102,374 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
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
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
The intracranial Windkessel implies arteriovenous pulsatile coupling increased by venous resistances
No full textVarious detailed models of cerebral circulation have been proposed, recently fostered by the hypothesized relationship between extracranial venous drainage impairment and neurodegenerative diseases. However, some basic model is missing, analogous to the 2-element Windkessel (WK) of the systemic circulation. This theoretical study focuses, in the simplest way, on the dependence of intracranial venous pressure (VP) pulsatility on the intracranial arterial 2-element WK and the venous resistance RV. The WK compliance is shown to exert an arteriovenous capacitive coupling (AV-CC), agumented by RV increments. The WK was estimated based on the intracranial arterial pressure (AP) and flow (ФICA) waves of an open database of 3325 virtual subjects. A normal RV was estimated imposing a mean VP of 10 mmHg, doubled to mimic hindered extracranial veins. The AP to VP transfer function showed: i) a gain almost proportional to RV; ii) a zero slightly below heart rate (HR) corresponding to the arterial WK pole; iii) a mid-frequency derivative band up to the AV-CC pole, the frequency of which was almost inversely proportional to RV; iv) full coupling at high frequencies, yet above the pulse harmonic content, at normal HR. In conclusion, besides the well-known effect of venous hindering on the mean VP, the results of this model support the hypothesis that abnormal pulsatility of cerebral veins may play a significant role in cerebrovascular imbalance and related neurodegeneration
Biomedical engineering education at Politecnico di Milano: development and recent changes
No full textAbstract: The biomedical engineering (BME) programme at the Politecnico di Milano (POLIMI) is characterized by a strong interdisciplinary background in a broad range of engineering subjects applied to biology and medicine. Accordingly, the undergraduate level (3 years) provides a general education, which includes mechanics, chemistry and materials, electronics, and information technology both in the context of general engineering and within BME foundations. In contrast, the postgraduate programme (2 years) offers a broad choice of specializations in BME fields in close connection with the BME research activities and laboratories of the campus and with active interchange with the other engineering disciplines. The history of BME development at POLIMI is briefly recalled, together with the characteristics of educational and research work, which is strongly biased by a large polytechnic university with no medical school within the same campus; points of strength and weakness due to this background are discussed. The introduction of a double cycle (undergraduate and postgraduate) according to the Bologna process (2000) and the effects on the programme structure is considered. An early phase in which professional education was emphasized at undergraduate level is recalled, which was followed by the actual revision fostering basic engineering and BME education at the first level while leaving in-depth specialization to postgraduate studies or to on-the-job training
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
The Synchrony between Baroreflex Sequences and Cardio-Respiratory Activity
No full textThe bias observed between methods developed to assess the baroreflex control of Heart Rate (HR) lead to gain further insight into those methods. In two groups of subjects were studied: a group of young adults, and a group of middle-aged adults, cardiovascular (CV) and respiratory parameters were continuously recorded during a graded bicycle exercise. This study focused on the sequence method, and its particular time sequence pattern (up and down sequences). Features of respectively the up and down sequences were analysed through comparative analysis and sequence pattern analysis. No significant changes were noticed between the up and down sequences for both the number of sequences and the baroreflex gain. A synchrony was present according to the phase of respiration and also with the diastolic arterial pressure (dap). It may suggest a relation between the baroreflex function and the Bainbridge reflex in governing CV oscillations
Opening the black box of machine learning in radiology: can the proximity of annotated cases be a way?
No full textMachine learning (ML) and deep learning (DL) systems, currently employed in medical image analysis, are data-driven models often considered as black boxes. However, improved transparency is needed to translate automated decision-making to clinical practice. To this aim, we propose a strategy to open the black box by presenting to the radiologist the annotated cases (ACs) proximal to the current case (CC), making decision rationale and uncertainty more explicit. The ACs, used for training, validation, and testing in supervised methods and for validation and testing in the unsupervised ones, could be provided as support of the ML/DL tool. If the CC is localised in a classification space and proximal ACs are selected by proper metrics, the latter ones could be shown in their original form of images, enriched with annotation to radiologists, thus allowing immediate interpretation of the CC classification. Moreover, the density of ACs in the CC neighbourhood, their image saliency maps, classification confidence, demographics, and clinical information would be available to radiologists. Thus, encrypted information could be transmitted to radiologists, who will know model output (what) and salient image regions (where) enriched by ACs, providing classification rationale (why). Summarising, if a classifier is data-driven, let us make its interpretation data-driven too
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