Chronic ventricular pacing in children: toward prevention of pacing-induced heart disease

In children with congenital or acquired complete atrioventricular (AV) block, ventricular pacing is indicated to increase heart rate. Ventricular pacing is highly beneficial in these patients, but an important side effect is that it induces abnormal electrical activation patterns. Traditionally, ventricular pacemaker leads are positioned at the right ventricle (RV). The dyssynchronous pattern of ventricular activation due to RV pacing is associated with an acute and chronic impairment of left ventricular (LV) function, structural remodeling of the LV, and increased risk of heart failure. Since the degree of pacing-induced dyssynchrony varies between the different pacing sites, ‘optimal-site pacing’ should aim at the prevention of mechanical dyssynchrony. Especially in children, generally paced from a very early age and having a perspective of life-long pacing, the preservation of cardiac function during chronic ventricular pacing should take high priority. In the perspective of the (patho)physiology of ventricular pacing and the importance of the sequence of activation, this paper provides an overview of the current knowledge regarding possible alternative sites for chronic ventricular pacing. Furthermore, clinical implications and practical concerns of the various pacing sites are discussed. The review concludes with recommendations for optimal-site pacing in children

On the Relation Between Unity Properties and Sequences of States

Stepwise refinement of programs has proven to be a suitable method for developing parallel and distributed programs. We examine and compare a number of different notions of program refinement for Unity. Two of these notions are based on execution sequences. Refinement corresponds to the reduction of the set of execution sequences, i.e. reducing the amount of nondeterminism. The other refinement notions are based on Unity properties as introduced by Chandy and Misra. The Unity approach is to refine specifications. Although it has proven a suitable formalism for deriving algorithms, it seems less suitable for handling implementation details. Following Sanders and Singh, we formalize program refinement in the Unity framework as the preservation of Unity properties. We show that Unity properties are not powerful enough to characterize execution sequences. As a consequence, the notion of property-preserving refinement differs from the notion of reducing the set of execution sequences. Keyw..

Coordination in the impunity framework

The ImpUNITY framework is an extension of the UNITY framework. It contains several program structuring mechanisms and puts special emphasis on compositional refinement of both specifications and programs. It has an associated temporal logic, formal refinement notions, and program transformation rules. In this paper we show how coordination in the form of a shared tuple space between communicating ImpUNITY programs is modelled and used during formal program specification and refinement. We exemplify our formalism by a larger case study on a phone system where communication in the system is partly taken care of via a tuple space

A step towards new irrigation scheduling strategies using plant-based measurements and mathematical modelling

Because of the increasing worldwide shortage of freshwater and costs of irrigation, a new plant-based irrigation scheduling method is proposed. In this method, two real-time plant-based measurements (sap flow and stem diameter variations) are used in combination with a mathematical water flow and storage model in order to predict the stem water potential. The amount of required irrigation water is derived from a time integration of the sap flow profile, while the timing of the irrigation is controlled based on a reference value for the predicted stem water potential. This reference value is derived from the relationship between midday values of maximum photosynthesis rates and stem water potential. Since modelling is an important part of the proposed methodology, a thorough mathematical analysis (identifiability analysis) of the model was performed. This analysis showed that an initial (offline) model calibration was needed based on measurements of sap flow, stem diameter variation and stem water potential. Regarding irrigation scheduling, however, only sap flow and stem diameter variation measurements are needed for online simulation and daily model calibration. Model calibration is performed using a moving window of 4 days of past data of stem diameter variations. The research tool STACI (Software Tool for Automatic Control of Irrigation) was used to optimally combine the continuous measurements, the mathematical modelling and the real-time irrigation scheduling. The new methodology was successfully tested in a pilot-scale setup with young potted apple trees (Malus domestica Borkh) and its performance was critically evaluated