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Biomedical subjects

M A Thomas

Publications and source records attributed to M A Thomas.

At least 19 recordsLinked to original sources
PubMed2001

Menstrual cycle-related brain metabolite changes using 1H magnetic resonance spectroscopy in premenopausal women: a pilot study.

Proton magnetic resonance spectroscopy (1H-MRS) was used to assess neurochemical brain changes across the menstrual cycle in five women with premenstrual dysphoric disorder (PMDD) and six control subjects. Women with PMDD and control subjects were scanned on days 8 and 26 within one menstrual cycle (i.e. at times of complete absence and height of PMDD symptoms, respectively). The point resolved spectroscopic sequence (PRESS) was used to localize a voxel of 8 ml in the medial frontal gray matter and in the occipito-parietal white matter. The ratio of N-acetyl-aspartate to creatine in the region of the medial prefrontal cortex and the cingulate gyrus declined significantly from the follicular to the luteal phase in both groups of subjects. The menstrual phase-dependent significant increase in the ratio of choline to creatine was observed in the parietal white matter. The myo-inositol/creatine ratio exhibited a trend toward higher levels in the PMDD patients in the luteal phase of the menstrual cycle. Differences between PMDD and control subjects were not statistically significant. Menstrual cycle phase-dependent changes in ovarian hormonal concentrations may influence the neurochemistry of brain activity in premenopausal women.

Adolescent↗
PubMed2001

Localized two-dimensional shift correlated MR spectroscopy of human brain.

A two-dimensional (2D) chemical shift correlated MR spectroscopic (COSY) sequence integrated into a new volume localization technique (90 degrees -180 degrees -90 degrees ) is proposed for whole-body MR spectroscopy (MRS). Using the product operator formalism, a theoretical calculation of the volume localization as well as the coherence transfer efficiencies in 2D MRS is presented. Phantom model solutions were used to test and optimize the efficiency of the proposed sequence. A combination of different MRI transmit/receive RF coils was used: a head MRI coil and a 3" surface coil receive combined with a body coil transmit. The J cross-peaks due to N-acetyl aspartate (NAA), glutamate/glutamine (Glx), myo-inositol (mI), creatine (Cr), choline (Ch), aspartate (Asp), gamma-aminobutyrate (GABA), taurine (Tau), glutathione (GSH), threonine (Thr), and macromolecules (MM) were identified. The cross-peak intensities excited by the proposed 2D sequence were asymmetric with respect to the diagonal peaks. Localized COSY (L-COSY) spectra of cerebral prefrontal and occipital gray/white matter regions in 15 healthy controls are presented. Magn Reson Med 46:58-67, 2001.

Adult↗
PubMed2001

Limited macular translocation for the management of subfoveal retinal pigment epithelial loss after submacular surgery.

PURPOSE: To report a case of subfoveal retinal pigment epithelial (retinal pigment epithelium) loss after submacular surgery managed successfully by limited macular translocation. METHODS: Case report. RESULTS: A 28-year-old woman presented with a visual acuity of 20/100 caused by subfoveal choroidal neovas-cularization secondary to ocular histoplasmosis syndrome. Submacular resection of the choroidal neovascularization was complicated by inadvertent retinal pigment epithelium loss from beneath the foveal center. She underwent limited macular translocation 5 days after the initial surgery and had successful displacement of the fovea to an area inferior to the retinal pigment epithelium defect. Her visual acuity was 20/60 4 months postoperatively. CONCLUSION: This report demonstrates the feasibility of using limited macular translocation for the management of eyes with central retinal pigment epithelium defect after submacular surgery and extends the clinical indications for limited macular translocation.

Adult↗
PubMed2001

Macular translocation: unifying concepts, terminology, and classification.

PURPOSE: To describe some unifying concepts, terminology, and classification of macular translocation so as to facilitate communication within the scientific community. METHODS: A panel of ophthalmologists with expertise in macular translocation reviewed available data and developed some unifying concepts, terminology, and classification of macular translocation. RESULTS: Macular translocation may be defined as any surgery that has a primary goal of relocating the central neurosensory retina or fovea intraoperatively or postoperatively specifically for the management of macular disease. It may be classified according to the size of the retinotomy and, where applicable, the technique of chorioscleral shortening used. The direction of macular translocation is denoted by the movement of the neurosensory macula relative to the underlying tissues. Effective macular translocation may be defined as successful intraoperative or postoperative relocation of the fovea overlying a subfoveal lesion to an area outside the border of the lesion. The concepts of minimum desired translocation and median postoperative foveal displacement can give some useful idea of the likelihood of effective macular translocation before surgery. CONCLUSIONS: Use of a common standardized terminology for macular translocation will facilitate communication within the scientific community and enhance further research in this area. However, the definitions, terms, classification, and concepts concerning macular translocation are likely to continue to evolve as macular translocation undergoes further modifications and refinements.

Humans↗
PubMed2001

An evaluation of the performance of blood gas analysis in the UK using tonometered haemolysate material.

WEQAS is one of the largest and the most rapidly expanding national EQA Schemes in the UK with over 500 participants. Since April 1995, the Scheme has distributed a tonometered protein-based aqueous material for blood gas analytes (H(+), pCO2, pO2), electrolytes, glucose and lactate. Current performance of the new generation of blood gas analysers show marked bias between analysers which a number of manufacturers have attributed to a "matrix" effect. This study was undertaken to investigate the "true" analytical performance of these analysers utilising a tonometered haemolysate blood product with oxygen saturation kinetics identical to that of fresh blood. One hundred laboratories that represented the major analyzers used in the UK were selected to participate in the study. Participants were asked to analyse the samples within 1 week of tonometry of the material. Performance data, expressed as interlaboratory variation, was compared with concentration matched data from the same group using the aqueous material. Significant improvement in instrument Bias was observed for the AVL Omni and iStat analysers for pO2). Surprisingly, there was also an improvement in bias for the electrolyte parameters on the IL synthesis. However, a significant positive bias was observed for the AVL Opti for Potassium and for the Nova analyzer for glucose using this material. Similar performance was observed for the co-oximetry, parametres for fresh and lyophilised material for the majority of analyzers.

Blood Gas Analysis↗
PubMed2001

Decreased anterior cingulate myo-inositol/creatine spectroscopy resonance with lithium treatment in children with bipolar disorder.

This project was designed to compare differences in brain proton spectra between children and adolescents with bipolar disorder (BPD) and gender and age-matched normal controls, and to measure changes in myo-inositol levels following lithium therapy, utilizing in vivo proton magnetic resonance spectroscopy (1H MRS). A single voxel (2x2x2 cm3) was placed in brain anterior cingulate cortex for acquisition of the 1H spectra at baseline and after acute (7 days) lithium administration in 11 children (mean age 11.4 years) diagnosed with BPD, and in 11 normal controls. Acute lithium treatment was associated with a significant reduction in the myo-inositol/creatine ratio. This decrement was also significant in lithium-responders when analyzed separate from non-responders. Compared to normal controls, BPD subjects showed a trend towards a higher myo-inositol/creatine during the manic phase. These preliminary data provide evidence that a significant reduction in anterior cingulate myo-inositol magnetic resonance may occur after lithium treatment, especially among responders. Follow-up studies involving a larger sample may allow us to confirm whether changes in myo-inositol associated with acute lithium therapy persist in long-term clinical response of patients with and without lithium compliance.

Adolescent↗
PubMed2001

Vascular function of the peripheral circulation in patients with nephrosis.

BACKGROUND: Nephrotic syndrome is associated with abnormal lipoprotein metabolism and increased risk of coronary heart disease. Endothelial dysfunction, an early phase of atherogenesis that manifests as impaired flow-mediated dilation (FMD) of the peripheral circulation, may link these associations. METHODS: We examined endothelial function of the brachial artery and forearm resistance arteries in 15 patients with nephrosis (NP), 15 patients with primary hyperlipidemia (HL) alone, and 15 normolipidemic, nonproteinuric subjects (NC) matched for age, sex, and weight. The NP and HL groups had similar serum cholesterol and triglyceride concentrations. Post-ischemic FMD (endothelium-dependent) and glyceryl trinitrate-mediated dilation (GTNMD; endothelium-independent) of the brachial artery were studied using ultrasonography and computerized edge detection software. Postischemic forearm blood flow was also measured using plethysmography. RESULTS: Postischemic FMD of the brachial artery was significantly lower in the NP and HL groups compared with NC group (mean +/- SE): NP 4.91 +/- 0.8%, HL 4.53 +/- 0.6%, NC 8.45 +/- 0.5% (P < 0.001). There were no significant differences among the groups in baseline diameter and GTNMD of the brachial artery, nor in maximal forearm blood flow and flow debt repayment of the forearm microcirculation. Significant differences in FMD among the groups were principally related to differences in serum low-density lipoprotein cholesterol. CONCLUSIONS: Patients with NP have abnormal endothelium-dependent but preserved endothelium-independent dilation of the brachial artery following an ischemic stimulus. Postischemic forearm microcirculatory function is unimpaired. Dyslipoproteinemia is probably the principal cause of endothelial dysfunction of conduit arteries in patients with NP and the basis for their increased risk of cardiovascular disease.

Adult↗
PubMed2001

Racial and economic demographics of couples seeking infertility treatment.

OBJECTIVE: We characterized new infertility patients on the basis of race and economic factors. STUDY DESIGN: A retrospective chart review was performed of all patients seeking infertility evaluation from 1998 to 1999 at two infertility centers in Cincinnati, Ohio. Patients were categorized by race (white, black, or other). Statistics were analyzed by chi2 and logistic regression. RESULTS: Of 756 patients, 85.2% were white, 10.2% were black, and 4.4% were other. Infertility diagnoses were placed into the following 7 categories: ovarian, salpingitis, surgical sterilization, male factor, endometriosis, unexplained, and other. Black women had significantly more salpingitis than did nonblack women (P <.001) regardless of insurance status. However, surgical sterilization was more prevalent in patients without insurance regardless of race (P <.001). CONCLUSIONS: Our findings are consistent with previous studies showing that black women have more risk factors for salpingitis. Surgical sterilization risk factors were concordant with those of the National Center for Health Statistics.

Black or African American↗
PubMed2000

Molecular phylogenetic analysis of evolutionary trends in stonefly wing structure and locomotor behavior.

Insects in the order Plecoptera (stoneflies) use a form of two-dimensional aerodynamic locomotion called surface skimming to move across water surfaces. Because their weight is supported by water, skimmers can achieve effective aerodynamic locomotion even with small wings and weak flight muscles. These mechanical features stimulated the hypothesis that surface skimming may have been an intermediate stage in the evolution of insect flight, which has perhaps been retained in certain modern stoneflies. Here we present a phylogeny of Plecoptera based on nucleotide sequence data from the small subunit rRNA (18S) gene. By mapping locomotor behavior and wing structural data onto the phylogeny, we distinguish between the competing hypotheses that skimming is a retained ancestral trait or, alternatively, a relatively recent loss of flight. Our results show that basal stoneflies are surface skimmers, and that various forms of surface skimming are distributed widely across the plecopteran phylogeny. Stonefly wings show evolutionary trends in the number of cross veins and the thickness of the cuticle of the longitudinal veins that are consistent with elaboration and diversification of flight-related traits. These data support the hypothesis that the first stoneflies were surface skimmers, and that wing structures important for aerial flight have become elaborated and more diverse during the radiation of modern stoneflies.

Animals↗
PubMed2000

Visual outcome after surgical removal of choroidal neovascularization in pediatric patients.

OBJECTIVE: To assess the visual outcome after surgical removal of choroidal neovascularization (CNV) in pediatric patients. METHODS: A retrospective, noncomparative, consecutive case series of 17 eyes undergoing surgical removal of CNV of various causes in patients aged 18 years and younger. RESULTS: The cause of the CNV was presumed ocular histoplasmosis syndrome in 11 eyes, idiopathic in 3, and optic nerve coloboma, ocular toxoplasmosis, and trauma in 1 eye each. Two eyes had CNV within 100 microm of the center of the foveal avascular zone (juxtafoveal CNV) and 1 eye had peripapillary CNV, while 14 eyes had CNV beneath the geometric center of the foveal avascular zone (subfoveal CNV). In eyes with subfoveal CNV, median preoperative Snellen visual acuity was 20/200 (range, 20/80-3/200). With a median follow-up of 27 months (range, 6-45 months), median final visual acuity was 20/50 (range, 20/20-2/200); 10 (72%) had improvement of 2 or more Snellen lines after surgery, and 6 eyes (43%) had final visual acuity of 20/40 or better. In 3 eyes with juxtafoveal CNV or peripapillary CNV, all eyes had improvement of 4 or more Snellen lines. Postoperative recurrent CNV developed in 6 (35%) of 17 patients; 2 of the eyes underwent a second vitrectomy and 4 received laser treatment for the recurrences. CONCLUSIONS: Pediatric patients may have good recovery of vision after surgical removal of CNV, and the removal of these membranes may be a viable alternative to laser photocoagulation in pediatric patients.

Adolescent↗
PubMed2000

Subretinal surgery for choroidal neovascularization in patients with high myopia.

OBJECTIVE: To analyze the visual outcome in patients undergoing surgical removal of subfoveal choroidal neovascularization (CNV) in eyes with high myopia. METHODS: We retrospectively reviewed the medical records of 48 consecutive patients with high myopia (> or =6 diopters [D]) who underwent vitrectomy with surgical removal of subfoveal CNV. The patient population consisted of 2 groups. Group 1 included 23 patients with findings only of myopic degeneration, and group 2 included 25 patients with presumed ocular histoplasmosis syndrome and myopia of 6 D or more. RESULTS: In group 1, the visual acuity improved by 2 or more Snellen lines in 9 eyes (39%), decreased in 8 eyes (35%), and remained unchanged in 6 (26%), with a mean follow-up of 24 months (range, 8-60 months). The preoperative visual acuity was 20/40 or better in only 1 eye (4%), but 8 (35%) achieved a final visual acuity of 20/40 or better. In group 2, the visual acuity improved in 16 eyes (64%), was stable in 4 (16%), and deteriorated in 5 (20%), with a mean follow-up of 18 months (range, 6-44 months). Only 3 eyes (12%) had a preoperative visual acuity of 20/40 or better, but 11 (44%) achieved a final visual acuity of 20/40 or better. Recurrence occurred in 13 (57%) of the 23 eyes in group 1 and in 9 (36%) of the 25 eyes in group 2. Univariate analysis demonstrated a significant relation between younger patient age (group 1) and absence of postoperative CNV recurrence (group 2) and an improvement of visual acuity (P<.01). CONCLUSIONS: Surgical removal of CNV may provide visual benefit in selected cases of subfoveal CNV associated with high myopia. The determination of whether surgical intervention is appropriate in these cases requires a prospective, randomized, clinical trial.

Adolescent↗
PubMed2000

Submacular surgery to remove choroidal neovascularization associated with central serous chorioretinopathy.

PURPOSE: To report the results of submacular surgery for removal of choroidal neovascularization associated with central serous chorioretinopathy. METHODS: Ten eyes of nine consecutive patients with central serous chorioretinopathy and subfoveal or juxtafoveal choroidal neovascularization underwent pars plana vitrectomy with removal of the choroidal neovascular membrane between January 1994 and January 1999. RESULTS: All 10 eyes (nine patients) were followed postoperatively for at least 6 months. The mean postoperative follow-up was 23 months (range, 6 to 56.5 months). The patients were followed for an average of 6.2 months from the time of symptoms to the removal of the choroidal neovascularization. Preoperative mean best-corrected visual acuity was 20/100 (range, 20/25 to 20/400), and postoperative best-corrected mean visual acuity was 20/60 + 2 (range, 20/20 to 20/400). Seven eyes had improved postoperative visual acuity, with an average of 3.4 lines gained. Of the three eyes that had worse acuity, an average of 1.3 lines of visual acuity was lost; final mean postoperative visual acuity was 20/80 + 1 (range, 20/25 to 20/400). Of the six eyes with symptoms of less than 3 months' duration, four had a final visual acuity of 20/50 or better. All three eyes with 20/300 or worse final visual acuity had loss of foveal retinal pigment epithelium after surgery; the remaining eyes had preserved retinal pigment epithelium with a visual acuity of 20/70 or better. Two eyes had intraoperative peripheral retinal tears, and two eyes had recurrence of the choroidal neovascular complex. CONCLUSIONS: The anatomic and visual results in eyes with choroidal neovascularization associated with central serous chorioretinopathy are modestly encouraging and suggest that submacular surgery for choroidal neovascularization in patients with central serous chorioretinopathy is a treatment option that may salvage good macular function in some eyes.

Adult↗
PubMed2000

Open retinotomy after submacular surgery.

PURPOSE: To report persistent open retinotomy after submacular surgery in patients with presumed ocular histoplasmosis. METHODS: Retrospective review. Five eyes of 5 patients with submacular choroidal neovascularization associated with presumed ocular histoplasmosis had pars plana vitrectomy, detachment of the posterior hyaloid, and surgical removal of the neovascular complex using the small retinotomy technique. All eyes were followed postoperatively for a mean of 47 months (range, 36 to 73 months). RESULTS: In all 5 patients, the open retinotomy persisted after submacular surgery. No complications were associated with the presence of an open retinotomy. CONCLUSION: Persistence of the retinotomy site may occur after submacular surgery. With follow-up of at least 36 months, no significant complication is associated with an open retinotomy site.

Adult↗
PubMed2000

Submacular surgery trials randomized pilot trial of laser photocoagulation versus surgery for recurrent choroidal neovascularization secondary to age-related macular degeneration: I. Ophthalmic outcomes submacular surgery trials pilot study report number 1.

PURPOSE: To report complications and changes in vision during 2 years of follow-up of patients with age-related macular degeneration assigned randomly to surgical removal or to laser photocoagulation of subfoveal recurrent neovascular lesions in a pilot trial designed to test methods, to refine estimates of outcome rates, and to project patient accrual rates for a larger multicenter randomized trial to evaluate submacular surgery. PATIENTS AND METHODS: Eligible patients with previous laser photocoagulation of extrafoveal or juxtafoveal choroidal neovascularization secondary to age-related macular degeneration were enrolled at 15 collaborating clinical centers. Assignments to treatment arm were made by personnel at a central coordinating center. Adherence to eligibility criteria and treatment assignment was assessed centrally at a photograph reading center. Patients were examined at 3, 6, 12, and 24 months after treatment for data collection purposes. Outcome measures reported include treatment complications, adverse events, requirements for additional treatment, and 2-year changes in visual acuity from baseline. RESULTS: Of 70 patients enrolled, 36 were assigned to laser photocoagulation and 34 to submacular surgery; all were treated as assigned. One patient in each group died before the 2-year examination. Visual acuity was measured at the 2-year examination for 31 of the surviving patients (89%) in the laser arm and for 28 of the surviving patients (85%) in the surgery arm. The 2-year measurements for 36 of the 59 patients (61%) were made by an examiner masked to treatment assignment and to the identity of the study eye. Improvements and losses of visual acuity were observed in both treatment arms; 20 of 31 study eyes (65%) in the laser arm and 14 of 28 study eyes (50%) in the surgery arm had visual acuity 2 years after enrollment that was better than or no more than 1 line worse than the baseline level. Changes in visual acuity and the size of the central macular lesions from baseline to the 2-year examination were similar in the treatment arms. Few serious complications were observed in either arm at the time of initial treatment; serious adverse events were rare. During follow-up, 11 laser-treated eyes and 18 surgically treated eyes had additional intraocular procedures. CONCLUSIONS: The data from this pilot trial suggest no reason to prefer submacular surgery over laser photocoagulation for treatment of patients with age-related macular degeneration who have lesions similar to those studied in this pilot trial. Any clinical trial designed to compare submacular surgery with laser photocoagulation in eyes with age-related macular degeneration and subfoveal recurrent neovascular lesions must enroll several hundred patients in order to reach a statistically valid conclusion regarding differences between these two methods of treatment with respect to either changes in visual acuity or complication rates.

Aged↗
PubMed2000

Update on surgical removal of choroidal neovascularization.

Surgical management of choroidal neovascularization may offer patients with subretinal membranes another therapeutic option. Current techniques allow extraction of subretinal membranes, but not all patients have favorable clinical outcomes with such an approach. This article reviews the current state of subretinal surgery and attempts to summarize those characteristics that may predict good surgical results. Vitreoretinal surgical techniques for the management of subretinal membranes are reasonably well established. Certain characteristics of choroidal neovascularization have been identified that may suggest favorable surgical outcomes; however, no randomized prospective data are yet available to show the role of these procedures. The National Institutes of Health-sponsored Submacular Surgery Trials are designed to determine whether surgery or observation is better for eyes with subfoveal choroidal neovascularization in presumed ocular histoplasmosis syndrome or age-related macular degeneration and in eyes with age-related macular degeneration-associated hematomas.

Choroidal Neovascularization↗
PubMed2000

Localization of the murine Niemann-Pick C1 protein to two distinct intracellular compartments.

Niemann-Pick type C (NPC) disease is characterized by an accumulation of cholesterol and other lipids in the lysosomal compartment. In this report, we use subcellular fractionation and microscopy to determine the localization of the murine Niemann-Pick C1 (NPC1) protein. Fractionation of mouse liver homogenates indicates that some NPC1 cosediments with lysosome-associated membrane protein 1 (LAMP1)-containing membranes. However, a significant amount of NPC1 is also found in membranes that do not contain LAMP1. Moreover, fractionation of liver membranes and fibroblasts in the presence of a nonionic detergent showed that a fraction of NPC1 cosediments with caveolin-1 in rafts. Immunofluorescence microscopy of cultured mouse fibroblasts showed that NPC1 is found in two morphologically distinct structures. The first population is characterized by large punctate structures that do not colocalize with major organelle protein markers, but do colocalize with filipin and a small fraction of caveolin-1. Examination of these large NPC1-containing compartments using electron microscopy shows that these structures contain extensive internal membranes. The second population is represented by smaller, more diffuse structures, a fraction of which colocalize with LAMP1-positive compartments. Incubation of fibroblasts with low density lipoprotein (LDL) increases colocalization of NPC1 with LAMP1-containing compartments. This colocalization can be further enhanced by treating fibroblasts with progesterone or chloroquine. The results indicate that NPC1 is associated with an unique vesicular compartment enriched with cholesterol and containing caveolin-1, and that NPC1 cycles to LAMP1-positive compartments, presumably to facilitate the processing of LDL-derived cholesterol.

Amino Acid Sequence↗