Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 10 de 10
Filter
Add more filters










Publication year range
1.
Phys Rev E Stat Nonlin Soft Matter Phys ; 81(3 Pt 2): 037201, 2010 Mar.
Article in English | MEDLINE | ID: mdl-20365906

ABSTRACT

We discuss the use of multivariate Granger causality in presence of redundant variables: the application of the standard analysis, in this case, leads to under estimation of causalities. Using the un-normalized version of the causality index, we quantitatively develop the notions of redundancy and synergy in the frame of causality and propose two approaches to group redundant variables: (i) for a given target, the remaining variables are grouped so as to maximize the total causality and (ii) the whole set of variables is partitioned to maximize the sum of the causalities between subsets. We show the application to a real neurological experiment, aiming to a deeper understanding of the physiological basis of abnormal neuronal oscillations in the migraine brain. The outcome by our approach reveals the change in the informational pattern due to repetitive transcranial magnetic stimulations.

3.
Physiol Meas ; 26(4): 363-72, 2005 Aug.
Article in English | MEDLINE | ID: mdl-15886432

ABSTRACT

In this paper, we consider systolic arterial pressure time series from healthy subjects and chronic heart failure patients, undergoing paced respiration, and show that different physiological states and pathological conditions may be characterized in terms of predictability of time series signals from the underlying biological system. We model time series by the regularized least-squares approach and quantify predictability by the leave-one-out error. We find that the entrainment mechanism connected to paced breath, that renders the arterial blood pressure signal more regular and thus more predictable, is less effective in patients, and this effect correlates with the seriousness of the heart failure. Using a Gaussian kernel, so that all orders of nonlinearity are taken into account, the leave-one-out error separates controls from patients (probability less than 10(-7)), and alive patients from patients for whom cardiac death occurred (probability less than 0.01).


Subject(s)
Algorithms , Blood Pressure , Diagnosis, Computer-Assisted/methods , Heart Failure/diagnosis , Heart Failure/physiopathology , Models, Biological , Respiration , Systole , Female , Humans , Male , Middle Aged , Reproducibility of Results , Risk Assessment/methods , Risk Factors , Sensitivity and Specificity , Severity of Illness Index , Statistics as Topic
4.
Phys Rev Lett ; 93(3): 038103, 2004 Jul 16.
Article in English | MEDLINE | ID: mdl-15323876

ABSTRACT

We investigate phase synchronization in EEG recordings from migraine patients. We use the analytic signal technique, based on the Hilbert transform, and find that migraine brains are characterized by enhanced alpha band phase synchronization in the presence of visual stimuli. Our findings show that migraine patients have an overactive regulatory mechanism that renders them more sensitive to external stimuli.


Subject(s)
Electroencephalography/methods , Evoked Potentials, Visual/physiology , Migraine Disorders/physiopathology , Adult , Humans , Middle Aged , Signal Processing, Computer-Assisted
5.
Phys Rev E Stat Nonlin Soft Matter Phys ; 69(6 Pt 1): 061923, 2004 Jun.
Article in English | MEDLINE | ID: mdl-15244633

ABSTRACT

We study the phase-synchronization properties of systolic and diastolic arterial pressure in healthy subjects. We find that delays in the oscillatory components of the time series depend on the frequency bands that are considered, in particular we find a change of sign in the phase shift going from the very low frequency band to the high frequency band. This behavior should reflect a collective behavior of a system of nonlinear interacting elementary oscillators. We prove that some models describing such systems, e.g., the Winfree and the Kuramoto models, offer a clue to this phenomenon. For these theoretical models there is a linear relationship between phase shifts and the difference of natural frequencies of oscillators and a change of sign in the phase shift naturally emerges.


Subject(s)
Biological Clocks/physiology , Blood Pressure/physiology , Diastole/physiology , Models, Cardiovascular , Pulsatile Flow/physiology , Systole/physiology , Computer Simulation , Humans , Middle Aged , Periodicity
7.
Bull Hosp Jt Dis ; 54(4): 215-21, 1996.
Article in English | MEDLINE | ID: mdl-8731413

ABSTRACT

The width of the weight-bearing surface (WBS) of the acetabulum and its obliquity; height, width, opening angle and alpha angle of the gothic arch; diameter of femoral head; the angle between the center of the femoral head and the most lateral point of the acetabulum (CE angle); neck-shaft angle (CCD angle); offset; angle of aperture, surface area, and volume of the spherical sector; radius and height of the spherical bowl; and distance from teardrop were assessed to study mechanically normal and frankly osteoarthritis hips. There appears to be a direct correlation between primary alterations of the above variables and development of osteoarthritis of the hip.


Subject(s)
Hip Joint/diagnostic imaging , Hip/anatomy & histology , Osteoarthritis, Hip/diagnostic imaging , Aged , Analysis of Variance , Biomechanical Phenomena , Female , Hip/diagnostic imaging , Hip Joint/pathology , Humans , Male , Middle Aged , Osteoarthritis, Hip/pathology , Radiography , Reference Values , Risk Factors
8.
Q J Nucl Med ; 39(4 Suppl 1): 86-9, 1995 Dec.
Article in English | MEDLINE | ID: mdl-9002758

ABSTRACT

The aim of this study was to use compartmental analysis as a theoretical tool to provide quantitative and unitary data for a more precise determination of 111In-OCT concentrations in a tumour site and various body organs. Five subjects (3 male and 2 female) with neoplasias were studied. Structural and parametric identification of the model was based on the plasma, urine, total body and ROI (soft tissue, spleen, kidney and tumour) activity values. The model was of the mammillary type with 5 compartments (blood, soft tissue, spleen, kidneys and urine) for the 4 patients with a negative scintiscan and 6 (blood, soft tissue, spleen, kidneys, urine and tumour) for the adenocarcinoma patient. Numerical constants were determined by running a best-fit procedure with the MINUIT minimisation program (CERN library) using a microVAX 3800 computer. The reliability of the models was also tested. 111In-OCT accumulates in the kidneys and spleen, from which it is slowly released into the blood. Elimination is via the urine at first rapidly, then more slowly. The maximum concentration in the tumour compartment is reached at 12-14 hours and remains almost constant.


Subject(s)
Indium Radioisotopes/pharmacokinetics , Models, Chemical , Octreotide/analogs & derivatives , Pentetic Acid/analogs & derivatives , Radiopharmaceuticals/pharmacokinetics , Adenocarcinoma/metabolism , Carcinoma, Small Cell/metabolism , Computer Simulation , Female , Humans , Indium Radioisotopes/blood , Indium Radioisotopes/urine , Kidney/metabolism , Lung Neoplasms/metabolism , Male , Metabolic Clearance Rate , Models, Biological , Neuroblastoma/metabolism , Neuroectodermal Tumors/metabolism , Octreotide/metabolism , Octreotide/pharmacokinetics , Pentetic Acid/metabolism , Pentetic Acid/pharmacokinetics , Radiopharmaceuticals/blood , Radiopharmaceuticals/urine , Reproducibility of Results , Spleen/metabolism , Tissue Distribution
9.
10.
Lab Invest ; 61(4): 381-8, 1989 Oct.
Article in English | MEDLINE | ID: mdl-2796287

ABSTRACT

IgA glomerulonephritis is associated with macromolecules of polymeric IgA in the circulation and mesangial deposits. An impairment in the reticulophagocytic function of patients with IgA nephropathy has been postulated as the potential cause for persistence of IgA immune complexes in the circulation and their eventual glomerular deposition. Since the fate and removal mechanisms of circulating macromolecular IgA are unknown in humans, we examined the blood clearance and organ uptake of purified IgA polymers and macromolecules in patients with IgA nephropathy and normal controls. The IgA macromolecules were prepared by covalent cross-linking of purified human polymeric IgA with a heterobifunctional reagent, N-succinimidyl 3-(2-pyridyldithio) propionate. After intravenous injection, large IgA molecules were removed rapidly from the circulation of patients (t1/2 = 3.8 +/- 1.0 minutes) and controls (t1/2 = 4.9 +/- 1.5 minutes). Dynamic gamma camera scintigraphy revealed the liver as the major organ that mediated the removal of the macromolecular IgA with no significant difference in the rate of hepatic uptake for patients (t1/2 = 3.4 +/- 0.6 minutes) and controls (t1/2 = 3.3 +/- 0.9 minutes). No significant amount of radioactivity could be detected in the lungs, kidneys, and spleen. The small polymers had a slower and similar clearance rates for patients (t1/2 = 29.3 +/- 7.9 h) and controls (t1/2 = 29.0 +/- 8.6 h). These findings have general significance in showing the liver as a major organ for removal of macromolecular IgA. In addition, the results have specific importance in showing that patients with IgA nephropathy do not suffer from an IgA removal dysfunction.


Subject(s)
Glomerulonephritis, IGA/metabolism , Immunoglobulin A/metabolism , Adolescent , Adult , Humans , Immunoglobulin A/analysis , Liver/metabolism , Liver/pathology , Middle Aged , Nephrons/metabolism , Nephrons/pathology
SELECTION OF CITATIONS
SEARCH DETAIL
...