Principles of light harvesting from single photosynthetic complexes.

Photosynthetic systems harness sunlight to power most life on Earth. In the initial steps of photosynthetic light harvesting, absorbed energy is converted to chemical energy with near-unity quantum efficiency. This is achieved by an efficient, directional and regulated flow of energy through a network of proteins. Here, we discuss the following three key principles of this flow and of photosynthetic light harvesting: thermal fluctuations of the protein structure; intrinsic conformational switches with defined functional consequences; and environmentally triggered conformational switches. Through these principles, photosynthetic systems balance two types of operational costs: metabolic costs, or the cost of maintaining and running the molecular machinery, and opportunity costs, or the cost of losing any operational time. Understanding how the molecular machinery and dynamics are designed to balance these costs may provide a blueprint for improved artificial light-harvesting devices. With a multi-disciplinary approach combining knowledge of biology, this blueprint could lead to low-cost and more effective solar energy conversion. Photosynthetic systems achieve widespread light harvesting across the Earth's surface; in the face of our growing energy needs, this is functionality we need to replicate, and perhaps emulate.

External beam irradiation as an adjunctive treatment in failing dialysis shunts.

PURPOSE: To evaluate the utility of low-dose irradiation as adjunctive treatment for failing dialysis shunts related to stenoses. MATERIALS AND METHODS: Thirty-one patients with 41 lesions in their dialysis shunts were successfully enrolled for this study. After imaging of the shunt and calculation of venous stenoses, each patient was randomized into one of two segments of the protocol: (i) angioplasty and/or stent placement alone, and (ii) angioplasty and/or stent placement followed by external beam irradiation. All patients with significant venous stenoses (> or =50%) were treated with appropriately sized PTA (percutaneous transluminal angioplasty) and Wallstents. Patients randomized to the external irradiation segment underwent localized irradiation via a Theratron cobalt unit of 7 Gy 0-24 hours and 24-48 hours after intervention. Those patients randomized to the control group received no additional treatment. Clinical follow-up included resumption of successful dialysis with appropriate hemodynamic parameters. Two follow-up shunt images were obtained, follow-up 1 (fu-1) from 90 to 179 days and follow-up 2 (fu-2) from 180 to 365 days. Percentages of significant recurrent stenoses, defined as greater than 50%, were recorded and re-treated as needed. RESULTS: Sixteen of the 31 patients underwent external beam irradiation. There were 21 lesions in the test group that underwent irradiation after intervention, and 20 lesions were treated with intervention alone. There were seven native arteriovenous fistulas and 24 Gore-tex grafts. All stenoses were either venous outflow stenoses (68%) or central stenoses (32%). The authors utilized chi2 analysis to compare restenoses rates between the control and irradiated groups at fu-1 (P<.99) and fu-2 (P<.10). CONCLUSIONS: Although the results show that external beam irradiation has minimal effects on the restenoses of dialysis grafts when used in conjunction with PTA and stent placement, further studies with a larger, more homogenous population are needed to assess the trend of improving patency rates after external beam irradiation.

Employee assistance programs: a preventive, cost-effective benefit.

Employee Assistance Programs (EAPs) provide a much-needed service to the employees of corporations. In these times of reduced benefits and diminished community resources, EAPs can dramatically compensate for those shortages. This article will explore the role of an EAP, the models of service available, and the selection process for choosing a program.

Analysis of stress levels among medical students, residents, and graduate students at four Canadian schools of medicine.

PURPOSE: To assess stress in medical students, residents, and graduate science students at four Canadian schools of medicine. METHOD: Four schools with different curricula in three different parts of Canada participated in the study: the University of Calgary Faculty of Medicine, the University of Alberta Faculty of Medicine, the Dalhousie University Faculty of Medicine, and the McMaster University Faculty of Health Sciences. All the medical students, residents, and graduate science students at each school were surveyed in 1994-95. The three instruments used were the University of Calgary Stress Questionnaire, the Social Readjustment Rating Scale (SRRS), and the Symptom Checklist-90. Demographic data were compared across all four schools. Analysis of variance was calculated for all test-item scores, utilizing a four (school) by three (program) by two (gender) design, which were all between subject factors. Significant main effects were followed up by using planned comparisons (Newman-Keuls, with a probability level of p < .05). Significant interaction effects were followed up by using an analysis of simple effects. RESULTS: A total of 1,681 questionnaires were returned as follows: 621 of 1,304 (48%) from the medical students, 645 of 1,495 (43%) from the residents, and 415 of 829 (50%) from the graduate science students. There were significant differences between the three groups in the natures and degrees of stress, with the graduate students reporting higher levels of stress. There were significant gender differences as well, with the women reporting higher levels of stress. Overall, stress levels were found to be mild, based on the University of Calgary Stress Questionnaire and the SRRS. CONCLUSION: This study suggests that medical students and residents experience stress at levels that appear acceptable, but ongoing monitoring and the provision of appropriate support systems will continue to be important.

An 18-month follow-up on the effectiveness of a sexuality workshop: some methodological pitfalls.

Students from four health sciences programs (Medicine, Nursing, Occupational Therapy and Physiotherapy) participated in a two-day Sexuality Workshop and completed pre- and post-workshop questionnaires dealing with sexual attitudes, comfort, and knowledge. Eighteen months later, these students were asked to complete the same questionnaires. Not only had they sustained the gains made during the workshop, but they continued to show improvement in the three areas during this interval. However, of greater importance than the positive finding is the need to understand the range of methodological problems encountered in carrying out this type of follow-up educational inquiry and in seeking measures for improving the validity and generalizability of such research.

Effort thrombosis: effective treatment with vascular stent after unrelieved venous stenosis following a surgical release procedure.

Acute symptomatic effort thrombosis in a 33-year-old male necessitated an aggressive approach consisting of thrombolysis, angioplasty, and surgical thoracic outlet release. The patient required postoperative placement of a Wallstent and was placed on anticoagulation. He has remained symptom free for the past 10 months, both clinically and sonographically.

Selective arterial embolization of idiopathic priapism.

We report a case of idiopathic priapism that was only identified as high-flow or arterial priapism after drainage of the corpora cavernosa. Following failure of conservative and surgical treatment attempts, two consecutive embolizations of a unilateral penile artery were performed with gelgoam particles.

Thrombolytic therapy in peripheral arterial occlusive disease: mechanisms of action and drugs available.

Catheter-directed thrombolytic therapy has become an important part of the treatment of patients with acute arterial and graft occlusion. The underlying pharmacologic principle is the activation of plasminogen, bound to fibrin within the thrombus. Guide-wire passage reliably predicts success of catheter-directed thrombolysis. The underlying disease process leading to thrombosis should be accurately identified and promptly corrected to reduce the probability of recurrent occlusion. Streptokinase (SK), urokinase (UK) and recombinant tissue plasminogen activator (rt-PA) are the three agents used to treat peripheral arterial occlusive disease. The evolution from SK to UK and rt-PA and improvements in techniques and delivery systems have led to improved success rates and lower complication rates. Patient selection, basic technical considerations and overall results are discussed here. The currently available thrombolytic agents, as well as those being developed, are reviewed to provide background information for current and future applications.

Urinoma secondary to surgical spinal fusion: radiologic diagnosis and treatment.

We have presented a case of urinoma secondary to ureteral injury during spinal fusion via retroperitoneal approach demonstrated by CT. The presumed diagnosis of urinoma was confirmed and treated by interventional radiologic techniques.