Limitations of pulse oximetry: respiratory insufficiency--a failure of detection.
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Acute Disease↗
Biomedical subjects
J A Davidson
Publications and source records attributed to J A Davidson.
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↗
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↗
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↗
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↗
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↗
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↗
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↗
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↗
The need for a randomised trial of hormone replacement therapy in women with breast cancer.
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Breast Neoplasms↗
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↗
HLA antigens and cervical carcinoma.
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Carcinoma, Squamous Cell↗
Professional challenges in the coming decade.
Last month, as part of our observance of the 15th anniversary of Physician Assistant journal, members of our Editorial Board offered their views on turning points in the history of the PA profession. In this issue, we jump from the past to the future, with perspectives on the main crises or changes facing the profession in the coming decade. You may agree or disagree with these viewpoints. Diversity of opinion keeps the PA profession dynamic and strong--which is exactly why Physician Assistant journal provides an open forum for letters and guest editorials.
Forecasting↗
A biomechanical study of two methods of internal fixation of unstable fractures of the femoral neck. A preliminary study.
A model of an unstable femoral neck fracture was used in this study to compare the axial and torsional displacement obtained when the neck was fixed by a compression hip screw (CHS) and side plate, or three Knowles pins. Six paired, embalmed femora were mounted on a special, custom-made jig that grasped the femoral head and shaft securely. A standardized osteotomy was made with an oscillating saw, bisecting the distance between the lower cartilaginous portion of the femoral head and the intertrochanteric line. A 5-mm thick slice of bone was excised from the posteromedial quadrant of the distal fragment. The right or left femur in each pair was then randomly assigned to internal fixation with either three Knowles pins or a keyed CHS plus a 130 degrees four-hole side plate. After potting of the specimens and application of rosette strain gauges, axial displacements were measured during the application of in-plane and out-of-plane compressive loads. The resistance to torsion was also determined. There were no statistical differences between the two devices for compressive or torsional loading using this model.
Biomechanical Phenomena↗
Combined chemical and mechanical effects on free radicals in UHMWPE joints during implantation.
An electron spin resonance (ESR) technique is employed to determine the free radical distribution in the articulating surfaces of retrieved acetabular cups and knee-joint plateaus (retrieved after more than 6 years of implantation). Similar measurements made on samples prepared from cyclically stressed and unstressed cups, and on samples following oxidations in nitric acid and intralipid solutions provided sufficient data to gain more knowledge about the combined chemical and mechanical effects on PE free radicals during implantation. In UHMWPE free radicals are primarily initiated by gamma-ray sterilization; however, during implantation, peroxy (scission type) free radicals are formed and reach a maximum concentration level (equilibrium state) due to oxidation by chemical (hemoglobin and/or synovial fluids) environment of the joints. Subsequently, due to frictional heating and stress in the loading zones, free radical reaction is accelerated and their number is reduced only in those areas. This is consistent with the observations of a temperature rise in acetabular cups during in vitro frictional wear stress tests and in vivo telemetry observations, as reported by others. Compared with the previously reported SEM micrographs the low-free-radical regions are correlated with high-wear areas and the high-free-radical regions with the low-wear areas.
Biocompatible Materials↗
Diabetes care in minority groups. Overcoming barriers to meet these patients' special needs.
Physicians play a critical role in reaching diabetic patients in minority groups. These patients need professional help to modify their diets and exercise patterns, to follow drug regimens and blood-testing programs, to comply with treatment over the long term, and to pay for treatment. Closing the gap between the treatment levels afforded different groups of Americans is an enormous challenge, but it is one that is critical to the health of our population.
Aftercare↗
Stiffness and strength tailoring of a hip prosthesis made of advanced composite materials.
This work is concerned with the design of hip prostheses using advanced fiber reinforced composite materials. The major focus of the study is to evaluate how the stiffness and strength of composite hip prostheses can be affected by variations in ply orientation and stacking sequence for a selected manufacturing method. This investigation involved both analytical and experimental work. An analytical model was developed which consists of a stress analysis and a failure analysis. A finite element program was developed during the course of the investigation for analyzing stresses, strains, and deformations of composite stems with a simplified configuration. Failure and mode of failure were predicted by appropriately selected failure criteria. Experiments were also performed on T300/976 graphite/epoxy composites to verify the analysis and the computer calculations. Both testing and analysis accounted for the various combinations of in-plane and out-of-plane (torsion) loading that can act on the prosthetic hip. Simplified composite stems with a 120 layer thickness were fabricated and tested. An excellent agreement was found between the measured strain data and the numerical calculations. Using the program, parametric studies were performed. It was found that an optimal design of hip stems can be achieved by using advanced fiber-reinforced composite materials, but great care must be taken when selecting the appropriate ply orientation and stacking sequence for a chosen fabrication method.
Biocompatible Materials↗