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Biomedical subjects

J A Davidson

Publications and source records attributed to J A Davidson.

At least 19 recordsLinked to original sources
PubMed1995

Comparison of the effects of four i.v. anaesthetic agents on polymorphonuclear leucocyte function.

Initial resistance of bacterial infection is mediated primarily by polymorphonuclear leucocytes (PMN). Anaesthetic agents have been reported to impair various aspects of PMN function. It is possible that the use of these agents to sedate critically ill patients may further compromise an already depressed host defence mechanism. A flow cytometric technique with fresh whole blood from 10 healthy volunteers was used. Phagocytic and respiratory burst activity of PMN incubated for 1 h with either propofol, thiopentone, midazolam or ketamine at both clinical plasma concentrations and 100 times this concentration were determined. Thiopentone at the higher concentration reduced both respiratory burst activity (mean peak channel 50.7 compared with control value of 77.6 (P < 0.0001)) and phagocytosis (mean peak channel 47.5 compared with 79.9 (P < 0.0001)). Ketamine at 100 times the clinical plasma concentration also reduced respiratory burst and phagocytosis, but this failed to reach statistical significance (P = 0.10 and P = 0.053, respectively). No significant depression occurred in the other groups. The results suggest that these i.v. anaesthetic agents, at clinically relevant concentrations, have minimal effects on PMN phagocytosis and oxygen free radical production. At higher concentrations thiopentone and ketamine may affect phagocytic function and thiopentone may impair intracellular cytolysis.

Anesthetics, Dissociative↗
PubMed1995

Attitudes to the Association of Anaesthetists recommendations for standards of monitoring during anaesthesia and recovery.

A questionnaire was sent to 293 anaesthetists in the West of Scotland to assess their attitudes to the recommendations for standards of monitoring during anaesthesia and recovery published by the Association of Anaesthetists of Great Britain and Ireland. Such standards are considered achievable and affordable in terms of costs and allow the early detection of events occurring during anaesthesia, which might lead to injury to the patient. The survey shows that there is wide acceptance of the recommendations by anaesthetists of all grades, with resultant improvements in the quality of patients care.

Anesthesia↗
PubMed1994

Effects of interferon-tau and interferon-alpha on proliferation of bovine endometrial cells.

The ruminant conceptus secretes a unique interferon, interferon-tau, that regulates endometrial prostaglandin secretion during early pregnancy. Because one of the pleiotropic effects of interferons is to inhibit cellular proliferation, a series of experiments was conducted to determine whether or not the bovine endometrium is sensitive to the antiproliferative effect of interferon-tau and the related interferon, interferon-alpha. Endometrial epithelial and stromal cells were prepared from the endometrium of cows from Days 11-17 after estrus and incubated with recombinant bovine interferon-tau (rbIFN tau; 1-1000 ng/ml), recombinant bovine interferon-alpha 1 (rbIFN alpha; 1-1000 ng/ml), recombinant human interferon-alpha 2b (rhIFN alpha; 100 ng/ml), or ovine interferon-tau (oIFN tau; 100 ng/ml). Proliferation was determined by monitoring uptake of [3H]thymidine into DNA. Generally, interferons did not inhibit proliferation of endometrial epithelial cells. Exceptions were for 1000 ng/ml rbIFN tau, which inhibited proliferation by 23%; 100 ng/ml rbIFN alpha, which inhibited proliferation by 28% in one of two experiments only; and 100 ng/ml oIFN tau, which inhibited proliferation by 17%. Proliferation of endometrial stromal cells was not inhibited by any concentration of any interferon in two separate experiments. Therefore, unlike other bovine cells tested previously (lymphocytes and oviductal cells), bovine endometrial cells were not consistently inhibited by IFN tau or IFN alpha. Such reduced responsiveness of endometrial cells to the antiproliferative effects of type I interferons could allow for growth of the endometrium during the period of pregnancy when the conceptus produces IFN tau.

Animals↗
PubMed1994

Abrasive wear of ceramic, metal, and UHMWPE bearing surfaces from third-body bone, PMMA bone cement, and titanium debris.

The debris generated by the progressive wear of total joint replacement (TJR) devices is considered a primary cause of osteolysis, bone resorption, and premature failure of artificial hips and knees. The vast majority of this debris originates from the UHMWPE articulating surfaces caused by tribological interaction with the opposing metal or ceramic surface and hard particulates contained in the sinovial fluid. Entrapment of third body debris, such as cortical bone, PMMA cement, and titanium debris, between the articulating surfaces can cause abrasion of both the hard bearing surface and the UHMWPE. The propensity for abrasive wear is dependent on the relationship between the hardness of the third-body debris and the hardness of the bearing surfaces. To gain a better understanding of this relationship and its effect on wear, the abrasive wear behavior of several metal and ceramic bearing surfaces was characterized in terms of the hardness of both the third-body debris and the metal or ceramic substrate. The effects of abrasion and increased surface roughness of the metal or ceramic surfaces on wear of the UHMWPE was also determined. In addition, the amount of UHMWPE wear was quantified in terms of the amount (particles/ml) of titanium fretting-type debris contained in solution. The results of this investigation showed the resistance to abrasive wear of the metal and ceramic bearing surfaces to increase with increasing surface hardness. Bone debris, PMMA cement, and titanium debris produced visible abrasion of all metal surfaces including nitrogen ion implanted Ti-6Al-4V. The ceramic bearing surfaces showed no evidence of abrasion and produced the least amount of UHMWPE wear. The wear of UHMWPE sliding against Co-Cr-Mo was found to increase with increasing levels of 1.48 microns titanium debris added to the wear test solution. The rate of UHMWPE wear increased rapidly for concentrations of titanium debris in the test solution exceeding about 10(5) particles/ml. These test results suggest that third-body particles, both large and small, are capable of causing increased abrasive wear of UHMWPE, and that abrasion of the hard bearing surfaces will occur if the hardness of the third-body debris exceeds the hardness of the metal or ceramic bearing surface.

Biocompatible Materials↗
PubMed1994

New surface-hardened, low-modulus, corrosion-resistant Ti-13Nb-13Zr alloy for total hip arthroplasty.

To optimize the performance of total hip replacement, scientists and clinicians are seeking new materials and noncemented, press-fit designs that can improve load transfer to the bone and reduce the incidence of loosening and thigh pain. Currently used Co-Cr-Mo alloy has a relatively high elastic modulus (E = 227 GPa), which limits its ability to transfer load to the surrounding bone in the proximal calcar region. Thus to improve load transfer, designs are considered with less cross-sectional area to increase flexibility, but at the expense of fit and fill, and thus stability of the implant within the bone. Should stem loosening occur, the stem stresses may exceed the relatively low fatigue strength of the Co-Cr-Mo alloy and lead to stem breakage. To improve these conditions, lower modulus Ti-6Al-4V alloy (E = 115 GPa) is being used. More recently, a new lower-modulus (E = 79 GPa) Ti-13Nb-13Zr alloy has been developed which does not contain any elemental constituents associated with adverse cell response (i.e., Co, Cr, Mo, Ni, Fe, Al, V), and which possesses comparable or superior strength and toughness to existing Ti-6Al-4V alloy. The carefully selected Nb and Zr constituents improve bone biocompatibility and corrosion resistance compared to that of currently used implant metals. Additionally, a unique diffusion hardening (DH) treatment can be conducted during the age-hardening process of this near-beta alloy to produce a hardened surface with abrasion resistance superior to that of Co-Cr-Mo alloy. This also provides an improvement in the micro-fretting tendencies that may occur within femoral head-neck taper regions and modular interfaces of other implant designs. The present study describes the metallurgy and mechanical properties of this unique low modulus Ti-13Nb-13Zr alloy, and the heat treatments used to obtain the high strength, corrosion resistance, and surface hardening that renders this biocompatible alloy well-suited for press fit hip replacement applications. Because of the relatively lower beta transus (735 degrees C), this alloy is also much easier to net shape forge into more complex stem designs.

Alloys↗
PubMed1993

Histological reaction to titanium alloy and hydroxyapatite particles in the rabbit tibia.

The interfacial membrane harvested from failed joint replacements contains particulate debris from the materials used for the implant. To define the tissue response to particulate titanium alloy and hydroxyapatite (HA) alone, 16 mature New Zealand white rabbits were divided into 2 groups of 8 rabbits. Using sterile technique, a drill hole was placed anteromedially in the tibia, 1 cm distal to the knee joint bilaterally. The marrow was scooped out and 0.25 mg of either titanium alloy particles or HA particles were inserted in the right tibia. The titanium alloy particles had a diameter averaging 4.0 +/- 4.4 microns (mean +/- standard deviation) and an aspect ratio (the ratio of the maximum length divided by the maximum width) of 1.84. The HA particles had a diameter of 4.4 +/- 3.3 microns and an aspect ratio of 1.76. The left leg was prepared in a similar fashion, but no biomaterial was implanted. The animals were killed after 16 wk. The harvested tibiae were processed with decalcification and the plastic-embedded sections were subjected to histomorphological analysis. Black titanium alloy particles were present within the bone marrow fat between haematopoietic cells, and within scattered macrophages. The surrounding bone appeared to be unaffected. Within the spongiosa, the HA particles were surrounded by small numbers of mononuclear histiocytes or encased within a shell of new appositional bone. Where HA deposits were exposed to the endosteal aspect of bone, there was scalloping of the surface of the HA in a pattern suggestive of resorption or dissolution of the HA particles.(ABSTRACT TRUNCATED AT 250 WORDS)

Alloys↗
PubMed1993

Visual and language processing deficits are concurrent in dyslexia.

Research has demonstrated that dyslexic subjects have language processing problems. More recent evidence indicates that dyslexic subjects also suffer a low-level visual information processing deficit. Little evidence is available to indicate the extent to which dyslexic subjects simultaneously show a visual and language processing dysfunction. In this study, 35 normal and 35 dyslexic subjects aged from 7.9 to 14 years of age were compared on three reading process variables, a visual processing score, a test of phonological coding and a test of language comprehension, each of which were shown to be related to reading performance. The visual processing score was the slope of the regression line predicting the duration of visible persistence as a function of spatial frequency. The language processing measures were a test of phonological coding of orthographically legal Non-Words and a test of language comprehension, the Token Test. The results showed that the visual processing score was significantly predictive of group membership with 91% of the dyslexic group and only 20% of the normal readers having low scores on this measure. The Non-Word test was found to be a perfect discriminator for dyslexia by indicating that every subject in this group had a major phonological coding deficit. An unexpected finding of the present results was that the Token Test did not discriminate between the groups. The results are interpreted as providing evidence for the concurrence of visual and language deficits in dyslexia.

Adolescent↗
PubMed1993

Tracheal intubation after induction of anaesthesia with propofol, alfentanil and i.v. lignocaine.

We have assessed tracheal intubating conditions in 60 ASA I or II patients after induction of anaesthesia with propofol 2.5 mg kg-1 and alfentanil 10 or 20 micrograms kg-1 with or without i.v. lignocaine 1 mg kg-1. No neuromuscular blocking agents were administered. Patients were allocated randomly to four groups: group 1 = propofol-alfentanil 10 micrograms kg-1; group 2 = propofol-alfentanil 10 micrograms kg-1-lignocaine 1 mg kg-1; group 3 = propofol-alfentanil 20 micrograms kg-1; group 4 = propofol-alfentanil 20 micrograms kg-1-lignocaine 1 mg kg-1. Intubating conditions were assessed as acceptable or unacceptable on the basis of a scoring system dependent on ease of laryngoscopy, vocal cord position and coughing on insertion of the tracheal tube. Intubating conditions were acceptable in 20%, 73%, 73% and 93% of patients in groups 1-4, respectively. Intubating conditions were better and there was less coughing in the lignocaine group.

Adult↗
PubMed1993

Laboratory assessment of the Baxter disposable patient-controlled analgesia system.

The performance of the Baxter patient-controlled analgesia infusor system was assessed in the laboratory. The flow of the 5 ml.h-1 infusor was measured gravimetrically with the flow restrictor maintained at 31 degrees C and the reservoir at either 20 degrees C or 25 degrees C. At 25 degrees C the mean flow was 4.98 (SEM 0.06) ml.h-1 and at 20 degrees C the mean flow was 4.32 (0.05) ml.h-1. The patient-control module performed reliably, delivering a mean of 0.42 (0.001) ml following depression of the button, slightly less than the manufacturer's quoted value of 0.5 ml.

Analgesia, Patient-Controlled↗
PubMed1993

Evaluation of three portable suction devices.

Three portable suction devices were evaluated and compared with a wall-mounted vacuum driven suction unit. The Repro-med Res-Q-Vac, the Dräger Sujector 2000 and the Laerdal suction unit were assessed by measuring the time taken to aspirate 140 ml of mock gastric contents. The respective times for each device, expressed as mean and (range) were 7.39 (4.3-10.4), 8.6 (7.8-9.4) and 11.4 (9.4-12.6) s. These compare favourable with the Ohmeda suction unit (7.27 (6.2-8.9)). Each type of device has advantages and disadvantages when factors such as size, power supply and portability are considered, and each will be the most suitable for a particular situation.

Equipment Design↗
PubMed1993

Effective concentration 50 for propofol with and without 67% nitrous oxide.

The Effective Blood Concentration (EC) of propofol required to prevent response to surgical incision was determined in 65 ASA I or II female patients breathing either 100% oxygen or 67% N2O in oxygen. Propofol was administered via a microcomputer-controlled infusion system programmed to maintain the blood propofol concentration at predetermined target values. The blood propofol concentrations predicted by the micro-computer were validated by measurement of whole blood propofol concentration. Predicted and measured concentrations differed during infusion of propofol, but became similar after discontinuing the infusion for at least 90 s, suggesting that equilibration within the central compartment was incomplete during infusion. The response to the initial incision was observed and probit analysis used to determine the predicted blood concentration at which 50% of patients responded. The predicted EC50 for propofol/N2O/O2 and propofol/O2 was 4.5 micrograms ml-1 and 6.0 micrograms ml-1 respectively, and the measured EC50 propofol/N2O/O2 and propofol/O2 was 5.36 micrograms ml-1 and 8.1 micrograms ml-1, 67% nitrous oxide in oxygen reducing the predicted EC50 by 25% and the measured EC50 of propofol by 33%. The predicted EC may be more representative of the equilibrated concentration in the central compartment and thus reflective of tissue propofol concentrations.

Adolescent↗
PubMed1993

Comparison of HA-1A and E5 monoclonal antibodies to endotoxin in rats with endotoxaemia.

OBJECTIVE: To investigate the ability of two anti-endotoxin IgM antibodies (10 mg/kg) to prevent the hyperdynamic response induced by infusion of Escherichia coli rough mutant endotoxin core types R1 and R2 in rats. DESIGN: Randomised blind laboratory study. SETTING: University department of surgery. MATERIAL: 8 groups of 5 male Sprague-Dawley rats and 10 control animals. MAIN OUTCOME MEASURE: Percentage change in cardiac output during the period of observation. RESULTS: E5 provided significant protection against R1 (p = 0.04) but not against R2. HA-1A gave significant protection against R2 (p < 0.04) but not against R1. In clinical isolates of E. coli the R1 type predominates (about 70%). CONCLUSION: These results may reflect true differences in specificity between the antibodies, but there remains the possibility that these are non-specific effects. Further controls with irrelevant murine and humanized IgM monoclonal antibodies are in progress.

Animals↗
PubMed1993

Characteristics of metal and ceramic total hip bearing surfaces and their effect on long-term ultra high molecular weight polyethylene wear.

The micromechanics of ultra high molecular weight polyethylene (UHMWPE) wear in total hip replacement are very complex. Polyethylene wear from the metal head and debris formation are two common types of wear. There are additional wear-related processes occurring at the metal-bearing surfaces that are not well-known, however. This study outlines these processes, including (1) surface wettability changes, (2) oxidative wear of metal surfaces, (3) microabrasion of metal surfaces from oxide film damage, and (4) surface abrasion from three-body polymethylmethacrylate and bone debris. These processes can contribute to metal ion release and a gradual increase in the roughness of the metal surfaces. This can lead to increased long-term UHMWPE wear. Of the metal alloys currently used in total hip replacements, Co-Cr-Mo alloy is significantly more resistant to roughening processes. Hard, stable, oxide: ceramic surfaces articulating against UHMWPE are essentially immune to these surface-roughening processes, however. In addition, they provide a more wettable surface, further minimizing polyethylene wear relative to metal surfaces. By analyzing metal release rates from metal-polyethylene wear tests, it is shown here that Co-Cr-Mo is gradually removed at a rate of about 0.1 micron per year (10(6) cycles), whereas 316L stainless steel is removed on the order of 0.2 microns per year and Ti-6Al-4V on the order of 1 micron per year. The wear rate of Co-Cr-Mo articulating against itself is reported to be still greater, at about 2-4 microns per year after an initial wear-in period. Because metal is gradually removed with articulation time, surface-hardening methods such as nitrogen ion implantation can be expected to provide only temporary resistance to these metal removal and surface-roughening processes. Hard, stable ceramic surfaces such as Al2O3 and ZrO2, however, can be expected to maintain their initial surface finish and thus minimize UHMWPE wear in the long term.

Alloys↗
PubMed1992

Warming lignocaine to reduce pain associated with injection.

OBJECTIVE: To investigate the effect of warming lignocaine on the pain associated with subcutaneous injection. DESIGN: Double blind, randomised, crossover study. SETTING: Hospital clinic. SUBJECTS: 40 healthy volunteers. INTERVENTIONS: Subcutaneous injection with 1 ml of 1% lignocaine at 20 degrees C and 1 ml of 1% lignocaine at 37 degrees C. MAIN OUTCOME MEASURES: Pain assessed by linear analogue pain scores and subjects' comparison of pain on injection. RESULTS: 25 subjects (89%; 95% confidence interval 72% to 98%) thought that lignocaine at 20 degrees C was more painful and 3 (11%; 2% to 28%) thought that lignocaine at 37 degrees C was more painful (p < 0.0001); 12 subjects did not express a difference. Median pain score for injection at 20 degrees C was 11.00 and at 37 degrees C was 3.25 (p < 0.001). Median difference was 8.25 (4.00 to 13.50). CONCLUSIONS: The simple procedure of warming to 37 degrees C reduced the pain associated with subcutaneous injection of lignocaine.

Adult↗