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G Ramsey

Publications and source records attributed to G Ramsey.

At least 37 records · Page 2Linked to original sources
PubMed1993

Spatio-temporal progression of the AEP P300 component using the cortical imaging technique.

The cortical imaging technique (CIT), a mathematical method for simulating the potential fields on the surface of the brain, was used to analyze the spatio-temporal progression of the AEP P300 component (as well as the preceding and subsequent N2a and N3 components) from thirty normal adult subjects recorded in a standard "oddball" paradigm. Comparisons were made between the progressions of the endogenous event-related cognitive potentials and the exogenous stimulus-dependent potentials (N1 component). Cortical imaging results suggest that different and multiple generator sites are involved in the production of exogenous and endogenous evoked responses. We particularly note the asymmetric development of the P300 component and the apparent anterior generator sites for the N2a component. This last result is interesting because the N2a precedes the P300 component and supports an earlier frontal contribution.

Adult↗
PubMed1993

A new biomechanical approach to assessing the fragility of the internal elastic lamina of the arterial wall.

Patterns of tearing of the internal elastic lamina induced by controlled tensile extension of the arterial wall in the axial direction are similar morphologically to those induced in vivo in the anastomosed arteries of experimental arteriovenous fistulae. The mural response is modelled with a simple bi-layer analogue and it is shown that the internal elastic lamina exhibits a greater degree of strain-limiting deformation behavior in the axial direction than the medial and adventitial layers. Application of laminate theory indicates that the frequency of intimal tearing along the vessel length is directly related to the failure strength of the intimal layer.

Animals↗
PubMed1991

Red cell antibodies arising from solid organ transplants.

RBC antibodies arising from transplanted organs and directed against recipient RBCs represent a well-established immunohematologic complication of solid organ transplantation. In ABO-unmatched organs, the frequency and severity of graft antibodies and hemolysis generally increase with the size (lymphoid content) of the organ, from kidney to liver to heart-lung transplants. In the cases reviewed here, the frequency of hemolysis increased in cyclosporine-treated kidney transplant recipients and O-to-A liver transplant recipients and decreased in group AB liver transplant recipients and kidney transplant recipients receiving azathioprine or low-dose postoperative graft irradiation. Available data cannot otherwise distinguish which cyclosporine-treated recipients of ABO-unmatched kidneys and livers (30-40% of total) will develop graft antibody. There has been no conclusive effect to date of the age, race, or gender of the donor or the recipient, of cadaver versus living kidney donors, or of patients' A2 or secretor status. In a few cases of living-donor kidney grafts, the donor was the patient's mother or wife who had been exposed to the recipient's RBC antigens via pregnancy. The ABO antibodies are typically IgG, appear 7 to 10 days after transplantation, and last for about a month. If immediate-spin crossmatching is done routinely, DATs are recommended in compatibility testing after ABO-unmatched transplants. Changes in the immunosuppressive regimen, such as a change from cyclosporine therapy, have not affected the duration of these antibodies. Most patients require only transfusions for this self-limited process, but six cases of hemolysis-induced acute renal failure have been reported, and one death was attributed to complications of hemolysis. RBC or plasma exchange has been performed in a few fulminant cases. RBCs of the donor's blood type are given when antibody appears. Some workers recommend such transfusion as prophylaxis at the time of surgery, although in liver transplants, the plasma accompanying a large amount of group O RBCs given perioperatively might be problematic. In several other centers, ABO-unmatched liver transplants have equivalent overall graft survivals, but the Pittsburgh adult patients with hemolysis have had reduced early graft survival. In the cases reviewed here, nine IgG Rh antibodies from kidney grafts directed against recipient RBCs have been observed, usually beginning 2 to 3 weeks after a cyclosporine-treated transplant, lasting for 2 to 6 months after operation, and causing mild hemolysis. One case represented a primary immune response from a previously unsensitized donor.(ABSTRACT TRUNCATED AT 400 WORDS)

ABO Blood-Group System↗
PubMed1991

Syphilis serology in blood donors: a possible surrogate marker for human immunodeficiency virus risk.

We report a preliminary study on whether syphilis serology might be reactive in some blood donors at risk for human immunodeficiency virus (HIV) infection. We retrospectively analyzed voluntary blood donations with reactive Treponema pallidum antibody (TPA) tests according to the type of donation, the presence of other safety markers, confidential unit exclusion, syphilis diagnosis, and HIV risk factors. Over 2 years (1987-1988), 1 in 8,900 regular homologous donations (n = 258,610) was TPA positive as compared with 1 in 2,200 directed donations (n = 6,685) and 1 in 300 autologous donations (n = 8,870; p less than 0.05 for both). The rate in directed donations was not significantly higher than in first-time regular donors (1 in 4,800; n = 57,000). TPA-positive donations had higher rates of antibody to hepatitis B core antigen and confidential unit exclusion than TPA-negative donations. Ten TPA-positive homologous or directed donors had latent or previously treated syphilis (1 in 26,500 such donations), and 2 of these had HIV risk factors. None of the autologous donors were determined to have active syphilis. Syphilis serology in blood donors bears further scrutiny as a possible surrogate marker for HIV risk.

Biomarkers↗
PubMed1990

Guidelines for transfusion support in patients undergoing coronary artery bypass grafting. Transfusion Practices Committee of the American Association of Blood Banks.

We have reviewed the impact of evolving issues in coronary artery bypass grafting (CABG) on transfusion support for these patients. Issues include increased awareness of transfusion risks, reappraisal of traditional indicators triggering transfusion, and evolving alternatives to homologous blood transfusion such as autologous blood and pharmacologic therapy. These issues have been prompted by programs, such as the National Institutes of Health Consensus Conferences, to provide physicians with guidelines for appropriate use of blood components. However, evidence suggests that transfusion practice in coronary artery bypass grafting procedures remains variable and does not take into account the results of recently published clinical studies. We have therefore developed guidelines and recommendations for transfusion support in patients undergoing coronary artery bypass grafting. In summary, they are the following. 1. Institutions with coronary artery bypass grafting programs should establish a multidisciplinary approach to use a combination of interventions designed to minimize homologous blood exposure. 2. Prophylactic transfusion of plasma and platelets are of no benefit and therefore carry an unnecessary risk to the patient. 3. Special request products such as designated blood donation from first-degree relatives should not be used because of the risk of transfusion-associated graft versus host disease. 4. For support of intravascular volume, crystalloids or colloids should be used because they do not have the potential to transmit infection.

Algorithms↗
PubMed1990

Age-related features of the resting and P300 auditory evoked responses using the dipole localization method and cortical imaging technique.

Two mathematical techniques, the dipole localization method (DLM) and the cortical imaging technique (CIT), are used to analyze the resting and P300 auditory responses in young and old normal volunteers. These methods identify certain age-related features of these evoked responses that are not found by standard topographic methods. These features include the orientation of the P200 resting response, and the laterality of the N120 response, and the eccentricity of the P300 response in the P300 stimulus condition. Theoretical dipole sources and simulated cortical surface maps are also constructed for one normal subject and one psychiatric inpatient and compared. These mathematical methods appear to enhance the discriminating power of traditional electrophysiological measures.

Adult↗
PubMed1990

In vivo cross-match by chromium-51 urinary excretion from labeled erythrocytes: a case of anti-Gerbich.

We studied a patient with an alloantibody to the high-frequency red blood cell (RBC) antigen Gerbich. A nationwide search for rare Gerbich-negative blood (less than 1:45,000 donors) located only seven units, and our supply was quickly exhausted. By using an in vivo cross-matching method, we demonstrated that this anti-Gerbich did not cause RBC destruction. Regular Gerbich-positive transfusions could then proceed without hemolysis. This cross-match test was based on the determination of the urinary excretion rates of injected radioactive chromium-labeled donor erythrocytes by which it was possible to determine compatibility only 24 hr after the test was begun. The procedure provides an easy and accurate means for in vivo cross-matching of conventionally incompatible donor blood.

Aged↗
PubMed1989

Strategies for the review of transfusion practices.

The intent of this report is to familiarize health care professionals with the concept of effective quality assurance in regard to blood use. Although evaluation of the appropriateness of transfusion therapy is now required by the Joint Commission on Accreditation of Health Organizations, health care facilities have little experience with this aspect of professional quality assurance. To this end, the Committee on Transfusion Practices of the American Association of Blood Banks, in Arlington, Va, in this report has provided examples of indications and audit criteria for individual blood components and products and commented on areas of controversy surrounding their use. Audit criteria from different institutions may vary because of differences in local interpretation of the indication, different patient populations, and, in some instances, the availability of blood and laboratory services. Several approaches to the review of transfusion practices are discussed in relation to clinical settings and pertaining to particular blood components. It is evident from these examples that there will be an increased need for trained personnel to perform the initial review process as well as for physicians trained in transfusion medicine to oversee the transfusions and provide the necessary consultation.

Blood Banks↗
PubMed1989

Red cell antibody problems in 1000 liver transplants.

Liver transplant patients frequently require large amounts of blood. The frequency and nature of their red cell (RBC) antibody problems were examined. Records were reviewed in 496 adults and 286 children undergoing 1000 consecutive transplants. Twenty-two percent of adults and 14 percent of children had RBC alloantibodies. Antibodies of potential clinical significance were found before transplant in 6.3 percent of adults and 1.0 percent of children; despite immunosuppression, they appeared 1 to 5 weeks after transplant in an additional 7.5 and 5.2 percent respectively. These antibodies probably represented secondary immune responses. Of 58 transplant patients with prior potentially significant antibodies, 8 required 7 to 110 units of antigen-untyped blood after 8 to 28 units of antigen-negative blood; of these patients, one had subsequent hemolysis. Positive direct antiglobulin tests in 24 percent of adults and 10 percent of children were most often thought to be due to nonspecific adsorption of IgG. Anti-recipient ABO antibodies developed in 22 of 60 (37%) evaluable ABO-unmatched grafts; 13 cases had associated hemolysis. In all, 36 percent of adults and 20 percent of children had diverse RBC antibody problems. Resolution of these problems is an important part of the laboratory support necessary for a liver transplantation program.

Adult↗
PubMed1989

Suitability of liquid-stored donor platelets in platelet compatibility testing.

Current platelet crossmatch procedures to select compatible donors for alloimmunized thrombocytopenic patients are hampered by the lack of a convenient platelet storage method. This study examined the feasibility of using washed apheresis donor platelets stored for up to 1 year in a modified Hank's buffer solution at 4 degrees C as crossmatch reagents in an indirect IgG-enzyme immunoassay. Pooled and monospecific HLA and PlA1 antisera were used to determine the antigenic reactivity of donor platelets in relation to duration of storage. There were no significant differences between mean HLA and PlA1 antigen expression in fresh and stored platelets. HLA reactivity was detected on 12 of 13 donor platelet samples stored for 3 to 9 months and on 14 of 17 platelets stored for 12 to 14 months. PlA1 reactivity was maintained at 12 to 14 months for all 12 donor platelet samples tested. In addition, incompatibility remained in 23 of 24 paired fresh and stored platelet crossmatches using individual alloimmunized patient plasmas. These data indicate that both HLA and platelet-specific PlA1 antigen reactivity can be maintained adequately in liquid storage at 4 degrees C for up to 1 year. The availability of a convenient platelet storage method should facilitate the general application of platelet crossmatching procedures for alloimmunized patients.

Antibodies, Anti-Idiotypic↗
PubMed1989

Low rate of Rhesus immunization from Rh-incompatible blood transfusions during liver and heart transplant surgery.

Transfusion of one unit or more of Rh-positive red blood cells normally causes circulating anti-D antibody to appear 2-6 months later in 80-95% of Rh- persons. We asked whether transplant immunosuppression with cyclosporine and corticosteroids affects Rh immunization. Nineteen Rh- liver, heart, and heart-lung transplant recipients received 3-153 (median: 10) units of Rh+ RBCs at surgery and were tested for anti-D greater than 2 months later. Three patients developed anti-D at 11-15 days; one may have had an unusually rapid primary immune response and two were secondary to previous exposure by pregnancy. None of the other 16 patients had anti-D when tested 2.5-51 months later (13 patients, greater than 11.5 months). This low rate of Rhesus immunization in association with cyclosporine immunosuppression allows greater flexibility in meeting the transfusion needs of Rh- liver and heart transplant patients. Caution is still advised in young females and in patients who may have been previously exposed to Rh+ RBCs by transfusion or by pregnancy prior to the availability of perinatal Rh immune globulin twenty years ago. Other humoral immune responses to some vaccines or infectious agents may also be impaired in transplant patients.

Adult↗
PubMed1988

Acute humoral rejection of an ABO-unmatched liver allograft in a pediatric recipient.

Acute humorally mediated rejection of organ allografts has long been recognized in kidney transplantation as the syndrome of hyperacute rejection. This reaction precludes renal transplantation across the major blood-group system and in many other instances in which preformed antibodies are present in the host. There is increasing evidence of the importance of humoral rejection in graft survival following liver transplantation. Although the antibodies responsible for this process have seldom been definitively identified, it is clear that the antibodies of the major blood-group system are of particular importance. Humoral rejection of a transplanted liver has not been well documented previously in a pediatric recipient. We present a case illustrating acute hepatic graft failure resulting from circulating anti-B IgM isohemagglutinins following an ABO-unmatched liver transplantation.

ABO Blood-Group System↗
PubMed1988

Antibody-mediated rejection of human orthotopic liver allografts. A study of liver transplantation across ABO blood group barriers.

A clinicopathologic analysis of liver transplantation across major ABO blood group barriers was carried out 1) to determine if antibody-mediated (humoral) rejection was a cause of graft failure and if humoral rejection can be identified, 2) to propose criteria for establishing the diagnosis, and 3) to describe the clinical and pathological features of humoral rejection. A total of 51 (24 primary) ABO-incompatible (ABO-I) liver grafts were transplanted into 49 recipients. There was a 46% graft failure rate during the first 30 days for primary ABO-I grafts compared with an 11% graft failure rate for primary ABO compatible (ABO-C), crossmatch negative, age, sex and priority-matched control patients (P less than 0.02). A similarly high early graft failure rate (60%) was seen for nonprimary ABO-I grafts during the first 30 days. Clinically, the patients experienced a relentless rise in serum transaminases, hepatic failure, and coagulopathy during the first weeks after transplant. Pathologic examination of ABO-I grafts that failed early demonstrated widespread areas of geographic hemorrhagic necrosis with diffuse intraorgan coagulation. Prominent arterial deposition of antibody and complement components was demonstrated by immunoflourescent staining. Elution studies confirmed the presence of tissue-bound, donor-specific isoagglutinins within the grafts. No such deposition was seen in control cases. These studies confirm that antibody mediated rejection of the liver occurs and allows for the development of criteria for establishing the diagnosis.

ABO Blood-Group System↗
PubMed1988

Rehabilitative optometric services for survivors of acquired brain injury.

In a retrospective study of clinical management practices, we assessed the impact of offering rehabilitative optometric services to a group of severely head-injured residents of a long-term rehabilitation facility. Each testable patient admitted (n = 55) was screened for visual function, and more than half were identified as having visual problems in need of treatment. A few were sent to local practitioners, but most (n = 26) were referred to a rehabilitative optometrist (with a specialty in low vision). For all but two patients, optometric treatment recommendations were implemented. All of those who received treatment benefited; indeed, in most cases the impact on participation in the overall rehabilitation program was significant. For the severely brain-injured, the study emphasized the need for (1) careful screening of visual-sensory function, (2) referral for rehabilitative optometric evaluation and treatment, (3) taking the necessary time for evaluations, and (4) the value of having a cognitive rehabilitation therapist assist the rehabilitative optometrist.

Adult↗