Behavior Modes, Pathways and Overall Trajectories: Eigenvector and Eigenvalue Analysis of Dynamic Systems

One of the most fundamental principles in system dynamics is the premise that the structure of the system will generate its behavior. Such philosophical position has fostered the development of a number of formal methods aimed at understanding the causes of model behavior. To most in the field of system dynamics, behavior is commonly understood as modes of behavior (e.g., exponential growth, exponential decay, and oscillation) because of their direct association with the feedback loops (e.g., reinforcing, balancing, and balancing with delays, respectively) that generate them. Hence, traditional research on formal model analysis has emphasized which loops cause a particular “mode” of behavior, with eigenvalues representing the most important link between structure and behavior. The main contribution of this work arises from a choice to focus our analysis in the overall trajectory of a state variable – a broader definition of behavior than that of a specific behavior mode. When we consider overall behavior trajectories, contributions from eigenvectors are just as central as those from eigenvalues. Our approach to understanding model behavior derives an equation describing overall behavior trajectories in terms of both eigenvalues and eigenvectors. We then use the derivatives of both eigenvalues and eigenvectors with respect to link (or loop) gains to measure how they affect overall behavior trajectories over time. The direct consequence of focusing on behavior trajectories is that system dynamics researchers' reliance on eigenvalue elasticities can be seen as too-narrow a focus on model behavior – a focus that has excluded the short term impact of a change in loop (or link) gain in its analysis

Does high-dose metformin cause lactic acidosis in type 2 diabetic patients after CABG surgery? A double blind randomized clinical trial

Metformin is a dimethyl biguanide oral anti-hyperglycemic agent. Lactic acidosis due to metformin is a fatal metabolic condition that limits its use in patients in poor clinical condition, consequently reducing the number of patients who benefit from this medication. In a double blind randomized clinical trial, we investigated 200 type 2 diabetic patients after coronary artery bypass surgery in the open heart ICU of the Mazandaran Heart Center, and randomly assigned them to equal intervention and control groups. The intervention group received regular insulin infusion along with 2 metformin 500 mg tablets every twelve hours, while the control group received only intravenous insulin with 2 placebo tablets every twelve hours. Lactate level, pH, base excess, blood glucose and serum creatinine were measured over five 12 h periods, with data averaged for each period. The primary outcome in this study was high lactate levels. Comparison between the 2 groups was made by independent Student’s t-test. To compare changes in multiple measures in each group and analysis of group interaction, a repeated measurement ANOVA test was used

Adopting Clinical Practice Guidelines for Pharmacologic Management of Acute Spinal Cord Injury from a Developed World Context to a Developing Global Region

Background: Proper utilization of high-quality clinical practice guidelines (CPGs) eliminates the dependence of patients\u27 outcomes on the ability and knowledge of individual health care providers and reduces unwarranted variation in care. The aim of this study was to adapt/adopt two CPGs for pharmacologic management of acute spinal cord injury (SCI) using guideline adaptation methods. Methods: This study was conducted based on the ADAPTE process. Following establishment of an organizing committee and choosing the health topics, we appraised the quality of the CPGs using the Appraisal of Clinical Guidelines for Research & Evaluation II (AGREE II). Then, the authors extracted and categorized suggestions according to Population, Intervention, Professions, Outcomes and Health care setting (PIPOH). The decision-making process was based on systemic evaluation of each suggestion, utilizing a combination of AGREE II scores, the quality of supporting evidence for or against each suggestion and the triad of feasibility, acceptance and adoptability for the Iranian health-care context. Results: Two guidelines were included in the adaptation process. Based on high-quality of these guidelines and the feasibility and adoptability evaluation of the organizing committee, we decided to adopt the suggestion of both guidelines. Overall, seven suggestions were extracted from the source guidelines. Conclusion: This work provides a framework to apply guidelines for acute SCI to the developing regions of the world. Attempts should be made to implement these suggestions in order to improve the health outcomes of Iranian SCI patients