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Biomedical subjects

K R Clark

Publications and source records attributed to K R Clark.

36 records · Page 2Linked to original sources
PubMed1994

The effects of pedicle screw fit. An in vitro study.

STUDY DESIGN: The effects of pedicle screw size (major diameter and length) on fixation stiffness in osteoporotic and nonosteoporotic vertebrae were evaluated in vitro. METHODS: Lumbar vertebrae were obtained from two fresh frozen human spines. Bone mineral densities were determined using dual energy radiograph absorptiometry, followed by nondestructive mechanical testing of the specimens instrumented with pedicle screws. A loading technique was used that more closely mimics loading of pedicle screws in vivo. RESULTS: Testing revealed that for good quality bone, screw size had a significant effect on fixation stiffness, but the effect of penetration depth depended on pedicle fill, and vice versa. In nonosteoporotic bone, the use of a longer screw increased fixation stiffness if the screw filled up the pedicle by 70% or more. The use of wider screws increased the fixation stiffness if the penetration depth was 80% or more. CONCLUSION: Screw size had little or no effect on fixation stiffness in osteoporotic bone.

Adult↗
PubMed1994

Characterization of donor-directed antibody class in the post-transplant period using flow cytometry in renal transplantation.

Over the past few years there has been increasing awareness of the importance of humoral mechanisms in the rejection of renal transplants. In this study we have monitored the development of antibodies directed against donor T and B lymphocytes using the sensitive flow cytometric technique. Forty-two cadaveric renal transplants were studied both before and for a maximum of 14 days after transplantation. Donor cells were separated from spleen on the day of transplantation and stored in liquid nitrogen until required. The dual colour flow cytometric assay was used to detect IgG or IgM directed against donor T or B lymphocytes. Using AB sera as controls, results were expressed as relative median fluorescence (RMF) and then correlated with the clinical performance of the grafts. Significant associations were found between the incidence of donor-directed antibodies and the development of clinical rejection. The magnitude of the rise in antibody levels was also related to graft performance. In patients showing severe graft rejection, high levels of antibodies of the IgG class developed before the clinical diagnosis of rejection was made. The routine use of this test allows the prediction of impending severe rejection to be made and may have important implications for immunosuppressive therapy.

B-Lymphocytes↗
PubMed1994

The S-ribonuclease gene of Petunia hybrida is expressed in nonstylar tissue, including immature anthers.

To determine the ability of isolated S-locus promoter sequences to direct organ-specific gene expression, we used microprojectile bombardment to introduce chimeric S-allele/beta-glucuronidase genes into different tissues of Petunia hybrida for transient expression. Histochemical staining showed that S-locus/beta-glucuronidase fusions were expressed in pistil, ovary, and petal tissue. No expression of the chimeric genes was detected in leaves or in mature pollen, either by histochemical staining or by fluorescence assays. RNA blot hybridization confirmed that low levels of S-locus mRNA accumulate in petals and ovaries in vivo. Analysis of the expression pattern of S-locus promoter deletions showed that sequences in the immediate vicinity of the TATA box were sufficient to confer qualitatively correct organ-specific expression of beta-glucuronidase. To further investigate the potential for S-ribonuclease expression in pollen, we used the polymerase chain reaction to amplify RNA accumulated in developing anthers. These assays demonstrated that mRNA for the S-ribonuclease accumulates to low levels in developing anthers several days prior to corolla opening and pollen anthesis. We discuss these results in light of current models of self-incompatibility.

Alleles↗
PubMed1993

Administration of ATG according to the absolute T lymphocyte count during therapy for steroid-resistant rejection.

In renal transplantation, treatment of steroid-resistant rejection (SRR) with antithymocyte globulin (ATG) has been widely reported but over-immunosuppression remains a common problem. In the first ten patients (group 1) treated for SRR with rabbit ATG, three developed serious viral infections and two deaths occurred due to CMV pneumonitis. ATG was only omitted if thrombocytopenia or neutropenia occurred. In the next 17 patients (group 2) with SRR, ATG was administered according to the absolute T lymphocyte count. T lymphocytes were measured by flow cytometric analysis of CD3-labelled lymphocytes. ATG dosage was adjusted on a daily basis to keep the absolute T lymphocyte count under 50 cells/microliters. Administration of ATG according to the absolute T lymphocyte count resulted in a significant reduction in the mean dose of ATG given to the group 2 patients (P < 0.001). A significant decrease in the incidence of serious viral infections (P = 0.04) was achieved without reducing the ability of ATG to reverse the SRR (P = 0.29) or increasing the number of grafts lost at 1 year in the group 2 patients (P = 0.23).

Adult↗
PubMed1993

Establishing intravenous access: a study of local anesthetic efficacy.

We performed a double-blind, randomized, prospective study to determine the local anesthetic that provided the best analgesia for insertion of an 18-gauge intravenous (i.v.) catheter and to determine whether alkalinization of lidocaine decreases the pain of intradermal injection. There were 280 healthy adult patients assigned randomly to seven different groups: benzyl alcohol 0.9% in normal saline, 2-chloroprocaine 3%, lidocaine 1%, lidocaine 1% with preservative, alkalinized lidocaine 1% with preservative, normal saline, and a control group that received i.v. catheter placement without previous drug injection. A 10-cm visual analog pain scale (VAPS) was used to obtain pain scores after pre-i.v. drug injection and after iv catheter insertion. Benzyl alcohol in normal saline (0.61 +/- 0.11) and alkalinized lidocaine (0.69 +/- 0.10) had the lowest mean pain scores for drug injection and these were significantly different from other drugs (P < 0.05). Alkalinized lidocaine (0.7 +/- 0.18) had the lowest mean pain score for i.v. catheter insertion with nothing (no previous drug injected) (3.47 +/- 0.38) and normal saline (3.97 +/- 0.18) had the highest mean pain scores (P < 0.05). We conclude that alkalinized lidocaine decreased the pain associated with its injection. Alkalinized lidocaine was the best local anesthetic for i.v. catheter placement. Benzyl alcohol in normal saline was also effective.

Adult↗
PubMed1993

Sensitive monitoring of polyclonal antilymphocyte agents in renal transplantation.

Recently, our unit has used a polyclonal antilymphocyte agent frequently to treat steroid-resistant rejection or induce immunosuppression. A system of monitoring has been developed to govern the use of this powerful agent. This technique has allowed reduction in the total dose of ATG with no loss of efficacy but a decrease in the rate of serious viral infection. Powerful polyclonal agents remain an important element of immunosuppression provided that the dose of the agent is tailored to the individual response.

Animals↗
PubMed1992

Surgical aspects of chronic peritoneal dialysis in the neonate and infant under 1 year of age.

Since 1982 eight patients under 1 year of age with end-stage renal failure have been treated by chronic peritoneal dialysis (CPD) following insertion of an abdominal Tenckhoff catheter. We routinely perform a partial omentectomy now, and in males undertake bilateral exploration of the groins at the time of catheter insertion, with herniotomy or ligation of the patent processus vaginalis as required. Up to January 1990, 19 straight double-cuff catheters had been inserted with a total follow-up of 244.5 patient months. The median age at the initial catheter insertion was 14.6 weeks (range, 2 days to 11 months) and the median weight was 3.89 kg (range, 2.2 to 5.5). Peritonitis was the most common complication, with 46 episodes, representing one episode of peritonitis per 5.3 patient months on dialysis. The frequency of peritonitis has decreased in the last 6 months since all patients have been dialysed by two caregivers. The present rate of peritonitis is 1 episode per 10 patient months on dialysis. One patient has died of septicemia secondary to associated congenital abnormalities, one patient has regained renal function, and two patients have been transplanted, one successfully. Five patients are currently dialysing via their abdominal Tenckhoff catheters and awaiting transplantation. We conclude that neonates and infants under 1 year of age can be treated satisfactorily by CPD to enable successful preparation for transplantation later in childhood.

Catheters, Indwelling↗
PubMed1991

Renal epithelium: reversal of cytotoxic damage by addition of anti-thymocyte globulin.

A novel in vitro assay of renal epithelium tight junction function was used to assess the efficacy with which rabbit anti-thymocyte globulin (ATG) blocks epithelium damage mediated by lymphokine-activated killer (LAK) cells. It was found that LAK cells lysed renal epithelial cells poorly in standard chromium-release assays but that they caused a rapid, and almost total, reduction in trans-epithelium monolayer resistance, indicating tight junction failure and, hence, loss of tissue function. LAK cell-mediated cytolysis of the sensitive K562 cell line was completely blocked in the presence of ATG at a concentration of 200 micrograms/ml. Addition of ATG at this concentration to damaged renal cell monolayers in the presence of LAK cells allowed the trans-monolayer resistance to recover rapidly to levels approaching the values recorded before initial addition of LAK cells. On this basis it seems likely that the rapid restoration of renal function frequently observed after appropriate "rescue" therapy during episodes of acute rejection may reflect subtle changes in tissue function rather than recovery from widespread graft cell cytolysis.

Animals↗
PubMed1991

Breast abscess following central venous catheterization.

We describe a case of late perforation of the right internal mammary vein by a central venous catheter inserted via the left subclavian vein. This resulted in extravasation of parenteral nutritional fluid and breast abscess formation. Delay in reaching the diagnosis was experienced in this case and in two cases previously reported. The clinical presentation was similar in all three cases with good early function of the catheters followed by symptoms of chest pain and signs of inflammation in the breast contralateral to the site of insertion of the central venous catheter. Confirmation of correct placement of the central venous catheter must be sought in any patient who develops these symptoms or signs so that the delay in diagnosis we experienced can be avoided. This may be obtained by a lateral or oblique chest radiograph or by contrast studies if preferable.

Abscess↗
PubMed1990

Sequence variability and developmental expression of S-alleles in self-incompatible and pseudo-self-compatible petunia.

We investigated the structure and expression of three S-alleles of Petunia hybrida in self-incompatible varieties and in a pseudo-self-compatible line in which the self-incompatibility response is defective. Comparison of derived amino acid sequences from different gametophytic S-alleles revealed a pattern of sequence conservation and variability that was highly nonrandom. In self-incompatible varieties, petunia S-locus mRNA accumulates preferentially in styles during the transition from bud self-compatibility to self-incompatibility. S-Allele sequences homologous to the cloned S1 allele were present in a pseudo-self-compatible variety, and were expressed at levels indistinguishable from those observed in a self-incompatible line homozygous for the S1 allele. Taken together, our data indicate that (1) limited sequence differences may confer allelic specificity, (2) S-locus mRNAs accumulate in a precise organ-specific pattern during floral development, and (3) the ability to inhibit the growth of incompatible pollen tubes appears to require a threshold accumulation of the stylar gene product, along with the participation of as yet undefined pollen gene products.

Alleles↗
PubMed1990

Urinary infection following out-patient flexible cystoscopy.

Of 161 flexible cystoscopies performed in an out-patient endoscopy suite, the incidence of urinary tract infection was 7.5%. Infection rates were higher in patients with a history of previous urinary tract infection or where an additional procedure was also performed. No difference was noted between the infection rates in men and women.

Ambulatory Care↗
PubMed1983

The implications of developing a profession-wide code of ethics.

Current efforts by two professional health education associations to draft a code of ethics could lead to the establishment of a profession-wide code serving as the basis for awareness, inspiration, training, and professional conduct. Such a code would also serve the social functions of professional protection and control. A coordinated attempt to formulate a profession-wide code could more closely unite all existing national health education organizations through a process of cooperative effort and value clarification, with implications for centralization, enforcement, and licensure. Members of the Society for Public Health Education, Inc. (SOPHE) and the Association for the Advancement of Health Education (AAHE) are currently engaged in an attempt to formulate a health education code of ethics. This article explores the history and purposes of such codes. In addition, it compares current health education professional concerns with those of the American Medical Association during the last century. Finally, it discusses the implications of a profession-wide code for centralization, enforcement, and licensure.

Codes of Ethics↗