PubMed Health⌕ Search

Biomedical subjects

M Nastasi

Publications and source records attributed to M Nastasi.

At least 19 recordsLinked to original sources
PubMed2002

Molecular dynamics simulation of brittle fracture in silicon.

Brittle fracture in silicon is simulated with molecular dynamics utilizing a modified embedded atom method potential. The simulations produce propagating crack speeds that are in agreement with previous experimental results over a large range of fracture energy. The dynamic fracture toughness is found to be equal to the energy consumed by creating surfaces and lattice defects in agreement with theoretical predictions. The dynamic fracture toughness is approximately 1/3 of the static strain energy release rate, which results in a limiting crack speed of 2/3 of the Rayleigh wave speed.

Journal Article↗
PubMed2001

Electrogram width parameter analysis in implantable cardioverter defibrillators: Influence of body position and electrode configuration.

The "EGM width criterion" is a discrimination algorithm that was available in the last generation ICDs. It improved ventricular tachycardia detection by withholding inappropriate therapy deliveries in the presence of narrow QRS tachycardias. The accuracy of the algorithm depends on the optimal settings of the intracardiac EGM source, the "slew thresholds," and the "width threshold." The possible dependence of these parameters on body position may affect the detection efficacy. Whether these effects can be minimized by a proper choice of the electrode configuration used for signal analysis is still to be investigated. This study aimed to evaluate the stability of the slew threshold and width threshold obtained in the supine and orthostatic positions detected by the tip-to-ventricular coil and can-to-ventricular coil electrode configurations. Their time dependence was also evaluated at the 6-month follow-up. Fifty-eight patients who were recipients of an ICD (model Medtronic 7223cx and 7227cx) were included in the study. Changing from supine to orthostatic position caused a marked variation of slew and width thresholds (21.0 +/- 13.9 V/s and 10.1 +/- 9.6 ms, respectively) in 36% of patients with tip-to-ventricular coil and in 44% of patients with can-to-defibrillating coil (the mean slew threshold variation was in this case 17.6 +/- 15.8 V/s, while the mean width threshold variation was 18.8 +/- 21.0 ms). Width threshold variation was statistically significant (P < 0.02) with the latter electrode configuration. Slew thresholds settings changed between the 1- and 6-month follow-ups in the 75% of patients with can-to-defibrillating coil configuration and in 50% with tip-to-defibrillating coil. These time related variations were significantly larger with the tip-to-defibrillating coil configuration (P < 0.01). In conclusion, EGM width parameters may change between supine and orthostatic position and over time with tip-to-defibrillating coil configuration and can-to-defibrillating coil configuration. The former configuration was less sensitive to body position changes, but more sensitive to time related variations. These findings may be useful for optimal programming of the EGM width criterion, but if parameter programming based on these results can improve the discrimination specificity still needs to be investigated.

Aged↗
PubMed2000

Latest generation of unipolar and bipolar steroid eluting leads: long-term comparison of electrical performance in atrium and ventricles.

One hundred and seventy-three patients, mean age 74 years permanently paced with 123 atrial (53 unipolar, 70 bipolar) and 143 ventricular (73 unipolar, 70 bipolar) pacing leads were included in this study. The pacing leads were recent generation low surface area steroid eluting leads from one manufacturer: leads with silicone and polyurethane insulation were studied, and they were combined with generations of one pacemaker family from the same manufacturer permitting identical measurements to be made over a follow-up of 2 years. Pacing threshold was measured using pulse duration at a fixed voltage of 1.5 V: peak to peak P and R wave amplitude and pacing impedance at 2.5 V and 0.5 ms were all measured using the manufacturer's standard programmer. Although many significant differences, in the parameters measures, existed between atrium and ventricle and unipolar and bipolar configurations, none was felt to be of clinical significance. These data permit the physician to choose the lead type with regard to sensing performance and long-term lead integrity.

Adult↗
PubMed1996

Novel lipid-lowering properties of Vaccinium myrtillus L. leaves, a traditional antidiabetic treatment, in several models of rat dyslipidaemia: a comparison with ciprofibrate.

Vaccinium myrtillus L. (blueberry) leaf infusions are traditionally used as a folk medicine treatment of diabetes. To further define this therapeutical action, a dried hydroalcoholic extract of the leaf was administered orally to streptozotocin-diabetic rats for 4 days. Plasma glucose levels were consistently found to drop by about 26% at two different stages of diabetes. Unexpectedly, plasma triglyceride (TG) were also decreased by 39% following treatment. Subsequent to the latter observation, possible lipid-lowering properties of the extract were investigated on other models of hyperlipidaemia and ciprofibrate, a well-established hypolipidaemic drug, was used as a reference compound. Both drug reduced TG levels of rats on hyperlipidaemic diet in a dose-dependent fashion. When administered at single doses over the same experimental period, blueberry and ciprofibrate were effective in lowering TG concentrations in ethanol-treated normolipidaemic animals and in genetically hyperlipidaemic Yoshida rats. Unlike ciprofibrate, however, blueberry failed to prevent the rise in plasma TG elicited by fructose and did not affect free fatty acid levels in any of the above experimental conditions. In rats treated with Triton WR-1339, blueberry feeding induced an hypolipidaemic activity one hour after injection but proved to be ineffective at later time points, thus suggesting that its hypolipidaemic action may reflect improved TG-rich lipoprotein catabolism. In addition, ciprofibrate and the extract were tested for antithrombotic activity using a collagen-triggered model of venous thrombosis in diabetic and Yoshida rats. Only ciprofibrate, however, significantly reduced thrombus formation in diabetics, possibly because of its effects on free fatty acid metabolism, whereas no effect was observed in Yoshida rats. In conclusion, the present findings indicate that active consituent(s) of Vaccinium myrtillus L. leaves may prove potentially useful for treatment of dyslipidaemiae associated with impaired TG-rich lipoprotein clearance.

Animals↗
PubMed1995

[Complications of pediatric anesthesia. Survey carried out by the Study Group SIAARTI for anesthesia and intensive therapy in children].

This study was designed to asses in a prospective survey the intra and post-operative adverse outcome of paediatric patients in Italy. The data was carried out in representative samples of anaesthetics performed in different Italian Institutions, which were chosen by the National Study Group for Paediatric Anaesthesia, and included: paediatric, general, specialistic hospitals and departments. A total of 9289 anaesthetics were collected and studied. The mean age of the patients was 62.5 months. In the 320 cases (3.4%) 299 minor (3.2%) and 21 major (0.2%) complications occurred during or within 24 hours of surgery and anaesthesia. Seven of the major complications resulted in the exitus of the patients (0.07%). Fifty percent of the accidents regarded respiratory and twenty percent cardiovascular systems. The major incidence (risk factors) of the minor complications was present in patients less than 6 months, ASA group 2-3-4, emergency surgery, patients with associated pathology, long duration of anaesthesia and high risk operations. The incidence of the major complications appears closely related to: patients age and clinical assessment, weight, ASA group, kind of the operation, indications and durations of the surgery, while in the exitus group the major risk factor is the preoperative pathology, surgical procedures, and then: age, weight, ASA and finally surgery.

Anesthesia↗
PubMed1987

[Supravalvular aortic stenosis. Analysis of a surgical series of 8 patients].

Supravalvular aortic stenosis (SAS) is an unusual form of progressive left ventricular outflow tract (LVOT) obstruction, frequently associated with others vascular and physical anomalies. Between July 1980 and July 1986 eight such patients have been operated upon. In seven patients patch aortoplasty (according to McGoon or Doty technique) relieved the stenosis; in one, a two years old boy, with associated severe hypoplasia of the ascending aorta and aortic arch, a left ventricle (LV) - abdominal aorta valved conduit was associated to aortoplasty. One patient died in the operating room with a severe anterior myocardial infarction; seven patients are in good clinical condition at a mean follow-up of 32 months. The aortic supravalvular gradient was dramatically reduced in all patients according with Doppler echocardiography. In our mind, patients with SAS would benefit from an early surgical repair, because of progressive involvement of the aortic valve, coronary arteries and LV. The surgical technique is strictly related to the anatomical situations. Per and postoperative management should rely on the pathophysiology peculiar to this malformation (especially about coronary perfusion). Taking care to these points, the surgical results at a mid term follow-up are now very satisfactory in this cardiac malformation.

Adolescent↗
PubMed1981

[Postoperative hypertension in the surgery of the large arteries].

High incidence of postoperative arterial hypertension, confined to the first 24-48 hours and independent of the preoperative pressure situation, has been noted in patients following vascular surgery. The phenomenon is more frequent in patients whose angiosclerotic symptomatology goes back more than 2 years, and in those in whom preoperative investigation showed high daily variability in measured values, always however within non-pathological limits. Analysis of possible intraoperative pathogenetic factors in postoperative hypertension reveals a significant relationship between this phenomenon and inhalatory anesthesia, particularly with fluothane and curarization with D-tubocurarine. Co-responsibility of respiratory factors, particularly hypercapnia, has never been documented by haemogasanalysis. As for the pathogenetic mechanisms responsible for this type of hypertension, measurement of urinary catecholamines has revealed a close relationship between the two phenomena. The same investigation, extended to a wider group of patients, showed that by comparison with patients submitted to balanced anaesthesia, those who had received inhalatory anaesthesia with fluothane show, with much greater frequency, increased urinary elimination of catecholamines during the operation and for 24-48 hours afterwards. Catecholaminic hyperincretion, more frequent in fluothane anaesthesia, thus seems to be an important pathogenetic factor in these hypertensive manifestations in which the angiosclerotic medium presumably acts as an amplifier.

Anesthesia↗