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Biomedical subjects

J Marshall

Publications and source records attributed to J Marshall.

At least 235 records · Page 13Linked to original sources
PubMed1994

A Shab potassium channel contributes to action potential broadening in peptidergic neurons.

We have cloned the gene for a potassium channel, Aplysia Shab, that is expressed in the bag cell neurons of Aplysia. The voltage dependence and kinetics of the Aplysia Shab current in oocytes match those of IK2, one of the two delayed rectifiers in these neurons. Like IK2, but in contrast with other members of the Shab subfamily, the Aplysia Shab current inactivates within several hundred milliseconds. This inactivation occurs by a process whose properties do not match those previously described for C-type and N-type mechanisms. Neither truncation of the N-terminus nor block by tetraethylammonium alters the time course of inactivation. By incorporating the characteristics of Aplysia Shab into a computational model, we have shown how this current contributes to the normal enhancement of action potentials that occurs in the bag cell neurons at the onset of neuropeptide secretion.

Action Potentials↗
PubMed1994

Simulated validation of a brief food frequency questionnaire.

Nutrient assessment by the brief 45-item food frequency questionnaire used in the New York State Cohort was simulated by reducing the food list and frequency-of-use categories of the extensive 131-food item semiquantitative questionnaire used in the Health Professionals Follow-up Study. As a validation of the brief questionnaire, daily nutrient intakes were calculated following simulation procedures for 127 men who completed the extensive questionnaire, and the values were compared with those from two 1-week diet records in the same population. Deattenuated correlation coefficients for 25 energy-adjusted nutrient values ranged from 0.12 for iron to 0.76 for vitamin C (mean, 0.26). The brief questionnaire appears reasonably effective in assessing relative dietary intakes of total fat, saturated fat, monounsaturated fat, carbohydrate, dietary fiber, carotene, vitamin C, calcium, potassium, and magnesium. Modest improvements in the correlations for most nutrients were seen when the number of frequency-of-use categories was increased. Correlations decreased when nutrient intakes were calculated using regression coefficients instead of a conventional nutrient database.

Adult↗
PubMed1994

Subtle tubal abnormalities adversely affect gamete intrafallopian transfer outcome in women with endometriosis.

OBJECTIVES: To evaluate prospectively the impact of subtle tubal disorders on GIFT pregnancy rates in women with pelvic endometriosis. DESIGN: A prospective comparison of pregnancy rates in different stages of endometriosis while controlling for the presence of tubal abnormalities. INTERVENTIONS: A total of 146 patients with endometriosis underwent 201 GIFT procedures. During laparoscopy special attention was brought to the fallopian tubes and any anatomical disorders were recorded. Tubal abnormalities included tubal sacculations, diverticulae, convolutions, phimosis, fimbrial agglutination, and peritubal adhesions. Best tube was considered in the final analysis. RESULTS: The presence of tubal abnormalities significantly lowered the pregnancy rates in all stages of endometriosis. When we controlled for age, semen characteristics, number of mature oocytes transferred, and tubal status, the extent of anatomical tubal disorders was the most important prognostic factor in determining pregnancy outcome. CONCLUSION: The extent of tubal abnormalities rather than the stage of endometriosis seems to be an important prognostic factor in determining GIFT pregnancy rates. Couples should be counseled accordingly and accurate prognostic parameters should be explained before enrollment in a GIFT program.

Adult↗
PubMed1994

The effects of topical corticosteroids and plasmin inhibitors on refractive outcome, haze, and visual performance after photorefractive keratectomy. A prospective, randomized, observer-masked study.

BACKGROUND: This study of 86 patients with 12 months of follow-up was designed to determine whether topical corticosteroids or plasmin inhibitors have an effect on the outcome of photorefractive keratectomy. METHODS: Patients were allocated randomly to either steroid (0.1% fluorometholone for 6 months), plasmin-inhibitor (aprotinin 40 IU/ml for 3 weeks), or control (no treatment) groups and underwent either -3.00- or -6.00-diopter (D) corrections. RESULTS: With -3.00-D corrections, the mean refractive change was significantly greater at 3 and 6 months (P < 0.05) in the steroid group compared with the control group. When steroids were discontinued, the difference became insignificant within 3 months. Similarly, with -6.00-D procedures the mean refractive change was greater at 6 weeks and 3 and 6 months (P < 0.01), but the refractive change again became insignificant 3 months after stopping steroid treatment. Four patients treated with steroids had a hyperopic shift greater than +2.00 D of that intended at 12 months. Similar overcorrections were not noted in the other treatment groups. There were no differences in refractive outcome between the aprotinin and control groups at any stage. With -6.00-D procedures, objective measurements of haze were significantly greater in the aprotinin group compared with the control group at 9 and 12 months (P < 0.05). With this exception, there were no differences in haze, forward or backward scatter of light, best-corrected visual acuity, or halo measurements between the groups. CONCLUSIONS: Corticosteroids can maintain a hyperopic shift during their administration, but this effect is reversed on cessation of treatment. Objective tests have shown that steroids have no effect on corneal haze or visual performance after PRK. There is no justification for routinely submitting all patients to long-term steroid regimens and their associated side effects. Treatment with aprotinin produced no beneficial effect on refractive outcome, and haze was greater in the -6.00-D procedures. The concept of modulating the plasminogen activator/plasmin system to regulate wound healing after PRK is discussed.

Adult↗
PubMed1994

Uvulopalatopharyngoplasty: The Leicester experience.

Twenty-nine patients undergoing uvulopalatopharyngoplasty (UPPP) for snoring are presented. Ninety per cent expressed an overall improvement in their symptoms: 21 per cent had complete abolition of snoring. Post-operative complications included nasal regurgitation of food/fluids and hyponasal speech development.

Adult↗
PubMed1994

The role of light scatter in the degradation of visual performance before and after Nd:YAG capsulotomy.

The aim of this study was to determine whether capsulotomy size influences visual performance. Snellen visual acuity and forward light scatter (light scattered towards the patient's retina, but out of the focussed retinal image) measurements using simple computer graphics based on van den Berg's technique were used to measure visual performance. Twelve patients were studied: 4 had small central capsulotomies through undilated pupils and 8 had wide capsulotomies through dilated pupils. The two groups were matched for age and pre-laser Snellen acuity. Following treatment, both groups had equal improvements in Snellen acuity. There was only a significant (p < 0.001) improvement in forward light scatter readings in the group who received wide capsulotomies. Measurements of forward light scatter are more sensitive than Snellen acuity testing in demonstrating loss of visual performance in patients with media opacities. It is recommended that pupils are dilated prior to Nd:YAG capsulotomy if forward light scatter from capsule remnants and the consequent glare disability are to be minimised.

Aged↗
PubMed1994

Disturbances in night vision after excimer laser photorefractive keratectomy.

Eighty-four patients with up to -6.00 dioptres of myopia underwent photorefractive keratectomy (PRK), using 5.00 mm ablation zones. Three months post-operatively 38 (45%) complained of disturbances in night vision, compared with 21 (25%) pre-operatively. In the majority, these disturbances were regarded as negligible. However, 9 (11%) reported significant problems, defined as an inability to drive safely at night with the treated eye. At 12 months, 32 patients (38%) complained of impaired night vision, 4 (5%) of whom had significant problems. A series of measurements were performed to investigate the origins of these disturbances, especially in patients reporting significant problems. Visual impairment from forward scattered light was investigated using a computerised technique. Back scattered light was measured with a charge coupled device-camera system and a computer program was used to assess the degree of halation around a bright light source on a high-resolution monitor. Pupillary diameters were measured by infrared television pupillometry. At 6 months, those reporting a starburst effect around lights at night had small hyperopic shifts, minimal halos and high forward and back light scatter measurements. Patients who reported halo phenomena had large hyperopic shifts, little light scatter and large pupillary diameters. Of the 4 patients who reported significant disturbances at 12 months, all had persistent halo problems. Those with starburst effects in the early post-operative period noticed an improvement with time as their corneal haze gradually improved. Perturbations of night vision after PRK manifest as starbursts and halos around lights.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Phototherapeutic keratectomy for recurrent corneal erosions.

Recurrent corneal erosion may be a difficult disorder to treat, with a number of patients suffering persistent symptoms despite conventional therapy. We present a series of 15 patients (17 eyes) who underwent excimer laser phototherapeutic keratectomy (PTK) for recurrent corneal erosion. In 9 patients a previous episode of corneal trauma could be identified, while in 6 (8 eyes) the problem had occurred spontaneously. The mean duration of symptoms prior to PTK was 13 months (range 6-60 months). All patients had received lubricant ointments, 7 had tried bandage contact lenses and 4 had undergone epithelial debridement with no amelioration of their symptoms. The affect area of epithelium was removed and a 20-30 pulse (5-7 microns) ablation was performed to Bowman's membrane. Great care was taken to avoid the edges of treatment zones from encroaching on the axial cornea. In 11 patients (13 eyes) there was a marked improvement in symptoms post-operatively with no recurrences. The mean follow-up was 11 months (range 6-24 months). Four patients experienced recurrent episodes 3-6 months after PTK and 2 have subsequently been retreated, 1 of whom has been symptom-free for 12 months. Post-operative best corrected visual acuity was unaltered in 9 eyes and improved by at least one Snellen line in 8 eyes. Excimer laser PTK appears to be a safe and promising procedure for recurrent corneal erosion in cases refractory to medical treatment. Further studies are indicated to compare its effectiveness with established surgical procedures.

Adult↗
PubMed1994

[Sensitivity to glare before and after Nd:YAG capsulotomy. Comparison between small and large capsulotomy].

AIM OF THE STUDY: The aim of this study was to determine whether capsulotomy size influences visual performance. PATIENTS AND METHODS: Twenty eyes were included in this study and were divided into two groups: 10 eyes had small central capsulotomies without dilating the pupil, and 10 eyes had large capsulotomies through dilated pupils. We measured both, visual acuity and glare due to forward light scatter using a computer system. RESULTS: Following treatment both groups had equally significant (< 0.001) improvements in visual acuity. However, a significant (p < 0.001) improvement of glare due to forward light scatter was only observed in the eyes with a large size capsulotomy. CONCLUSIONS: Our study showed that measurements of forward light scatter are more sensitive than visual acuity testing in demonstrating loss of visual performance in patients with media opacities. It is recommended that pupils are dilated prior to Nd:YAG capsulotomy if forward light scatter from capsule remnants and the subsequent glare disability are to be minimised.

Aged↗
PubMed1994

The shape of the corneal apical zone after excimer photorefractive keratectomy.

Applying an experimental photo-keratoscope, which assesses the shape of cornea within the pupillary region, to a group of subjects who have undergone excimer laser photorefractive keratectomy over a central 4 mm chord diameter of the cornea, we report the shape of the typical cornea within the ablated zone conforms to a steepening ellipse (average shape factor, 1.25). A statistically significant difference in the mean shape factor (asphericity) between the photoablated and the normal cornea (average shape factor 0.89) was not confirmed. However, there is more variability in the shape factors found in the photorefractive keratectomy group compared with normals, within the same distance from the corneal apex. Using the criterion of overlap within two standard deviations, averaging the vertical horizontal meridians, 75% of photorefractive keratectomy eyes fall within the shape factor limits of the normal eye group. In all cases the post-ablated corneal surface was found to be regular in terms of surface quality alone. The excimer photorefractive keratectomy technique is therefore a clinically acceptable method of refractive surgery.

Adult↗
PubMed1994

[Biochemical and histochemical analysis of age related lipid deposits in Bruch's membrane].

In histochemical studies the age-related deposition of different lipids in Bruch's membrane has been seen. This is important for the pathogeneses of age-related macular degeneration due to changes in diffusion characteristics. Because the specificity of histochemical results is limited, a correlation of histochemical lipid analysis with biochemical methods was performed. The macular Bruch's membrane of 27 donors (age 1-97 years) was analyzed. The results of this analysis demonstrated that the increasing histochemical staining for lipids in Bruch's membrane corresponded with an increasing amount of lipids extracted from Bruch's membrane in biochemical analysis. This lipid deposition progressed exponentially with age. However, a large variation in the type of lipid deposited could be observed, with predominant deposition of phospholipids in some eyes and of neutral lipids in others. Furthermore, the phospholipids extracted were differentiated into 50% phosphatidylcholine, 30% phosphatidylethanolamine and 20% phosphatidylinositol and phosphatidylserin. The deposition of lipids, especially neutral lipids, in Bruch's membrane may change its diffusion characteristics. This appears to be important for the pathogenesis of age-related pigment epithelium detachments. The composition of the phospholipids extracted from Bruch's membrane supports, furthermore, the concept that the material deposited is the result of metabolic limitations in the degradation of photoreceptor outer segment material.

Adolescent↗
PubMed1994

[A description of a new method of quantifying the regurgitant flow in patients with an incompetent mitral valve].

BACKGROUND: It has been shown previously that using color Doppler flow mapping, simple measurements of apparent jet size do not correlate closely with regurgitant flow rate and regurgitant fraction. Recently the proximal flow convergence method has been proposed to quantify valvular regurgitation by analysis of the converging flow field proximal to a regurgitant lesion. Flow rate Q can be calculated as Q = 2 pi r2va where va is the aliasing velocity at a distance r from the orifice. PATIENTS AND METHODS: In 54 patients (43 in sinus rhythm, 11 with atrial fibrillation) with at least mild mitral regurgitation by semi-quantitative assessment, regurgitant stroke volume, regurgitant flow rate, and regurgitant fraction were calculated using the proximal flow convergence method and compared with values obtained by the Doppler/two-dimensional echocardiographic method. RESULTS: Regurgitant stroke volumes (VL) calculated by the proximal flow convergence method correlated very closely with values obtained by the Doppler-2D method with r = 0.93 (y = 0.95x + 0.55) and delta VL = -0.3 +/- 4.0 cm3. Regurgitant flow rates (Q) calculated by both methods showed a similar correlation: r = 0.93 (y = 0.95x + 54) and delta Q = -34 +/- 284 cm3/min. The correlation for regurgitant fraction (RF) calculated by both techniques showed r = 0.89 (y = 0.98x + 0.006) and delta RF = -0.005 +/- 0.06. All correlations were slightly better for the group of patients in sinus rhythm compared with the study group in atrial fibrillation. CONCLUSION: This study demonstrates that the proximal flow convergence method is an accurate and reproducible technique to quantify mitral regurgitation. This approach is easy and less time-consuming than the Doppler-echocardiographic method. While future improvements of this method are to be expected, flow calculations based on the assumption of simple hemispheric symmetry of the proximal flow field appear suitable for clinical application at the present time.

Adult↗
PubMed1993

Sequence and structure of a new coiled coil protein from a microtubule bundle in Giardia.

The flagellate Giardia is reportedly (and controversially) the most primitive eukaryotic organism known to us. The trophozoite is without organelles but has an extensive cytoskeleton of microtubules and associated structural proteins. We have cloned and sequenced overlapping cDNAs and genomic DNAs for a 101,000 M(r) protein involved in microtubule bundling in the median body of G. lamblia cells. The polypeptide chain appears to be mainly alpha-helical with the repeating amphipathic heptapeptides characteristic of a coiled coil molecule, but without homology to known microtubule-associated proteins. Domain analysis suggests a structure in which a rod of three linked coils spans 695 residues (approximately 103 nm), with the ends of the chain forming compact globular head and tail domains of approximately 11 kDa and approximately 7 kDa. The rod domain has internal sequence repeats of 24 residues caused by multiple phase shifts in the coiled coil heptapeptide positions. These repeats have a conserved side-chain pattern which contributes the most significant periodicities in Fourier transforms of the linear distributions of apolar and charged residues. Our best alignment of the pattern has 21 complete repeats of 24 residues and 9 partial repeats of 21 or fewer residues. The apolar residue phase shifts will produce a regular stutter in the hydrophobic core of the coiled coil. This structure is reminiscent of beta-giardin, another coiled coil protein with a broken seam found in the Giardia cytoskeleton. Although the underlying sequence motif is different for the two proteins, the general feature of being regularly divided into segments might relate to a similar mechanism of interaction with microtubules.

Amino Acid Sequence↗
PubMed1993

Corneal light scattering and visual performance in myopic individuals with spectacles, contact lenses, or excimer laser photorefractive keratectomy.

Corneal transparency and visual performance are currently receiving much attention after excimer laser surgery. To date, emphasis has been on comparison of eyes on which laser surgery has been performed to eyes with emmetropia. A more appropriate comparison should be between eyes on which laser surgery has been performed and eyes with other forms of correction for myopia. Forward-scattered light, back-scattered light, and visual acuity were investigated and data were collected from 35 myopic individuals with various types of correction for myopia (spectacles, hard and soft contact lenses, and excimer laser surgery). Forward-scattered light was measured by using a new computerized technique, back-scattered light was measured with a charge coupled device-camera system, and visual acuity was measured with a computerized system at various levels of contrast. Spectacles, hard contact lenses, and excimer laser surgery are all superior to soft contact lenses in terms of light scatter and low-contrast visual acuity and excimer laser photorefractive keratectomy produces comparable results to spectacles one year postoperatively. At low-contrast visual acuity, mean visual acuity was 2.45 minutes of arc for the spectacle wearers, 3.21 minutes of arc for the hard contact-lens wearers, and 5.04 minutes of arc for the soft contact-lens wearers. Excimer laser patients had a mean visual acuity of 9.04 minutes of arc three months postoperatively, and 2.53 minutes of arc after one year. A mean value of 2.4% contrast for forward light scatter was obtained for spectacle wearers compared with a level of 3.84% contrast for hard contact-lens wearers and 16.1% contrast for soft contact-lens wearers. The mean value for excimer laser patients was 20% contrast three months postoperatively and 2.1% contrast one year postoperatively.

Contact Lenses↗
PubMed1993

BK virus infection of the human urinary tract.

By screening consecutive autopsy cases with an antibody that recognizes human polyomaviruses, we found a case of malignant lymphoma in which the virus infection was confined to epithelia of the renal calyces, renal pelvis, ureter, and urinary bladder. The virus was confirmed as BK virus by a specific monoclonal antibody against BK virus T antigen, and numerous virus particles were identified by electron microscopy. The results showed that BK virus is a human urotheliotrophic virus.

Antibodies, Monoclonal↗