68 research outputs found
Why Monte Carlo Simulations are Inferences and not Experiments
No full textMonte Carlo Simulations arrive at their results by introducing randomness, sometimes derived from a physical randomizing device. Nonetheless, we argue, they open no new epistemic channels beyond that already employed by traditional simulations: the inference by ordinary argumentation of conclusions from assumptions built into the simulations. We show that Monte Carlo simulations cannot produce knowledge other than by inference; and that they resemble other computer simulations in the manner in which they derive their conclusions. Simple examples of Monte Carlo simulations are analyzed to identify the underlying inferences
A lumped hydrodynamic model to assess ageing and hypertension effects on the aortic stiffness
No full textA Windkessel model is used to evaluate and separate the effects of ageing from those of hypertension on the aortic flow and pressure waveforms. The ageing- and hypertension-induced changes in the blood flow and pressure behaviour are simulated by using clinical data concerning the dependence of the Young modulus and aortic input impedance on age. The simulated pressure and flow waveforms show a typical steepening due to the ageing process. Using the model outcomes, we separate the effect of arterial tissue ageing from the effect of hypertension (here intended as a generic increase in mean blood pressure). The age-dependent component results to be more important than the pressure-dependent one especially in young and middle-aged individuals. However, the relative importance of the hypertension-driven term increases for the elderly, and reaching a value of the order of 20% becomes relevant. All the obtained results agree well with the qualitative expected behaviour
Compensatory Effect between Aortic Stiffening and Remodelling during Ageing
No full textThe arterial tree exhibits a complex spatio-temporal wave pattern, whose healthy behaviour depends on a subtle balance between mechanical and geometrical properties. Several clinical studies demonstrated that such a balance progressively breaks down during ageing, when the aorta stiffens and remodels by increasing its diameter. These two degenerative processes however, have different impacts on the arterial wave pattern. They both tend to compensate for each other, thus reducing the detrimental effect they would have had if they had arisen individually. This remarkable compensatory mechanism is investigated by a validated multi-scale model, with the aim to elucidate how aortic stiffening and remodelling quantitatively impact the complex interplay between forward and reflected backward waves in the arterial network. We focus on the aorta and on the pressure at the ventricular-aortic interface, which epidemiological studies demonstrate to play a key role in cardiovascular disease
Non-invasive aortic systolic pressure and pulse wave velocity estimation in a primary care setting: An in silico study
No full textThe methodology of experimental economics
No full textThe experimental approach in economics is a driving force behind some of the most exciting developments in the field. The ‘experimental revolution’ was based on a series of bold philosophical premises which have remained until now mostly unexplored. This book provides the first comprehensive analysis and critical discussion of the methodology of experimental economics, written by a philosopher of science with expertise in the field. It outlines the fundamental principles of experimental inference in order to investigate their power, scope and limitations. The author demonstrates that experimental economists have a lot to gain by discussing openly the philosophical principles that guide their work, and that philosophers of science have a lot to learn from their ingenious techniques devised by experimenters in order to tackle difficult scientific problem
Characterizing the cardiovascular functions during atrial fibrillation through lumped-parameter modeling
No full textAtrial fibrillation (AF), causing irregular and rapid heartbeats, is the most common arrhythmia. Due to the widespread impact on the population and the disabling symptoms related to rapid heart rate, AF is a subject of growing interest under several aspects: statistical analyses on the heartbeat distributions, risk factors, impact on quality of life, correlation with other cardiac pathologies. However, several key points on the consequences induced by AF on the cardiovascular system are still not completely understood. The proposed work aims at quantifying the impact of AF on the most relevant cardiovascular parameters by means of a lumped-parameter modeling, paying particular attention to the stochastic nature of the irregular heartbeats and the reduced contractility of the heart. The global response leads to a rather impressive overall agreement with the clinical state-of-the-art measures regarding AF: reduced cardiac output with correlated arterial hypotension, as well as higher left atrial volume and pressure values are some of the most representative outcomes emerging during AF. Moreover, new insights on hemodynamic parameters such as cardiac flow rates, which are difficult to measure and almost never offered in literature, are here provide
Impact of atrial fibrillation on the cardiovascular system through a lumped-parameter approach
No full textAtrial fibrillation (AF) is the most common arrhythmia affecting millions of people in the Western countries and, due to the widespread impact on the popu- lation and its medical relevance, is largely investigated in both clinical and bioengineering sciences. However, some important feedback mechanisms are still not clearly estab- lished. The present study aims at understanding the global response of the cardiovascular system during paroxysmal AF through a lumped-parameter approach, which is here performed paying particular attention to the stochastic modeling of the irregular heartbeats and the reduced con- tractility of the heart. AF can be here analyzed by means of a wide number of hemodynamic parameters and avoiding the presence of other pathologies, which usually accom- pany AF. Reduced cardiac output with correlated drop of ejection fraction and decreased amount of energy con- verted to work by the heart during blood pumping, as well as higher left atrial volumes and pressures are some of the most representative results aligned with the existing clini- cal literature and here emerging during acute AF. The pre- sent modeling, providing new insights on cardiovascular variables which are difficult to measure and rarely reported in literature, turns out to be an efficient and powerful tool for a deeper comprehension and prediction of the arrythmia impact on the whole cardiovascular system
Fluid dynamics of heart valves during atrial fibrillation: a lumped parameter-based approach
No full textAtrial fibrillation (AF) consequences on the heart valve dynamics are usually studied along with a valvular disfunction or disease, since in medical monitoring the two pathologies are often concomitant. Aim of the present work is to study, through a stochastic lumped-parameter approach, the basic fluid dynamics variations of heart valves, when only paroxysmal AF is present with respect to the normal sinus rhythm (NSR) in absence of any valvular pathology. Among the most common parameters interpreting the valvular function, the most useful turns out to be the regurgitant volume. During AF both atrial valves do not seem to worsen their performance, while the ventricular efficiency is remarkably reduced
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