93,329 research outputs found
Simulating the interactions among vasomotion waves of peripheral vascular districts
No full textSimulations are performed in order to analyze the tendency of oscillating peripheral vascular districts (PVDs) to maintain equal phases thus inducing low frequency (LF) waves in systemic arterial pressure (AP). A PVD model regulating the local flow by means of a delayed non-linear feedback displayed spontaneous oscillations with a 12 sec period in the pressure range (40-150 mmHg) of active flow compensation. Two identical PVDs loading the same windkessel compartment could oscillate in phase inducing significant (10% of mean) AP waves: however, this behavior was unstable. On the contrary, phase opposition (without AP waves) was stable and corresponded to an energetic minimum (-9 % compared to the unstable solution). The introduction of either baroreflex mechanisms or a central drive was able to steadily align the PVD phases. Vasomotion synchronization can be a powerful modulation mechanism of LF waves in systemic AP
Modeling the Role of Arterial Windkessel in the Enhancement and Synchronization of Low Frequency Vasomotor Activity
No full textArterial windkessel mechanisms and arterial pressure (AP) low frequency (LF) waves were investigated by means of simple lumped models of a compliant resistant/arterial tree and of flow regulation in peripheral vascular districts (PVDs) with three types of feedback: J) delay, 2) Van der Pol oscillator, 3) relay; all were able to actively compensate flow changes and to simulate peripheral LF vasomotion. Each PVD connected to a Windkessel compartment displayed a reduction and a disappearance of oscillations with low compliance, when the Windkessel equivalent time constant T/sub eq/ fall below 2s. Two PVDs connected to the same Windkessel tended to phase opposition with a negative interference canceling their LF oscillations from AP. With a modest neural drive, cancellation was imperfect and AP waves appeared. Vasomotion, arterial compliances and neural triggers are all essential informing LF AP variability
Spontaneous baroreflex sensitivity estimates during graded bicycle exercise : a comparative study
No full textIn the literature, several methods have been proposed for the assessment of the baroreflex sensitivity from spontaneous variability of heart period and systolic arterial pressure. The present study compares the most utilized approaches for the evaluation of the spontaneous baroreflex sensitivity (i.e. sequence-based, spectral, cross-spectral and model-based techniques) over a protocol capable of inducing a progressive decrease of the baroreflex sensitivity in the presence of a relevant respiratory drive (i.e. a stepwise dynamic bicycle exercise at 10%, 20% and 30% of the maximum nominal individual effort) in 16 healthy humans. Results demonstrated that the degree of correlation among the estimates is related to the structure of the model explicitly or implicitly assumed by the method and depends on the experimental condition (i.e. on the physiological mechanisms contemporaneously active with baroreflex, e. g. cardiopulmonary reflexes). However, even in the presence of a significant correlation, proportional and/or constant biases can be present, thus rendering spontaneous baroreflex estimates not interchangeable. We suggest that the comparison among different baroreflex sensitivity estimates might elucidate physiological mechanisms responsible for the relationship between heart period and systolic arterial pressure
Diffuse and Localized Functional Dysconnectivity in Schizophrenia: a Bootstrapped Top-Down Approach
No full textSchizophrenia (SZ) is a brain disorder leading to detached mind's normally
integrated processes. Hence, the exploration of the symptoms in relation to
functional connectivity (FC) had great relevance in the field. FC can be
investigated on different levels, going from global features to single edges
between regions, revealing diffuse and localized dysconnection patterns. In
this context, SZ is characterized by a diverse global integration with reduced
connectivity in specific areas of the Default Mode Network (DMN). However, the
assessment of FC presents various sources of uncertainty. This study proposes a
multi-level approach for more robust group-comparison. FC between 74 AAL brain
areas of 15 healthy controls (HC) and 12 SZ subjects were used. Multi-level
analyses and graph topological indexes evaluation were carried out by the
previously published SPIDER-NET tool. Robustness was augmented by bootstrapped
(BOOT) data and the stability was evaluated by removing one (RST1) or two
subjects (RST2). The DMN subgraph was evaluated, toegether with overall local
indexes and connection weights to enhance common activations/deactivations. At
a global level, expected trends were found. The robustness assessment tests
highlighted more stable results for BOOT compared to the direct data testing.
Conversely, significant results were found in the analysis at lower levels. The
DMN highlighted reduced connectivity and strength as well as increased
deactivation in the SZ group. At local level, 13 areas were found to be
significantly different (), highlighting a greater divergence in the
frontal lobe. These results were confirmed analyzing the negative edges,
suggesting inverted connectivity between prefronto-temporal areas. In
conclusion, multi-level analysis supported by BOOT is highly recommended,
especially when diffuse and localized dysconnections must be investigated in
limited samples.Comment: 28 pages, 8 figure
Coupling arterial windkessel with peripheral vasomotion : modelling the effects on low frequency oscillations
No full textArterial pressure (AP) and heart rate (HR) waves have long been recognized as an important sign of cardiovascular regulation, however, the underlying interactions involving vasomotion, arterial mechanisms and neural regulation have not been clarified. With the aid of simple dynamical models consisting of active peripheral vascular districts (PVDs) fed by a compliant/resistant arterial tree, the relationship between local AP and flow and systemic AP waves were analyzed. A PVD was described as a nonlinear flow regulation loop. Various feedback dynamics were experimented and general properties were focused. The PVDs displayed a region of active flow compensation against pressure changes, in which self-sustained low-frequency (LF, 0.1 Hz) appeared. Oscillations critically depended on parameter, Teq, analogous to a windkessel time constant, proportional to arterial compliances: a value of about 2 s (consistent with a normal pulse pressure) performed a buffering effect essential for LF oscillations in peripheral flow; conversely, stiffer arteries damped LF vasomotion. Two PVDs fed by a common compliance oscillated in phase opposition; the consequent negative interference cancelled systemic AP waves, even in presence of large peripheral oscillations. The partial disruption of phase opposition by a common neural drive oscillating at a LF proximal to that of the PVDs unveiled LF waves in AP. Also, several PVDs with randomly different natural frequencies displayed a tendency to reciprocal cancellation, while a limited neurally induced phase alignment unmasked LF oscillations at systemic level. It is concluded that vasomotion, arterial compliances and, neural drives are all elements which may cooperate in forming AP waves
Movement-related frequency modulation of beta oscillatory activity in the human subthalamic nucleus
No full textEvent-related changes of brain electrical rhythms are typically analysed as amplitude
modulations of local field potential (LFP) oscillations, like radio amplitude modulation broadcasting. In telecommunications, frequency modulation (FM) is less susceptible to
interference than amplitude modulation (AM) and is therefore preferred for high-fidelity
transmissions. Here we hypothesized that LFP rhythms detected from deep brain stimulation (DBS) electrodes implanted in the subthalamic nucleus (STN) in patients with Parkinson’s disease could represent movement-related activity not only in AM but also in FM. By combining adaptive autoregressive identification with spectral power decomposition, we were able to show
that FM of low-beta (13–20 Hz) and high-beta (20–35 Hz) rhythms significantly contributes to the involvement of the human STN in movement preparation, execution and recovery, and that the FM patterns are regulated by the dopamine levels in the system. Movement-related FM of beta oscillatory activity in the human subthalamic nucleus therefore provides a novel informational domain for rhythm-based pathophysiological models of cortico-basal ganglia processing
Adaptive autoregressive identification with spectral power decomposition for studying movement-related activity in scalp EEG signals and basal ganglia local field potentials
No full textWe propose a method that combines adaptive autoregressive (AAR) identification and spectral power decomposition for the study of movement-related spectral changes in scalp EEG signals and basal ganglia local field potentials (LFPs). This approach introduces the concept of movement-related poles, allowing one to study not only the classical event-related desynchronizations (ERD) and synchronizations (ERS), which correspond to modulations of power, but also event-related modulations of frequency. We applied the method to analyze movement-related EEG signals and LFPs contemporarily recorded from the sensorimotor cortex, the globus pallidus internus (GPi) and the subthalamic nucleus (STN) in a patient with Parkinson's disease who underwent stereotactic neurosurgery for the implant of deep brain stimulation (DBS) electrodes. In the AAR identification we compared the whale and the exponential forgetting factors, showing that the whale forgetting provides a better disturbance rejection and it is therefore more suitable to investigate movement-related brain activity. Movement-related power modulations were consistent with previous studies. In addition, movement-related frequency modulations were observed from both scalp EEG signals and basal ganglia LFPs. The method therefore represents an effective approach to the study of movement-related brain activity
The Strange Cerebrovascular Windkessel: a Simplified Model
No full textChronic cerebrospinal venous insufficiency (CCSVI) has been focused as a hypothetical concause in neurodegeneration. Mechanisms related to venous stasis are mainly considered; conversely, effects on venous pulse in the stiff intracranial (IC) compartment are poorly understood. Insight is here sought through a hyper-simplified model, including the IC arterial Windkessel (WK) and the arterio-venous capacitive coupling. The IC-WK was dimensioned by an open database. The resulting arterio-venous propagation of pulse showed phase anticipation and amplification of higher harmonics, which effect were noticeably augmented in CCSVI
Relationship between RR and RT variability. A measure of dispersion of ventricular repolarisation
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