Nils S. Peterson

Simulation and evaluation with energy systems blocks

Abstract By using blocks programmed for each symbol, models using energy systems language can now be computer-simulated directly, by-passing the mathematics, which is done automatically. Energy systems methodology was introduced in 1967 to help aggregate systems overview and connect human verbal thinking to quantitative models constrained by principles of energy and hierarchy. The GENSYS library of symbol blocks for the simulation program EXTEND, when connected on screen, sets up a system of equations and generates output graphs by sending information back and forth between the blocks. The process of programming helped define EMERGY (spelled with an ‘m’), empower and transformity mathematically so that the simulations can plot quantity, flow, EMERGY, empower and transformity. Examples include ecological and economic systems. Blocks and models for elementary teaching use pictorial icons, which help bring systems modeling and simulation to general education without the necessity of writing equations. This paper explains the modeling concepts and how to prepare and use blocks.

Representations of Perceived Relations among the Properties and Variables of a Complex System

Three different techniques for representing human understanding of complex systems were compared. Novice veterinary students and cardiovascular research experts made judgments of the relations among the properties and variables of a complex system, the mechanical heart / blood vessel system. They also described the variables and properties by a series of bipolar ratings. A variety of analyses showed that the novices tended to conceptualize the system in static anatomic terms. Experts showed a more integrative conceptualization and distinguished more clearly than students between relations involving only system properties and those involving system variables. The methods of multidimensional scaling, agglomerative hierarchical clustering, and elementary digraphs were used to represent perceived relations among system variables and properties. It was concluded that the simplest form of representation, a digraph, has several advantages over the other representations.

The Impact of the Internet on Learners and Schools

Nils S. Peterson is principal and Kevin C. Facemyer is researcher, both at the Virtual Professional Development School, Washington State University, Pullman; readers may continue the dialogue on the Internet with Peterson at nils_peterson@wsu.edu and with Facemyer at KCFacemyer@wsu.edu. What changed learning opportunities does on-line technology present] to students? What are the implications of these changes on teachers?

Frequency Modulation of Heart Rate to Increase Low-Frequency Content of Cardiovascular Signals

Vital physiologic infonnation about the cardiovascular system resides in the low-frequency range of the frequency spectrum. The regularity of cardiac pulsations generaily restricts their frequency spectrum to a few lines corresponding to the hannonics of the regular wave-forms with little or no information at frequencies below the natural heart rate. To obtain accurate infonnation at frequencies above zero but below the natural heart rate, a simple experimental technique has been developed which introduces a periodic perturbation to the heart rate by electrical pacing. This frequency-modulated heart rate results in predictable increases in the low-frequency content of the pressure (F) and flow (Q) signals corresponding to the period and associated harmonics of the perturbation. Using this technique, curves are plotted for the modulus of the low-frequency hydraulic input impedance of a canine systemic arterial system.

Sensitivity Analysis of Interaction between the Left Ventricle and the Systemic Arteries

In an earlier work (Campbell et al. 1984) we proposed that a useful interpretation of interaction between the left ventricle (LV) and systemic arteries (SA) could come from couching the relationship between them in a block diagram form. Such a representation would emphasize the relationship between system components and the flow of information within the system. With the block diagram it was possible to refer to elementary linear system concepts, to understand how a change in LV/SA properties might affect LV/SA behavior. Predictions based on these elementary considerations were compared with more detailed calculations of sensitivities derived from mathematical models of the system, and there was general agreement between the predictions and the calculations. Even though the LV/SA system was nonlinear and time varying, the simple linear block diagram analysis was useful in generating insights and hypotheses about interactions within the system. We felt that this approach would prove fruitful in relating LV/SA interaction to other cardiovascular interactions as more and more aspects of the cardiovascular system were taken into account.

The MacCycle: an extensible multimedia for teaching the physiology and histology of the menstrual cycle

The development of MacCycle, a multimedia visual database of the female menstrual cycle, stemmed from two related events. First, the School of Biological and Medical Sciences at St Andrews University began to make contingency plans to update a computer classroom which had been used to teach physiology for about five years. Second, staff retirements were about to change the profile of the School′s teaching coverage in the key area of preclinical medicine. We anticipated that the introduction of a more flexible delivery system for the histology course might go some way to offsetting potential staff shortages.

Real-time cardiovascular simulation using two microcomputers☆

Abstract Cardiovascular simulations have been developed for a number of different classes of applications: systems identification, benchmarks, physiologic research and teaching. The model presented in this paper is similar in structure to the PHYSBE benchmark model. Our purpose, however, is to teach medical students about the complex interactions of the cardiovascular system. Commonly, cardiovascular simulations have been implemented on poweful research computers using high-level languages. This paper reports on the use of a microprocessor, programmed in assembler, as the simulation engine. This more limited machine was chosen to minimize the cost of developing multiple student workstations while still providing real physiologic time analog outputs. A number of different models have been developed for teaching cardiovascular physiology using mainframe, mini, micro and analog computers. Of these, only the analog simulations and the present work are capable of real-physiologic time computation and pulsatile display. The digital computer system presented here achieves this result with a more flexible student interface.