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Biomedical subjects

P Walker

Publications and source records attributed to P Walker.

At least 145 records · Page 8Linked to original sources
PubMed1992

Clinical experience and comparative analysis of the standard and fast peritoneal equilibration tests (PET).

The fast peritoneal equilibration test (PET) has been proposed as a substitute procedure for the standard PET because it is less expensive and less time consuming since fewer samples must be drawn. This study was undertaken to compare the fast and standard PETs to determine if the fast PET is a viable alternative. Fifteen patients participated in the study. Results from the standard PETs indicate 13 patients had average permeability and 2 patients had high transport. Corresponding fast PETs indicate 10 patients with average permeability, 2 patients with high transport, 1 patient had discrepancies between the D/P ratios and drain volume, and 2 patients were noncompliant and did not complete the fast PET. We conclude that the fast PET is a valid screening tool to evaluate peritoneal membrane permeability in patients who have previously undergone a standard PET. It is cost effective and timesaving. The test is easily invalidated if patients fail to comply with instructions for the test. The fast PET is primarily useful as a screening device to determine whether permeability has changed.

Adult↗
PubMed1992

[24-hour blood pressure measurement in children and adults with type I diabetes mellitus: relation to duration of diabetes, obesity, albuminuria].

Early antihypertensive therapy in patients with diabetes mellitus reduces cardiovascular risk and improves long-term prognosis. Therefore, mildly hypertensive patients have to be discriminated from patients with "white coat" hypertension. 24-h-blood pressure profiles were recorded in 153 patients (age 7.9-26 years, duration of diabetes 0-21 years). The fraction of elevated blood pressure readings allows to classify these profiles independent of the age of the patient. This parameter was not related to either duration of diabetes or nocturnal excretion of albumin. In contrast, blood pressure correlated significantly with age- und sex-adjusted weight (z-score). Among 38 patients with elevated blood pressure recordings during outpatient visits, 24 (63%) displayed a normal 24-h-profile (less than 30% of blood pressure values are above the 95% limit for the respective age). These data indicate that hypertension might be independent of the metabolic derangement during the first years of diabetes.

Adolescent↗
PubMed1991

Auto-immune spondylodiscitis associated with collagen induced arthritis in rats: high field MRI findings.

The spinal involvement of the tail was studied in Wistar Furth rats immunized with bovine native type II collagen. Focal caudal autoimmune spondylodiscitis occurred 5 weeks after sensitization, as assessed histopathologically. High field Magnetic Resonance Imaging (MRI) was useful in depicting these caudal abnormalities that were related to juxta-diskal enthesitis. The occurrence of such inflammatory enthesopathies could serve as an experimental approach for physiopathological and therapeutical studies of spondylarthropathies.

Animals↗
PubMed1991

Management of airway obstruction in the Pierre Robin sequence.

A 10-year retrospective study of the management of airway obstruction in 26 infants with Pierre Robin sequence was made. It was not possible when the infant was first seen to assess the future severity of the airway obstruction but later 3 distinct groups could be identified according to the airway management which had become necessary. The deaths from respiratory obstruction indicate the prime importance of airway management. Laryngoscopy for intubation or endoscopic evaluation was often difficult and sometimes could not be achieved. 'Awake intubation' without general anesthesia has proved to be safer and less difficult using a special purpose slotted laryngoscope. Airway management should be individualized following the progressive sequence of posturing in the prone position, nasopharyngeal tube, endotracheal intubation and tracheotomy until successful control is achieved as indicated by the clinical features and pulse oximetry.

Airway Obstruction↗
PubMed1991

The role of neuropeptide Y in cardiovascular regulation.

Neuropeptide Y (NPY) is a 36 amino acid peptide present in the brain, the adrenal medulla and peripheral sympathetic nerves. The localization and mode of release of NPY led to the proposal that this peptide plays an important role in modulating the contribution of the sympathetic nervous system to blood pressure control. In this paper Bernard Waeber and colleagues review the current knowledge about the mechanisms involved in NPY signal transduction and the different mechanisms whereby NPY, released by the peripheral nervous system, may influence vascular tone and cardiac function.

Animals↗
PubMed1991

The role of articulation in the parsing and retention of letter strings in tachistoscopic free recall.

In Mewhort and Campbell's (1981) model of visual word recognition, a scan-parse mechanism transfer information from a character buffer to a short-term store and is largely responsible for the familiarity effects observed in tachistoscopic free recall. Although Mewhort and Campbell do not elaborate on the role of articulation in this task, they do suggest that the scan-parse mechanism acts prior to any involvement of articulatory processes (see Mewhort & Campbell, 1980). However, proponents of working memory (see Baddeley, 1986) are clear that articulation is necessary for the transfer of visual information to a phonological short-term store. In order to clarify the role of articulation in the parsing and retention of letter string, we asked subjects to undertake a tachistoscopic free-recall task, involving first- and fourth-order letter strings, with and without articulatory suppression and/or unattended speech. Unattended speech was observed to interfere with recall, but only when subjects were free to articulate the strings. This implies that subjects were retrieving information from the phonological store and that articulation is necessary for the registration of visual information in this store. The lack of interaction between order-of-approximation and suppression supports the view that the scan-parse mechanism acts independently of articulation. It appears, therefore, that letter strings are parsed at a stage preceding their transfer of the pharmacological store. Finally, the results indicate that subjects are able to draw directly on a representation of the parsed components of a letter string and may do so when phonological storage is difficult.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

In vitro effects of DuP 753, a nonpeptide angiotensin II receptor antagonist, on human platelets and rat vascular smooth muscle cells.

These experiments were designed to assess the ability of the new nonpeptide angiotensin II antagonist DuP 753 to inhibit the binding and, particularly, to antagonize the cellular response to angiotensin II in human platelets and primary cultures of rat aortic smooth muscle cells (SMC). The binding of 125I-angiotensin II was competitively inhibited by DuP 753 with a 50% binding inhibition (IC50) of 5 to 6 x 10(-8) mol/L in platelets and 1 x 10(-8) mol/L in vascular SMC as compared to an IC50 of 5 to 7.5 x 10(-9) mol/L with nonlabeled angiotensin II. In vascular SMC, DuP 753 completely abolished the effects of angiotensin II on 45CaCl2 efflux and 45CaCl2 uptake. Moreover, in these latter cells, DuP 753 prevented the angiotensin II but not the vasopressin induced increase in cytosolic calcium. These results demonstrate that DuP 753 competes with angiotensin II binding to its receptor in both animal and human cells and selectively blocks the cellular response to angiotensin II.

Angiotensin II↗
PubMed1991

31P-NMR study of different hypothyroid states in rat leg muscle.

Using phosphorus nuclear magnetic resonance spectroscopy, this study was undertaken to determine the effects of experimental hypothyroidism on muscle bioenergetics. The peaks of phosphocreatine (PCr), Pi, phosphodiesters (PDE), sugar phosphomonoesters, and ATP were obtained at rest, during a 2-Hz hindleg muscle stimulation, and during a subsequent recovery period from four groups of anesthetized rats as follows: one control and three hypothyroid (HT) groups treated by propylthyouracil during 2, 4, and 6 wk, respectively. Resting spectra showed a significant rise in Pi by 30% and decreased intracellular pH and PCr/Pi in all three HT groups. PDE progressively increased to 200% of its initial value with hypothyroidism duration. Muscle stimulation did not lead to significant differences in PCr depletion. The percentage of PCr recovery is less in HT muscle than in control muscle. An abnormal H+ metabolism is obvious in all three HT groups. These results indicate abnormal bioenergetics in HT muscle and suggest an impairment of mitochondrial metabolism and of the H+ efflux. They also evoke a high sensitivity of cellular energetics to thyroid deficiency.

Animals↗
PubMed1991

Muscle bioenergetic impairment in hyperthyroid man: a study by 31P NMR spectroscopy.

Phosphorus nuclear magnetic resonance spectroscopy was used to investigate muscle bioenergetics in 9 hyperthyroid patients who were compared with 9 normal subjects. Using the thenar muscle group as reference, the inorganic phosphate, phosphocreatine and intracellular pH were calculated at rest, during aerobic exercise (0.13 w) and post-exercise recovery. No difference was found at rest. After 5 min of exercise, the hyperthyroid patients exhibited a more important phosphocreatine depletion (41.2 +/- 8.2 vs 31.1% +/- 6.5, p less than 0.02) and a larger pH fall (6.65 +/- 0.04 vs 7.01 +/- 0.10, p less than 0.001) than the control subjects. The phosphocreatine recovery rate was not significantly different in hyperthyroid patients and control subjects. These results suggest that exercise requires more ATP in hyperthyroid patients than in normal subjects and that there is excessive dependence on glycolytic metabolism for ATP synthesis in hyperthyroidism. Phosphocreatine resynthesis, reflecting the oxidative metabolism, is not increased. These metabolic disturbances could also supply a partial explanation to the frequent exercise intolerance in hyperthyroid patients.

Adenosine Triphosphate↗
PubMed1991

A meta-analysis of intervention research with problem behavior: treatment validity and standards of practice.

Published intervention research to remediate problem behavior provides a major source of empirical evidence regarding standards of practice and the relative effectiveness of intervention strategies. A meta-analysis of the developmental disabilities literature for the years 1976 through 1987 was performed. Two measures of intervention effectiveness were employed to evaluate the relations between standards of practice, intervention and participant characteristics, and the treatment validity of different levels of intervention for a range of excess behaviors. The results largely failed to support several widespread assumptions regarding precepts of clinical practice. Suggestions were made concerning clinical-experimental research and publication practices to ensure that future work will provide a more conclusive base.

Adult↗
PubMed1990

Identification of T- and B-cell epitopes in synthetic peptides derived from a Streptococcus mutans protein and characterization of their antigenicity and immunogenicity.

Natural immunity to synthetic peptides (SP) derived from the sequences of a 3800 Mr Streptococcus mutans antigen was found in human subjects. Significant serum IgG antibodies were detected both to the native streptococcal antigen and to the SP17, containing essentially residues 1-15. A series of short peptides with deletions at the amino- and carboxy-termini were then tested to identify the B-cell epitopes. Residues 8-13 and 1-6 bound significant serum IgG antibodies but only the former consistently inhibited human antibodies, suggesting that residues 8-13 constitute a major B-cell epitope. The human CD4 subset of T-cells was then examined and this showed a significant uptake of [3H]-thymidine when stimulated with both the native streptococcal antigen and the SP17. The series of short peptides was then used to stimulate CD4 cells, in order to determine the T-cell epitope. The synthetic peptide with residues 6-15 was the shortest peptide that stimulated significant [3H]-thymidine uptake and this peptide was designated as a T-cell epitope. The immunogenicity and antigenicity of SP17 was also investigated in macaques. Immunization of monkeys with the free SP17 failed to elicit serum antibodies or T-cell responses. However, immunization with SP17 linked to tetanus toxoid as a carrier elicited serum antibodies and proliferative responses of lymphocytes, not only to the synthetic peptide but also to the native streptococcal antigen. As in the human studies a B-cell epitope was found in residues 8-13, whereas an overlapping T-cell epitope was located in residues 7-15.(ABSTRACT TRUNCATED AT 250 WORDS)

Adjuvants, Immunologic↗
PubMed1990

The role of extracellular calcium in ischemia/reperfusion injury in skeletal muscle.

Ischemia-reperfusion injury to skeletal muscle, following an acute arterial occlusion is a significant cause of morbidity and mortality. The purpose of this study is to examine the role of extracellular calcium in the production of cellular necrosis following a prolonged period of normothermic ischemia. Bilateral canine gracilis muscles were made ischemic for 4.5 to 5 hr. The control muscle had normal blood reperfusion (ionized Ca2+ 1.2 mM). The treated muscle was perfused for 30 min with an oxygenated solution (ionized Ca2+ 0.11 mM) containing free radical scavengers followed by normal blood perfusion. Necrosis was determined by nitroblue tetrazolium staining after 48 hr of reperfusion. Total muscle Ca2+ was measured by atomic absorption spectrometry. Pre- and postischemic muscle Ca2+ levels were similar (2.8 +/- 0.4 vs 3.2 +/- 0.8 nmole/mg protein, n = 13, P greater than 0.1). After 30 min of reperfusion the treated muscle Ca2+ was 2.4 +/- 0.4 compared to control levels of 8.6 +/- 0.8 nmole/mg protein (P less than 0.001). Total tissue calcium returned to normal at 60 min in viable muscle, but continued to accumulate in necrotic tissue. However, the delay in initial muscle Ca2+ influx was not associated with increased overall salvage of muscle 78 +/- 9% vs 77 +/- 8% necrosis, (P greater than 0.1). In conclusion we could not demonstrate a protective effect of reduced extracellular Ca2+ during early reperfusion, and it negated our previously demonstrated beneficial effects of free radical scavengers. It was shown however that the early ability to extrude intracellular calcium was associated with significant salvage of muscle tissue.

Animals↗