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Biomedical subjects

R A Myers

Publications and source records attributed to R A Myers.

At least 19 recordsLinked to original sources
PubMed2004

Premorbid proneness to distress and episodic memory impairment in Alzheimer's disease.

BACKGROUND: Chronic stress has been associated with impaired episodic memory, but the association of premorbidly experienced distress with memory function in Alzheimer's disease is unknown. OBJECTIVE: To investigate the link between proneness to distress and Alzheimer's disease. METHODS: Participants were 363 persons with clinically diagnosed Alzheimer's disease. At baseline, a knowledgeable informant rated each person's premorbid personality (that is, before dementia onset) along five dimensions, one of which was the tendency to experience psychological distress. Participants underwent structured clinical evaluations at baseline and then annually for up to four years. Each evaluation included 17 cognitive tests from which previously established measures of episodic memory, visuoconstruction, repetition, and naming were derived. RESULTS: In a series of random effects models adjusted for age, sex, and education, premorbid distress proneness was associated with baseline impairment in episodic memory but not with impairment in other cognitive domains, or with change in any cognitive domain. No other trait was related to baseline function or rate of decline in any cognitive domain. CONCLUSIONS: The results suggest that premorbid proneness to experience psychological distress is related to level of impairment in episodic memory in persons with Alzheimer's disease, but neither distress proneness nor other personality traits are related to disease progression.

Aged↗
PubMed2001

Targeting acute ischemic stroke with a calcium-sensitive opener of maxi-K potassium channels.

During ischemic stroke, neurons at risk are exposed to pathologically high levels of intracellular calcium (Ca++), initiating a fatal biochemical cascade. To protect these neurons, we have developed openers of large-conductance, Ca++-activated (maxi-K or BK) potassium channels, thereby augmenting an endogenous mechanism for regulating Ca++ entry and membrane potential. The novel fluoro-oxindoles BMS-204352 and racemic compound 1 are potent, effective and uniquely Ca++-sensitive openers of maxi-K channels. In rat models of permanent large-vessel stroke, BMS-204352 provided significant levels of cortical neuroprotection when administered two hours after the onset of occlusion, but had no effects on blood pressure or cerebral blood flow. This novel approach may restrict Ca++ entry in neurons at risk while having minimal side effects.

Animals↗
PubMed2000

The microbiology of necrotizing soft tissue infections.

OBJECTIVE: A large number of necrotizing soft tissue infections (NSTI) treated at a single institution over an 8-year period were analyzed with respect to microbial pathogens recovered, treatment administered, and outcome. Based on this analysis, optimal empiric antibiotic coverage is proposed. METHODS: A retrospective chart review of all patients with documented NSTI was conducted. Microbiologic variables were tested for impact on outcome using Fisher's exact test and multivariate analysis by logistic regression. RESULTS: Review of the charts of 198 patients with documented NSTI revealed 182 patients with sufficient microbiologic information for analysis. These 182 patients grew an average of 4.4 microbes from original wound cultures, although a single pathogen was responsible in 28 patients. Eighty-five patients had combined aerobic and anaerobic growth, the most common organisms being, in order, Bacteroides species, aerobic streptococci, staphylococci, enterococci, Escherichia coli, and other gram-negative rods. Clostridial growth was common but did not affect mortality unless associated with pure clostridial myonecrosis. Mortality was affected by the presence of bacteremia, delayed or inadequate surgery, and degree of organ system dysfunction on admission. CONCLUSIONS: NSTI are frequently polymicrobial and initial antibiotic coverage with a broad-spectrum regimen is warranted. The initial regimen should include agents effective against aerobic gram-positive cocci, gram-negative rods, and a variety of anaerobes. The most common organisms not covered by initial therapy were enterococci. All wounds should be cultured at initial debridement, as changes in antibiotic coverage are frequent once isolates are recovered.

Algorithms↗
PubMed2000

Cervical necrotizing fasciitis of odontogenic origin: a case report and review of 12 cases.

PURPOSE: This article reviews the demographics, presentation, cause, clinical findings, and treatment of 12 cases of cervical necrotizing fasciitis of odontogenic origin. PATIENTS AND METHODS: A retrospective chart review of 12 cases treated between 1987 and 1997 was done. RESULTS: Most cases resulted from an abscessed mandibular molar. The most common significant medical conditions in the patient's history were diabetes, hypertension, obesity, and substance abuse. All patients were treated surgically within 24 hours of admission. Hyperbaric oxygen (HBO) was used as adjunctive treatment in all cases. The average length of hospital stay was 31 days. All patients recovered. CONCLUSION: Early surgical intervention and the use of HBO decreases morbidity and improves the clinical outcome.

Anti-Bacterial Agents↗
PubMed2000

Hyperbaric oxygen therapy for trauma: crush injury, compartment syndrome, and other acute traumatic peripheral ischemias.

In the future, the indications for HBO therapy in acute peripheral ischemic injuries will likely be based on objective criteria rather than, as at present, on clinical diagnoses alone. This chapter offers objective criteria for using HBO in crush injuries and compartment syndromes. The pathophysiology of ATPI are well defined. Hyperbaric oxygen mediates the effects of ATPI through four mechanisms: hyperoxygenation, vasoconstriction, reperfusion, and host factors. The cost benefits of using HBO will be substantial, since complications from ATPI are very expensive. As objective criteria replace the presently used subjective criteria, hyperbaric oxygen therapy will become an integral part of trauma management of these injuries.

Acute Disease↗
PubMed1998

Chronic carbon monoxide exposure: a clinical syndrome detected by neuropsychological tests.

Chronic exposure to carbon monoxide produces a clinical syndrome that is often overlooked because of obscure symptomatology, a range of presentations, and lack of awareness of the problem. To help physicians recognize and treat the chronic carbon monoxide exposure syndrome, the authors present its objective symptomatology, an approach to diagnosis emphasizing neuropsychological tests, a treatment protocol, and theoretical considerations for the mechanism of hyperbaric oxygen's therapeutic action. For elucidation, eight patients treated in the hyperbaric chamber at a tertiary care facility are described. Diagnosis can be facilitated by recognizing the syndrome based on the patient's history, as well as physical and neuropsychological examinations, with emphasis on identifying potential sources of carbon monoxide exposure. The evaluation and treatment protocols presented, though still experimental, show promise for improving functional, cognitive, and psychiatric capacities.

Adult↗
PubMed1998

Outpatient management of HIV-infected adults. The varied challenges for primary care.

Care of persons infected with HIV presents many challenges to primary care physicians. In addition to keeping current on the rapidly advancing medical aspects of the disease, physicians also must be prepared to recognize the complex psychosocial issues that confront their patients. In this article, Dr Myers reviews essential aspects of primary care for HIV-infected adults.

AIDS-Related Opportunistic Infections↗
PubMed1997

Confirmation of the pulse oximetry gap in carbon monoxide poisoning.

STUDY OBJECTIVES: To demonstrate the degree to which pulse oximetry overestimates actual oxyhemoglobin (O2Hb) saturation in patients with carbon monoxide (CO) poisoning. This phenomenon has been reported in fewer than 20 humans in the English medical literature. METHODS: A retrospective chart review of 191 patients evaluated for CO poisoning at a regional hyperbaric center identified 124 patients 10 years of age and older who had had both arterial blood gas and pulse oximetry measurements and who had received either high-flow oxygen through a nonrebreather mask or 100% inspired oxygen through an endotracheal tube. Blood gas measurements, including direct spectrophotometric determination of O2Hb and carboxyhemoglobin (COHb) saturation values, were compared with finger-probe pulse oximetry readings. RESULTS: Measured O2Hb saturation (mean +/- SD, 88.7 +/- 10.2%; range, 51.4% to 99.0%) decreased linearly and predictably with rising COHb levels (10.7 +/- 10.4%; range, .2% to 46.4%). Pulse oximetry saturation (99.2% +/- 1.3%; range, 92% to 100%) remained elevated across the range of COHb levels and failed to detect decreased O2Hb saturation. The pulse oximetry gap, defined as the difference between pulse oximetry saturation and actual O2Hb saturation (10.5% +/- 9.7%; range, 0% to 40.6%), approximated the COHb level. CONCLUSION: There is a linear decline in O2Hb saturation as COHb saturation increases. This decline is not detected by pulse oximetry, which therefore overestimates O2Hb saturation in patients with increased COHb levels. The pulse oximetry gap increases with higher levels of COHb and approximates the COHb level. In patients with possible CO poisoning, pulse oximetry must be considered unreliable and interpreted with caution until the COHb level has been measured.

Adolescent↗
PubMed1996

An augmented Clark model for stability of populations.

A simple modification of a frequently employed age-structured model for population dynamics is presented. This augmented formulation allows the assessment of the impact of age-dependent harvest mortality on population stability. The characteristic frequencies of the predicted oscillations are discussed. The period of oscillation is almost independent of survival and the exact functional form of the recruitment function, and it is not equal to twice the mean age of mature animals, as suggested earlier. It is shown that increased survival before reproduction has a destabilizing influence for populations exhibiting an overcompensatory recruitment function.

Age Factors↗
PubMed1996

Necrotizing soft tissue infections. Risk factors for mortality and strategies for management.

OBJECTIVE: The authors evaluate in a retrospective fashion the factors influencing outcome in a large group of patients presenting with necrotizing soft tissue infections, and, based on this analysis, propose a plan for optimal care of such patients. SUMMARY BACKGROUND DATA: In many smaller series of patients with necrotizing soft tissue infections, similar analyses of risk factors for mortality have been performed, producing conflicting conclusions regarding optimal care. In particular, debate exists regarding the impact of concurrent physiologic derangements, type and extent of infection, and the role of hyperbaric oxygen in treatment. METHODS: A retrospective chart review of 198 consecutive patients with documented necrotizing soft tissue infections, treated at a single institution during an 8-year period, was conducted. Using a model for logistic regression analysis, characteristics of each patient and his/her clinical course were tested for impact on outcome. RESULTS: The mortality rate among the 198 patients was 25.3%. The most common sites of origin of infection were the perineum (Fournier's disease; 36% of cases) and the foot (in diabetics; 15.2%). By logistic regression analysis, risk factors for death included age, female gender, extent of infection, delay in first debridement, elevated serum creatinine level, elevated blood lactate level, and degree of organ system dysfunction at admission. Diabetes mellitus did not predispose patients to death, except in conjunction with renal dysfunction or peripheral vascular disease. Myonecrosis, noted in 41.4% of the patients who underwent surgery, did not influence mortality. CONCLUSIONS: Necrotizing soft tissue infections represent a group of highly lethal infections best treated by early and repeated extensive debridement and broad-spectrum antibiotics. Hyperbaric oxygen appears to offer the advantage of early wound closure. Certain markers predict those individuals at increased risk for multiple-organ failure and death and therefore assist in deciding allocation of intensive care resources.

Adolescent↗
PubMed1995

A preliminary report on hyperbaric oxygen in the relief of migraine headache.

Oxygen inhalation was early advocated as a treatment for migraine headache. It has been theorized that the efficacy of raising blood oxygen levels in vascular headache is mediated by vasoconstriction and metabolic effects. Hyperbaric oxygen can provide a much greater level of blood oxygenation than can provide a much greater level of blood oxygenation than normobaric oxygen, and in recent studies it has been used in the treatment of cluster headache. The purpose of this study was to compare the effects of hyperbaric oxygen and normobaric oxygen in migraine. Twenty migraineurs were divided randomly into two groups and studied in a hyperbaric chamber during a typical headache attack. Global headache severity was measured by a verbal descriptor scale before and after exposure to oxygen. One group received 100% oxygen at 1 atmosphere of pressure (normobaric) while the other received 100% oxygen at 2 atmospheres of pressure (hyperbaric). One of the 10 patients in the normobaric group achieved significant relief of headache symptoms, while 9 of 10 in the hyperbaric group found relief. Based on a chi-square test, this difference is significant at the P < .005 level. Those patients who did not find significant relief from normobaric oxygen were given hyperbaric oxygen as above. All nine found significant relief. The results suggest that hyperbaric (but not normobaric) oxygen may be useful in the abortive management of migraine headache. Possibilities for the mechanism of this effect, in addition to vasoconstriction, include an increase in the rate of energy-producing and neurotransmitter-related metabolic reactions in the brain which require molecular oxygen.

Female↗
PubMed1994

Regional hemodynamics in 1-day-delayed rodent island flaps.

We have studied the recovery of microvascular function in ischemic epigastric skin flaps by characterizing the regional hemodynamics in the axial and random portions of double- and single-pedicle island skin flaps in the rat. Blood flows were measured with radiolabeled microspheres 1 day after bipedicle flaps were elevated and at 4 hr, 72 hr, and 1 week after ligation of one of the pedicles. These hemodynamic measurements were correlated with assessments of angiogenesis and skin necrosis performed by lectin histochemistry and histopathology. Twenty-four hours after the skin flap elevation, the mean blood flow was 0.26 ml.min-1.g-1. After the ligation of one pedicle, the blood flow in the axial portion of the skin flap was unchanged at 4 hr (0.22 ml.min-1.g-1), declined insignificantly at 72 hr (0.15 ml.min-1.g-1), and remained normal at 1 week. In the random portion of the skin flap very little collateral blood flow was present at 4 hr (0.06 ml.min-1.g-1) and 72 hr (0.09 ml.min-1.g-1). Blood flow in the random skin flap returned to normal by 1 week (0.27 ml.min-1.g-1). Reelevation of the skin flap at 1 week caused an insignificant decline (10%) in total blood flow to the skin flap. Skin necrosis was detected histologically at 72 hr only in the lateral portion of the random skin flap, where blood flow was less than 0.03 ml.min-1.g-1. Increased areas of lectin binding to vascular endothelium were seen in the subdermal layers of the skin flap by 1 week, presumably due to angiogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Toxityping rat brain calcium channels with omega-toxins from spider and cone snail venoms.

Different types of voltage-sensitive Ca2+ channels in the brain can be defined by specific ligands: L-type Ca2+ channels are uniquely sensitive to dihydropyridines, and N-type Ca2+ channels are selectively blocked by the Conus peptide omega-CTX-GVIA. Cloning data have revealed additional calcium channel types in mammalian brain for which selective ligands would be desirable. We describe binding experiments involving three newer ligands that block dihydropyridine- and omega-CTX-GVIA-resistant Ca channels: omega-Aga-IIIA and omega-Aga-IVA from venom of the spider Agelenopsis aperta and omega-CTX-MVIIC from Conus magus. [125I]omega-Aga-IVA binds with high affinity (IC50 = approximately 50 nM) to receptors in rat brain which may correspond to P-like calcium channels. A second high-affinity site (IC50 = approximately 1 nM) is defined by [125I]omega-CTX-MVIIC, proposed here to be on an "O"-type calcium channel. [125I]omega-Aga-IIIA targets homologous binding sites present on multiple Ca channel types. The IIIA sites overlap with the binding sites for [125I]omega-CTX-GVIA and [125I]omega-CTX-MVIIC. The IIIA sites do not overlap with the site defined by omega-Aga-IVA. Thus toxin ligands may be highly specific for a particular Ca channel (i.e., GVIA for the N-type channel) or exhibit broader specificity (i.e., omega-Aga-IIIA, which appears to bind L-, N-, P-, and O-type Ca2+ channels).

Agatoxins↗
PubMed1993

Hyperbaric oxygen treatment for experimental cyclophosphamide-induced hemorrhagic cystitis.

Acrolein is a toxic metabolite of cyclophosphamide that causes hemorrhagic cystitis in 2 to 40% of treated patients. Hyperbaric oxygen (HBO) is used to treat poorly healing wounds in conditions such as Fournier's gangrene and radiation-induced cystitis. The present study was designed to evaluate the effects of HBO on acute acrolein-induced hemorrhagic cystitis in a rat model. Rats were divided into 4 groups. Group I served as a control and received only HBO prior to sacrifice. Group II received acrolein only, while groups III and IV received acrolein as well as HBO therapy. Hyperbaric oxygen (100% oxygen, 2.8 atmospheres, 90 minutes) was delivered twice a day for 4 days, with group III receiving a fifth HBO treatment just before acrolein and group IV receiving the fifth HBO treatment just after acrolein. After therapy, the amount of urothelial injury was determined morphometrically. Group II untreated rat bladders had only 33% of the urothelium intact after acrolein injury, whereas groups III and IV rat bladders had 93% (p < 0.01) and 55% (p < 0.01) intact urothelium, respectively, after treatment with HBO. The timing of the HBO treatment appeared to be a critical factor, with less injury occurring if the fifth HBO treatment immediately preceded acrolein. These results suggest that HBO may be useful as prophylaxis and treatment of cyclophosphamide-induced hemorrhagic cystitis.

Acrolein↗
PubMed1993

Hyperoxia and prolongation of aminoglycoside-induced postantibiotic effect in Pseudomonas aeruginosa: role of reactive oxygen species.

Hyperoxia prolongs the postantibiotic effect (PAE) of the aminoglycoside tobramycin in Pseudomonas aeruginosa. We tested the hypothesis that the PAE is prolonged because hyperoxia increases free radical flux while tobramycin inhibits the induction of antioxidant defenses. Exposure of P. aeruginosa to hyperoxia (100% O2) for 1 h increased superoxide dismutase, catalase, and glutathione levels. In the presence of tobramycin (1x the MIC), the induction of antioxidant defenses by hyperoxia was nearly abrogated. Neither preexposure of P. aeruginosa to hyperoxia nor supplementation with the antioxidants copper(II) (diisopropylsalicylate)2 (superoxide dismutase-like), catalase, or dimethyl sulfoxide abolished prolongation of the PAE of tobramycin induced by hyperoxia.

Anti-Bacterial Agents↗
PubMed1992

Regulation of protein degradation in normal and transformed human bronchial epithelial cells in culture.

Protein degradation rates are decreased in some transformed cells of mesenchymal origin. We have tested the generality of this phenomenon and evaluated the role of the lysosomes in this down-regulation. To this end we have compared the induction of lysosomal protein degradation among normal, transformed (BEAS-2B), and transformed tumorigenic (BZR, Calu-1) human bronchial epithelial cells in culture. Serum and/or nutrient deprivation, cell confluency, and Ca2+ were used to modulate lysosomal protein degradation. Protein degradation and synthesis were determined by the release or incorporation of [14C]valine in the cells. Autophagic degradation of cytoplasm by lysosomes was evaluated by ultrastructural morphometry. Basal protein degradation was lower (27%) in two of the transformed cell lines (BEAS-2B and BZR). Incorporation of [14C]valine label was raised approximately 4-fold in the transformed cells. Nutrient deprivation stimulated protein degradation equally (2-fold) in transformed and normal cells. Postconfluency increased (1.5-fold) basal protein degradation in Calu-1 cells and a marked enhancement (4-fold) of degradation occurred during nutrient deprivation. Culture of normal human bronchial epithelial cells in high Ca2+ caused phenotypic changes and increased (30%) the degradation of protein induced by nutrient deprivation. In Calu-1, high Ca2+ caused only phenotypic changes. The volume density (Vd) of autophagic vacuoles and dense bodies in the transformed cells was lower under basal conditions but increased markedly during nutrient deprivation. A marked accumulation of lysosomes also occurred in transformed cells during postconfluency. We conclude that cell transformation lowers basal protein degradation in some human epithelial cells. Lysosomal proteolysis of transformed cells is not down-regulated and can be markedly enhanced during nutritional deprivation by the autophagic degradation pathway.

Analysis of Variance↗
PubMed1992

Non-obstructive colonic dilatation in the trauma patient: an analysis of six patients.

Non-obstructive colonic dilatation was diagnosed in six of 13,641 patients admitted to a Level I trauma centre over a 70-month period (incidence, less than 0.05 per cent). Four were older than 60 years, and five required long-term support on a ventilator. Successful treatment depends on expeditious decompression of the dilated colon. Fibreoptic colonoscopy is the recommended method.

Accidents, Traffic↗