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Biomedical subjects

A Leviton

Publications and source records attributed to A Leviton.

At least 19 recordsLinked 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↗
PubMed1979

Deficits in psychologic and classroom performance of children with elevated dentine lead levels.

To measure the neuropsychologic effects of unidentified childhood exposure to lead, the performance of 58 children with high and 100 with low dentine lead levels was compared. Children with lead levels scored significantly less well on the Wechsler Intelligence Scale for Children (Revised) than those with low lead levels. This difference was also apparent on verbal subtests, on three other measures of auditory or speech processing and on a measure of attention. Analysis of variance showed that none of these differences could be explained by any of the 39 other variables studied. Also evaluated by a teachers' questionnaire was the classroom behavior of all children (2146 in number) whose teeth were analyzed. The frequency of non-adaptive classroom behavior increased in a dose-related fashion to dentine lead level. Lead exposure, at doses below those producing symptoms severe enough to be diagnosed clinically, appears to be associated with neuropsychologic deficits that may interfere with classroom performance.

Attention↗
PubMed1979

Seasonal variation in the birth of left-handed schoolgirls.

The birth of left-handed girls in a school population displayed a seasonal trend, with a peak in November. No seasonal trend was seen in the birth of left-handed boys. The seasonal pattern of birth of left-handed girls is compatible with the hypothesis that nongenetic factors contribute to the occurrence of left-handedness.

Child↗
PubMed1979

Training in developmental pediatrics. How practitioners perceive the gap.

Ninety-seven randomly selected, board-certified pediatricians in five New England states were interviewed by two physicians to explore attitudes toward previous training and current sources of knowledge in developmental pediatrics. Formal training in development was rated as inadequate by 79%, of residency experience was viewed as highly valuable by only 30%, and 47% rated medical school as having no value. Although clinical experience was reported as a valuable source of knowledge by 99% of the sample, almost two thirds did not regard it as an adequate substitute for formal training. Frequent interdisciplinary communication was reported, and professional contacts were described as a highly valuable ongoing source of knowledge. Social class and size of practice did not correlate with differences in consultation patterns. A part-time longitudinal clinical experience for further education was preferred by 97%. Improved training with greater interdisciplinary content is needed.

Child↗
PubMed1979

Use of a self-administered questionnaire for detection of transient cerebral ischemic attacks: I. Survey of elderly persons living in retirement facilities.

A self-administered questionnaire designed to identify people with transient cerebral ischemia (TIA) in large population groups was distributed to approximately 10,000 elderly persons living in public and private retirement facilities in the United States. The population resided in eight cities, and 74% completed the survey. Transient focal neurological symptoms compatible with a diagnosis of TIA within the previous year were reported by 6.4% of the respondents. Uncertain manifestations of TIA, i.e., dizziness, light-headedness, or loss of balance, were noted by an additional 15.4%; the remaining 78.2% had no manifestations of this disorder. A clinical history for TIA was taken by a neurologist in a sample of 1,712 respondents to determine the validity of the questionnaire responses. Thirty (7.1%) of 423 persons presumed by the questionnaire to have TIA met the standard clinical criteria for the diagnosis. An additional 8 cases of TIA were found by the neurologist among the 1,289 interviewed persons presumed by the questionnaire to have uncertain TIA or no evidence of the disorder. The twelve-month period prevalence of TIA was estimated to be 8.2 per 1,000 in the total respondent population and 5.8 per 1,000 among those without a history of prior completed stroke. Despite the high proportion of false-positive neurological symptoms of TIA elicited by the questionnaire, this survey instrument nevertheless screened out for further study the 6% of the population in whom 55% of the TIAs occurred.

Aged↗