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Biomedical subjects

R Walker

Publications and source records attributed to R Walker.

At least 487 records · Page 27Linked to original sources
PubMedDate not supplied

Pitfalls in quantitative contrast echocardiography: the steps to quantitation of perfusion.

Current methods used clinically to assess myocardial perfusion are invasive and expensive. As the technology of ultrasound imaging improves, CE may provide a relatively inexpensive, noninvasive means of quantitating myocardial perfusion. Issues regarding stability of microbubble contrast agents must be studied more closely under physiologic conditions. As such, encapsulated microbubbles may provide more stability under physiologic pressures than free gas microbubbles. Introducing high concentrations of contrast, either by hyperconcentrating the contrast agent or by increasing the injection rate, may provide greater stability under physiologic conditions. Further, before quantitative statement of tissue perfusion can be made, the relationship between tracer concentration and system response must be established. Further, a "linear" postprocessing ultrasound setting does not eliminate this requirement as data must still undergo nonlinear transformation during log compression and time-gain compensation. Additionally, issues regarding "electronic thresholding" must be explored more extensively in vivo. Commercial ultrasound scanners, in their present form, may not offer adequate sensitivity for absolute quantitative studies. Further development of modified ultrasound systems may provide sufficient sensitivity for quantitative perfusion imaging. CE offers a potentially powerful tool in the clinical management of patients with ischemic heart disease. Conventional coronary angiography provides information on the size of a lesion, but accompanying tissue perfusion distal to the lesion cannot be determined. Doppler ultrasonography determines velocity of blood flow in large vessels but does not offer the potential to quantitate tissue perfusion. Clearly, CE has a place in the future of diagnostic imaging. The recent work of Ito et al. demonstrated the qualitative potential of CE in the identification of "areas at risk" in patients who had undergone thrombolysis or percutaneous transluminal coronary angioplasty after an acute myocardial infarction. With further improvement in the ultrasound imaging techniques and microbubble stability, CE may offer an inexpensive, noninvasive means of assessing myocardial perfusion.

Albumins↗
PubMedDate not supplied

Randomized clinical trial of the effect of semi-occlusive dressings on the microflora and clinical outcome of acute facial wounds.

This study investigated whether treatment with occlusive, hydroactive polyurethane dressings affects the microflora and clinical outcome of acute wounds. A randomized, controlled trial was performed on 60 patients with acute facial lacerations. Following primary closure, patients were provided with either a dry-gauze dressing or a hydroactive polyurethane dressing (Cutinova Thin). The wounds were assessed clinically and microbiologically prior to closure, then after 5, 28 and 56 days. The dressing, which was removed at day 5, was also sent for microbiological culture. Wounds treated with the polyurethane dressing showed improved comfort and contour (p < 0.04), less erythema (p < 0.03) and less potential for scarring (p < 0.01) at day 5. At day 28 and day 56, there were no significant differences in the clinical assessment between the test and control groups (p > 0.05). A total of 518 isolates were recovered from the patients during the study. Mean number of isolates and bacterial growth density were calculated in both groups. A similar range of microorganisms were obtained from both treatment groups with no clear difference in organism colonization. This study shows the potential usefulness of facial wounds as a human model for studying acute wound healing responses and anti-scarring therapy. While short-term, clinical benefits of occlusive dressings were evident in the management of acute wounds, these data clearly show that all studies of scarring following acute wounding should extend over at least 3 months post-injury to allow for spontaneous improvement to occur.

Adolescent↗
PubMedDate not supplied

Sulphiting agents in foods: some risk/benefit considerations.

The current toxicological status of sulphiting agents is reviewed, including evidence of adverse reactions to sulphited foods by a sub-population of asthmatics. Against this background are assessed the applications and benefits of sulphiting agents in foods. It is concluded that further information is required to determine the magnitude of risk and that, in the interim, the controlled use of sulphiting agents is justifiable.

Animals↗
PubMedDate not supplied

Toxicology of sorbic acid and sorbates.

Sorbic acid and its salts have been subjected to an extensive battery of tests, including acute, short-term and chronic toxicity/carcinogenicity tests, two-generation reproduction and teratogenicity studies. These studies show that sorbic acid and sorbates have a very low level of mammalian toxicity, even in chronic studies at up to 10% of the diet, and are devoid of carcinogenic activity. They are non-mutagenic and non-clastogenic in vitro and in vivo. The low toxicity is explicable by the fact that sorbic acid is metabolized rapidly by similar pathways to other fatty acids. In humans, a few cases of idiosyncratic intolerances have been reported (non-immunological contact urticaria and pseudo-allergy). The frequency appears low but there are too few reported data for an accurate assessment of the true incidence. In extreme conditions (high concentrations and temperature) sorbic acid may react with nitrite to form mutagenic products but these mutagens are not detectable under normal conditions of use, even in curing brines.

Animals↗
PubMedDate not supplied

Nitrates, nitrites and N-nitrosocompounds: a review of the occurrence in food and diet and the toxicological implications.

Data on occurrence of nitrate, nitrite and N-nitrosocompounds in food and drinking water, and on total dietary intakes are reviewed. Metabolic, toxicological and epidemiological studies are surveyed and the implications with respect to safety evaluation are addressed. It is concluded that, on the basis of recent long-term animal studies and of clinical experience in man, the current Acceptable Daily Intake (ADI) allocated to nitrate by the Joint FAO/WHO Expert Committee on Food Additives of 0-5 mg/kg body weight/day (expressed as sodium nitrate) might be increased to 0-25 mg/kg body weight/day. Based on similar criteria, the ADI for nitrite would be 0-0.1 mg/kg body weight/day (expressed as sodium nitrite). In view of the known carcinogenicity of N-nitrosocompounds, exposure to these compounds in food should be minimized by appropriate technological means, such as lowering the nitrite concentration in preserved foods to the minimum required to ensure microbiological safety and use of inhibitors of nitrosation like alpha-tocopherol or ascorbic acid. Further work is needed to define the minimal levels of nitrite in foods needed to inhibit outgrowth of Clostridium botulinum and toxin production.

Animals↗
PubMedDate not supplied

The importance of endogenous histamine relative to dietary histamine in the aetiology of scombrotoxicosis.

Deliberately spoiled mackerel samples and mackerel samples implicated in outbreaks of scombrotoxicosis were, under medical supervision, tested blind on normal, healthy volunteers of both sexes. These experiments identified batches of fish which could induce nausea/vomiting and/or diarrhoea when 50 g samples were consumed. It was also established that the fillets in a batch were neither of equal potency nor homogeneous with respect to histamine content. Strong evidence was obtained that dietary histamine is not a major determinant of scombrotoxicosis since potency was not positively correlated with the dose, and volunteers appeared to fall into susceptible and non-susceptible subgroups. However, there is no reason to suspect allergy as being solely responsible for these differences in sensitivity. It is also possible to discount body weight as a factor. While the data suggest that females may be more susceptible than males, this effect cannot be confirmed at the present time. Studies with susceptible volunteers predosed with either placebo or H1 antagonist (chlorpheniramine 4 mg) demonstrated convincingly that the antihistamine can abolish vomiting and diarrhoea associated with the ingestion of 50 g of scombrotoxic fish. It is therefore postulated that endogenous histamine released by mast cell degranulation has a significant role in the aetiology of scombrotoxicosis, whereas the role of dietary histamine is minor. The nature and origin of the agent responsible for mast cell degranulation is being investigated.

Chlorpheniramine↗
PubMedDate not supplied

Is there a role for amines other than histamines in the aetiology of scombrotoxicosis?

Mackerel fillets associated with an outbreak of scombrotoxicosis have been analysed for their contents of cadaverine, histamine, putrescine, spermidine, spermine and tyramine, and fed to informed, healthy volunteers of both sexes under medical supervision. Of the 86 fillets examined, 30 rapidly induced nausea/vomiting and/or diarrhoea when 50 g were consumed. The remaining fillets failed to provoke such symptoms, even though 17 of them were tested by volunteers proven to be susceptible to scombro-intoxication. Statistical analysis failed to detect any differences in amines content between fillets shown to be scombrotoxic and those failing to induce nausea/vomiting and/or diarrhoea, and failed also to establish any significant relationships between the amines doses and volunteer responses, even after manipulations to simulate additive or synergistic interactions. Accordingly it is concluded that the content of such amines in mackerel have little or no role in the aetiology of scombrotoxicosis.

Amines↗
PubMedDate not supplied

Do saxitoxin-like substances have a role in scombrotoxicosis?

Evidence is presented which establishes that mackerel fed in captivity can, by relay from contaminated shellfish via sand eels, accumulate paralytic shellfish poisons (PSP) in the edible flesh at a level (250 micrograms saxitoxin equivalents per kg) similar to that in the contaminated shellfish. Data from ELISAs performed independently in two laboratories show that commercial mackerel fillets which have been associated with incidents of scombrotoxicosis contained 0.02-1.30 micrograms saxitoxin equivalents per kg, concentrations some two to four orders of magnitude below that normally detectable by the mouse bioassay. The doses, expressed as saxitoxin equivalents, administered inadvertently during volunteer testing of such fillets ranged up to 0.5 ng/kg bw, at least four orders of magnitude less than the fatal oral dose for an adult. The doses associated with the rapid induction of nausea/vomiting and/or diarrhoea, 0.11-1.0 ng/kg bw, could not be distinguished from the doses which failed to produce such symptoms in susceptible volunteers (up to 0.5 ng/kg bw). Factors that might explain this lack of correlation between dose (saxitoxin equivalents) and volunteer response are discussed along with previously published reports of PSP relay through the food web. It is suggested that the relay of algal toxins, particularly PSP, but possibly in combination with diarrheic shellfish poisons, may be responsible for scombrotoxicosis.

Animals↗
PubMedDate not supplied

Quantitative structure-activity relationships and COMPACT analysis of a series of food mutagens.

Quantitative structure-activity relationships between chemical structure and Ames mutagenicity for a group of 24 food mutagens, including 17 cooked-food heterocyclic amines, have been determined. For the TA98 strain of Salmonella typhimurium (frameshift mutagens) the best correlation of mutagenicity is with molecular diameter (R = 0.91), while for the TA100 strain (base-pair mutations) the best correlation is with delta E, the energy difference between the lowest unoccupied and highest occupied molecular orbitals. High mutagenicity is related to high values of molecular diameter, hence to planarity and to high values of the COMPACT ratio ([area/depth2]/delta E). High mutagenicity is also related to low values of delta E. Consequently, highly mutagenic and potentially carcinogenic food chemicals can readily be identified as substrates of cytochrome P4501 (CYP1) and may therefore be detected by the COMPACT procedure. Highly mutagenic compounds also exhibit high values of dipole moment.

Carcinogens↗
PubMedDate not supplied

Substance abuse and B-cluster disorders. I: Understanding the dual diagnosis patient.

The patient population that presents with both a B-cluster personality disorder and substance abuse is a challenge to professionals in both the mental health and substance abuse treatment fields. The coexistence of both disorders is not uncommon and is frequently encountered in substance abuse treatment, social welfare, and mental health settings. The complexity of the clinical picture for these patients and their greater resistance to treatment severely taxes the practitioner's skills. Even without a clear understanding of the primary causative pathology, effective treatment modes based on a recognition of the interactive and interdependent nature of the two disorders can be developed. Part I of this two-part article presents the characteristics and clinical features of the population as well as a model for understanding some of the motivating principles behind the patient's conduct, feelings, thoughts. This is followed by guidelines for the clinician's attitude, desired characteristics, and role in dealing with this population. Part II presents guidelines for the treatment of this patient population.

Antisocial Personality Disorder↗
PubMedDate not supplied

Substance abuse and B-cluster disorders. II: Treatment recommendations.

Part I of this two-part article described the characteristics and clinical features of the patient population that presents with both a B-cluster personality disorder and substance abuse. It also included guidelines for the clinician. Part II presents further recommendations for the treatment of this population, taking into account how the combination of these disorders manifests itself. The treatment approach should be kept simple and easy for patients to understand and should promote their ability to think rationally about the effect of their emotions on their behavior and its outcomes. A firm structure is critical to compensate for the lack of internal control of these patients and to prevent the manipulation that results from their view of the instrumentality of others. Denial, resistance, countertransference, and relapse to addictive behaviors are all potential barriers that are often encountered when attempting to treat this population. Group therapy with this population presents unique challenges to the clinician. As with individual therapy, a firm structure is imperative, with the clinician in charge of process and content.

Antisocial Personality Disorder↗
PubMedDate not supplied

History of head injury among substance users: preliminary findings.

Traumatic brain injury is associated with a variety of problems in cognitive functioning that may be related to substance use and that may influence recovery. This pilot study of 591 inmates in medium and minimum-security prisons examined self-reports of head injury, mental health problems, and health service utilization in three groups: no head injury, one head injury, and two or more head injuries. The group with multiple head injuries reported significantly more emergency room visits, more hospital admission, and number of hospital stays when compared with those with no head injury. This preliminary analysis reflects a need for additional research on brain injury among substance misusers.

Adult↗
PubMedDate not supplied

The effects of a 9-week program of aerobic and upper body exercise on the maximal voluntary ventilation of chronic obstructive pulmonary disease patients.

PURPOSE: The purpose of this study was to evaluate the effects of a 9-week exercise program that emphasized aerobic and upper body strength on the maximal voluntary ventilation (MVV) of patients with chronic obstructive pulmonary disease (COPD). An experimental and control group totaling 40 patients with a diagnosis of COPD was studied. METHODS: Experimental group subjects were given a pre- and post-MVV breathing test, a Patient's Attitude Toward Health (PATH) questionnaire, a knowledge of disease questionnaire and a 6-minute walk test. Pre- and post-MVV breathing tests were performed on the control group. Dependent t-test and analysis of covariance were utilized to evaluate the results. RESULTS: Significant differences were found between the pre-test and post-test within the experimental group on MVV results, program attitudes toward health (PATH scores), knowledge level about their disease state after the rehabilitation program, and 6-minute walk distance. There were no significant differences found in the MVV results between the pre-test and post-test for the control group. There was a significant difference when comparing the control group MVV results to the MVV results of the exercise group. CONCLUSIONS: These findings indicate that pulmonary rehabilitation programs can help patients realize improved lung function, improved emotional states, increased knowledge about their disease states, and an increased cardiovascular fitness level. The results of this study suggest a regimen that can improve the quality of life for patients with chronic lung disease.

Aged↗
PubMedDate not supplied

Thermal collateral damage in porcine corneas after photoablation with free electron laser.

BACKGROUND: The study describes a quantitative and systematic investigation of the collateral thermal damage during infrared photoablation as a function of wavelength between 2.7 and 6.7 microns. METHODS: Using the tunable Free Electron Laser at Vanderbilt University, Nashville, Tenn, 60 freshly removed porcine cadaver eyes were irradiated at wavelengths between 2.7 and 6.7 microns, at a fluence of 1.3 J/cm2. For wavelengths where no photoablation occurred, fluence was increased to 3.5 J/cm2; pulse length (macropulse) was 4 microseconds, consisting of a train of micropulses (pulse duration 2 ps at a 2.9 GHz repetition rate). The corneal buttons were removed and stained with hematoxylin and eosin (H&E) and analyzed by histologic micrometry. RESULTS: Two thermal damage zones in the remaining tissue were observed: zone 1 showed superficial carbonization and measured between 2 and 4 microns; beyond, the eosinophilic zone 2 measured between 10 and 100 microns. The extent of zone 2 was inversely related to the absorption spectra of the cornea; it was minimal at the 3- and 6-micrometer water absorption bands and maximal at minimal target absorption. CONCLUSION: The results correlated well with a model of the ablation process. The study provides a systematic and predictive element for the determination of collateral thermal adverse effects; it does not yet include pulse length variation as a determining factor.

Animals↗