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Biomedical subjects

R W Parks

Publications and source records attributed to R W Parks.

At least 73 records · Page 4Linked to original sources
PubMed1994

Prospective study of postoperative renal function in obstructive jaundice and the effect of perioperative dopamine.

A prospective study was undertaken to assess postoperative renal dysfunction in patients with obstructive jaundice and to determine the effectiveness of dopamine in reducing its incidence. A total of 23 patients undergoing surgical relief of obstructive jaundice (serum bilirubin level above 100 mumol l-1) were randomized into two groups. Those in the control group (n = 10) received 3 litres 5 per cent dextrose intravenously during the 24 h before surgery plus a bolus of intravenous frusemide 1 mg kg-1 at induction of anaesthesia. The second group (n = 13) received a similar fluid and frusemide regimen plus an infusion of dopamine 3 micrograms kg-1 min-1 starting at induction of anaesthesia and continuing for 48 h after surgery. Postoperative oliguria occurred in two of the ten patients in the control group and in three of the 13 given dopamine (P = 0.74). No patient developed acute renal failure. There was no significant difference in mean levels of serum bilirubin, urea and creatinine, creatinine clearance and 24-h urinary output, on the day before and on days 1-5 after operation, between the two groups. It is concluded that, with careful preoperative resuscitation and control of fluid and electrolyte balance, the incidence of postoperative renal dysfunction in patients with obstructive jaundice is not as high as in some previous studies and is unaltered by administration of perioperative low-dose dopamine.

Acute Kidney Injury↗
PubMed1994

A review of the management of iatrogenic bile duct injuries.

Injuries to the extrahepatic biliary tree occurring during cholecystectomy or other upper gastrointestinal surgical procedures are not uncommon. The consequences are often catastrophic. We report the results of a personal series of bile duct repairs from a tertiary referral centre over a twenty-one year period. A total of 33 patients were referred. Percutaneous transhepatic cholangiography was the radiological investigation of choice to outline the biliary system. Percutaneous transhepatic dilatation was performed in six patients and 22 patients had either primary surgical repair, or reconstruction of their biliary tree performed by hepaticojejunostomy with an 80 cm Roux-en-Y limb. Of these only two have required revision surgery. We recommend early referral of patients with recognised iatrogenic injuries to specialist hepatobiliary units with no attempt at repair prior to referral.

Adult↗
PubMed1993

Methodological and theoretical issues in neural network models of frontal cognitive functions.

Neural network models have made significant strides in recent years toward modeling of neuropsychological data. In particular, three different research groups, including that of the present authors, have simulated in model networks some of the behavioral effects of frontal lobe damage. In this article we review these models and discuss their significance in terms of hierarchical organization in the nervous system. These models, to varying degrees, incorporate several widely used neural network principles that have also been used to model a wide range of data in other areas such as categorization, conditioning, and motor control. These principles include associative learning, competition, opponent processing, neuromodulation, and interlevel resonant feedback. Specifically, we show how combinations of these principles serve to model the attentional requirements of cognitive tasks and motor plans.

Animals↗
PubMed1992

Parallel distributed processing and neuropsychology: a neural network model of Wisconsin Card Sorting and verbal fluency.

Neural networks can be used as a tool in the explanation of neuropsychological data. Using the Hebbian Learning Rule and other such principles as competition and modifiable interlevel feedback, researchers have successfully modeled a widely used neuropsychological test, the Wisconsin Card Sorting Test. One of these models is reviewed here and extended to a qualitative analysis of how verbal fluency might be modeled, which demonstrates the importance of accounting for the attentional components of both tests. Difficulties remain in programming sequential cognitive processes within a parallel distributed processing (PDP) framework and integrating exceedingly complex neuropsychological tests such as Proverbs. PDP neural network methodology offers neuropsychologists co-validation procedures within narrowly defined areas of reliability and validity.

Attention↗
PubMed1991

Parallel distributed processing and neural networks: origins, methodology and cognitive functions.

Parallel Distributed Processing (PDP), a computational methodology with origins in Associationism, is used to provide empirical information regarding neurobiological systems. Recently, supercomputers have enabled neuroscientists to model brain behavior-relationships. An overview of supercomputer architecture demonstrates the advantages of parallel over serial processing. Histological data provide physical evidence of the parallel distributed nature of certain aspects of the human brain, as do corresponding computer simulations. Whereas sensory networks follow more sequential neural network pathways, in vivo brain imaging studies of attention and rudimentary language tasks appear to involve multiple cortical and subcortical areas. Controversy remains as to whether associative models or Artificial Intelligence symbolic models better reflect neural networks of cognitive functions; however, considerable interest has shifted towards associative models.

Artificial Intelligence↗
PubMed1991

Electrocortical mapping, MRI, and neuropsychological measures: evidence of Alzheimer's disease in the presence of vascular lesions.

We report here a case study of a 76-year-old woman with a high school education, whose presenting psychiatric symptomatology indicated dementia of unknown etiology. Neuropsychological test results were consistent with AD, but diagnosis was complicated by an MRI showing a large right hemisphere cortical infarct and scattered subcortical changes leading to a diagnosis of possible AD. Electrocortical mapping showed the right hemisphere infarct, and gave independent evidence suggestive of AD in the relatively intact left hemisphere. This case demonstrates the utility of multidimensional assessment as an aid to differential diagnosis.

Clinical Conference↗
PubMed1989

Neuropsychological "systems efficiency" and positron emission tomography.

Positron emission tomography (PET) has dramatically improved our ability to examine the functioning of the living brain. PET studies of neural pathways of the major sensory modalities--auditory, visual, somatosensory--have confirmed many traditional neuropsychological concepts, such as cross-lateral representation and regional functioning to particular primary sensory cortical areas. Other PET studies have used radioisotopes to examine relationships between radiopharmaceutical agents and neurobehavioral functioning in both normal and neuropathological states. In some areas, PET methodology requires further refinement. For example, effort should be made to develop the technology to do multiple scans within a short time frame; statistical procedures to examine relationships between neuropsychological tasks and the activity or presence of radiopharmaceutical agents in multiple sites; adequate controls for experimental error; and activation paradigms controlling the nonspecific effects of simple arousal. PET activation models of cognition suggest that a "systems efficiency" approach to assessing neuropsychological test performance involving both serial and parallel processing would be useful. These developments will improve empirical methodology and our understanding of brain-behavior relationships.

Arousal↗
PubMed1989

Systems model of cortical organization: positron emission tomography and neuropsychological test performance.

Positron Emission Tomography (PET) has allowed researchers to examine in vivo brain-behavior relationships. Correlations of metabolic increases measured by PET with simple sensory tasks involving hearing, vision, and tactile/motor responses have generally produced metabolic changes in agreement with known neuronal pathways. However, complex neuropsychological tests such as Raven's Matrices and Verbal Fluency have resulted in cortical activation of unexpected areas as well as some negative correlations between test performance and metabolism. These observations provide the first demonstration of complex relationships between neuropsychological functioning and activation of the normal brain. Since PET technology offers a means of computing the simultaneous proportional contribution of multiple brain regions, the issue of "localization" of neuropsychological test performance might appropriately be considered for redefinition in terms of a "systems" approach. In spite of the advances brought about by PET, methodological problems still remain for researchers. Future studies will need to take into account the subtle regional effects of neuropsychological paradigms.

Journal Article↗
PubMed1988

Cerebral metabolic effects of a verbal fluency test: a PET scan study.

Sixteen normal volunteers were studied with [F-18] fluorodeoxyglucose and positron emission tomography scans during behavioral activation with a verbal fluency test, and 35 age-matched controls were studied with resting-state scans. There was an overall increase of the cerebral glucose metabolic rate of 23.3% during verbal fluency activation, compared to the resting state, with the greatest activation in bilateral temporal and frontal lobes. A negative correlation between test performance scores and indices of metabolism was found in frontal, temporal, and parietal regions. Damage to the left frontal lobe maximally affects scores on verbal fluency tests, but performing the test activates a network of regions, of which the left frontal lobe is only one. Proficient performance in verbal fluency seems to require less metabolic activation than poor performance, perhaps because of the efficiency of cognitive strategies employed.

Adult↗
PubMedDate not supplied

Glutamine improves intestinal barrier function in experimental biliary obstruction.

OBJECTIVE: To determine the effects of enteral administration of glutamine on intestinal barrier function in experimental biliary obstruction. BACKGROUND: Extrahepatic biliary obstruction is associated with the failure of intestinal barrier function, allowing bacteria and other substances from the intestine to enter the circulation and initiate a systemic inflammatory response, causing impairment of multiple organs. The amino acid glutamine has been shown to improve intestinal barrier function in other conditions, but its effects in biliary obstruction have not been fully examined. METHODS: This study examined the effects of enteral administration of glutamine on intestinal permeability and on bacterial translocation from the intestine in a rodent model of biliary obstruction. RESULTS: Glutamine was shown to reduce intestinal permeability measured as percentage excretion of 14C 7 days after biliary obstruction (0.35+/-0.03 vs. 0.56+/-0.085% in controls, p=0.028), and glutamine administration was also associated with a decreased incidence of bacterial translocation to extra-intestinal sites (p=0.03). Radiolabelled bacterial studies also demonstrated reduced translocation of bacterial fragments to extra-intestinal sites in glutamine-treated animals (p=0.01). There was also some evidence of decreased exposure to endotoxin, reduced systemic inflammation and increased bacterial killing by the immune system in glutamine-treated animals. CONCLUSIONS: Glutamine modulates intestinal permeability and reduces bacterial translocation in an animal model of experimental biliary obstruction and may increase bacterial killing by the immune system.

Administration, Oral↗
PubMedDate not supplied

Delayed diagnosis of an enteric duplication cyst.

Enteric duplication cysts are rare and often prove extremely difficult to diagnose. We report a case in which the definitive diagnosis was made 40 years after first presentation and following five exploratory laparotomies. A review of the literature is presented, with discussion regarding the presenting features, potential complications, radiological investigations and surgical treatment of this uncommon clinical entity.

Adult↗
PubMedDate not supplied

Small bowel carcinoid tumour presenting with intestinal ischaemia.

A rare cause of intermittent intestinal ischaemia is presented to highlight the importance of thorough investigation, including the usefulness of laparoscopy, in the assessment of patients with persistent postprandial abdominal pain and hyperactive bowel sounds.

Aged↗