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Biomedical subjects

S C Johnson

Publications and source records attributed to S C Johnson.

At least 55 records · Page 3Linked to original sources
PubMed1999

Head trauma and intellectual status: relation to quantitative magnetic resonance imaging findings.

This article contrasts 2 groups that sustained somewhat similar moderate to severe closed-head traumatic brain injury (TBI), but were deliberately selected to be different with regard to postinjury intellectual status--one group average or above, the other below. The purpose of this comparison was to describe any morphological characteristics of the 2 groups ascertained from quantitative magnetic resonance (QMR) imaging. Thirty-five TBI participants with Full Scale IQ (FSIQ) less than or equal to 90 were compared to 33 TBI participants whose FSIQ was above 90. A group of normal volunteer participants, age and gender matched, constituted a third magnetic resonance comparison group. All participants received uniform MRI from which QMR analysis was performed, including total cranial volume, subarachnoid cerebral spinal fluid ventricular volume, and hippocampal volume. Both TBI groups received neuropsychological testing in the course of clinical follow-up. Morphological comparisons between groups were made using multivariate analysis of variance. The TBI group with an IQ less than or equal to 90 had significantly enlarged third and temporal horn compartments. Total intracranial volume was smaller in this group as well. Lower psychometric intelligence postinjury may be associated with more temporal lobe atrophy and subcortical pathology. Smaller premorbid brain size may be another risk factor.

Adult↗
PubMed1999

Effect of antioxidant supplementation on urine and blood markers of oxidative stress during extended moderate-altitude training.

OBJECTIVE: To investigate the increase in oxidative stress during work at moderate altitudes due to additional energy expenditure, tissue anoxia, and UV light exposure. METHODS: Thirty US Marine Corps volunteers were divided into placebo (P) and antioxidant supplement (S) groups and tested for markers of oxidative stress before (t0), at the midpoint of (t1), and after (t2) 14 days of winter training at a moderate altitude (approximately 2700 m). The antioxidant supplement consisted of a daily dose of 20,000 IU beta-carotene, 400 IU vitamin E, 500 mg vitamin C, 100 micrograms selenium, and 30 mg zinc. The following markers of oxidative stress were measured: urine thiobarbituric acid reactive substances (TBARSs), urine hydroxynonenal (HNE), urine 8-hydrodeoxyguanosine (8-OHdG), plasma total peroxyl radical trapping potential (TRAP), and plasma lipid hydroperoxides (LPOs). Urine was collected on a 24-hr basis at t0, t1, and t2; blood samples were collected at t0 and t2. RESULTS: P group LPOs increased 30% (p < 0.05) between t0 and t2, whereas S group LPOs did not increase. Both groups exhibited significant increases in urine TBARSs, HNE, and 8-OHdG by t2. Urine TBARSs, HNE, and 8-OHdG increased between t0 and t1 in both groups, with the greater increase in the S group. The conflicting results between the plasma and urine markers of oxidative stress may be due to a time-phase relationship. CONCLUSIONS: The results of this study suggest that work in a moderate-altitude cold-weather environment is accompanied by increased oxidative stress, despite relatively high intakes of dietary and supplemental antioxidants.

Adult↗
PubMed1998

Knowledge enrichment and conceptual change in folkbiology: evidence from Williams syndrome.

Ten participants with Williams syndrome (WS) (average verbal mental age of 11;5) were compared to two groups of normally developing children (average mental ages 10;11 and 6;7 years) with respect to intuitive biological knowledge about people, animals, and plants. Participants in the older control group were individually matched to the participants with WS on verbal mental age. The probes for biological understanding were drawn from the existing literature on the development of folkbiology and were divided into two batteries based on the hypothesized distinction of (1) general knowledge consistent with the conceptual repertoire of normally developing preschool children (the T1/T2-Neutral Animal Knowledge battery) and (2) folkbiological concepts normally acquired between ages 6 and 12 which require conceptual change for their construction (life, death, people-as-one-animal-among-many, species kind as determined by origin of the animal; the T2-Dependent battery). The two task batteries were equated for task demands, differing only in the content of the concepts probed. It was hypothesized that if this distinction is a false one, and the construction of folkbiology is accomplished entirely by enrichment of the preschooler's knowledge, there should never be a population with differential performance on these two batteries. People with WS were nonetheless found to be differentially impaired on the T2-Dependent battery. They performed at the level of the older control group on the T1/T2-Neutral battery, but at the level of the 6-year-olds on the T2-Dependent battery. These data support the distinction between two types of conceptual knowledge acquisition: acquisition of new knowledge formulated over an existing conceptual base (enrichment), on the one hand, and knowledge acquisition that results in genuine conceptual change, on the other. The implication of these results for a precise characterization of how concepts of people with "cocktail party syndrome" may be "superficial" is also discussed.

Adolescent↗
PubMed1998

The nitric oxide synthesis inhibitor nitro-L-arginine (L-NNA) attenuates nicotine abstinence syndrome in the rat.

Nitric oxide synthesis contributes to opiate tolerance and dependence. Nicotine dependence and abstinence syndrome in the rat appear to involve opiate mechanisms. Therefore, it was postulated that nitric oxide synthase (NOS) activity might be essential for the expression of nicotine abstinence syndrome. Twenty-one rats were rendered dependent by SC infusion of 9 mg/kg per day nicotine tartrate via Alzet osmotic minipump. Rats were pretreated SC with vehicle alone, or with 18 or 30 mg/kg of the NOS inhibitor L-NNA (nitro-L-arginine). Thirty minutes later, rats were challenged by 1 mg/kg of the nicotinic antagonist mecamylamine SC and observed for 30 additional minutes. Rats pretreated with vehicle displayed a total of 68.7+/-8.0 mecamylamine-precipitated abstinence signs (mean+/-SEM), while those receiving 18 or 30 mg/kg L-NNA had 12.7+/-2.0 and 5.1+/-1.7 signs, respectively. All three groups differed significantly from one another according to Dunn's post-hoc procedure. Rats pretreated with L-NNA combined with an excess of the NOS substrate L-arginine had significantly more mecamylamine-precipitated abstinence signs than rats receiving L-NNA combined with D-arginine. Also, D-NNA, which does not selectively bind to NOS, was significantly less effective than L-NNA in preventing mecamylamine-precipitated abstinence syndrome. Additional studies determined the effect of L-NNA on spontaneous nicotine abstinence syndrome. Rats were assessed for abstinence signs at 17 and 20 h after termination of nicotine infusion. They received injections of 9, 18, or 30 mg/kg L-NNA SC or vehicle alone immediately before the 20-h observation; all rats were observed for 30 min. Signs at 20 h (post-injection) as a percentage of signs at 17 h (pre-injection) declined significantly as a function of L-NNA dose. Once again, this effect was attenuated significantly more by co-administration of L-arginine than by D-arginine. The overall pattern of results suggests that nitric oxide synthesis is critical to the expression of nicotine abstinence syndrome.

Animals↗
PubMed1998

Anterior uveitis and hypotony after intravenous cidofovir for the treatment of cytomegalovirus retinitis.

OBJECTIVE: This study aimed to describe the incidence and risk factors for the development of anterior uveitis in patients receiving intravenous cidofovir for the treatment of longstanding cytomegalovirus retinitis. DESIGN: The study design was a retrospective cohort. PARTICIPANTS: Eighteen patients (30 eyes) receiving parenteral cidofovir for the treatment of complicated cytomegalovirus retinitis participated. MAIN OUTCOME MEASURES: The clinical response to parenteral cidofovir; the occurrence of anterior uveitis, and the management and outcome of patients with this complication; and the effect of cidofovir on intraocular pressure measurements were measured. RESULTS: There was no progression or relapse of retinitis in patients receiving intravenous cidofovir. Eight (44%) of the 18 patients developed anterior uveitis, which occurred after a median of 4 doses of intravenous cidofovir. The median CD4+ cell count at the time of development of iritis was 101/mm3. Patients who developed uveitis had a mean increase in serum creatinine over baseline measurements (P = 0.05). The use of human immunodeficiency virus type-1 (HIV-1) protease inhibitors was not different between both groups of patients (P = 1.0). The development of anterior uveitis and visually significant hypotony necessitated withdrawal of cidofovir in only one patient. CONCLUSIONS: Anterior uveitis was a common complication after intravenous cidofovir therapy. Despite the frequency of this complication, continued treatment with intravenous cidofovir was possible in the majority of patients. Patients with anterior uveitis after intravenous cidofovir may be treated successfully with topical corticosteroid therapy and cycloplegic agents.

AIDS-Related Opportunistic Infections↗
PubMed1998

Safety and efficacy of intravenous sodium stibogluconate in the treatment of leishmaniasis: recent U.S. military experience.

The efficacy and toxicity of sodium stibogluconate (SSG) at a dosage of 20 mg/(kg.d) for either 20 days (for cutaneous disease) or 28 days (for visceral, mucosal, or viscerotropic disease) in the treatment of leishmaniasis is reported. Ninety-six U.S. Department of Defense health care beneficiaries with parasitologically confirmed leishmaniasis were prospectively followed for 1 year. One patient was infected with human immunodeficiency virus; otherwise, comorbidity was absent. Clinical cure occurred in 91% of 83 cases of cutaneous disease and 93% of 13 cases of visceral/viscerotropic disease. Adverse effects were common and necessitated interruption of treatment in 28% of cases, but they were generally reversible. These included arthralgias and myalgias (58%), pancreatitis (97%), transaminitis (67%), headache (22%), hematologic suppression (44%), and rash (9%). No subsequent mucosal leishmaniasis was identified, and there were no deaths attributable to SSG or leishmaniasis.

Adolescent↗
PubMed1997

A randomized trial of enhanced therapy for early syphilis in patients with and without human immunodeficiency virus infection. The Syphilis and HIV Study Group.

BACKGROUND: Reports of neurosyphilis and invasion of cerebrospinal fluid by Treponema pallidum in patients with human immunodeficiency virus (HIV) infection have led to doubts about the adequacy of the recommended penicillin G benzathine therapy for early syphilis. METHODS: In a multicenter, randomized, double-blind trial, we assessed two treatments for early syphilis: 2.4 million units of penicillin G benzathine and that therapy enhanced with a 10-day course of amoxicillin and probenecid. The serologic and clinical responses of patients with and without HIV infection were studied during one year of follow-up. RESULTS: From 1991 through 1994, 541 patients were enrolled, including 101 patients (19 percent) who had HIV infection but differed little from the uninfected patients in their clinical presentations. The rates at which chancres and rashes resolved did not differ significantly according to treatment assignment or HIV status. Serologically defined treatment failures were more common among the HIV-infected patients. The single clinically defined treatment failure was in an HIV-infected patient. Rates of serologically defined treatment failure did not differ according to treatment group (18 percent at six months with usual therapy; 17 percent with enhanced therapy). T. pallidum was found at enrollment in the cerebrospinal fluid of 32 of 131 patients (24 percent) and after therapy in 7 of 35 patients tested. None had clinically evident neurosyphilis, and the rate of detection of T. pallidum did not differ according to HIV status. CONCLUSIONS: After treatment for primary or secondary syphilis, the HIV-infected patients responded less well serologically than the patients without HIV infection, but clinically defined failure was uncommon in both groups. Enhanced treatment with amoxicillin and probenecid did not improve the outcomes. Although T. pallidum was detected in cerebrospinal fluid before therapy in a quarter of the patients tested, such a finding did not predict treatment failure. The current recommendations for treating early syphilis appear adequate for most patients, whether or not they have HIV infection.

Adult↗
PubMed1997

Corpus striatum and traumatic brain injury.

The possibility of a 'subcortical' syndrome differentially affecting memory in traumatic brain injury (TBI) subjects was examined. Magnetic resonance imaging scans of 46 traumatic brain injured male patients were compared with those of 34 male control subjects. Surface area measurements of the corpus striatum were calculated for both groups. Results demonstrated no significant differences in corpus striatum surface area measurements. Additionally, TBI patients were grouped according to severity of injury, as well as degree of corpus striatum atrophy, and neuropsychological outcome was examined. There were modest (r = 0.35) but significant correlations between corpus striatum degeneration and the delayed recall trial and total score of the Rey Auditory Verbal Learning Test, but no other correlations between neuropsychological and corpus striatal surface area were significant. Because subcortical pathology may have a differential effect on memory, recognition and recall memory were further analysed, but no significant differences were found. TBI subjects with the smallest corpus striatum values did not test significantly different from TBI patients with normal corpus striatum values or differences in cortical atrophy, as determined by a ventricle-to-brain ratio. These findings suggest that there is not a unique pattern of subcortical pathology involving the corpus striatum in TBI.

Adolescent↗
PubMed1997

Apolipoprotein E epsilon 4 allele and hippocampal volume in twins with normal cognition.

We examined the relation of APOE-epsilon 4, hippocampal volume, and cognitive performance in ten pairs of cognitively normal twins who had a mean age of 62.5 years (SD = 7.8). There were no significant differences in neuropsychological measures of the groups categorized by the presence of an epsilon 4 allele. However, the mean normalized right and left hippocampal volumes were smaller in the epsilon 4 groups compared to the group without epsilon 4. Combined with prior reports, these findings suggest that epsilon 4 is associated with differences in brain morphology that may be evident when no symptoms of dementia are present.

Alleles↗
PubMed1997

MR-based brain and cerebrospinal fluid measurement after traumatic brain injury: correlation with neuropsychological outcome.

PURPOSE: To determine the magnitude and time course of changes in the volume of brain and intracranial cerebrospinal fluid (CSF) spaces in patients who have sustained traumatic brain injury and to assess the relationship between these findings and long-term cognitive traumatic outcome. METHODS: Axial intermediate and T2-weighted MR images of 123 patients with traumatic brain injury were quantified using a multispectral segmentation algorithm. Measurements were corrected for differences in age, sex, and head size using a previously reported normative database. Brain morphology was compared across groups formed on the basis of chronicity of injury. Cognitive functioning and severity of injury were statistically correlated with brain measurements. RESULTS: Time-dependent expansion of CSF spaces and decreases in brain volume were observed. Increases in ventricular CSF volume, particularly in the temporal horns and third ventricle, preceded subsequent changes in total brain and subarachnoid CSF. High and moderate correlation was observed between volume measures and cognitive outcome and injury severity. Particularly strong was the relation between the volume of the left temporal horn and verbal IQ scores. CONCLUSION: Predictable time-dependent atrophic changes occurring after traumatic brain injury can be quantified using MR volumetric studies. Our results suggest significant contributions by both diffuse and focal mechanisms of injury. In the postacute period (more than 70 days after injury), MR volumetric studies may be predictive of eventual cognitive outcome.

Adolescent↗
PubMed1997

Hippocampal volume in normal aging and traumatic brain injury.

PURPOSE: To present a normative database of hippocampal and temporal horn volume and to clarify the relationship between these measures and cognitive outcome in patients with traumatic brain injury. METHODS: Ninety-six healthy volunteers and 94 patients with traumatic brain injury were examined with coronal intermediate and T2-weighted MR imaging. Multispectral segmentation and volume analyses were performed. The volumetry of the hippocampus and temporal horn was characterized in the control subjects. Volumetric measures in a group of patients with traumatic brain injury who had received MR imaging 3 months or less after injury were compared with measurements in other patients in the chronic phase of recovery. The relationship between neuropsychological testing and volumetric measures was analyzed with particular emphasis on the correlation between cognitive outcome and hippocampal and temporal horn volumes. RESULTS: No significant age group differences were found in the normative group from age 16 to 65. Left and right hippocampal volumes were interrelated and did not differ from each other. This was also true for the temporal horns. Hippocampal and temporal horn volumes were not significantly related. Women had larger hippocampi relative to cranial volume. Comparisons between patients with traumatic brain injury and control subjects showed significant yet modest bilateral atrophic changes in hippocampal and temporal horn enlargement in the patients with brain injury. Hippocampal and temporal horn volumes correlated significantly with each other in the group with traumatic brain injury. Cognitive outcome was modestly related to hippocampal and temporal horn volumes. However, in a specific subgroup whose images were acquired between 71 and 210 days after injury, strong correlations were noted in which temporal horn volume correlated highly with IQ and hippocampal volume correlated with verbal memory function. CONCLUSION: Hippocampal and temporal horn volumes appear to be independent variables in healthy control subjects. Traumatic brain injury results in significant hippocampal atrophy and temporal horn enlargement. The hippocampus and temporal horn volumes were inversely correlated in the group with traumatic brain injury, suggesting a differential relationship of these structures in patients with brain injury as compared with control subjects. In the subacute phase, the volume of the temporal horn may be indicative of intellectual outcome and that of the hippocampus appears to be indicative of verbal memory function.

Adolescent↗
PubMed1997

Why dogs have puppies and cats have kittens: the role of birth in young children's understanding of biological origins.

Three studies examined young children's understanding of the biologically causal role of birth in determining animal properties and species kind identity. In Studies 1 and 2, 4- to 7-year-olds and adults were told stories in which a baby was born to an animal of one species (e.g., a horse) but was adopted and raised by an animal of another species (e.g., a cow). In Study 1, children were asked to judge which parent the baby would resemble on a set of physical properties and beliefs. The majority of children were unable to say that the baby would resemble the birth parent on physical properties but share the beliefs of the adoptive parent. These results indicate that children were not using domain-specific causal understandings to reason about the origins of these properties. In Study 2, however, when asked to explicitly predict the kind of the baby, even 5-year-olds were able to reliably judge that the baby would be of the same species kind as the birth parent rather than the adoptive parent. This result suggests that children do understand at some level that birth determines species kind. Study 3 examined further the extent to which knowledge about birth influenced children's inferences about properties. Five-year-olds were asked to judge whether a baby would share a set of physical and nonphysical properties with its mother or its father. The results showed that children who knew the factual information about where babies come from (i.e., inside mommies' tummies) were more likely to attribute the mother's properties to the baby than the father's, regardless of whether the properties were physical or nonphysical. But this finding was true only if the property of one of the parents was not inherently more desirable or true than that of the other parent. In sum, the results of these 3 studies indicate that knowledge of birth does play a role in children's inferential reasoning, even for 5-year-olds, but that that role is not domain-specific. The implications for children's understanding of biological inheritance are discussed.

Age Factors↗
PubMed1996

Evidence of a secondary hypervolemia in trained man following acute high intensity exercise.

Exercise induced hypervolemia is well documented following the initial onset of chronic exercise. In trained man, however, it might be difficult to induce further PV expansion with exercise induced hypervolemia already present. Therefore the primary goal of this study was determine the effect of acute high intensity exercise on plasma volume (PV), cardiac output (CO), stroke volume (SV), heart rate (HR), and oxygen consumption (VO2), in fourteen male competitive runners (VO2max 60.7 +/- 6.4 ml.kg-1.min-1) in the middle of their season. In this well trained state, subjects twice performed three steady state runs at different speeds, and one maximal graded exercise test (baseline). After this baseline evaluation, subjects exercised at a high intensity (approximately 90-95% of VO2max) on 2 consecutive days (short-term high intensity STHI exercise). Subjects then repeated the submaximal runs and maximal exercise test (post high intensity exercise, PHIE). Following the intense exercise period, the subjects experienced an increase in PV of 4.4% (p < 0.05), HR was significantly reduced for any given running speed (p < 0.05) as was blood lactate concentration (p < 0.05), and SV was significantly increased by 4% (p < 0.05). Both CO and VO2 at submaximal running speeds were unaffected by the acute increase in exercise intensity. Maximal HR was also significantly reduced following the intense exercise (p < 0.05), but VO2max was unchanged. These data illustrate that STHI exercise can induce a secondary hypervolemia at a given work rate in trained man. These findings support scientific and anecdotal reports of a reduced HR response at a given work rate PHIE.

Adult↗
PubMed1996

Traumatic brain injury, alcohol and quantitative neuroimaging: preliminary findings.

Magnetic resonance (MR) quantitative neuroimaging analysis was undertaken with a large group of normal (n = 197) and traumatically brain injured (TBI, n = 99) adults. Of the TBI subjects 18 patients were identified with a history of substance-related abuse (TBI/Abuse group). Both the TBI/ Abuse group and the remaining sample of TBI patients (n = 81, TBI/Non-abuse group) without a history of substance-related abuse differed significantly from the control group on most quantitative MR imaging analyses. The TBI/Abuse group displayed the greatest degree of atrophic change. However, the TBI/Abuse group had a significantly lower Glasgow Coma Scale (GCS) score, ostensibly suggesting that those with substance-related abuse suffered more severe brain injury than non-abuse TBI patients. When a subset (n = 18) of the TBI/Non-abuse group was matched by GCS, gender and age to the TBI/Abuse group, both groups differed significantly from the control group on most morphometric measures, but did not differ from one another. Results are discussed in terms of the potential adverse role that substance-related abuse, particularly alcohol, plays in the individual who sustains traumatic injury to the brain.

Adolescent↗
PubMed1996

Advance directives: from the perspective of the patient and the physician.

American physicians and patients share some common ground in their perspectives on advance directives. The majority in both groups strongly endorse the use of these documents. Both groups believe it is the physician's responsibility to initiate the discussion about advance directives. However, a gap between the two perspectives can be defined. In end-of-life decision making, physicians balance the ethical principle of patient autonomy with other principles such as appropriate withholding of care in the setting of futility. Patients' preferences for end-of-life care are most influenced by expected outcomes. Physicians tend to be selective in their indications for initiating a discussion about advance directives, according to clinical factors. In contrast, most patients want to discuss advance directives with their physician under all circumstances.

Advance Directives↗
PubMed1996

Tricare: the military's version of managed care.

The Tricare program is a triple-option health delivery model that integrates health services for the nation's military. The author reviews the newest incarnation of the Department of Defense's attempts at providing managed care to CHAMPUS beneficiaries.

Catchment Area, Health↗
PubMed1996

Like father, like son: young children's understanding of how and why offspring resemble their parents.

4 studies investigated the broad claim that preschoolers understand biological inheritance. In Study 1, 4-7-year-old children were told a story in which a boy was born to one man and adopted by another. The biological father was described as having one set of features (e.g., green eyes) and the adoptive father as having another (e.g., brown eyes). Subjects were asked which man the boy would resemble when he grew up. Preschoolers showed little understanding that selective chains of processes mediate resemblance to parents. It was not until age 7 that children substantially associated the boy with his biological father on physical features and his adoptive father on beliefs. That is, it was not until age 7 that children demonstrated that they understood birth as part of a process selectively mediating the acquisition of physical traits and learning or nurturance as mediating the acquisition of beliefs. In Study 2, subjects were asked whether, as a boy grew up, various of his features could change. Children generally shared our adult intuitions, indicating that their failure in Study 1 was not due to their having a different sense of what features can change. Studies 3 and 4 replicated Study 1, with stories involving mothers instead of fathers and with lessened task demands. Taken together, the results of the 4 studies refute the claim that preschoolers understand biological inheritance. The findings are discussed in terms of whether children understand biology as an autonomous cognitive domain.

Adoption↗