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Biomedical subjects

J Chambers

Publications and source records attributed to J Chambers.

At least 55 records · Page 3Linked to original sources
PubMed1995

Life-threatening degeneration of the Accufix active-fixation atrial-pacing electrode.

More than 47,000 patients world wide have had the Accufix atrial-pacemaker lead implanted. The company has issued warnings because degeneration of the electrode has occurred, with two deaths. We detected a fractured electrode that was successfully removed with insertion of a new type of electrode. Action is required to prevent further possibly fatal complications occurring.

Adolescent↗
PubMed1995

Ethical dilemmas in the lived experience of nursing practice.

Through a series of semistructured interviews with 12 nurses delivering direct patient care in acute, long-term and home care settings, information was sought regarding the ethical concerns of practicing nurses. Although these nurses frequently did not specifically identify the areas of expressed concern as ethical in nature, thematic analysis of the transcribed interviews uncovered four major ethical areas of concern common to these 12 nurses. These areas are: (1) Withholding of information and truth-telling; (2) Unequal access or inequalities in care; (3) Differences between business and professional values; (4) Breaking and reporting broken rules. Several reasons are offered to explain the failure of nurses accurately to identify specific practice dilemmas as ethical in nature and the sequelae of these failures. Possibilities involving ongoing education and mentored experiences in practice areas are reported.

Adult↗
PubMed1995

The effect of left ventricular function on the echocardiographic assessment of heart valve disease.

Transvalvar velocities or derived pressure differences are highly dependent on flow. They must be corrected for flow for research studies or in the clinical situation where values are intermediate and difficult to interpret. This can be done using the continuity equation or using formulae based on ratios of mean pressure drop and flow of which resistance is probably more accurate than the Gorlin formula. Left ventricular diastolic behavior is a major determinant of mitral pressure half-time where the mitral stenosis is mild and also of the slope of the continuous wave recording in mild or moderate aortic regurgitation. Methods for assessing mitral regurgitation including patterns of pulmonary vein flow are also dependent on left ventricular function. The echocardiographic methods of describing valve function cannot be interpreted without regard to left ventricular function and loading conditions.

Aortic Valve Insufficiency↗
PubMed1995

Lumbar spine arthrodesis. A comparison of hospital costs between 1986 and 1993.

The purpose of this project was to evaluate the hospital costs of one- and two-level spinal arthrodesis and to determine areas where costs may be effectively reduced. The hospital bills of 40 patients (20 each in 1986 and 1993) who had undergone single-level and double-level lumbar arthrodesis were reviewed. Each patients's bill was examined and the specific charge items were assigned to one of seven "service centers." To effectively compare costs in the two different years, dollar values on 1986 bills were converted to inflation-adjusted 1993 amounts (the consumer price index over this interval was about 35%). The hospital cost (mean) for single- and double-level spinal arthrodesis increased from $7,457 (1986) to $19,712 (1993). In inflation-adjusted 1993 dollars the actual increase was 97%. All but two service centers demonstrated increased costs. The most dramatically increased in price was implant cost ($300 in 1986 vs $2,967 in 1993, a 638% increase with inflation adjustment). When adjusted for inflation, surgeons' fees actually decreased by 18% at our institution ($7,503 in 1986 vs $8,338 in 1993). The other service center that showed a decrease was the hospital room (-15%). The anesthesia charge, recovery-room fee, operating-room charge, and the "other" charges increased between 36% and 288%. As a percentage of the total hospital bill, implant cost accounted for approximately 4% of the 1986 charges, whereas in 1993 it accounted for more than 15% of the total bill. None of the other service centers showed such a drastic increase. Increasingly sophisticated technology has dramatically raised hospital charges. Strategies to reduce the overall cost of spinal surgery should concentrate on controlling the cost of spinal implants.

Cost Control↗
PubMed1995

Doppler echocardiography in normally functioning replacement heart valves: a literature review.

BACKGROUND AND AIM OF THE STUDY: The English literature on replacement heart valves up to the end of 1994 was reviewed to establish normal ranges for forward function and patterns of regurgitation. METHODS: A total of 48 papers were collected, but 16 were excluded leaving normative data for 14 different designs on a total of 1595 valves in the aortic and 1127 valves in the mitral position. Values for velocity, derived pressure drop, effective orifice area and pressure half-time were tabulated by annulus diameter for each class of valve. RESULTS: Comparison between valve designs was difficult as a result of differences in methodology. For the aortic position, differences in velocity and derived pressure drop within one valve type were similar to those between all valve designs. The homograft and Labcor-Santiago valves appeared the least obstructive although using flow-corrected effective orifice area, there were no material differences between the valve designs. For the mitral position, there was a narrow range in mean pressure drop of 2.0 mmHg to 7.8 mmHg. Little data for the tricuspid position were available. Patterns of normal transvalvar regurgitation varied widely between the valves, but obvious transvalvar regurgitation was a feature of most mechanical valves. CONCLUSION: Much work using standardized protocols and with appropriate hemodynamic formulae needs to be done to improve our knowledge of replacement valve function.

Echocardiography, Doppler↗
PubMed1994

Beta 3-adrenoceptor agonist-induced down-regulation of Gs alpha and functional desensitization in a Chinese hamster ovary cell line expressing a beta 3-adrenoceptor refractory to down-regulation.

Chinese hamster ovary (CHO) cells transfected to express human beta 2- or beta 3-adrenoceptors (beta 2-CHO and beta 3-CHO cells) were exposed to the beta-adrenoceptor agonist isoprenaline at various concentrations and for differing times. Sustained exposure of the beta 2-CHO but not beta 3-CHO cells to isoprenaline resulted in a time- and concentration-dependent down-regulation of the receptor as measured by a reduction in specific binding of [125I]cyanopindolol. Such maintained exposure of cells expressing either receptor to the agonist produced a marked down-regulation of immunologically detectable levels of the alpha subunit of the stimulatory guanine-nucleotide-binding protein Gs. This effect was specific for Gs because levels of both G12 alpha and Gq alpha/G11 alpha were unaltered by isoprenaline treatment of both beta 2-CHO and beta 3-CHO cells. The effect of isoprenaline on Gs alpha down-regulation was some 30-fold more potent in the beta 2-CHO than in the beta 3-CHO cells. Time courses of isoprenaline-induced down-regulation of Gs alpha were not different, however, in the two cell lines. Isoprenaline treatment of the beta 3-CHO cells produced a desensitization of agonist-mediated regulation of adenylyl cyclase, manifested by a 4-fold reduction in the potency and a 30% reduction in maximal effect of the agonist, whereas desensitization of the beta 2-CHO cells was considerably greater (25-fold reduction in potency and 70% reduction in maximal effect). These results demonstrate that agonist-induced down-regulation of the G-protein which interacts with a receptor can be produced by both beta 2- and beta 3-adrenoceptors. Despite apparent concurrence of down-regulation of receptors and G-proteins in other systems [e.g. Adie, Mullaney, McKenzie and Milligan (1992) Biochem. J. 285, 529-536], agonist-induced receptor down-regulation does not appear to be a prerequisite for down-regulation of the G-protein. Furthermore, the results suggest that agonist-induced down-regulation of a G-protein may be sufficient, in the absence of receptor regulation, to induce some agonist desensitization of effector function.

Amino Acid Sequence↗
PubMed1994

Variability of left atrial bloodflow predicts intolerance of ventricular demand pacing and may cause pacemaker syndrome.

Variability of left and right atrial and left ventricular bloodflow was studied using transthoracic and transesophageal Doppler echocardiography and related to pacemaker mode preference during everyday activity. Bloodflow variability was less at all sites during dual chamber pacing compared to single chamber pacing. However, in patients suffering from pacemaker syndrome and who prefer DDDR pacing, significantly increased variability of left atrial antegrade (but not retrograde) bloodflow during VVIR pacing compared to DDDR pacing was noted, which was not evident in patients tolerating VVIR mode pacing. This effect was not detected at any other site and suggests that adverse left atrial hemodynamics may result in intolerance to VVI/R mode pacing and might cause pacemaker syndrome.

Adult↗
PubMed1994

Serial investigation of balloon angioplasty induced changes in the superficial femoral artery using colour duplex ultrasonography.

Percutaneous transluminal balloon angioplasty (PTA) of superficial femoral artery lesions is associated with similar initial success rates in coronary and iliac artery angioplasty but its application is limited by a much higher incidence of restenosis. To improve understanding of the trauma caused to the vessel by balloon angioplasty and the mechanisms contributing to the subsequent processes of healing and restenosis requires serial investigations of the treated arteries in vivo. This paper describes a prospective study using colour duplex ultrasonic imaging to assess arterial changes in 51 patients with atherosclerotic disease undergoing PTA of superficial femoral artery stenoses and occlusions. Each patient was scanned prior to angioplasty and at intervals up to 6 months post-angioplasty. On each scan, measurements were made of the overall vessel and lumen diameters at each site of angioplasty. These measurements indicate that angioplasty improves vessel patency mainly by stretching of the vessel wall, with compression and/or redistribution of the atherosclerotic plaque contributing less than 25% to the improvement of lumen diameter. Serial measurements after angioplasty show complex patterns of change at the angioplasty sites indicating that several mechanisms may be contributing to the processes of vessel healing and subsequent restenosis. Possible mechanisms which could explain the measured changes in overall vessel and lumen diameters are discussed.

Adult↗
PubMed1993

Simple and rapid method for the determination of the diastereomers of difenacoum in blood and liver using high-performance liquid chromatography with fluorescence detection.

A rapid and sensitive high-performance liquid chromatographic method for the analysis of cis and trans diastereomers of the anticoagulant rodenticide difenacoum has been described. The methodology demonstrates potential for the analysis of diastereomers of related 4-hydroxycoumarin anticoagulants. Separations were achieved by reversed-phase chromatography on a Zorbax ODS column with gradient elution using acetonitrile-water, modified with 0.1% acetic acid, as the mobile phase. Detection of the analytes was effected by fluorescence at excitation and emission wavelengths of 310 and 390 nm, respectively. Sample preparation from both plasma and liver has been simplified to reduce preparation time and manipulation. The minimum detectable concentration of each diastereomer was 5 ng/ml. Recoveries of 100% were obtained from plasma and 93% from liver tissue. This method has been used for the investigation of the pharmacokinetics of difenacoum diastereomers in rats, and for investigation of unexplained hypoprothrombinaemic events encountered clinically.

4-Hydroxycoumarins↗
PubMed1993

Hospital mortality in acute myocardial infarction in the era of reperfusion therapy (the Myocardial Infarction Triage and Intervention Project).

This study was conducted in 19 hospitals in the metropolitan Seattle area and included 6,270 unselected patients who had acute myocardial infarction (AMI) between January 1988 and April 1991. Hospital mortality was determined and related to patient demographic and clinical characteristics, the use of reperfusion therapies, and to complications after AMI. Thrombolytic therapy or direct coronary angioplasty < 6 hours from symptom onset was used to treat 1,185 (19%) and 524 (9%) patients, respectively. There were 629 (10%) hospital deaths; most occurred during the first 3 days of hospitalization. Factors affecting mortality after admission included: recurrent chest pain, recurrent AMI, development of heart failure, and the occurrence of stroke. After adjustment for age, treatment with thrombolytic therapy or direct angioplasty had no independent effect on reducing the overall mortality rate. Hospital mortality rates for AMI have improved considerably since 1970, although recurrent myocardial ischemic events continue to have an adverse effect on outcome. The current use of reperfusion treatments has had minimal causal impact on overall mortality rates, principally because less than one third of patients, who are relatively "low risk," are eligible and receive these treatments.

Adult↗