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Biomedical subjects

K Stokes

Publications and source records attributed to K Stokes.

30 records · Page 2Linked to original sources
PubMed1987

Limitations of indirect methods of estimating small bowel transit in man.

Experiments were carried out in healthy volunteers to explore the utility of a new [14C]lactulose breath test for measuring small intestinal transit time in man and to use this procedure to test whether two antidiarrheal agents, codeine and clonidine, alter small intestinal transit time during digestion of a liquid meal. In an initial validation study performed in 12 subjects (three studies in each subject), a liquid test meal containing 10 g [14C]lactulose was administered and the colonic entry time estimated from the time course of 14CO2 excretion in breath compared with that of H2 excretion. There was a fair correlation (r = 0.77; P less than 0.001) between results obtained by the two methods; both methods gave similar results, but 14CO2 output was delayed when compared to H2 output and was incomplete. The meal also contained xylose and [13C]glycine, permitting the duodenal entry time of the meal to be estimated by the appearance of xylose in blood and 13CO2 in breath, respectively. The same liquid meal was then used to examine the effect on small intestinal transit time (colonic entry time minus duodenal entry time) of codeine or clonidine. 99Tc-sulphur colloid was also added to the meal to permit a comparison of small intestinal transit estimated by imaging with that estimated by the 14CO2-lactulose breath test. 99Tc radioactivity appeared in the cecum (as assessed using gamma scintigraphy) about 2 hr before 14CO2 radioactivity appeared in breath; the correlation between transit time estimated by the two methods was moderate (r = 0.61; P less than 0.05). Based on the [14C]lactulose data, small intestinal transit time ranged from less than 1 to 3 hr for a liquid meal containing 10 g lactulose; within-subject variation (coefficient of variation 17%) was considerably less than between-subject variation (coefficient of variation 56%). Codeine increased the small intestinal transit time significantly (from 2.7 +/- 0.3 hr to 5.0 +/- 0.9 hr; mean +/- SE), whereas clonidine did not alter small intestinal transit time, as estimated by the colonic entry time minus duodenal entry time. Neither drug influenced duodenal entry time. These results suggest that the [14C]lactulose breath test, which has only moderate accuracy, may have occasional utility as a convenient, noninvasive method for estimating small intestinal transit time in man. However, this study also suggests that indirect methods of estimating small bowel transit in man have limitations, variability, and possibly may lack the desired sensitivity.

Antidiarrheals↗
PubMed1987

Autooxidative degradation of implanted polyether polyurethane devices.

While certain polyether polyurethanes have been shown to be biostable, undesirable interactions between polymer, the body environment and device can occur. For example, the corrosion products of metallic parts can cause relatively rapid autooxidation of polyether soft segments. This phenomenon was first demonstrated in our laboratories by immersing polyurethane test specimens in metal ion solutions of different oxidation potentials. Subsequently, the mechanism was reasonably duplicated by immersing Pellethane 2363-80A insulated cardiac pacing leads in 3%, 37 degrees C hydrogen peroxide. In vivo studies after 1 year show that corrosion products from pure Co and Fe produce the most rapid degradation of the polyurethane.

Animals↗
PubMed1985

Identification of a tumor cell-derived differentiation antigen on mouse colony-forming units in the spleen and progenitor cells.

Surface membrane antigen(s) expressed on a mouse mast cell line (FMP1) have also been shown to occur on hemopoietic spleen colony-forming units (CFU-S) and granulocyte/macrophage colony- and erythroid burst-forming cells, using a xeno-antiserum raised against FMP1 cells. This mast cell model has been used to obtain antiserum and large quantities of antigen for the biochemical identification of CFU-S and progenitor cell antigen(s). Immunoprecipitation of FMP1 membrane antigens with the antiserum and subsequent polyacrylamide gel electrophoresis revealed the presence of five membrane proteins with molecular weights of 28,000, 32,000, 36,000, 50,000, and 70,000. Mouse B-lymphoma cell line W279 which reacted with anti-FMP1 serum was found to possess three immunoprecipitable surface proteins with molecular weights of 32,000, 50,000, and 70,000. Attempts have been made to identify the antigen(s) expressed by CFU-S and progenitors which were revealed by immunoprecipitation from the tumor lines. The three lower-molecular-weight proteins (Mr 28,000-36,000) were chosen for initial study. Membrane extracts of FMP1 cells were fractionated on Sephacryl S-200, and selective pools of these antigens were made. Antisera to these pools exhibited complement-dependent cytotoxicity to FMP1 cells, bone marrow CFU-S, granulocyte/macrophage colony-forming cells, and erythroid burst-forming units. These antisera immunoprecipitated Mr 28,000, 32,000, and 36,000 proteins from FMP1 cell membrane extracts but not the Mr 50,000 and 70,000 antigens. The W279 line has only one antigen (Mr 32,000) in the lower-molecular-weight range and is able to absorb anti-CFU-S and anti-progenitor activity, which suggests that it is this antigen which is expressed on hemopoietic cells. In addition, thymocytes react with anti-FMP1 serum, and the Mr 32,000 antigen was immunoprecipitated from thymus cell extracts. Binding studies with concanavalin A, wheat germ agglutinin, and lentil lectin indicated that the Mr 28,000-36,000 proteins were glycoproteins. The apparent molecular weights of these proteins on polyacrylamide gels were not altered by reduction and alkylation and therefore do not contain disulfide-linked subunits.

Animals↗
PubMed1984

Wallbar clamp.

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Exercise Therapy↗
PubMed1983

Sexual orientation and sex role conformity.

Homosexuals are stereotypically viewed as deviating from the conventional sex role standards of our society. Homosexual males are regarded as effeminate, while homosexual females are seen as masculine. Some limited empirical support for these stereotypes has been reported in the literature. However, results remain inconclusive. In order to provide a further test of these stereotypes, 186 male and female homosexual, bisexual, and heterosexual subjects were administered the Bem Sex Role Inventory. Results showed no significant support for prevailing stereotypes. Possible reasons for the discrepancy between these findings and previous reports are explored and suggestions are offered for future research.

Adult↗
PubMed1983

Experimental and clinical study of a new permanent myocardial atrial sutureless pacing lead.

A new permanent lead has been developed for atrial epicardial use. Early clinical evaluation (26 human implants) following thorough canine studies indicates that the new lead is safe, effective, and reliable. Canine thresholds and P-wave amplitudes as a function of implant time are similar to those of transvenous atrial "J" leads. Human thresholds at implant are higher than canine, but change less with time. Implant and acute repositioning were found to be easy. There have been no lead-related operations.

Animals↗
PubMed1983

A combined atrial/ventricular lead for permanent dual-chamber cardiac pacing applications.

A new urethane insulated dual unipolar atrial/ventricular transvenous lead has been developed to facilitate implantation of permanent dual-chamber cardiac pacing systems in man. The atrial portion of the lead has tines and is designed to retain a permanent J configuration, while the coaxially situated ventricular lead is freely and independently adjustable and incorporates a ring tip electrode with four urethane tines. Our initial experience with the dual lead in one patient is reported herein and suggests that combined atrial/ventricular pacing leads are feasible and may obviate need for implantation of two separate pacing electrodes in patients being considered for permanent dual-chamber pacing.

Electrodes, Implanted↗
PubMed1983

Implant experience with unipolar polyurethane pacing leads.

A total of 905 unipolar polyurethane pacing leads have been implanted by the first author's group, between April 1978 and February 1982, with a mean implant of 1.4 years. Twelve leads were explanted and analyzed. Eleven of the explanted leads exhibited some degree of surface damage or "frosting." Of the 11, five atrial (Medtronic 6991 U) and one ventricular (Medtronic 6971) lead suffered complete insulation failure. One lead was completely free from surface damage. Clinically, insulation failure presented as muscle stimulation and/or battery depletion. Surface damage appears to be due to an environmental stress cracking (ESC) mechanism. ESC requires both a surface active agent from the hostile biological environment, and stress in excess of a threshold value. The minor surface damage or "frosting" of the eleven explanted leads was typically 10 to 15 microns deep on leads implanted about one year, although one device (15 months) had 30 micron cracks. No lead failures in this series were attributed to this shallow cracking mechanism. The severe cracking of the six Medtronic leads leading to insulin failure was thought to be due to the unusually high tensile stresses imposed by manufacturing processes and ligatures. The incidence of failure was 7% (5/74) for the Medtronic 6991 U and 0.2% (1/454) for the Medtronic 6971. Medtronic lead manufacturing processes have been modified to reduce the high residual tensile stresses and a fixation sleeve has been added to reduce ligature stress.

Arrhythmias, Cardiac↗
PubMed1982

Polyether polyurethanes for implantable pacemaker leads.

Two variations of a commercially available polyether polyurethane were evaluated for certain physical properties and the changes in those properties as a result of plasticization by absorbed moisture. Appropriate tests were done to establish biocompatibility. A two-year rat implant study evaluated chronic biocompatibility and biostability. Ten tumours were found in 34 animals, of which eight were considered unrelated to the materials. Two fibrosarcomas were presumed to be the result of solid-state carcinogenesis, not related to the material per se. Material testing included analysis of density, tensile strength, elongation, molecular weight, intrinsic viscosity, scanning electron microscopy, differential scanning calorimetry, and infrared spectrum changes. The polyether polyurethane was considered to be biocompatible and biostable for long-term implant.

Animals↗
PubMed1976

Peptic stricture of the oesophagus: the role of oesophagogastrostomy.

Sixteen patients with severe peptic stricture of the oesophagus were treated by oesophagogastrostomy at the Royal Children's Hospital, Melbourne, during the period 1948 to 1968. It has been possible to obtain a follow up on all patients, so that the period of follow up has varied from seven to 24 years. Although the early postoperative results were promising, later problems occurred in over half of the patients, the major complication being recurrence of peptic stricture at the anastomotic site.

Adult↗
PubMedDate not supplied

Case report: legionella infected thoracic aortic graft.

A case of a thoracic aortic graft in a patient with Marfan's syndrome infected with legionella is presented. The pathogenesis of graft infection and aspects of examination with aortography, gallium scanning, magnetic resonance imaging (MRI), and spiral volumetric computed tomography (CT) are presented, and the pathophysiology and management of thoracic aortic graft infections is briefly discussed.

Aortic Dissection↗