Challenging the anterior attentional system with a continuous performance task: a functional magnetic resonance imaging approach

Combining the Continuous Performance Test (CPT) with a modern functional imaging technique provides a powerful tool for investigating neurophysiological processes in the human brain. There is increasing evidence from single photon emission tomography (SPECT), positron emission tomography (PET) and presently also functional magnetic resonance imaging (fMRI) studies proposing the existence of a distributed large-scale attentional network, mediated by the dorsolateral prefrontal and mesial frontal cortex, thalamus, basal ganglia and posterior parietal and superior temporal lobe. The aim of this study is to show that fMRI is a useful tool for in vivo localization of attentional tasks and to compare the results with established imaging techniques. Functional MRI was performed on a clinical 1.5-T system using gradient-echo acquisition. For data processing, the Statistical Parametric Mapping (SPM96) package was used. A right lateralized activation pattern in the dorsolateral prefrontal and mesial frontal cortex, the thalamus and the basal ganglia was found in a group of 12 male subjects. These findings support theories suggesting right hemispheric dominance of human attention. Received: 18 September 1997 / Accepted: 9 March 1998     

Fracture/dissociation of the polyethylene in metal-backed patellar components in total knee arthroplasty

We encountered a complication that is unique to the use of a metal-backed patellar component in total knee replacement--namely, fracture and separation of the polyethylene bearing from its metal counterpart. The cases of seventeen patients who were treated at several institutions were studied. Patellar malalignment, especially in heavy patients who had a high level of activity, was a contributory cause of the complication, but we thought that deficiencies in the design of the prosthesis were also an important factor.     

The current status of total joint replacement

The last two decades have witnessed tremendous strides in the evolution of acceptable and successful methods of prosthetic replacement for the arthritic joint. By and large, these techniques are predictable and durable, though not always to the complete satisfaction of the patient and surgeon. Despite the recent emphasis on alternative forms of implant fixation, cemented total joint replacements remain the standard by which all others are judged. In some settings, non-cemented implants appear to function as well as cemented ones in providing pain relief. The acetabular component in the hip and the femoral component in knee replacement are two such areas. This has resulted in the emergence of the "hybrid" joint replacement where one component is cemented while the other is not. The long-term function and durability of these non-cemented components remains to be seen. The future of joint replacement lies in the development of new "composite" materials which can more closely match the structural characteristics of the bone into which they are being implanted. Until we better understand and are able to prevent the disease processes which lead to total joint replacement, this area will continue to be the focus of intense research and development.     

A possible non-oncogenic effect of C type bone cell virus on serum calcium levels of potentially leukemic mice

In bone of C3H/Fg mice, particles structurally identical toC-type leukemia virus arise from membranes of osteocytes and osteoblasts. Although these virus apparently do not induce morphologic or neoplastic change in bone they may have other, more subtle, effects. Thus, comparison of sera form male C3H/Fg mice, a high leukemia-prone strain, with C57BL and C3H/HeJ mice, low leukemia strains which do not containC-type virus in bone, reveals that serum calcium levels are significantly lower in the former than in the latter. Further, when C3H/Fg mice develop frank leukemia there is a corresponding increase in virus particles while the serum calcium concentration levels fall to even lower values. The presence of leukemia itself appears not to be the cause as indicated by the failure of implanted lymphocytic leukemic cells in C3H/Fg mice to significantly affect serum calcium concentration. It is postulated that the effects of the virus could be due either to increased osteoblastic activity or to inhibition of osteocytic osteolytic activity or to both.     

Gross quaternary changes in aspartate carbamoyltransferase are induced by the binding of N-(phosphonacetyl)-L-aspartate: A 3.5-A resolution study.

The three-dimensional structure of the complex of N-(phosphonacetyl)-L-aspartate with aspartate carbamoyltransferase (carbamoylphosphate:L-aspartate carbamoyltransferase, EC 2.1.3.2) has been determined to a nominal resolution of 3.5 A by single-crystal x-ray diffraction methods. Initial phases were obtained by the method of "molecular tectonics": beginning with the structure of the CTP-protein complex, the domains of the catalytic and regulatory chains were manipulated as separate rigid bodies. The resulting coordinates were used to calculate an electron density map, which was then back transformed to give a set of calculated amplitudes and phases. Using all observed data, we obtained a crystallographic R factor between observed and calculated amplitudes Fo and Fc of 0.46. An envelope was then applied to a 2Fo - Fc map and the density was averaged across the molecular twofold axis. Two cycles of averaging yielded an R factor of 0.25. In this complex, we find that the two catalytic trimers have separated from each other along the threefold axis by 11-12 A and have rotated in opposing directions around the threefold axis such that the total relative reorientation is 8-9 degrees. This rotation places the trimers in a more nearly eclipsed configuration. In addition, two domains in a single catalytic chain have changed slightly their spatial relationship to each other. Finally, the two chains of one regulatory dimer have rotated 14-15 degrees around the twofold axis, and the Zn domains have separated from each other by 4 A along the threefold axis. These movements enlarge the central cavity of the molecule and allow increased accessibility to this cavity through the six channels from the exterior surface of the enzyme.     

Predictors of readmission and health related quality of life in patients with chronic heart failure: a comparison of different psychosocial aspects

Psychological distress is common in patients with chronic heart failure. The impact of different psychological variables on prognosis has been shown but the comparative effects of these variables remain unclear. This study examines the impact of depression, anxiety, vital exhaustion, Type D personality, and social support on prognosis in chronic heart failure patients. One hundred eleven patients (mean age 57 ± 14 years) having participated in an exercise based ambulatory cardiac rehabilitation program were enrolled in a prospective cohort study. Psychological baseline data were assessed at program entry. Mortality, readmission, and health-related quality of life were assessed at follow up (mean 2.8 ± 1.1 years). After controlling for disease severity none of the psychological variables were associated with mortality, though severe anxiety predicted readmission [HR = 3.21 (95% CI, 1.04–9.93; P = .042)]. Health-related quality of life was independently explained by vital exhaustion, anxiety and either body mass index (physical dimension) or sex (emotional dimension). As psychological variables have a strong impact on health-related quality of life they should be routinely assessed in chronic heart failure patients` treatment.