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Biomedical subjects

R Livi

Publications and source records attributed to R Livi.

At least 19 recordsLinked to original sources
PubMed2006

Circulating levels of Nepsilon-(carboxymethyl)lysine are increased in systemic sclerosis.

OBJECTIVE: Advanced glycation endproducts (AGEs), including Nepsilon-(carboxymethyl)lysine-protein adducts (CML) are involved in micro/macrovascular changes and are co-localized with adhesion molecules in inflamed tissues. Serum levels of CML were investigated in systemic sclerosis (SSc) characterized by microvascular modifications and correlated with indices of micro/macrovascular damage. METHODS: In 66 SSc patients (limited SSc, n = 55; diffuse SSc, n = 11) and 20 controls, CML serum levels were measured by enzyme-linked immunosorbent assay. Nailfold capillaroscopy, intima-media thickness (IMT) and the ankle-brachial index (ABI) were also recorded, to characterize micro/macrovascular involvement. RESULTS: CML levels were significantly higher in SSc (79.2 +/- 39 mg/ml vs 49.6 +/- 26.1 mg/ml, mean +/- s.d.; P<0.01), without significant differences between SSc subsets. CML levels were significantly higher in all capillaroscopic patterns: the 'early' pattern showed higher levels than 'active' and 'late' patterns. IMT was significantly higher in SSc (P<0.01) than in controls, whilst ABI was no different from controls. CONCLUSIONS: These data indicate that although both CML formation and macrovascular involvement are increased in SSc, there is no correlation between these two parameters. However, the characteristic early nailfold capillaroscopy changes of SSc are associated with proportionally greater CML formation, suggesting that AGEs are involved in SSc microangiopathy.

Adult↗
PubMed2005

Raloxifene reduces urokinase-type plasminogen activator-dependent proliferation of synoviocytes from patients with rheumatoid arthritis.

Extracellular fibrinolysis, controlled by the membrane-bound fibrinolytic system, is involved in cartilage damage and rheumatoid arthritis (RA) synovitis. Estrogen status and metabolism seem to be impaired in RA, and synoviocytes show receptors for estrogens. Our aims in this study were to evaluate in healthy and RA synoviocytes the effects of Raloxifene (RAL), a selective estrogen receptor modulator (SERM), on: proliferation; the components of the fibrinolytic system; and chemoinvasion. The effects of RAL were studied in vitro on synoviocytes from four RA patients and four controls. Proliferation was evaluated as cell number increase, and synoviocytes were treated with 0.5 microM and 1 microM RAL with and without urokinase-plasminogen activator (u-PA) and anti-u-PA/anti-u-PA receptor (u-PAR) antibodies. Fibrinolytic system components (u-PA, u-PAR and plasminogen activator inhibitor (PAI)-1) were assayed by ELISA with cells treated with 0.5 microM and 1 microM RAL for 48 h. u-PA activity was evaluated by zymography and a direct fibrinolytic assay. U-PAR/cell and its saturation were studied by radioiodination of u-PA and a u-PA binding assay. Chemoinvasion was measured using the Boyden chamber invasion assay. u-PA induced proliferation of RA synoviocytes was blocked by RAL (p < 0.05) and antagonized by antibodies alone. The inhibitory effect of RAL was not additive with u-PA/u-PAR antagonism. RA synoviocytes treated with RAL showed, compared to basal, higher levels of PAI-1 (10.75 +/- 0.26 versus 5.5 +/- 0.1 microg/10(6) cells, respectively; p < 0.01), lower levels of u-PA (1.04 +/- 0.05 versus 3.1 +/- 0.4 ng/10(6) cells, respectively; p < 0.001), and lower levels of u-PAR (11.28 +/- 0.22 versus 23.6 +/- 0.1 ng/10(6) cells, respectively; p < 0.001). RAL also significantly inhibited u-PA-induced migration. Similar effects were also shown, at least partially, in controls. RAL exerts anti-proliferative and anti-invasive effects on synoviocytes, mainly modulating u-PAR and, to a lesser extent, u-PA and PAI-1 levels, and inhibiting cell migration and proliferation.

Arthritis, Rheumatoid↗
PubMed2005

Directed percolation with long-range interactions: Modeling nonequilibrium wetting.

It is argued that some phase transitions observed in models of nonequilibrium wetting phenomena are related to contact processes with long-range interactions. This is investigated by introducing a model where the activation rate of a site at the edge of an inactive island of length l is 1+a l(-sigma) . Mean-field analysis and numerical simulations indicate that for sigma>1 the transition is continuous and belongs to the universality class of directed percolation, while for 0<sigma<1 , the transition becomes first order. This criterion is then applied to discuss critical properties of various models of nonequilibrium wetting.

Journal Article↗
PubMed2003

From multiplicative noise to directed percolation in wetting transitions.

A simple one-dimensional microscopic model of the depinning transition of an interface from an attractive hard wall is introduced and investigated. Upon varying a control parameter, the critical behavior observed along the transition line changes from a directed-percolation type to a multiplicative-noise type. Numerical simulations allow for a quantitative study of the multicritical point separating the two regions. Mean-field arguments and the mapping on yet a simpler model provide some further insight on the overall scenario.

Journal Article↗
PubMed2003

Wetting under nonequilibrium conditions.

We report a detailed account of the phase diagram of a recently introduced model for nonequilibrium wetting in (1+1) dimensions [H. Hinrichsen, R. Livi, D. Mukamel, and A. Politi, Phys. Rev. Lett. 79, 2710 (1997)]. A mean-field approximation is shown to reproduce the main features of the phase diagram, while providing indications for the behavior of the wetting transition in higher dimensions. The mean-field phase diagram is found to exhibit an extra transition line which does not exist in (1+1) dimensions. The line separates a phase in which the interface height distribution decays exponentially at large heights from a superexponentially decaying phase. Implications to wetting in dimensions higher than (1+1) are discussed.

Journal Article↗
PubMed2003

Relationship between directed percolation and the synchronization transition in spatially extended systems.

We study the nature of the synchronization transition in spatially extended systems by discussing a simple stochastic model. An analytic argument is put forward showing that, in the limit of discontinuous processes, the transition belongs to the directed percolation (DP) universality class. The analysis is complemented by a detailed investigation of the dependence of the first passage time for the amplitude of the difference field on the adopted threshold. We find the existence of a critical threshold separating the regime controlled by linear mechanisms from that controlled by collective phenomena. As a result of this analysis, we conclude that the synchronization transition belongs to the DP class also in continuous models. The conclusions are supported by numerical checks on coupled map lattices too.

Journal Article↗
PubMed2003

Mechanical model of normal and anomalous diffusion.

The overdamped dynamics of a charged particle driven by an uniform electric field through a random sequence of scatterers in one dimension is investigated. Analytic expressions of the mean velocity and of the velocity power spectrum are presented. These show that above a threshold value of the field normal diffusion is superimposed to ballistic motion. The diffusion constant can be given explicitly. At the threshold field, the transition between conduction and localization is accompanied by an anomalous diffusion. Our results exemplify that, even in the absence of time-dependent stochastic forces, a purely mechanical model equipped with a quenched disorder can exhibit normal as well as anomalous diffusion, the latter emerging as a critical property. Via another interpretation, as the motion of a particle on an inclined rough surface, our results are relevant for the problem of segregation by flow.

Journal Article↗
PubMed2002

Renal functional reserve is impaired in patients with systemic sclerosis without clinical signs of kidney involvement.

OBJECTIVE: To evaluate the functional response of the kidney to an amino acid challenge (the so called renal functional reserve (RFR)) in patients with systemic sclerosis (SSc) with no clinical sign of renal involvement. METHODS: Before and after an intravenous amino acid load (Freamine III Baxter, 8.5% solution, 4.16 ml/min for two hours), glomerular filtration rate (GFR, as creatinine clearance), effective renal plasma flow (ERPF, as para-aminohyppurate clearance), and calculated total renal vascular resistance (TRVR) were measured in 21 patients with SSc with apparently normal renal function and 10 normal controls. RESULTS: In basal conditions, patients had lower ERPF (403.5 (SD 43.8) v 496.4 (SD 71.3) ml/min, p<0.0002) and higher TRVR (10 822 (SD 2044) v 8874 (SD 1639) dyne/sxcm(-5), p<0.014) than controls. The RFR, evaluated as the percentage increase of GFR after the amino acid load, was significantly reduced in patients with SSc (SSc +1.9 (SD18.6)%, controls +34.8 (SD 13.9)%; p<0.0002). However, the response of patients was not uniform. Multiple regression analysis showed that the RFR was inversely dependent on the patients' mean arterial pressure at admission and basal GFR (R(2)=65%, p<0.0001). CONCLUSIONS: Most patients with SSc cannot increase renal filtration under the challenge of a protein overload. This defective renal response to the amino acid load test sustains the concept of the prevalence of vasoconstrictor over vasodilating factors in the kidney of these patients.

Amino Acids↗
PubMed2001

Transition to stochastic synchronization in spatially extended systems.

Spatially extended dynamical systems, namely coupled map lattices, driven by additive spatio-temporal noise are shown to exhibit stochastic synchronization. In analogy with low-dimensional systems, synchronization can be achieved only if the maximum Lyapunov exponent becomes negative for sufficiently large noise amplitude. Moreover, noise can suppress also the nonlinear mechanism of information propagation, which may be present in the spatially extended system. An example of phase transition is observed when both the linear and the nonlinear mechanisms of information production disappear at the same critical value of the noise amplitude. The corresponding critical properties cannot be estimated numerically with great accuracy, but some general argument suggests that they could be ascribed to the Kardar-Parisi-Zhang universality class. Conversely, when the nonlinear mechanism prevails on the linear one, another type of phase transition to stochastic synchronization occurs. This one is shown to belong to the universality class of directed percolation.

Journal Article↗
PubMed2000

Finite thermal conductivity in 1D lattices

We discuss the thermal conductivity of a chain of coupled rotators, showing that it is the first example of a 1D nonlinear lattice exhibiting normal transport properties in the absence of an on-site potential. Numerical estimates obtained by simulating a chain in contact with two thermal baths at different temperatures are found to be consistent with those based on linear response theory. The dynamics of the Fourier modes provides direct evidence of energy diffusion. The finiteness of the conductivity is traced back to the occurrence of phase jumps. Our conclusions are confirmed by the analysis of two variants of this model.

Journal Article↗
PubMed2000

First-order phase transition in a (1+1)-dimensional nonequilibrium wetting process

A model for nonequilibrium wetting in 1+1 dimensions is introduced. It comprises adsorption and desorption processes with a dynamics that generically does not obey detailed balance. Depending on the rates of the dynamical processes the wetting transition is either of first or second order. It is found that the wet (unbound) and the nonwet (pinned) states coexist and are both thermodynamically stable in a domain of the dynamical parameters that define the model. This is in contrast with equilibrium transitions where coexistence of thermodynamically stable states takes place only on the transition line.

Journal Article↗
PubMed1998

Reproducibility of ambulatory blood pressure monitoring results in pregnancy.

Blood pressure (BP) differences between two consecutive 24-h monitoring periods (P1, P2) were analyzed in 159 hospitalized pregnant women. Reproducibility index, or twice the standard deviation of differences between individual systolic and diastolic means, was better for 24-h (7.8 and 5.8) and daytime (8.7 and 6.3) than for nighttime (12.2 and 9.7) BP means. It did not depend on BP level or gestation week. Alert reaction to monitoring procedure increased BP only in the first 2 h of P1. The high overall reproducibility of ambulatory BP in pregnancy supports the expanding use of the technique also in this condition.

Adult↗
PubMed1996

Simultaneous and sequential same-arm measurements in the validation studies of automated blood pressure measuring devices.

The oscillometric ambulatory blood pressure recorder Daypress 500 was validated according to the British Hypertension Society protocol. Both sequential and simultaneous measurements were used. Multiple regression analysis demonstrated a significant influence of subject pulse pressure and arm circumference on device-observer systolic pressure differences. Differences between observer consecutive readings were inversely related to heart rate. Device and observer blood pressure readings were closer at simultaneous than at sequential measurements. However, both kinds of measurement led to the same final evaluation (A for diastolic and B for systolic blood pressure), provided that the appropriate grading criteria were applied for each method.

Adult↗