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Biomedical subjects

M A Weber

Publications and source records attributed to M A Weber.

At least 19 recordsLinked to original sources
PubMed2006

Diagnostic performance of spectroscopic and perfusion MRI for distinction of brain tumors.

OBJECTIVE: To assess the value of spectroscopic and perfusion MRI for glioma grading and for distinguishing glioblastomas from metastases and from CNS lymphomas. METHODS: The authors examined 79 consecutive patients with first detection of a brain neoplasm on nonenhanced CT scans and no therapy prior to evaluation. Spectroscopic MRI; arterial spin-labeling MRI for measuring cerebral blood flow (CBF); first-pass dynamic, susceptibility-weighted, contrast-enhanced MRI for measuring cerebral blood volume; and T1-weighted dynamic contrast-enhanced MRI were performed. Receiver operating characteristic analysis was performed, and optimum thresholds for tumor classification and glioma grading were determined. RESULTS: Perfusion MRI had a higher diagnostic performance than spectroscopic MRI. Because of a significantly higher tumor blood flow in glioblastomas compared with CNS lymphomas, a threshold value of 1.2 for CBF provided sensitivity of 97%, specificity of 80%, positive predictive value (PPV) of 94%, and negative predictive value (NPV) of 89%. Because CBF was significantly higher in peritumoral nonenhancing T2-hyperintense regions of glioblastomas compared with metastases, a threshold value of 0.5 for CBF provided sensitivity, specificity, PPV, and NPV of 100%, 71%, 94%, and 100%. Glioblastomas had the highest tumor blood flow values among all other glioma grades. For discrimination of glioblastomas from grade 3 gliomas, sensitivity was 97%, specificity was 50%, PPV was 84%, and NPV was 86% (CBF threshold value of 1.4), and for discrimination of glioblastomas from grade 2 gliomas, sensitivity was 94%, specificity was 78%, PPV was 94%, and NPV was 78% (CBF threshold value of 1.6). CONCLUSION: Perfusion MRI is predictive in distinguishing glioblastomas from metastases, CNS lymphomas and other gliomas vs MRI and magnetic resonance spectroscopy.

Brain Neoplasms↗
PubMed2006

Rationale and design of a study to evaluate management of proteinuria in patients at high risk for vascular events: the IMPROVE trial.

Declining kidney function predicts increasing cardiovascular risk in people with hypertension. Microalbuminuria is a marker for cardiovascular risk and declining kidney function. Agents that block the renin-angiotensin-aldosterone system (RAAS), notably angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs), reduce proteinuria and microalbuminuria, lower blood pressure and slow the progression of proteinuric kidney disease. Evidence is accumulating that the combination of an ACE inhibitor and an ARB is the optimal means of RAAS blockade in this setting, slowing the progression of nephropathy independently of blood pressure lowering to a greater degree than can be achieved using maximum approved doses of either agent alone. However, the emerging therapeutic potential of ACE inhibitor/ARB combination therapy in hypertensive kidney disease requires further characterization. The Irbesartan in the Management of PROteinuric patients at high risk for Vascular Events trial aims to determine definitively whether the combination therapy of an ARB, irbesartan and an ACE inhibitor, ramipril, is more effective than ramipril alone in reducing the urinary albumin excretion rate in patients at high cardiovascular risk with hypertension and proteinuria or microalbuminuria.

Angiotensin Receptor Antagonists↗
PubMed2006

Effects of a structured treatment algorithm on blood pressure goal rates in both stage 1 and stage 2 hypertension.

This study analysed the efficacy of an angiotensin receptor blocker-based treatment algorithm for achieving goal blood pressure (BP) in patients with stage 1 (systolic BP (SBP) 140-159 mmHg or diastolic BP (DBP) 90-99 mmHg) or stage 2 (SBP > or = 160 mmHg or DBP > or = 100 mmHg) hypertension. In this 24-week, open-label, multicentre study, patients followed a six-step algorithm until goal BP (< or = 130/85 mmHg) was attained. Initially, olmesartan medoxomil 20 mg/day was administered for 4 weeks. The regimen was modified every 4 weeks until goal BP was attained: increase olmesartan medoxomil to 40 mg/day; add hydrochlorothiazide (HCTZ) 12.5 mg/day; increase HCTZ to 25 mg/day; add amlodipine besylate 5 mg/day; increase amlodipine besylate to 10 mg/day. In patients with stage 1 hypertension, 80% (63/79) and 56% (44/79) achieved BP goals of < or = 140/90 mmHg and < or = 130/85 mmHg, respectively, with olmesartan medoxomil monotherapy (94% (74/79) and 89% (70/79) with olmesartan medoxomil/HCTZ double therapy, and 96% (76/79) and 98% (77/79) with addition of amlodipine besylate (triple therapy)). Mean SBP/DBP reductions were 16.7/11.6, 24.8/15.8, and 26.4/16.5 mmHg for mono-, double-, and triple-therapy, respectively. In patients with stage 2 hypertension, 42% (42/100) and 19% (19/100) achieved BP goals of < or = 140/90 mmHg and < or = 130/85 mmHg, respectively, with monotherapy (75% (75/100) and 54% (54/100) with double therapy, and 90% (90/100) and 81% (81/100) with triple-therapy). Mean SBP/DBP reductions in stage 2 patients were 18.4/10.0, 32.7/16.3, and 39.1/19.4 mmHg for mono-, double, and triple therapy, respectively. Overall, most patients with stage 1 or stage 2 hypertension achieved goal BP.

Adult↗
PubMed2005

Angiotensin-II receptor blockers: benefits beyond blood pressure reduction?

Effective treatment of hypertension is essential to reduce the risk of renal and cardiovascular (CV) morbidity. The risks associated with hypertension are modulated by the presence of other factors. This has prompted the quest for agents that have benefits beyond blood pressure (BP) lowering. The angiotensin II receptor blocker (ARB) class of antihypertensive agents represents an important addition to the therapeutic options for elevated BP. Their ability to control BP is equivalent to existing therapies and there is a considerable and mounting evidence-base for their ability to reduce hypertension-associated target organ damage and comorbidities. Studies show that ARBs have clinical benefits across the spectrum of disease severity. In particular, recent large studies have demonstrated that these benefits extend to patients with conditions predisposing to CV events, such as diabetes, left ventricular hypertrophy and microalbuminuria, and where risk factors coexist. Data from these studies suggest that the CV protective effects of ARBs are at least, in part, independent from the BP lowering action. In addition, ARBs are extremely well tolerated, and strong evidence suggests that compliance with therapy--a key factor in achieving adequate BP control--with ARBs is higher than with other antihypertensive agents. Furthermore, flexible dosing and good tolerability profile mean that, where necessary, ARBs can be combined with other classes of antihypertensive agents to achieve adequate BP control and reduce the risk of hypertension-associated morbidity.

Angiotensin II Type 1 Receptor Blockers↗
PubMed2005

[MR-based methods of the functional imaging of the central nervous system].

This review presents the basic principles of functional imaging of the central nervous system utilizing magnetic resonance imaging. The focus is set on visualization of different functional aspects of the brain and related pathologies. Additionally, clinical cases are presented to illustrate the applications of functional imaging techniques in the clinical setting. The relevant physics and physiology of contrast-enhanced and non-contrast-enhanced methods are discussed. The two main functional MR techniques requiring contrast-enhancement are dynamic T1- and T2*-MRI to image perfusion. Based on different pharmacokinetic models of contrast enhancement diagnostic applications for neurology and radio-oncology are discussed. The functional non-contrast enhanced imaging techniques are based on "blood oxygenation level dependent (BOLD)-fMRI and arterial spin labeling (ASL) technique. They have gained clinical impact particularly in the fields of psychiatry and neurosurgery.

Animals↗
PubMed2005

In-hospital time to treatment of patients with acute ST elevation myocardial infarction treated with primary angioplasty: determinants and outcome. Results from the registry of percutaneous coronary interventions in acute myocardial infarction of the Arbeitsgemeinschaft Leitender Kardiologischer Krankenhausarzte.

OBJECTIVE: To determine the predictors of time between presentation and primary angioplasty and the influence of this delay time on in-hospital mortality in clinical practice. DESIGN: Analysis of data from the registry of percutaneous coronary interventions in acute myocardial infarction of the Arbeitsgemeinschaft Leitender Kardiologischer Krankenhausärzte (ALKK). PATIENTS: Data of 4815 patients registered at 80 hospitals between 1994 and 2000 were analysed. RESULTS: Mean age of the patients was 61.4 (12.5) years. Cardiogenic shock was present in 14.1%. Mean time from admission to primary angioplasty ("door to angiography" time) was 83 (122) minutes. Logistic regression analysis showed the presence of a bundle branch block (odds ratio (OR) 1.95, 95% confidence interval (CI) 1.15 to 3.29), prior coronary artery bypass grafting (OR 1.67, 95% CI 1.08 to 2.59), pre-hospital delay > 3 hours (OR 1.61, 95% CI 1.37 to 1.89), and female sex (OR 1.21, 95% CI 1.01 to 1.45) to be independently associated with longer door to angiography times, whereas a higher hospital volume of performing primary angioplasty (OR 0.53, 95% CI 0.46 to 0.62) and the year of the investigation (OR 0.96, 95% CI 0.92 to 1.00) were independently associated with shorter door to angiography times. Independent predictors of in-hospital mortality were cardiogenic shock (41.6% v 4.0% without cardiogenic shock, p < 0.0001), technical success (29.2% with TIMI (thrombolysis in myocardial infarction) flow < 3 v 6.5% with TIMI flow 3, p < 0.0001), age (16.5% > or = 70 years v 6.6% < 70, p < 0.0001), three vessel disease (16.5% v 6.8% with < 3 vessel disease, p < 0.0001), anterior location of infarction (12% v 7.4% without anterior infarction, p < 0.0001), year of inclusion (adjusted OR 0.92 per year, p = 0.011), and volume of primary angioplasty at the hospital (11% for < 20 angioplasty procedures/year v 8.3% for > or = 20/year, p = 0.027) but not the door to angiography time (adjusted OR 1.14 per tertile, p = 0.397). CONCLUSIONS: In current clinical practice in Germany median door to angiography time is quite short (83 (122) minutes). Some patients and hospital factors are independently associated with a longer door to angiography time. Within the observed short in-hospital delays door to angiography time did not influence in-hospital mortality. However, efforts to keep them as short as possible should be continued.

Angioplasty, Balloon, Coronary↗
PubMed2003

[Functional magnetic resonance imaging and dementia].

Currently, different cerebral neuroimaging methods are being applied to varying questions in the diagnosis of dementia. In patients with manifest Alzheimer's disease a reduction of cortical perfusion and metabolism in temporal and temporoparietal regions has been demonstrated when compared to healthy controls on a diversity of memory tasks. Since differing levels of performance and varying degrees of cortical atrophy may influence functional results considerably, an understanding of the processes associated with normal ageing is perceived as prerequisite for studies applying functional neuroimaging. The integration of knowledge concerning neuropsychological and neurobiological alterations associated with healthy ageing allows hypotheses for the differentiation of pathological ageing processes to be phrased. In this connection non-invasive methods such as fMRI and ASL are of increasing importance.

Adult↗
PubMed2002

[Magnetic resonance tomography of xanthogranulomatous pyelonephritis. Epidemiology, pathogenesis and symptoms].

Xanthogranulomatous pyelonephritis (XGP) is a rare chronic infection of the kidney. In this overview article we reevaluated the magnetic resonance imaging (MRI) findings of our four patients with histologically proven XGP and correlated them with the CT and ultrasound findings described in the literature. Additionally, we give an overview of the pathogenesis and epidemiology. The following criteria were found in MRI: hydronephrosis and/or urethral stricture, vesicoureteral reflux or neurogenic bladder depletion disorders, and calculus as the origin of urinary obstruction. Moreover, in contrast to normal pyelonephritis, XGP is accompanied by fatty deposits in the peripelvic parenchyma, which demonstrate contrast enhancement and form the typical so-called bear paw sign. As XGP is often accompanied by severe kidney failure, contrast-enhanced CT with nephrotoxic contrast agents should be avoided and MRI should be performed instead. Because of proven reduced nephrotoxicity of gadolinium chelates, MRI seems to be superior to CT in patients with suspected XGP. Essential for the correct diagnosis is consideration of the complete medical history including recurrent pyelonephritis to avoid malpractice.

Adolescent↗
PubMed2002

Post-natal development of the rat testis: steroid hormone receptor distribution and extracellular matrix deposition.

The control of testicular development and differentiation depends on hormones and a variety of cell-cell interactions mediated mainly by paracrine factors. In the second and third weeks of post-natal development important changes take place in the rat testis, e.g. the tubular lumen starts to open on post-natal day 10, the blood-testis barrier starts to form on day 15, and Sertoli cell proliferation ceases on day 15. In the present study the expression in different testicular compartments of the androgen receptor (AR), progesterone receptor (PR), and extracellular matrix proteins such as laminin, entactin-1 (nidogen-1) and fibronectin, during post-natal development was examined using immunohistochemistry and semiquantitative image analysis. An intratubular AR peak on days 14-17, an increase in intratubular PR expression on days 14-16, and an increase in peritubular entactin-1 expression during the second and third weeks post-partum are demonstrated. These results suggest that a variety of changes occur at the cellular level during this period when certain milestones of testicular development occur, substantiating the hypothesis of a particular role for paracrine interactions during the development of the rat testis.

Aging↗
PubMed2001

Vasopeptidase inhibitors.

Vasopeptidase inhibitors are a new class of cardiovascular drug that simultaneously inhibit both neutral endopeptidase and angiotensin-converting enzyme (ACE). They increase the availability of peptides that have vasodilatory and other vascular effects; they also inhibit production of angiotensin II. In animal models vasopeptidase inhibitors decrease blood pressure in low, medium, and high renin forms of hypertension, and they also appear to confer benefits in models of heart failure and ischaemic heart disease. Studies in human hypertension show that these agents are effective in decreasing blood pressure regardless of race or age. Experience with omapatrilat, the most clinically advanced of these drugs, has shown it to be more effective than currently available ACE inhibitors or other widely used antihypertensive agents. Studies with omapatrilat in congestive heart failure have shown beneficial effects on haemodynamics and symptoms. The vasopeptidase inhibitors appear to have safety profiles similar to ACE inhibitors, though the frequency of side-effects such as angio-oedema and cough remains to be established. Large trials with clinical endpoints, some already in progress, are needed to establish the place of this class of drug beside that of established therapies in conditions such as hypertension, heart failure, ischaemic heart disease, and nephropathy.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2001

Incidence, risk factors, and clinical outcome of stroke after acute myocardial infarction in clinical practice. MIR and MITRA Study Groups. Myocardial Infarction Registry. Maximal Individual Therapy in Acute Myocardial Infarction .

In this analysis of ischemic and hemorrhagic strokes after acute myocardial infarction (AMI) in 21,330 consecutively included patients with AMI, we found an incidence of stroke after AMI of 1.2% and a very poor prognosis. Previous stroke, atrial fibrillation, and older age were the strongest predictors of stroke after AMI; thrombolysis was a borderline risk factor and early therapy with aspirin was associated with a reduction in stroke after AMI.

Aged↗
PubMed2001

The effect of antihypertensive drugs on vascular compliance.

Measurement of vascular compliance has assumed increasing importance as a marker of early disease of the vascular wall, a predictor of future vascular disease, and a way to monitor the effects of vasoactive agents on arterial wall stiffness. Vascular compliance can be estimated by several methods: measurement of the pulse pressure, or pulse pressure-stroke volume ratio; analysis of the systolic pulse wave augmentation index and the diastolic pulse wave contour; ultrasonic echo-tracking; and MRI. Because few comparative studies have been done, the physiologic significance of the measures of compliance obtained by each method is uncertain. Antihypertensive drugs may improve vascular compliance by reducing blood pressure, relaxing vascular smooth muscle, or promoting long-term effects on vascular smooth muscle and cardiomyocyte growth and remodeling. Angiotensin converting enzyme (ACE) inhibitors have been reported to improve vascular compliance in nearly all studies, suggesting a beneficial class effect independent of blood pressure reduction. Favorable changes in the vascular wall-lumen ratio of small vessels from subcutaneous gluteal biopsy specimens after treatment with ACE inhibitors and the persistence of improved vascular compliance after withdrawal of therapy indicate that these agents may produce long-term vascular remodeling. Although few studies have been done, angiotensin II receptor antagonists improve vascular compliance, possibly by blocking angiotensin II-mediated cell proliferation and increasing apoptosis via unopposed AT1 receptor stimulation. In contrast, calcium antagonists and beta-blockers have variable effects on vascular compliance, although beta-blockers with intrinsic sympathomimetic activity improve vascular compliance. Diuretics have little effect on vascular compliance beyond their blood pressure-lowering actions, except for spironolactone, which by improving vascular compliance may have contributed to the reduction in heart failure mortality seen in the Randomized Aldactone Evaluation Study.

Antihypertensive Agents↗