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Biomedical subjects

M H Johnson

Publications and source records attributed to M H Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1999

The medical ethics of paid egg sharing in the UK.

Paid egg sharing occurs when infertile patients receive infertility treatment free or at reduced cost in exchange for sharing some of their eggs with patients who require donated eggs. This approach to treatment is discussed in the context of the four principles of medical ethics, namely respect for autonomy, justice, beneficence and non-maleficence. The implications of these ethical considerations for responsible practice and regulation are considered.

Ethics, Medical↗
PubMed1999

Treatment of posttraumatic ocular dysmotility using autogenous buccal fat grafts in a porcine model.

Diplopia occurring after orbital trauma is a complex and difficult clinical problem. Numerous potential mechanisms exist by which it may occur. Restrictive ocular dysmotility caused by intraorbital scarring is a major component in diplopia's pathogenesis. The current large animal study was conducted to develop an experimental model of restrictive ocular dysmotility that would quantitatively characterize the biomechanical properties of the globe rotations. Using this model, a novel method of restoring the low-friction milieu within the orbit by interposing a buccal fat graft was tested. In the initial stage, the baseline force duction was measured in 20 pig eyes using a highly sensitive, digital tensiometer. Traumatic violation of Tenon's fascia with electrocautery into the extraconal fat and the periorbita was followed by direct suturing of the extraocular muscle to the nearest orbital periosteum. After 6 weeks, the measurements (again in the field of the traumatized muscle) were repeated, and the eyes were divided into two treatment groups (n = 10 eyes per group). The left eye received the standard lysis of adhesion, whereas the right eye received lysis and buccal fat interposition grafting. The third and final force measurements were performed 6 weeks after treatment. The results showed a baseline linear load-displacement curve of 0 to 8 mm, with the globe rotating 400 microm for every 1000 mg of tensile load. Surgical trauma increased the slope as defined by load/displacement but, surprisingly, the relationship remained linear in the entire range from 2 to 8 mm. This linear relationship was seen in all stages: baseline, after trauma to Tenon's fascia, after surgical lysis alone, and after lysis with buccal fat interposition. The difference was in the slope, or stiffness. Lysis alone partially reduced the slope, but it was still higher than baseline. Lysis and buccal fat grafting returned the slope to near baseline. This, however, did not reach the level of statistical significance. It seems that a focal intervention along the course of an extraocular muscle altered the composite behavior of orbital resistance to globe rotation. Although buccal fat grafting did not significantly improve motility, it did not worsen it.

Adipose Tissue↗
PubMed1999

Sham radiation in clinical trials assessing radiotherapy for exudative age-related macular degeneration.

BACKGROUND: To evaluate the effectiveness of sham radiation treatments in masking patients to their randomization group in the Radiation of Age-Related Macular Degeneration (ROARMD) Study. METHODS: Patients with choroidal neovascularization complicating age-related macular degeneration were randomized to a treatment (RAD) group that received external beam irradiation (seven treatment sessions) or to a control (SHAM) group that received sham radiation (one sham treatment session). During a telephone survey, 62 of 73 randomized patients responded to the following questions: Do you think you received radiation? Why do you feel that way? Did the vision in your study eye worsen after enrollment? RESULTS: Eighty-one percent of the RAD group and 59% of the SHAM group thought that they had received radiation. In patients who thought that their vision had stabilized or improved, 82% thought that they had received radiation. In patients who thought that their vision was worse, only 39% thought that they had received radiation. In 54% of patients, subjective perception of vision influenced their guess as to whether they received radiation. CONCLUSIONS: Subjective patient perception of visual outcome was the most influential variable for masking. Variation between radiation treatment and sham session techniques, such as equipment used and duration of treatments, played a lesser role in the masking of patients. Seven treatment days correlated with a higher number of patients who thought that they had received radiation. Although our procedures do not strictly mask the two groups, one sham radiation session was effective in keeping patients guessing their randomization group.

Aged↗
PubMed1999

The effect of blood transfusion protocol on retinopathy of prematurity: A prospective, randomized study.

OBJECTIVE: Controversy exists regarding the potential influence of anemia and blood transfusions on the rate of retinopathy of prematurity (ROP) in premature infants. A prospective, randomized, masked trial was performed to determine the influence of red blood cell transfusion protocol on ROP incidence and severity in a population of high-risk infants. METHODS: A total of 50 infants with birth weights <1251 g were divided randomly into two groups beginning on day of life 29. Group 1 (n = 24) received red cell transfusions during the 6-week study period, only if certain symptom-based guidelines were met. Group 2 (n = 26) received red cell transfusions to maintain the hematocrit level above 40% for the entire 6 weeks. Infants were monitored for ROP, growth, and associated morbidity. Serial measurements of serum glucose, lactate, ferritin, total iron-binding capacity, and iron were performed. RESULTS: ROP occurred in 83% of infants in group 1, and 73% of infants in group 2. There were no statistically significant differences in ROP severity, intraventricular hemorrhage, bronchopulmonary dysplasia, necrotizing enterocolitis, or any of the laboratory values except hemoglobin (10.8 vs 13.2 g/dL) and hematocrit (33.9% vs 41.8%) between the groups. Combining data from both groups, there was no association between hemoglobin or hematocrit ratios and ROP incidence or severity. CONCLUSIONS: A transfusion policy aimed at limiting the amount of blood given to premature infants (symptom-based) during the neonatal period does not impart a significantly different risk for ROP or other associated conditions, than does a policy in which transfusions are given more liberally for replacement purposes.

Erythrocyte Transfusion↗
PubMed1999

Contact transscleral diode cyclophotocoagulation for refractory glaucoma.

PURPOSE: To evaluate the effect of contact transscleral diode cyclophotocoagulation on intraocular pressure (IOP), vision, number of medications, and complications in a heterogenous population of patients with refractory glaucoma. METHODS: Clinical data for all patients undergoing contact transscleral diode cyclophotocoagulation for refractory glaucoma at the Medical College of Georgia between November 1994 and November 1996 were reviewed. Forty-seven eyes of forty-seven patients followed for at least one month were included. Visual acuity, IOP, number of medications, and complications were noted for follow-up periods as long as 24 months. RESULTS: At final follow-up examination (range 1-24 months, median 9 months), the average decrease in IOP was 21+/-16 mmHg. Thirty-one (66%) patients had final IOP between 7 and 21 mmHg. Medications were decreased by an average of 1.1. Twenty-six (62%) of 42 patients with vision before surgery had stable or improved visual acuity at the final follow-up visit; 16 (38%) had a deterioration in visual acuity. Neovascular glaucoma was associated with a posttreatment IOP less than 7 mmHg. CONCLUSION: Contact transscleral diode cyclophotocoagulation is effective in lowering IOP in eyes with refractory glaucoma. It also serves to reduce the number of medications required for appropriate IOP control. Loss of visual acuity remains an important concern. Acute complications tend to be transient. Further study is needed to identify patients at risk for markedly reduced IOP after this procedure and for modulation of the protocol to decrease such risk.

Adolescent↗
PubMed1998

How tumor stage affects surgeons' surveillance strategies after surgery for carcinoma of the upper aerodigestive tract.

BACKGROUND: The factors that influence decision-making among surgeons are not well understood. The authors evaluated how tumor stage in otherwise healthy patients subjected to potentially curative surgery for upper aerodigestive tract (UADT) epidermoid carcinoma affects the self-reported follow-up strategies employed by practicing surgeons. METHODS: Hypothetical patient profiles and a detailed questionnaire based on these profiles were mailed to the 824 members of the Society of Head and Neck Surgeons (SHNS) and the 522 members of the American Society for Head and Neck Surgery who were not members of SHNS. The effect of TNM stage on the surveillance strategies chosen by the respondents was analyzed. RESULTS: Ten of the 14 most commonly employed surveillance modalities were ordered significantly more frequently with increasing TNM stage. This effect persisted through 5 years of follow-up, but the differences across stages were small. Only 30% of respondents modified their strategies according to the patient's TNM stage. CONCLUSIONS: Most surgeons performing surveillance after potentially curative surgery in otherwise healthy patients with UADT carcinoma use the same follow-up strategy irrespective of TNM stage. These data permit rational design of a randomized clinical trial of two alternate follow-up plans.

Adult↗
PubMed1998

Fulminant jejuno-ileitis following ablation of enteric glia in adult transgenic mice.

To investigate the roles of astroglial cells, we targeted their ablation genetically. Transgenic mice were generated expressing herpes simplex virus thymidine kinase from the mouse glial fibrillary acidic protein (GFAP) promoter. In adult transgenic mice, 2 weeks of subcutaneous treatment with the antiviral agent ganciclovir preferentially ablated transgene-expressing, GFAP-positive glia from the jejunum and ileum, causing a fulminating and fatal jejuno-ileitis. This pathology was independent of bacterial overgrowth and was characterized by increased myeloperoxidase activity, moderate degeneration of myenteric neurons, and intraluminal hemorrhage. These findings demonstrate that enteric glia play an essential role in maintaining the integrity of the bowel and suggest that their loss or dysfunction may contribute to the cellular mechanisms of inflammatory bowel disease.

Animals↗
PubMed1998

A cytoplasmic cell cycle controls the activity of a K+ channel in pre-implantation mouse embryos.

We previously have reported that the activity of a 240 pS K+ channel varies during the cell cycle in pre-implantation mouse embryos. In the present study, we show that: (i) the cycling of channel activity is not prevented by inhibiting protein synthesis and hence does not involve cyclin-dependent kinase 1 (cdk1)-cyclin B; and (ii) the cycling of channel activity continues in anucleate zygote fragments with a time course similar to that observed in nucleate fragments. We further demonstrate that: (i) persistent activation of the K+ channel in one-cell embryos arrested in metaphase requires the maintenance of an active cdk1-cyclin B complex; and (ii) both DNA synthesis inhibition with aphidicolin and DNA damage produced by mitomycin C prevent the down-regulation of the channel at the start of S phase by a mechanism that requires tyrosine kinase activation. Thus, the 240 pS K+ channel in these cells is controlled by a previously unsuspected cytoplasmic clock that functions independently of the well-known clock controlling the chromosomal cell cycle, but can interact with it.

Actin Cytoskeleton↗
PubMed1998

Tropomyosin in preimplantation mouse development: identification, expression, and organization during cell division and polarization.

Tropomyosin is an actin-binding cytoskeletal protein which has been extensively characterized in a variety of cell types and tissues, with the exception of very early developmental stages during which cellular polarization first occurs. We have identified five polypeptides in mouse preimplantation conceptuses which show many of the characteristics of tropomyosin. They form the major portion of the heat-stable cytoskeletal protein fraction of blastomeres and have the characteristic isoelectric and SDS-PAGE migration characteristics on 1-D and 2-D gels. All five polypeptides were synthesized in late 2- and 4-cell, and all 8-cell stages, with three of the five polypeptides showing lower synthetic levels in fertilized eggs and early 2-cell conceptuses. These heat-stable proteins showed specific differences from proteins isolated from mouse 3T3 fibroblasts by the same method, namely higher Mr isoforms were not represented, also some of the isoforms can be labeled by incorporation of [14C]proline. The cellular distribution of tropomyosin in early stage conceptuses was examined using monoclonal and affinity-purified polyclonal antibodies. Tropomyosin becomes associated both with the blastomere cortex postfertilization and with the cleavage furrow during cytokinesis. The interphase cortical association is uniform until the 8-cell stage, when tropomyosin becomes associated with the developing apical pole and is excluded from the basolateral cortex. This polar localization is inherited along with the pole at the 8- to 16-cell division, but experiments in which cell division is artificially prolonged show that tropomyosin localization does not represent a permanent marking of the pole. We conclude that the early mouse conceptus contains a unique and specific set of tropomyosins which respond to polarizing signals.

3T3 Cells↗
PubMed1998

Cell cycle regulation of a T-type calcium current in early mouse embryos.

In this paper we report that the amplitude of the T-current changes in a cell cycle-dependent manner in single- and two-cell embryos, being large in unfertilized oocytes and decreasing after fertilization throughout the first cell cycle to a minimum in early M phase, before increasing again during late telophase. This increase can be prevented by arresting the cell cycle in metaphase, but is not prevented by cytochalasin D. During the second cell cycle the T-current remains large until late G2 phase when it decreases. Protein synthesis inhibition has no effect on the changes in T-current amplitude during the cell cycle. This finding, along with the observation that the size of the T-current does not increase until mitosis exit, suggests that cell cycle regulation of the current does not involve the cycling of cyclin-dependent kinase (cdk)1/cyclin B activity. Inhibition of the T-current with pimozide has no effect on cleavage. The cell cycle-dependent changes in T-current amplitude appear to be driven by the same cdk1/cyclin-B-independent clock that we have previously shown to drive cyclic changes in K+ channel activity in early mouse embryos. Thus, multiple ion transport systems in the preimplantation mouse embryo are controlled by this cdk1/cyclin-B-independent clock.

Animals↗
PubMed1998

Neural correlates of saccade planning in infants: a high-density ERP study.

Neural correlates of saccade planning in 6-month-old infants were investigated by high-density event-related potentials. Subjects made saccades to a target stimulus following a time gap from fixation stimulus offset (gap trials) or with the fixation stimulus still present (overlap trials). Like adults, infants were slower to make a saccade to the target when the fixation stimulus was still present. Strikingly, infants did not show clear evidence of the pre-saccadic components observed in adults which are thought to reflect cortical saccade planning processes. They did, however, show a left frontal positivity, which we suggest reflects cortical disinhibition of the colliculus initiated by fixation stimulus offset, and clear post-saccadic lambda waves. These results indicate that the frontal cortex already plays a role in action control by 6 months of age, while other aspects of cortical action planning may not yet be present in certain task situations.

Electroencephalography↗
PubMed1998

A neuro-ophthalmologist's perspective on neuroradiology.

The practice of neuro-ophthalmology includes evaluating patients for visual signs and symptoms for neurological causes. Responsible lesions are often small and in places not well imaged on routinely ordered brain imaging studies. To achieve a proper diagnosis, the clinician must have a close working relationship with the radiologist to choose the appropriate imaging study and to correctly focus the study based on clinical findings.

Adult↗
PubMed1998

Restricted ocular motility after orbital trauma--studies with an animal model.

OBJECTIVE: Our purpose was to develop a quantitative model of restricted ocular motility (fat adherence syndrome) in the pig orbit to facilitate research into pathogenesis and treatment. METHODS: Twenty eyes of 10 pigs were used in an attempt to create a fibrous adhesion between either the inferior rectus or the medial rectus muscle and the adjacent periorbita. Quantitative forced ductions were performed preoperatively and 6 weeks postoperatively with an electronic force gauge. RESULTS: Forced ductions displayed a linear relationship to displacement over the range tested, both preoperatively and postoperatively. Although increased resistance to forced ductions was produced in 10 of the 20 (50%) eyes, the average changes were not statistically significant. The absolute change in force (Postoperative--Preoperative) was linearly related to the amount of ocular rotation. Reproducibility of measurements was markedly improved by the use of a motorized forced duction apparatus compared with manual rotation. CONCLUSIONS: The results from this study, and those from previous work, suggest that the classic fat adherence syndrome is an uncommon event, even after significant soft tissue injury in the orbit. Further studies are needed to more completely define the risk factors and pathogenesis of the fat adherence syndrome and the suitability of the pig orbit as a model.

Adipose Tissue↗
PubMed1998

A survey of the effectiveness of the assessment of the welfare of the child in UK in-vitro fertilization units.

Seventy-one clinics in the UK offering in-vitro fertilization (IVF) treatment were surveyed for their protocols on the assessment of the welfare of the children produced. A total of 44 (62%) responded. Of these, five (12%) did not have operational protocols, seven (16%) declined to provide their protocols, and 32 (73%) provided information used in the survey. The information was in the form of a protocol for only 16 (50%) of these clinics. The remaining clinics submitted as their 'protocols' letters to general practitioners, patient information, patient questionnaires and/or a copy of their policy on the assessment of child welfare. From the submitted material, it was possible to determine that 94% of clinics seek information on aspects of child welfare assessment, 78% have a procedure for making further enquiries where there is any cause for concern, 44 % include counselling opportunities explicitly in protocols, 30-38% of clinics see a full medical and social history from each prospective parent as part of the child welfare assessment, 16% include explicit consideration of the impact of multiple births on the welfare of the child, and 3% include consideration of the issue of disclosure of the mode of conception of the child on its welfare. Most clinics did not have clearly defined procedures on how to reach a decision on whether or not to treat. Eight clinics (25%) made explicit in their protocols any exclusion criteria. It is concluded that clinics are not currently producing completely effective protocols. Two possible reasons for this are considered: lack of technical knowledge about what constitutes an effective protocol, and lack of clear policy development and propagation underlying protocols within clinics. Possible approaches to improving the situation are considered.

Adult↗
PubMed1998

The effects of imagery and sensory detection distractors on different measures of pain: how does distraction work?

OBJECTIVES: Two experiments compared the effects of different distraction tasks on pain. Based on multiple-resource theory, Expt 1 predicted that the more a distractor shares processing resources with pain perception the greater the interference between the two. Experiment 2 tested whether the emotional content of the distractor would differentially effect measures that are supposedly reflective of the affective component of pain. DESIGN: Both experiments used repeated measures designs, with counterbalanced distraction conditions. METHODS: In Expt 1 20 participants indicated their pain threshold. No instructions, or one of three distraction conditions were presented across four blocks of potassium iontophoresis. The distractors were: thermal and light detection, and neutral imagining. In Expt 2 30 participants had three blocks of pain threshold, pain tolerance, and pain rating trials. For threshold, tolerance, and rating trials, one block was without distraction, a second block was completed during light detection, and a third block while imagining an enjoyable holiday. RESULTS: In Expt 1 all the distractors increased pain threshold. The two detection tasks were similarly effective, and more so than the imagination task. Performance on the two detection tasks was impaired by painful stimulation similarly for both tasks. In Expt 2 the visual detection distractor increased pain threshold and tolerance and reduced pain ratings while pleasant imagery only increased pain threshold. CONCLUSIONS: These results indicate that a task that requires attention to external cues has more impact on pain than either a positive or neutral imagination task. However, it is not clear that the specific resources used by the distraction tasks moderated pain differentially as predicted by multiple-resource theory.

Adult↗
PubMed1998

The prevalence of multiple sclerosis in the Leeds Health Authority.

OBJECTIVES: To determine the prevalence of multiple sclerosis in the Leeds Health District. METHODS: Multiple sources of case ascertainment were used-namely, neurology departments, hospital episode statistics, general practitioners, the Leeds branch of the Multiple Sclerosis Society, the West Yorkshire Multiple Sclerosis Therapy Centre, community physiotherapists and occupational therapists, the Leeds Wheelchair Centre, and the Young Disabled Unit. Data collection was from retrospective analysis of hospital and primary care case records. A population based incidence register was established by prospectively registering all new patients with diagnoses of multiple sclerosis. RESULTS: On prevalence day, 30 April 1996, 712 people with multiple sclerosis were identified living in Leeds (population 732,061), giving a prevalence of 97/10(5). The prevalence for definite and probable multiple sclerosis was 84/10(5), and for suspected multiple sclerosis it was 13/10(5). The sex ratio of prevalent people with multiple sclerosis was 2.79 to 1 women to men. The mean age of prevalent cases was 51 years, the mean age at symptom onset was 34 years, and the mean duration of disease was 16 years. Forty cases were prospectively reported as incident cases from 1 November 1995 to 1 February 1996. CONCLUSIONS: The prevalence of multiple sclerosis in Leeds was found to be similar to that in the south of the United Kingdom but lower than that in Scotland. There is no evidence of a latitudinal gradient of increasing prevalence of multiple sclerosis from the south to the north of England.

Adult↗
PubMed1998

Head and neck vascular anatomy.

Conventional computed tomography (CT) and magnetic resonance (MR) angiography provide excellent vascular images; however, every radiologist interpreting routine cross-sectional imaging of the head and neck must recognize normal and abnormal vascular structures. Knowledge of the normal cross-sectional appearance of vessels can help to define spacial anatomy and provide for recognition of abnormal vessels. Intracranially, the major arterial branches of the Circle of Willis are routinely visualized on MR and CT, as are the dural venous sinuses and major tributaries to the deep and superficial venous system. Using a combination of CT and MR images, we demonstrate the normal cross-sectional vascular anatomy of the head and neck and the important anatomic relationships key to accurate imaging analysis.

Angiography↗