Biomedical subjects

V Papavassiliou

Publications and source records attributed to V Papavassiliou.

At least 19 recordsLinked to original sources

PubMed2005

Strange-quark contributions to parity-violating asymmetries in the forward g0 electron-proton scattering experiment.

We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < or =Q2 < or =1.0 GeV2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate nonzero, Q2 dependent, strange-quark contributions and provide new information beyond that obtained in previous experiments.

Journal Article↗

PubMed2004

Hemostatic function and carotid artery disease.

AIM: Since conventional risk factors predict less than one half of future cardiovascular events, other factors that contribute to atherogenesis need to be evaluated. The aim of this study was to investigate whether clotting factors are associated with carotid artery disease. Furthermore, we tried to determine whether clotting factors could be used to predict the risk of cerebrovascular events in patients with internal carotid artery stenosis. METHODS: Twenty-six patients with high-grade (>70%) internal carotid artery stenosis and 43 age-matched controls were evaluated for atherogenic risk factors and hemostatic function. Laboratory tests included plasma assays of fibrinogen, tissue plasminogen activator (TPA), D-dimer, plasminogen activator inhibitor 1 (PAI-1), plasminogen and factor VII:c. Nineteen (72%) patients had history of stroke or transient ischemic attack, while the remaining 7 (28%) were asymptomatic. Statistical analysis was performed using multiple linear regression analysis. RESULTS: Carotid artery stenosis was associated with high levels of TPA (p<0.001), D-dimer (p=0.019) and PAI-1 (p<0.001). No statistically significant correlation was found between the presence of carotid artery disease and the levels of fibrinogen (p=0.28), plasminogen (p=0.96) or factor VII:c (p=0.19). As regards the clinical manifestations, none of the studied clotting factors was correlated with the history of cerebrovascular events in the patients with carotid stenosis. CONCLUSION: The results of this study show that the hemostatic system may play a role in the development of carotid artery atherosclerotic disease, while it does not seem to affect the development of symptoms in patients with carotid stenosis.

Aged↗

PubMed2003

J/psi polarization in 800-GeV p-Cu interactions.

We present measurements of the polarization of the J/psi produced in 800-GeV proton interactions with a copper target. Polarization of the J/psi is sensitive to the ccmacr; production and hadronization processes. A longitudinal polarization is observed at large x(F), while at small x(F) the state is produced essentially unpolarized or slightly transversely polarized. No significant variation of the polarization is observed versus p(T).

Journal Article↗

PubMed2003

Duplicated inferior vena cava and crossed renal ectopia with abdominal aortic aneurysm: preoperative anatomic studies facilitate surgery.

Abdominal aortic aneurysm in association with duplication of the inferior vena cava and crossed renal ectopia is described for the first time. Preoperative imaging with computer-aided tomography provided good visualization of the local anatomy, allowing the surgical approach to be adapted for the best access to the surgical site. A retroperitoneal approach was successfully used for repair of the abdominal aortic aneurysm.

Abnormalities, Multiple↗

PubMed2003

The physiological effects of elevated intra-abdominal pressure following aneurysm repair.

OBJECTIVES: Elevated intra-abdominal pressure (IAP) may cause widespread organ dysfunction (abdominal compartment syndrome) through effects on the respiratory, cardiac, renal and gastro-intestinal systems. The aim of this study was to document IAP following aneurysm surgery, and to determine the effect of IAH on outcome. DESIGN: Prospective observational study. SETTING: University Hospital. SUBJECTS: The patient cohort comprised 75 patients undergoing infra-renal aneurysm repair (53 non-ruptured [40 conventional--1 death, 13 endovascular] and 22 conventionally repaired ruptured AAA--8 deaths). IAP was quantified by bladder manometry at the termination of the procedure and at 24 h intervals in patients who remained intubated. Physiological indices of organ function were recorded. Statistical analysis utilized the unpaired t-test, Fischer's exact test and Pearson's correlation. RESULTS: IAP was significantly higher at abdominal closure following ruptured aneurysm repair (15.4 mmHg [SE 1.6]) than conventional (10.5 [0.89]) or endovascular elective repair (6.4 [1.0]) of non-ruptured AAA. The sensitivity and specificity of IAP to predict subsequent mortality was analysed using a receiver characteristic operating curve. This analysis demonstrated that a cut off of 15 mmHg was the most useful for indicating patients at risk (sensitivity 0.66, specificity 0.79). Physiological indices of organ dysfunction (pH[P = 0.027], base excess [p = 0.005], peak inspiratory pressure [p = 0.0015], CVP and urine output [p = 0.0029]) were significantly impaired in patients with IAP > or = 15 mmHg, in comparison to patients with lower pressures. IAP correlated significantly with indices of cardiac (CVP p = 0.038), respiratory (PaO2/FiO2, p = 0.026), and renal function (urine output p = 0.046). CONCLUSIONS: These data suggest that the management of IAH may have a role following repair of ruptured AAA. High intra-abdominal pressures rarely complicate elective or endovascular aneurysm repair.

Abdomen↗

PubMed2001

Longitudinal electroproduction of charged pions from (1)H, (2)H, and (3)He.

Separated longitudinal and transverse cross sections for charged pion electroproduction from (1)H, (2)H, and (3)He were measured at Q(2) = 0.4 (GeV/c)(2) for two values of the invariant mass, W = 1.15 GeV and W = 1.60 GeV, in a search for a mass dependence which would signal the effect of nuclear pions. This is the first such study that includes recoil momenta significantly above the Fermi surface. The longitudinal cross section, if dominated by the pion-pole process, should be sensitive to nuclear pion currents. Comparisons of the longitudinal cross section target ratios to a quasifree calculation reveal a significant suppression in (3)He at W = 1.60 GeV. The W = 1.15 GeV results are consistent with simple estimates of the effect of nuclear pion currents, but are also consistent with pure quasifree production.

Journal Article↗

PubMed2001

Measurement of the high energy two-body deuteron photodisintegration differential cross section.

The first measurements of the d(gamma,p)n differential cross section at forward angles and photon energies above 4 GeV were performed at the Thomas Jefferson National Accelerator Facility (JLab). The results indicate evidence of an angular dependent scaling threshold. Results at straight theta(cm) = 37 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 4 GeV, while those at 70 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 1.5 GeV.

Journal Article↗

PubMed2001

Observation of polarization in bottomonium production at square root of s = 38.8 GeV.

We present a measurement of the polarization observed for bottomonium states produced in p-Cu collisions at square root of s = 38.8 GeV. The angular distribution of the decay dimuons of the Upsilon(1S) state shows no polarization at small values of the fractional longitudinal momentum x(F) and transverse momentum p(T) but significant positive transverse production polarization for either p(T)>1.8 GeV/c or for x(F)>0.35. The Upsilon(2S+3S) (unresolved) states show a large transverse production polarization at all values of x(F) and p(T) measured. These observations challenge NRQCD calculations of the polarization expected in the hadronic production of bottomonium states.

Journal Article↗

PubMed2000

Measurement of differences between J/psi and psi(') suppression in p-A collisions

Measurements of the suppression of the yield per nucleon of J/psi and psi(') production for 800 GeV/ c protons incident on heavy nuclear targets, relative to light nuclear targets, have been made with very broad coverage in x(F) and p(T). The observed suppression is smallest at x(F) values of 0.25 and below, and increases at larger values of x(F). It is also strongest at small p(T). Substantial differences between psi(') and J/psi production are observed for the first time in p-A collisions. The suppression for psi(') production is stronger than that for J/psi for x(F) near zero, but becomes comparable to that for J/psi for x(F)>0.6.

Journal Article↗

PubMed2000

Aneurysms of the distal branches of the external carotid artery.

Aneurysms of the distal branches of the external carotid artery are rare and usually traumatic in origin. We present two cases which were treated in our clinic. The first case is about a traumatic aneurysm of the left superficial temporal artery (STA) in a young boy 8 years old. The young patient developed a pulsatile mass above his left eyebrow ten days after a bite by a boy of the same age. The second case is referred in a 36-year old woman with a pulsatile mass behind the right ear, which was an aneurysm of the posterior auricular artery. The treatment was ligation and resection under local anesthesia in the first case and under general anesthesia in the latter. Surgeons' familiarity with this entity is important for diagnosis and treatment.

Adult↗

PubMed2000

Internal carotid artery stenosis: rate of progression.

OBJECTIVES: to assess the incidence and the rate of progression of internal carotid artery (ICA) stenosis and to determine the related risk factors. DESIGN: open prospective study. MATERIALS AND METHODS: between 1988-1997, 442 carotid arteries with various degrees of stenosis were followed using colour duplex ultrasonography every 6 months. Of these arteries, 290 (66%) were asymptomatic, 62 (14%) had caused transient ischaemic attack and 90 (20%) a stroke. In 145 cases (33%), there was concomitant coronary artery disease (CAD), in 134 (30%) diabetes mellitus, in 248 (56%) hypertension, in 139 (31%) hypercholesterolaemia and in 370 (84%) history of smoking. Of the plaques, 44 (10%) were uniformly echolucent, 19 (4%) haemorrhagic, 136 (31%) predominantly echolucent, 146 (33%) predominantly echogenic and 97 (22%) uniformly echogenic. RESULTS: significant progression of stenosis occurred in 82 cases (19%). The mean progression rate in these cases was 15% annually (range: 5-50%). There was no statistically significant correlation between the progression of the ICA stenosis and initial neurological status, age, gender, diabetes mellitus, hypertension, hypercholesterolaemia and smoking habit. Stenosis progression was correlated only with CAD and the ultrasonographic characteristics of the plaques. Patients with CAD as well as those with uniformly echolucent plaques presented a higher incidence and rate of stenosis progression (p<0.05). CONCLUSIONS: progression of internal carotid artery stenosis occurred in 19% of cases. The mean progression rate in these patients was 15% annually and was correlated with CAD and the ultrasonographic characteristics of the plaque.

Adult↗

PubMed2000

Changes of the infrarenal aortic segment after conventional abdominal aortic aneurysm repair.

OBJECTIVES: to delineate the natural history of the residual infrarenal aortic segment after conventional abdominal aortic aneurysm (AAA) repair. DESIGN: open prospective study. PATIENTS AND METHODS: between 1990 and 1997, 100 patients, who underwent conventional infrarenal AAA repair at our department, were followed annually by means of colour duplex ultrasonography. Data from 76 patients who had at least 3 scans were analysed. RESULTS: mean duration of follow-up was 4.7 years (range: 3-8 years). The residual infrarenal aorta dilated a mean of 0.57 mm annually. No patient required reoperation. There was no significant correlation between dilatation and any of the recorded risk factors except for the initial neck diameter (p=0.03). CONCLUSIONS: conventional AAA surgery is durable so that surveillance, during the first 5 postoperative years, is not justified in terms of cost-effectiveness. The impact of such a dilatation on endovascular AAA repair requires further investigation.

Aged↗

PubMed1997

Fournier's gangrene: still highly lethal.

Five patients with necrotizing soft tissue infections of the perineum and scrotum are presented. There were one female and four male patients, aged from 35 to 70 years. Portals of entry were perirectal abscesses in four cases and a scrotal abscess in one case. All patients required extensive surgical debridement and intravenous broad-spectrum antibiotics. Operative debridement involved the scrotum, the perineal and inguinal area, the upper thighs and the anterior abdominal wall. One patient required transverse loop colostomy and one loop sigmoidostomy. One patient was reoperated on after inadequate drainage of a perirectal abscess. Three patients were referred to our unit after some delay, while one patient did not seek medical care until after being febrile for 2 weeks. Despite aggressive debridement, this last patient died of fulminant sepsis. Fournier's gangrene, which is not so rare as in generally considered, is still associated with a high mortality, which can be reduced only by improving medical awareness and early treatment both of the primary cause and of necrotizing fasciitis.

Adult↗

PubMed1996