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Biomedical subjects

John Marshall

Publications and source records attributed to John Marshall.

104 records · Page 6Linked to original sources
PubMed2002

[Laser epithelial keratomileusis (LASEK): histological investigation for vitality of corneal epithelial cells after alcohol exposure].

BACKGROUND: Laser epithelial keratomileusis (LASEK) is a new surgical procedure to treat myopia. An epithelial flap is created after the exposure to 20 % alcohol and following the laser ablation the epithelium is repositioned to its original location. The advantage of LASEK is that the ablated corneal surface is covered by a full thickness epithelium immediately after surgery. It is hypothesised that this epithelial coverage inhibits the wound healing response of the cornea. However, this concept will only work if the epithelial cells are still vital after the exposure to alcohol. MATERIAL AND METHODS: The vitality of the corneal epithelial cells was investigated in 6 human cadaver eyes after the exposure to 20 % alcohol over 15 to 60 s. The vitality of the corneal epithelial cells was assessed by soaking the specimen in a 0.1 % trypan blue solution and incubated at 37 degrees C for 2 min. After a wash with BSS the specimen were re-incubated at 37 degrees C for 30 min in culture medium. After one more wash with BSS the cells were observed with a standard light microscope. Cells which retained the blue colour would be dead and vital cells would appear clear. Light microscopy and transmission electron microscopy was used to detect morphological changes. RESULTS: Mainly vital corneal epithelial cells were seen for an alcohol exposure time of up to 30 s. In particular the basal epithelial cells appeared alive. With a exposition time of 60 s most cells were dead. CONCLUSION: In LASEK the exposure time of 20 % alcohol is between 20 and 30 s. Based on our results we can conclude that after such exposure time most cells are alive, which is essential for the postoperative wound healing response.

Cell Count↗
PubMed2002

Age-related alterations in the diffusional transport of amino acids across the human Bruch's-choroid complex.

Photoreceptor maintenance is dependent on effective delivery of nutrients from the choroidal circulation by way of the acellular Bruch's membrane and the retinal pigment epithelium. Aging of Bruch's membrane is associated with thickening, increased cross linking of fibers, and deposition of debris culminating in reduced porosity. The present study has investigated the effects of aging on the diffusional transport of eight amino acids across Bruch's membrane in 19 human donors. Diffusion studies were carried out in Ussing chambers, and the amount of time-dependent transfer of amino acids across the preparation was quantified by reverse-phase high-performance liquid chromatography. Diffusion rates for all amino acids showed a significant linear decline with aging of donor. The importance of this reduction in delivery of amino acids is discussed with reference to both normal physiology and age-related macular degeneration.

Adolescent↗
PubMed2002

The design of randomized clinical trials in critically ill patients.

There are a number of difficulties in the conduct of randomized trials in the critically ill. These include difficulties in the definition of diseases and syndromes, a heterogenous population of patients undergoing a variety of therapeutic interventions, and outcomes that may not be able to discriminate between beneficial and risky therapies. Following a brief description of different randomized clinical trials (RCTs) and design philosophies, we outline the effects of different design choices in the complex critical care environment. Once the study topic has been determined to be relevant and important, then the potential investigator must establish whether efficacy or effectiveness will be the focus of the RCT. If an effectiveness design philosophy is chosen, then broad representation of study sites, liberal eligibility criteria, easily implemented intervention study protocols, and patient-centered outcomes should be chosen. The potential investigator wishing to establish efficacy will conduct the study in the centers of excellence and adopt stringent eligibility criteria, rigorous study protocols, and opt for outcomes that will be sensitive to change. In conclusion, we describe some of the major challenges and possible solutions to help a potential investigator through the myriad of difficulties in initiating an RCT in a complex environment.

Critical Care↗
PubMed2002

Expression of metalloproteinases from human retinal pigment epithelial cells and their effects on the hydraulic conductivity of Bruch's membrane.

PURPOSE: To evaluate the expression pattern of matrix metalloproteinases (MMPs) from retinal pigment epithelial (RPE) cells in culture, and to determine their ability to alter the transport properties of human Bruch's membrane. METHODS: Human RPE cells from either primary cultures or a cell line were maintained under culture conditions. At different time intervals after subculturing of cells the presence of MMPs in the bathing medium was determined by zymography. Cellular MMP activity was determined in a similar series of experiments where serum was omitted from the culture medium. Cultured cells were introduced onto Bruch's membrane, mounted in a modified Ussing chamber, to assess entry of MMPs into the membrane. Fluid flow across Bruch's membrane was determined by hydraulic conductivity for different ages of donor tissue, before and after 24 hours' incubation with active MMPs from the RPE-conditioned medium or after incubation with purified activated MMPs. Latent (inactive) MMPs from medium containing serum were used in control experiments. RESULTS: Cultured RPE cells expressed both MMP-2 and -9, with active MMP-2 becoming detectable from 4 days after subculture through to confluence and activated MMP-9 becoming abundant up to 24 hours after subculture. Both active MMPs significantly increased hydraulic conductivity of Bruch's membrane, with the increase after MMP-9 incubation being far greater than that for MMP-2. Both enzymes showed a trend in hydraulic conductivity change with age such that, MMP-2 produced a relatively constant change, whereas MMP-9 showed a greater increase in older eyes. CONCLUSIONS: Activation of both MMP-2 and -9 by cultured RPE cells appeared to show a temporal relationship with the growth cycle of the cells. The activated enzymes increased fluid flow of Bruch's membrane, and the marked effect observed with MMP-9 in older eyes suggests a mechanism that may allow debris removal.

Aged↗
PubMed2001

The PDZ1 domain of SAP90. Characterization of structure and binding.

The structural features of the PDZ1 domain of the synapse-associated protein SAP90 have been characterized by NMR. A comparison with the structures of the PDZ2 and PDZ3 domains of SAP90 illustrates significant differences, which may account for the unique binding properties of these homologous domains. Within the postsynaptic density, SAP90 functions as a molecular scaffold with a number of the protein-protein interactions mediated through the PDZ1 domain. Here, using fluorescence anisotropy and NMR chemical shift analysis, we have characterized the association of PDZ1 to the C-terminal peptides of the GluR6 subunit of the kainate receptor, voltage-gated K(+) channel Kv1.4, and microtubule-associate protein CRIPT, all of which are known to associate with SAP90. The latter two, which possess the consensus sequence for binding to PDZ domains (T/S-X-V-oh), have low micromolar binding affinities (1.5-15 microm). The C terminus of GluR6, RLPGKETMA-oh, lacking the consensus sequence, binds to PDZ1 of SAP90 with an affinity of 160 microm. The NMR data illustrate that although all three peptides occupy the binding groove capped by the GLGF loop of PDZ1, specific differences are present, consistent with the variation in binding affinities.

Adaptor Proteins, Signal Transducing↗
PubMedDate not supplied

Processing of serum proteins underlies the mass spectral fingerprinting of myocardial infarction.

The MALDI-TOF spectra of peptides from the sera of normal and myocardial infarction patients produced patterns that provided an accurate diagnostic of MI. In myocardial infarction, the spectral pattern originated from the cleavage of complement C3 alpha chain to release the C3f peptide and cleavage of fibrinogen to release peptide A. The fibrinogen peptide A and complement C3f peptide were in turn progressively truncated by aminopeptidases to produce two families of fragments that formed the characteristic spectral pattern of MI. Time course and inhibitor studies demonstrated that the peptide patterns in the serum reflect the balance of disease-specific-protease and aminopeptidase activity ex vivo.

Amino Acid Sequence↗
PubMedDate not supplied

Human serum proteins preseparated by electrophoresis or chromatography followed by tandem mass spectrometry.

Electrophoretic and chromatographic sample preparations were compared and together detected the presence of some 600 types of protein products in human serum. Proteins from crude serum preseparated by ionic electrophoresis, chromatography, or a combination of both were analyzed. Proteins were digested with trypsin or chymotrypsin. Naturally occurring peptides were also collected by reversed-phase chromatography. The resulting peptides were identified by tandem mass spectrometry. The peptides were either desorbed by a laser from a metal chip into a quadrupole-time-of-flight mass spectrometer or ionized as an electro-spray from reversed-phase chromatography via a metal needle under voltage into an ion-trap mass spectrometer. All of the commonly known proteins associated with serum were detected, and the two mass spectrometers agreed on the identity of abundant serum proteins. Preseparation of serum proteins prior to digestion markedly enhanced the capacity to detect un-common proteins from blood. Electrophoretic- and chromatography-based experiments were found to be complementary. Many novel cellular proteins not previously associated with serum were recorded.

Blood Proteins↗
PubMedDate not supplied

Cost-effectiveness and cost-utility of long-term management strategies for heartburn.

OBJECTIVES: To compare the expected costs and outcomes of seven alternative long-term primary care strategies for the management of patients with moderate-to-severe heartburn over a 1-year period. METHODS: A decision-analytic model was developed to estimate costs and effects (weeks with heartburn symptoms and quality adjusted life years [QALYs]) for each strategy. Meta-analyses were used to synthesize acute treatment and maintenance studies and physician surveys to collect information on patient management. The impact of uncertainty on the base case results was assessed using probabilistic sensitivity analysis. Probability distributions were defined for key model parameters and techniques of Monte Carlo simulation were used to draw values from these distributions. Cost-effectiveness acceptability curves (CEACs) conditional on the monetary value decision makers are willing to pay for a symptom-free day or QALY were created for each strategy. RESULTS: In the base case, no strategy was strictly dominated by any other strategy. However, two strategies (maintenance H2-receptor antagonists H2RA] and step-down proton pump inhibitor PPI]) were dominated through principles of extended dominance. The least costly and least effective strategy was intermittent H2RA, while maintenance PPI was the most costly and most effective. CONCLUSIONS: This analysis showed that the best way of managing patients with heartburn depends on how much society is willing to pay to achieve health improvements. Based on the commonly quoted threshold of US 50,000 dollars per QALY, the optimal primary care strategy for managing patients with moderate-to-severe heartburn symptoms is to treat the symptoms with a PPI followed by maintenance therapy with an H2RA to prevent symptomatic recurrence.

Canada↗
PubMedDate not supplied

An exploration of relative health stock in advanced cancer patients.

OBJECTIVE: The authors sought to empirically test whether relative health stock, a measure of patients' sense of loss in their health due to illness, influences the treatment decisions of patients facing life-threatening conditions. Specifically, they estimated the effect of relative health stock on advanced cancer patients' decisions to participate in phase I clinical trials. METHOD: A multicenter study was conducted to survey 328 advanced cancer patients who were offered the opportunity to participate in phase I trials. The authors asked patients to estimate the probabilities of therapeutic benefits and toxicity, their relative health stock, risk preference, and the importance of quality of life. RESULTS: Controlling for health-related quality of life, an increase in relative health stock by 10 percentage points reduced the odds of choosing to participate in a phase I trial by 16% (odds ratio = 0.84, 95% confidence interval = 0.72, 0.97). CONCLUSION: Relative health stock affects advanced cancer patients' treatment decisions.

Clinical Trials, Phase I as Topic↗
PubMedDate not supplied

Effect of hyperopic photorefractive keratectomy on corneal sensitivity: a longitudinal study.

PURPOSE: To investigate corneal sensitivity after photorefractive keratectomy (PRK) for low hyperopia, as measured with a non-invasive stimulus. METHODS: Two experimental groups were recruited: a control group of 17 patients (mean age 61.65 years) who underwent no treatment, and a PRK group of 11 patients (mean age 58.64 years) who underwent one of three attempted hyperopic corrections: +2.00 D (two patients), +3.00 D (four patients), +4.00 D (five patients). Corneal sensitivity was assessed centrally and peripherally, at temporal, medial, and inferior locations, approximately 1 mm from the limbus, using the Non-Contact Corneal Aesthesiometer (NCCA). Measurements were taken at each location for the control group and at preoperative, and postoperative weeks 1 and 2, 1, 3, and 6 months for the PRK group. RESULTS: Comparison of control and PRK groups (preoperative sensation threshold) (t-test): central P=.715, temporal P=.719, medial P=.943, inferior P= .920. Comparison of longitudinal changes in PRK group (one-way ANOVA): central P=.612, temporal P=.997, medial P=.981, inferior P=.993. CONCLUSIONS: Using the Non-Contact Corneal Aesthesiometer, no significant difference was found between the control and PRK groups for preoperative sensation thresholds, and no significant change in corneal sensitivity was found between any of the test time periods at any of the four corneal test locations for the PRK group.

Adult↗
PubMedDate not supplied

Persistent haze and disorganization of anterior stromal collagen appear unrelated following phototherapeutic keratectomy.

PURPOSE: The theoretical effects on corneal transparency induced by changes in collagen fibril packing following phototherapeutic keratectomy were compared to changes in objective measurements of haze. METHODS: Phototherapeutic keratectomy was performed on the right eyes of four young rabbits; left eyes were used as controls. Postoperative slit-lamp measurements of haze were taken at regular intervals up to 19 months. Wounded stromas were studied by synchrotron x-ray diffraction to calculate the average interfibrillar spacing of the collagen fibrils. These data were combined with transmission electron microscope measurements, and the summation of scattered fields method was used to predict the transmission of visible light. RESULTS: Objective measurements of haze were higher than the baseline control throughout the study. Electron micrographs of anterior stroma in 8-month-old wounds displayed irregularly spaced and poorly organized fibrils and x-ray diffraction indicated larger mean interfibrillar spacing compared to the controls. However, the predicted transmission of visible light through the anterior stromal scar tissue was not significantly different than normal. CONCLUSIONS: Following phototherapeutic keratectomy, anterior corneal collagen fibrils were more widely spaced and unevenly organized than in the normal rabbit cornea. However, this did not cause a significant loss of transparency and was therefore unlikely to contribute to haze.

Animals↗
PubMedDate not supplied

Reinventing radiology reimbursement.

Lee Memorial Health System (LMHS), located in southwest Florida, consists of 5 hospitals, a home health agency, a skilled nursing facility, multiple outpatient centers, walk-in medical centers, and primary care physician offices. LMHS annually performs more than 300,000 imaging procedures with gross imaging revenues exceeding dollar 350 million. In fall 2002, LMHS received the results of an independent audit of its IR coding. The overall IR coding error rate was determined to be 84.5%. The projected net financial impact of these errors was an annual reimbursement loss of dollar 182,000. To address the issues of coding errors and reimbursement loss, LMHS implemented its clinical reimbursementspecialist (CRS) system in October 2003, as an extension of financial services' reimbursement division. LMHS began with CRSs in 3 service lines: emergency department, cardiac catheterization, and radiology. These 3 CRSs coordinate all facets of their respective areas' chargemaster, patient charges, coding, and reimbursement functions while serving as a resident coding expert within their clinical areas. The radiology reimbursement specialist (RRS) combines an experienced radiologic technologist, interventional technologist, medical records coder, financial auditor, reimbursement specialist, and biller into a single position. The RRS's radiology experience and technologist knowledge are key assets to resolving coding conflicts and handling complex interventional coding. In addition, performing a daily charge audit and an active code review are essential if an organization is to eliminate coding errors. One of the inherent effects of eliminating coding errors is the capturing of additional RVUs and units of service. During its first year, based on account level detail, the RRS system increased radiology productivity through the additional capture of just more than 3,000 RVUs and 1,000 additional units of service. In addition, the physicians appreciate having someone who "keeps up with all the coding changes" and looks out for the charges. By assisting a few physicians' staff with coding questions, providing coding updates, and allowing them to sit in on educational sessions, at least 2 physicians have transferred some their volume to LMHS from a competitor. The provision of a "clean account," without coding errors, allows the biller to avoid the rework and billing delays caused by coding issues. During the first quarter of the RRS system, the billers referred an average of 9 accounts per day for coding resolution. During the fourth quarter of the system, these referrals were reduced to less than one per day. Prior to the RRS system, resolving these issues took an average of 4 business days. Now the conflicts are resolved within 24 hours.

Delivery of Health Care, Integrated↗