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Biomedical subjects

Ernst Wellnhofer

Publications and source records attributed to Ernst Wellnhofer.

8 recordsLinked to original sources
PubMed2003

Noninvasive determination of coronary blood flow velocity with cardiovascular magnetic resonance in patients after stent deployment.

BACKGROUND: In patients with coronary artery stents, no direct noninvasive coronary artery imaging is possible with magnetic resonance (MR). A well-established method for the assessment of the functional significance of a coronary lesion is the measurement of coronary flow reserve by invasive intracoronary Doppler. The purpose of the study was to determine coronary flow velocity reserve (CFVR) with MR after stent deployment. METHODS AND RESULTS: Thirty-eight patients after successful PTCA and stent deployment were included. CFVR was measured perpendicular to the artery distal to the stent using phase-contrast velocity quantification at rest and during adenosine-stimulated hyperemia with a 1.5T MR tomograph (ACS NT, Philips). Measurements were repeated after 3 months and compared with invasive coronary angiography. In 18 patients, additional invasive Doppler flow measurements were obtained. CFVR could be determined in 29 of 38 (76%) of the patients. After 3 months, significant differences were obtained between coronary arteries with and without restenosis. Using a threshold of 1.2, a sensitivity of 83% with a specificity of 94% was achieved for > or =75% stenoses. CFVR with CMR was similar to Doppler results (r=0.87), with a mean relative difference of 7.5%. CONCLUSIONS: In patients with preserved coronary microcirculating vasoreactivity that are suitable for MR coronary angiography and flow assessments, CMR measures of coronary blood flow velocities reserve may be used to detect in-stent restenosis.

Blood Flow Velocity↗
PubMed2002

Progression of coronary atherosclerosis quantified by analysis of 3-D reconstruction of left coronary arteries.

OBJECTIVES: Quantitative measurements on three-dimensional (3-D) reconstructed coronary trees permit accurate evaluation of vascular volumes, lengths and diameters. We applied this technique to investigate diffuse luminal narrowing in patients with the clinical manifestation of progressive atherosclerosis. METHODS: In 13 patients who presented repeatedly for coronary angioplasty (at least 4 years of invasive follow-up), left coronary arteries were reconstructed in 3-D from biplane coronary angiograms. Mean diameter, cross-sectional areas, total length, and volume were calculated for segments and branches. Five patients without coronary artery disease served as controls. RESULTS: Patients with progressive coronary atherosclerosis demonstrated a significant reduction of total vascular volumes, mean diameters and cross-sectional areas at the initial investigation when compared with controls. Progressive luminal shrinkage occurred during follow-up (-0.04+/-0.13 mm per year and per segmental diameter). The progress of luminal narrowing in patients with coronary artery disease is related to the number of coronary risk factors and the duration of follow-up. CONCLUSION: Quantitative measurements on 3-D reconstructed coronary trees are a useful investigative tool for the assessment of progression of coronary atherosclerosis.

Coronary Angiography↗
PubMed2002

Shear stress and vascular remodeling: study of cardiac allograft coronary artery disease as a model of diffuse atherosclerosis.

BACKGROUND: The assessment of remodeling in diffuse atherosclerosis by intravascular ultrasound is hampered by the lack of an appropriate reference segment. Transplant coronary artery disease is an accepted model of diffuse atherosclerosis. Flow-dependent remodeling is regulated by shear stress. Thus, normal levels of shear stress at baseline flow reflect adequate regulation and provide a functional assessment of flow-dependent remodeling. METHODS: The approach was evaluated in 91 patients with transplant coronary artery disease and in 9 non-transplanted controls and 16 control transplant recipients. Quantitative coronary angiography, intracoronary ultrasound and intracoronary velocity studies were performed at baseline and after pharmacologic intervention. Calculated shear stress was compared between these groups and a sub-group with coronary angioplasty at follow-up (8 of 60 patients with control angiography after 23 +/- 8 months). The relation of shear stress to flow, diameter, flow/area ratio and endothelial function was analyzed. RESULTS: Normal shear stress was found in non-transplanted controls and transplant recipients without coronary artery disease. Patients with coronary angioplasty at follow-up had elevated shear stress and enhanced endothelial dysfunction on the initial investigation. Shear stress was not correlated with flow (r = 0.062, non-significant), but with diameter (r = -0.654), flow/area ratio (r = 0.814) and endothelial dysfunction (r = 0.722). CONCLUSION: Calculated local shear stress appears to be useful for the assessment of the adequacy of flow-dependent macrovascular remodeling in diffuse atherosclerosis. Elevated blood flow/area ratio is a potential clinical marker of increased shear stress that reflects inadequate flow-dependent remodeling.

Adult↗
PubMed2002

Improved accuracy of quantitative assessment of left ventricular volume and ejection fraction by geometric models with steady-state free precession.

The purpose of this study was to determine whether steady-state free precession (SSFP) could improve accuracy of geometric models for evaluation of left ventricular (LV) function in comparison to turbo gradient echo (TGrE) and thereby reduce the acquisition and post-processing times, which are commonly long by use of the Simpson's Rule. In 25 subjects, cine loops of the complete heart in short and horizontal long-axis planes were acquired using TGrE (TR/TE/flip = 5.0/1.9/25) compared with SSFP (TR/TE/flip = 3.2/1.2/60). LV volumes and EF were measured with various geometric models for TGrE and SSFP. With three-dimensional data, the LV volumes were higher and the resulting EF lower for SSFP in contrast to TGrE (51 +/- 15% vs. 57 +/- 15%, p < 0.001). With SSFP, various geometric models yielded good to excellent correlations for LV volumes and LVEF compared to volumetric data (r = 0.94-0.98, mean relative difference 7.0-11.4%). In contrast, correlations were low using biplane or single-plane ellipsoid models in TGrE (r = 0.71-0.75, mean relative difference 15.9-30.2%). A new combined geometric model, taking all three dimensions into account, yielded the highest accuracy for SSFP in comparison to volumetric data (r = 0.99, mean relative difference 4.7%). Geometric models for assessment of LV volumes and EF yield higher accuracy and reproducibility by use of the SSFP sequence than by standard TGrE. This may increase clinical utility of magnetic resonance by shorter acquisition and processing times.

Adult↗
PubMed2002

Intravascular ultrasound assessment of longitudinal plaque distribution patterns in patients with angiographically silent coronary artery disease after heart transplantation.

AIMS: The purpose of this three-dimensional intracoronary ultrasound (ICUS) study was to assess longitudinal plaque distribution patterns in patients with angiographically silent coronary artery disease (CAD) after heart transplantation (HTX). METHODS AND RESULTS: Out of 334 patients without diameter stenosis >/=25% determined by coronary angiography, 321 underwent successful three-dimensional ICUS (30 MHz) of the left main coronary artery (LMCA) and all segments of the left anterior descending coronary artery (LAD). Early plaque formation was found in 296 patients (92.2%). Single (focal CAD, n = 65) or multiple (polyfocal CAD, n = 77), discrete coronary lesions were found in 142 patients and continuous plaque formation of at least one entire coronary segment (diffuse CAD) in 154 patients. Using multivariate regression analysis, male sex (P = 0.01), increasing post-transplantation time (P = 0.003) and increasing donor age (P = 0.001) were independent clinical predictors for diffuse CAD. Both focal and diffuse CAD most frequently affected the proximal LAD (88% compared with 89.6%, NS). The mean intimal index of each LAD segment was significantly higher in patients with diffuse CAD (P < 0.001) and showed a proximal-to-distal decline in patients with focal/polyfocal (LMCA, 10.1 +/- 14.3, LAD-6, 30.1 +/- 17.4%, LAD-7, 16.3 +/- 14.1%, LAD-8, 4.6 +/- 11.1%; P < 0.001) and diffuse (LMCA, 27.0 +/- 16.0, LAD-6, 47.8 +/- 16.1%, LAD-7, 41.9 +/- 14.5%, LAD-8, 24.9 +/- 23.3%; P < 0.01) CAD. CONCLUSION: Evaluation of longitudinal plaque distribution after HTX by three-dimensional ICUS revealed a time-dependent increase in the incidence of diffuse CAD and a proximal-to-distal decline in frequency and magnitude of early plaque formation.

Cohort Studies↗
PubMed2002

X-ray-based flow visualization and measurement: application in multiphase flows.

Information concerning continuous or discreet phase flow in multiphase systems is desired for various practical and analytical applications. The potential of X-ray-based flow visualization and measurement of multiphase flow is demonstrated here by two non-intrusive methods: (1) Measurement of the three-dimensional (3D) velocity field of the continuous liquid phase in a bubble column by X-ray-based particle tracking velocimetry (PTV) of seeded particles. (2) Liquid flow visualization in a bubble column by injecting an X-ray absorbing liquid into the bubble column. X-rays have the advantage that they are not affected by the various refraction indices of the multiphase system and penetrate the multiphase flow in undistorted straight lines. Hence, in contrast to optical methods, both of these X-ray-based methods are independent of the void fraction and are applicable to opaque liquids.

Biotechnology↗