Biomedical subjects

G Porenta

Publications and source records attributed to G Porenta.

40 records · Page 3Linked to original sources

PubMed1987

Platelet deposition at angioplasty sites and platelet survival time after PTA in iliac and femoral arteries: investigations with indium-111-oxine labelled platelets in patients with ASA (1.0 g/day)-therapy.

In this study we have assessed the deposition of 111-In-oxine-labelled platelets--using a dual radiotracer method--at angioplasty sites of the lower extremities in 20 patients (14 male, 6 female; median age: 60 years) with ASA (1.0 g/day)-therapy. The platelet survival time (PST)--using the multiple hit model--was evaluated before and after percutaneous transluminal angioplasty, and we also measured the plasma levels of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF 4) before and after PTA. Before PTA, scintigraphy was positive in only one patient, while 24 hours after PTA a positive scintigraphic result was observed in 16/20 patients. The median target/non target-ratio was 1.0 (0.66-1.3) before PTA, and this ratio increased significantly (p less than 0.0005) to 1.53 (1.0-3.3) after PTA. The median PST decreased significantly (185.0 hours before PTA----145.2 hours after PTA; p less than 0.001), while the median platelet turnover increased from 34,000/microliter/day to 47,900/microliter/day (p less than 0.01). The median plasma levels of the platelet specific proteins increased significantly immediately after PTA (p less than 0.001), but one day later they were not significantly different from the pretreatment values. The quantitative methods used in this study seem a valuable tool to evaluate the effects of different therapeutical--especially antiplatelet--interventions after PTA in humans, thus helping to find the best antithrombotic regimen for this widely used therapeutical procedure.

Adult↗

PubMed1986

A computer model of neuronal pathways in the basal ganglia.

Disorders of the basal ganglia and the extrapyramidal motor system exhibit an imbalance of neurotransmitter concentrations in affected neurons. For three synapses with dopamine, acetylcholine, and gamma-amino butyric acid (GABA), mathematical models of synaptic transmission are developed. To describe the kinetics of transmitter substances, compartment analysis is used. Membrane potential behaviour is described by the Hodgkin-Huxley equations with an additional equation accounting for a presynaptic calcium current mediating transmitter release. At the postsynaptic site, activated receptor molecules control the activity of ion channels, eliciting either inhibitory or excitatory postsynaptic potentials. A simple model of the feedback loop connecting the caudate nucleus and the substantia nigra is simulated on a digital computer using the simulation language ACSL. A comparison of the control case with a model of Parkinson's disease shows a shift of eigenvalues towards zero in the diseased state.

Acetylcholine↗

PubMed1986

A finite-element model of blood flow in arteries including taper, branches, and obstructions.

A nonlinear mathematical model of arterial blood flow, which can account for tapering, branching, and the presence of stenosed segments, is presented. With the finite-element method, the model equations are transformed into a system of algebraic equations that can be solved on a high-speed digital computer to yield values of pressure and volume rate of flow as functions of time and arterial position. A model of the human femoral artery is used to compare the effects of linear and nonlinear modeling. During periods of rapid alternations in pressure or flow, the nonlinear model shows significantly different results than the linear model. The effect of a stenosis on pressure and flow waveforms is also simulated, and the results indicate that these waveforms are significantly altered by moderate and severe stenoses.

Arteries↗

PubMedDate not supplied

Functional assessment of coronary arteries by poststenotic intravascular Doppler ultrasound.

This study sought to delineate the impact of the rate pressure product on intraluminal Doppler velocity measurements and to determine the relation between poststenotic vasodilator reserve and percent luminal obstruction in coronary vessels. Twenty patients with single-vessel coronary disease were studied prior to coronary angioplasty and at follow-up 6 months later. Intracoronary velocity reserve after administration of adenosine was measured distal to the stenosis with a Doppler-tipped guide wire and was compared to quantitative coronary angiography and adenosine myocardial perfusion scintigraphy. The rate pressure product was confirmed as significant covariate (ANCOVA, p < 0.005) of intracoronary Doppler reserve. When normalized to rate pressure product, poststenotic Doppler velocity reserve in stenosed arteries was significantly lower than in patent arteries as classified by quantitative coronary angiography (1.7 +/- 0.6 vs. 2.9 +/- 0.5, p < 0.001) and perfusion scintigraphy (1.5 +/- 0.4 vs. 2.8 +/- 0.5, p < 0.001). Normalized Doppler velocity reserve showed a nonlinear but highly significant relation to percent area stenosis [y = 3.0.(1 - exp[0.081 (x - 100)]), p < 0.001]. When normalized Doppler velocity reserve was less than 2.0, coronary disease was identified with 95% specificity and 94% sensitivity in comparison to perfusion scintigraphy. Thus, in coronary arteries poststenotic Doppler reserve and percent area stenosis show a significant nonlinear relation. Doppler velocity reserve when normalized to rate pressure product can be used to characterize the hemodynamic impact of coronary obstructions.

Adenosine↗