Search results for " causality"
showing 9 items of 109 documents
Investigating cardiovascular and cerebrovascular variability in postural syncope by means of extended Granger causality
2014
The patterns of Granger causality (GC) between heart period (HP), mean arterial pressure (AP) and cerebral blood flow velocity (FV) were investigated in ten subjects with postural related syncope (PRS). The classic GC measure based on vector autoregressive (VAR) modeling was compared with a novel extended GC (eGC) measure derived from VAR models incorporating instantaneous causal effects among the series. The analysis was performed in the supine and in the upright position during early (ET) and late (LT, close to presyncope) epochs of head-up tilt. Moving from ET to LT, both GC and eGC decreased from AP to HP, and increased from AP to FV, reflecting baroreflex impairment and loss of cerebra…
Causal analysis of short-term cardiovascular variability: state-dependent contribution of feedback and feedforward mechanisms.
2016
Baroreflex function is usually assessed from spontaneous oscillations of blood pressure (BP) and cardiac RR interval assuming a unidirectional influence from BP to RR. However, the interaction of BP and RR is bidirectionalâRR also influences BP. Novel methods based on the concept of Granger causality were recently developed for separate analysis of feedback (baroreflex) and feedforward (mechanical) interactions between RR and BP. We aimed at assessing the proportion of the two causal directions of the interactions between RR and systolic BP (SBP) oscillations during various conditions, and at comparing causality measures from SBP to RR with baroreflex gain indexes. Arterial BP and ECG sig…
Information domain approach to the investigation of cardio-vascular, cardio-pulmonary, and vasculo-pulmonary causal couplings
2011
The physiological mechanisms related to cardio-vascular (CV), cardio-pulmonary (CP), and vasculo-pulmonary (VP) regulation may be probed through multivariate time series analysis tools. This study applied an information domain approach for the evaluation of non-linear causality to the beat-to-beat variability series of heart period (t), systolic arterial pressure (s), and respiration (r) measured during tilt testing and paced breathing (PB) protocols. The approach quantifies the causal coupling from the series i to the series j (C(ij)) as the amount of information flowing from i to j. A measure of directionality is also obtained as the difference between two reciprocal causal couplings (D(i…
Wiener-Granger Causality in Network Physiology with Applications to Cardiovascular Control and Neuroscience
2016
Since the operative definition given by C. W. J. Granger of an idea expressed by N. Wiener, the Wiener–Granger causality (WGC) has been one of the most relevant concepts exploited by modern time series analysis. Indeed, in networks formed by multiple components, working according to the notion of segregation and interacting with each other according to the principle of integration, inferring causality has opened a window on the effective connectivity of the network and has linked experimental evidences to functions and mechanisms. This tutorial reviews predictability improvement, information-based and frequency domain methods for inferring WGC among physiological processes from multivariate…
Dynamical Casimir-Polder forces
2010
We consider the dynamical (time-dependent) Casimir-Polder force between an atom and a perfectly conducting wall, as well as the dynamical Casimir-Polder force between two atoms in the presence of a boundary condition such as a conducting wall. The dynamical Casimir-Polder forces are obtained from iterative solutions of the Heisenberg equations for the time evolution of the electric and magnetic field operators around one atom in the presence of the conducting wall and related field energy densities, which are valid for any initial state. We consider both the case of an initially bare atomic state and of an initially partially dressed atomic state. The problem of relativistic causality in th…
Rule of the One: Avicenna, Bahmanyār, and al-Rāzī on the Argument from the Mubāḥathāt
2020
Avicenna is a strong proponent of what some of the later ones call qāʻidat al-wāḥid or ‘rule of the one’ (RO). The gist of RO states: from the one only one directly proceeds. In the secondary literature, discussion of this Avicennian rule is usually limited to a particular application of it i.e., the issue of emanation. As result, it’s not really clear what RO means, nor why Avicenna endorsed it. In this paper, I try and remedy this situation by doing two things – one on the taṣawwur front, the other on the tasdīq. First, explain just what the terms of RO amount to – that is, its subject and predicate. In doing this, I distinguish between a narrow and a broad understanding of RO, and the sh…
The Joint Distribution Criterion and the Distance Tests for Selective Probabilistic Causality
2010
A general definition and a criterion (a necessary and sufficient condition) are formulated for an arbitrary set of external factors to selectively influence a corresponding set of random entities (generalized random variables, with values in arbitrary observation spaces), jointly distributed at every treatment (a set of factor values containing precisely one value of each factor). The random entities are selectively influenced by the corresponding factors if and only if the following condition, called the joint distribution criterion, is satisfied : there is a jointly distributed set of random entities, one entity for every value of every factor, such that every subset of this set that corr…
Assessing Transfer Entropy in cardiovascular and respiratory time series: A VARFI approach
2021
In the study of complex biomedical systems represented by multivariate stochastic processes, such as the cardiovascular and respiratory systems, an issue of great relevance is the description of the system dynamics spanning multiple temporal scales. Recently, the quantification of multiscale complexity based on linear parametric models, incorporating autoregressive coefficients and fractional integration, encompassing short term dynamics and long-range correlations, was extended to multivariate time series. Within this Vector AutoRegressive Fractionally Integrated (VARFI) framework formalized for Gaussian processes, in this work we propose to estimate the Transfer Entropy, or equivalently G…
Onko urbanisaatio maaseudun turma? : kaupunkien väestönkasvun vaikutukset erityyppisen maaseudun väestökehitykseen Suomessa ajanjaksolla 1990-2015
2018
Kaupungistuminen on edennyt nopeasti Suomessakin, ja samalla maaseutu on menettänyt väestöään ja aktiviteettejaan. Miten urbanisaation eteneminen on vaikuttanut maaseudun kehitykseen? Artikkelin mukaan urbanisaatio levittää kaupunkien ympäristöön sekä ”varjoa” että ”valoa”, mutta ydinmaaseudun ja harvaan asutun maaseudun negatiiviseen kehitykseen se ei ole vaikuttanut. peerReviewed