Variability of the steady-state visually evoked potential: Interindividual variance and intraindividual reproducibility of spatial frequency tuning

At low contrast levels there is good agreement between the psychophysical contrast sensitivity function and the tuning curve of the visually evoked potential (i.e., VEP amplitude vs spatial frequency). At high contrast, however, some researchers have found bimodal VEP tuning curves whereas others have not. We studied the VEP in 22 subjects in a short-term cross-sectional study and in 13 subjects in a longitudinal study over 8 sessions covering 28 days. Grating stimuli with 60% contrast were square-wave modulated in time (7.8 reversals/s) and space (0.06–16 cycles/degree). We found large interindividual variance in the shape of the tuning curves; about half of the subjects showed a unimodal shape, while the other half showed a bimodal one (with a notch between 1 and 2 cycles/degree). These features turned out to be stable in the longitudinal study, where variability could mainly be ascribed to a multiplicative influence common to all spatial frequencies. The marked interindividual differences in the shape of the tuning curve, which seem to be intraindividually stable, may explain previous discrepancies. It is not yet clear why the notch exists in about half of our subjects.     

Cost-effectiveness analysis in anaesthesia

In order to preserve the quality of anaesthetic care under cost containment programmes, the concept of value-based anaesthesia was introduced. To achieve this goal, namely, the provision of the best possible care attainable at a reasonable cost, studies are necessary that compare anaesthetic techniques in terms of both quality and costs, e.g. by means of cost-effectiveness analyses.     

Cell subsets responding to purified hepatocytes and evidence of indirect recognition of hepatocyte major histocompatibility complex class I antigen. I. The role of L3T4+ T cells in the development of allospecific cytotoxicity in hepatocyte-sponge matrix allografts.

The purpose of this study was to determine the role of L3T4+, Ly2- T cells in the development of allospecific cytolytic T cells in response to purified allogeneic MHC class I+, class II- hepatocytes in vivo in hepatocyte-sponge matrix allografts (HC-SMA). In previous studies we have shown that 99% pure murine hepatocytes stimulate the development of allospecific cytolytic T cells in vitro in mixed lymphocyte-hepatocyte culture (MLHC) and in vivo in HC-SMA. Furthermore, depletion of L3T4+, Ly2- T cells from responder splenocytes inhibits the development of allo-CTLs in response to purified hepatocytes in mixed lymphocyte-hepatocyte culture. Here, using an anti-L3T4 monoclonal antibody, we tested the effect of in vivo immunodepletion of L3T4+, Ly2- T cells on the subsequent development of allo-CTLs in HC-SMA. Sponge cells were harvested on day 4 and day 12 after grafting from control and treated groups and phenotypically analyzed by FACS and immunofluorescent labelling. Splenocytes from the same animals were similarly analyzed to assess for completeness of immunodepletion. Allospecific cytotoxicity was assessed on day 12 after grafting. We found that immunotherapy with anti-L3T4 mAb was effective in depleting L3T4+, Ly2- T cells from the spleen; however, a similar number of L3T4+ cells was isolated from the sponge between control and treated groups. Furthermore, the development of allo-CTLs in response to hepatocytes in HC-SMA was completely abrogated by both local and systemic immunotherapy with anti-L3T4 mAb. We conclude from these and previous data that host or responder L3T4+, Ly2- T cells and responder accessory cells in MLHC or host macrophages in HC-SMA may participate in "indirect" recognition of hepatocyte class I antigen both in vitro and in vivo.     

Ethical issues in health care institutions. Lesson three: Hospital ethics committees

The hospital ethics committee serves as the topic for this third lesson of a five-part WMU/AHRA magazine course on ethics. Proliferating during the last ten years and fostered by the Karen Ann Quinlan case, hospital ethics committees today function in three areas: education, development of guidelines and policies, and individual case consultation. Using specific examples in the discussion of each function, the authors give a detailed picture of the valuable contribution these committees make to the institutions they serve.     

Patterns of structural deterioration due to ischemia in Purkinje fibres and different layers of the working myocardium

Cellular and mitochondrial swelling are regarded as typical intra-ischemic alterations ("IIA"), contraction band lesions (CBL), in contrast, as products of post-ischemic reperfusion. The occurrence of both types of structural deterioration was investigated in Purkinje fibres and subendocardial and intramural working myocardium: initially after St. Thomas- or HTK cardioplegia, then during ensuing global ischemia up to the "practical limit of resuscitability", and following post-ischemic reperfusion. Generally, Purkinje fibres are not better preserved than neighbouring working myocardium. Comparing St. Thomas- and HTK cardioplegia, considerable quantitative, but not qualitative differences in the reaction patterns of different cell types or layers arise. Immediately after cardioplegia, CBL are completely lacking in both cell types. During ischemia, CBL occur occasionally in Purkinje fibres and seldom in subendocardial working myocardium, "IIA" predominate. During post-ischemic reperfusion "IIA" tend to reverse in all layers, whereas CBL are found to remain in the subendocardial cell types. In intramural layers, CBL occur only during reperfusion. Thus, we deduce that cardioplegia only modulates the severity of "IIA" and the frequency of CBL, but cannot abolish the particular sensitivity of subendocardial Purkinje fibres to global ischemia. Prerequisites for the development of irreversible CBL are on the one hand ischemic metabolic alterations and corresponding energy deficits, and, on the other hand, a supply of oxygen. The oxygen may be inadequately supplied via diffusion during ischemia or may be subsequently provided by reperfusion.     

Circadian rhythm of lithogenic substances in the urine

Summary After determination of the lithogenic and inhibitory substances in serum and urine of 18 healthy control subjects and 20 patients with calcium oxalate urolithiasis on an uncontrolled diet, the alteration of the parameters while taking a standard diet was investigated. After attainment of a steady state, the investigations were performed over 48h on 3-h aliquots of urine. Typical circadian rhythms were detected for all lithogenic parameters in the urine and normal ranges were established. This special investigation permits detection of peaks in the excretion of lithogenic substances which were masked in investigation of 24-h urine samples alone.     

Survival and developmental disability in infants with birth weights of 501 to 800 grams, born between 1979 and 1994

OBJECTIVE: Because the survival rate has increased for extremely low birth weight neonates, many have raised the concern that the rate of developmental disability among survivors will also increase. To address this concern, we analyzed changes over time in survival and major neurosensory impairment in a sample of extremely low birth weight infants born between July 1, 1979, and June 30, 1994. METHODS: The study sample included 513 infants with birth weights of 501 to 800 g who were cared for in either of the two neonatal intensive care units that serve a 17-county region in northwest North Carolina and who were born to mothers residing in that region. At 1 year of age (corrected for gestation), survivors were examined by a pediatrician and were tested using the Bayley Scales of Infant Development. Major neurosensory impairment was defined as cerebral palsy, a Bayley Mental Developmental Index <68, or blindness. A total of 209/216 (97%) of survivors were examined at 1 year of age. Epoch of birth was defined as follows: epoch 1, July 1, 1979 to June 30, 1984; epoch 2, July 1, 1984 to June 30, 1989; and epoch 3, July 1, 1989 to June 30, 1994. RESULTS: Survival rates for epochs 1, 2, and 3 were, respectively, 24/120 (20%), 63/175 (36%), and 129/218 (59%). In contrast, the proportions with a major neurosensory impairment did not increase over time; rates for successive epochs were 6/24 (25%), 17/61 (28%), and 26/124 (21%). Rates of cerebral palsy were 3/24 (13%), 12/61 (20%), and 9/124 (7%); rates of delayed mental development were 4/24 (17%), 12/61 (20%), and 17/124 (14%); and rates of blindness were 2/24 (8%), 0/62, and 5/124 (4%), respectively. CONCLUSIONS: This analysis suggests that the increasing survival of extremely low birth weight neonates since the late 1970s has not resulted in an increased rate of major developmental problems identifiable at 1 year of age.