Biomedical subjects

Walter Silva

Publications and source records attributed to Walter Silva.

6 recordsLinked to original sources

PubMed2007

Functional properties of fresh and cryopreserved carotid and femoral arteries, and of venous and synthetic grafts: comparison with arteries from normotensive and hypertensive patients.

The ideal arterial graft must share identical functional properties with the host artery. Surgical reconstruction of the common carotid artery (CA) is performed in several clinical situations, using expanded polytetrafluoroethylene prosthesis (ePTFE) or saphenous vein (SV) grafts. At date there is interest in obtaining an arterial graft that improves the results of that nowadays available. The use of a fresh or cryopreserved/defrosted artery appears as an interesting alternative. However, if the fresh and cryopreserved/defrosted arteries allow an adequate viscoelastic and functional matching with the host arteries needs to be established. The aims were to compare the viscoelastic and functional performance of: (1) conduits used in CA reconstruction (SV and ePTFE) with those of the fresh and cryopreserved/ defrosted CA and femoral arteries (FA), and (2) normotensive and hypertensive patients' arteries with those of the arterial substitutes in vitro analyzed. Pressure, diameter and wall thickness of the CA were recorded in 15 normotensive and 15 hypertensive patients (in vivo studies), and in SV, fresh and cryopreserved/defrosted CA and FA (obtained from 15 donors), and ePTFE segments (in vitro studies). From stress-strain relationship we calculated elastic and viscous modulus, and the characteristic impedance. The local buffer and conduit functions were quantified as the viscous/elastic quotient and the inverse of the characteristic impedance. Fresh and cryopreserved/defrosted CA and FA were more alike, both in viscoelastic and functional levels, respect to normotensive and hypertensive patients' arteries, than the ePTFE and SV grafts. CA and FA cryografts could be considered an important alternative for carotid reconstruction.

Adult↗

PubMed2006

Cryopreservation procedure does not modify human carotid homografts mechanical properties: an isobaric and dynamic analysis.

The viscoelastic and inertial properties of the arterial wall are responsible for the arterial functional role in the cardiovascular system. Cryopreservation is widely used to preserve blood vessels for vascular reconstruction but it is controversially suspected to affect the dynamic behaviour of these allografts. The aim of this work was to assess the cryopreservation's effects on human arteries mechanical properties. Common carotid artery (CCA) segments harvested from donors were divided into two groups: Fresh (n = 18), tested for 24-48 h after harvesting, and Cryopreserved (n = 18) for an average time of 30 days in gas-nitrogen phase, and finally defrosted. Each segment was tested in a circulation mock, and its pressure and diameter were registered at similar pump frequency, pulse and mean pressure levels, including those of normotensive and hypertensive conditions. A compliance transfer function (diameter/pressure) derived from a mathematical adaptive modelling was designed for the on line assessment of the arterial wall dynamics and its frequency response. Assessment of arterial wall dynamics was made by measuring its viscous (eta), inertial (M) and elastic (E) properties, and creep and stress relaxation time constant (tauC and tauSR, respectively). The frequency response characterization allowed to evaluate the arterial wall filter or buffer function. Results showed that non-significant differences exist between wall dynamics and buffer function of fresh and cryopreserved segments of human CCA. In conclusion, our cryopreservation method maintains arterial wall functional properties, close to their fresh values.

Carotid Arteries↗

PubMed2005

Automatic detection of interictal spikes using data mining models.

A prospective candidate for epilepsy surgery is studied both the ictal and interictal spikes (IS) to determine the localization of the epileptogenic zone. In this work, data mining (DM) classification techniques were utilized to build an automatic detection model. The selected DM algorithms are: Decision Trees (J 4.8), and Statistical Bayesian Classifier (naïve model). The main objective was the detection of IS, isolating them from the EEG's base activity. On the other hand, DM has an attractive advantage in such applications, in that the recognition of epileptic discharges does not need a clear definition of spike morphology. Furthermore, previously 'unseen' patterns could be recognized by the DM with proper 'training'. The results obtained showed that the efficacy of the selected DM algorithms is comparable to the current visual analysis used by the experts. Moreover, DM is faster than the time required for the visual analysis of the EEG. So this tool can assist the experts by facilitating the analysis of a patient's information, and reducing the time and effort required in the process.

Action Potentials↗

PubMed2005

Nephron-sparing surgery for renal tumours using selective renal parenchymal clamping.

OBJECTIVE: To describe a technical modification that facilitates nephron-sparing surgery (NSS) for renal tumours, without clamping the renal pedicle or promoting renal surface hypothermia. PATIENTS AND METHODS: Seventeen patients with renal tumours had NSS using the selective renal-parenchymal clamping technique. In 11 patients the tumour was polar and in six it was central. The mean (range) size of the tumours was 3.6 (2-6) cm. The technique was performed using one or two large Satinsky vascular clamps. Time was not limited as there was no clamping of the renal pedicle, or renal hypothermia. RESULTS: The mean (range) operative duration was 190 (120-300) min. Only one patient needed a blood transfusion. There were no complications in 13 patients after NSS. The mean (range) hospital stay was 5 (3-12) days. The pathological examination detected malignant tumours in 13 patients, and a microscopic examination showed adequate surgical margins in all. The mean (range) follow-up was 24.5 (4-60) months. No patients required haemodialysis immediately after surgery or later. CONCLUSIONS: Selective renal parenchymal clamping is a simple and efficient technical manoeuvre that facilitates NSS without dissection or clamping of the renal pedicle. Time is not limited as the ischaemia is limited to the tissue surrounding the tumour. The operative duration and blood loss are acceptable and the complications similar to those with the conventional technique. The size and position of the tumour could be limiting factors to this technique.

Adult↗

PubMed2003

Mesial temporal lobe epilepsy and hippocampal sclerosis: cognitive function assessment in Hispanic patients.

PURPOSE: The goal of this study was to assess the cognitive function status in patients with mesial temporal lobe epilepsy and hippocampal sclerosis (TLE+HS) to determine their cognitive function profile and to correlate material-specific memory deficits with HS laterality diagnosed by MRI. METHODS: Seventy-one patients were assessed with a neuropsychological protocol that includes IQ, attention, handedness, verbal memory, visual memory, language, and the executive function. chi(2) and correlation tests were used. RESULTS: Memory impairment was found in 46 patients (66%): patients without any memory deficit (n=25), patients with verbal memory deficit (n=21), patients with visual memory deficit (n=17), patients with deficit for both types of memory (n=8). Correlation between MRI lesion and memory was 66%. Language was impaired in 33 patients (46%). Eighteen patients (25%) had a deficit of the executive function. CONCLUSIONS: Patients with TLE+HS presented with a deficit in material-specific episodic memory correlating in large proportion with HS lateralization. We also found language and executive function impairments.

Adult↗

PubMed2003

Progress of National Multi-tissue Bank in Uruguay in the International Atomic Energy Agency (IAEA) Tissue Banking Programme.

The transplant law of 1971 based on informed consent, allows people to register their willingness to be a donor upon death. Since 1978 the governmental Institution, the National Bank of Organs and Tissues (BNOT), have been regulated the organ and tissue donation. Important progress was implemented in the BNOT and specially in the National Multi-tissue Bank (NMTB). Since 2001 with the participation in the IAEA Tissue Banking Programme, Quality System Management has been implemented in the NMTB. New bio-production for radiosterilized tissues for the first time and improved procedures were carried out. As a result an increased production of high-quality tissues was obtained and distributed for clinical use.

Journal Article↗