cerebral Hemorrhage↗
PubMed1991

Labor and delivery characteristics and the risk of germinal matrix hemorrhage in low birth weight infants.

To assess the influence of labor and delivery events on the risk of germinal matrix hemorrhage in preterm newborns, we conducted a review of data collected on 449 babies who weighed 1.5 kg or less. Babies delivered vaginally were more likely to have germinal matrix hemorrhage than were babies delivered abdominally (odds ratio, 2.5; 95% confidence interval, 1.4,3.3). Among babies delivered vaginally, the risk of germinal matrix hemorrhage was increased by 39% if labor lasted more than 12 hours. Among babies delivered abdominally, the occurrence of any labor was accompanied by a 150% increased risk of germinal matrix hemorrhage. The only indication for abdominal delivery associated with an increased risk of germinal matrix hemorrhage was impending amnionitis (odds ratio, 2.6; 95% confidence interval, 1.2,5.7), whereas the only indication associated with a decreased risk was preeclampsia (odds ratio, 0.2; 95% confidence interval, 0.6). Epidural and local anesthesia were associated with a reduced risk of germinal matrix hemorrhage among babies delivered abdominally. We conclude that delivery practices, or their indications, appear to influence the risk of germinal matrix hemorrhage in low birth weight babies.

Cerebral Hemorrhage↗
PubMed1991

Low-level lead exposure and children's cognitive function in the preschool years.

In a cohort of 170 middle and upper-middle class children participating in a prospective study of child development and low-level lead exposure, higher blood lead levels at age 24 months were associated with lower scores at age 57 months on the McCarthy Scales of Children's Abilities. The mean blood lead level at age 24 months was 6.8 micrograms/dL (SD = 6.3; 75th, 90th, and 99th percentiles: 8.8, 13.7, 23.6, respectively) and for all but 1 child was less than 25 micrograms/dL, the current definition of an "elevated" level. After adjustment for confounding, scores on the General Cognitive Index decreased approximately 3 points (SE = 1.4) for each natural log unit increase in 24-month blood lead level. The inverse association between lead level and performance was especially prominent for visual-spatial and visual-motor integration skills. Higher prenatal exposures were not associated with lower scores at 57 months except in the subgroup of children with "high" concurrent blood lead levels (ie, greater than or equal to 10 micrograms/dL). The concentration of lead in the dentine of shed deciduous teeth was not significantly associated with children's performance after adjustment for confounding.

Age Factors↗
PubMed1990

Methylxanthine consumption and the risk of ovarian malignancy.

Between 1970 and 1988, reports were published about two ecological studies, six case-control studies and one cohort study that evaluated the relationship between methylxanthine consumption and the risk of ovarian cancer. Because of the limitations of ecological studies, no inferences are based on them. All of the case-control studies recruited hospital controls. Nevertheless, four of the six had risk ratios of 1.5 or less. The one cohort study, which showed no relationship between coffee drinking and ovarian cancer, has low power. From these studies, it appears that coffee and tea consumption do not increase the risk of ovarian cancer.

Adult↗
PubMed1990

The long-term effects of exposure to low doses of lead in childhood. An 11-year follow-up report.

To determine whether the effects of low-level lead exposure persist, we reexamined 132 of 270 young adults who had initially been studied as primary school-children in 1975 through 1978. In the earlier study, neurobehavioral functioning was found to be inversely related to dentin lead levels. As compared with those we restudied, the other 138 subjects had had somewhat higher lead levels on earlier analysis, as well as significantly lower IQ scores and poorer teachers' ratings of classroom behavior. When the 132 subjects were reexamined in 1988, impairment in neurobehavioral function was still found to be related to the lead content of teeth shed at the ages of six and seven. The young people with dentin lead levels greater than 20 ppm had a markedly higher risk of dropping out of high school (adjusted odds ratio, 7.4; 95 percent confidence interval, 1.4 to 40.7) and of having a reading disability (odds ratio, 5.8; 95 percent confidence interval, 1.7 to 19.7) as compared with those with dentin lead levels less than 10 ppm. Higher lead levels in childhood were also significantly associated with lower class standing in high school, increased absenteeism, lower vocabulary and grammatical-reasoning scores, poorer hand-eye coordination, longer reaction times, and slower finger tapping. No significant associations were found with the results of 10 other tests of neurobehavioral functioning. Lead levels were inversely related to self-reports of minor delinquent activity. We conclude that exposure to lead in childhood is associated with deficits in central nervous system functioning that persist into young adulthood.

Adolescent↗
PubMed1990

Asthma and eczema in children born to women with migraine.

Migraine and asthma have been reported to occur in the same person more commonly than would be expected if they are independent. The large Collaborative Perinatal Project provided an opportunity to see if children born to women with migraine or with the group of disorders characterized by asthma and/or allergies were more likely to manifest asthma or eczema in the first 7 years of life. Among children whose mothers had neither migraine nor asthma/allergies, 3.2% had asthma. Of children whose mothers had migraine, but not asthma/allergies, more than 6% had asthma. The risk of asthma among children born to women who had both migraine and asthma/allergies was greater than the risk associated with each maternal disease. The risk of eczema in children was not appreciably influenced by the mother's propensity to migraine or asthma/allergies. The results of this first study of migraine in one generation and asthma in the next lead to the conclusion that the two disorders are probably related.

Adolescent↗