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Biomedical subjects

F M Bengel

Publications and source records attributed to F M Bengel.

29 records · Page 2Linked to original sources
PubMed2000

Effect of thyroid hormones on cardiac function, geometry, and oxidative metabolism assessed noninvasively by positron emission tomography and magnetic resonance imaging.

Thyroid hormones influence cardiac performance directly and indirectly via changes in peripheral circulation. Little, however, is known about the effect on myocardial oxidative metabolism and its relation to cardiac function and geometry. Patients with a history of thyroidectomy for thyroid cancer present a unique model to investigate the cardiac effects of hypothyroidism. Ten patients without heart disease were investigated in the hypothyroid state and again 4-6 weeks later under euthyroid conditions. Myocardial oxidative metabolism was measured by positron emission tomography with [11C]acetate and the clearance constant k(mono). Cine magnetic resonance imaging was applied to determine left ventricular geometry. A stroke work index (SWI = stroke volume x systolic blood pressure/ventricular mass) was calculated. Then, to estimate myocardial efficiency, a work metabolic index [WMI = SWI x heart rate/k(mono)] was obtained. Compared to hormone replacement, systemic vascular resistance and left ventricular mass were significantly higher in hypothyroidism. Ejection fraction and SWI were significantly lower. Despite an additional reduction of k(mono), the WMI was significantly lower, too. In summary, cardiac oxygen consumption is reduced in hypothyroidism. This reduction is associated with increased peripheral resistance and reduced contractility. Estimates of cardiac work are more severely suppressed than those of oxidative metabolism, suggesting decreased efficiency. These findings may provide an explanation for development or worsening of heart failure in hypothyroid patients with preexisting heart disease.

Acetates↗
PubMed2000

Coronary microvascular reactivity to sympathetic stimulation in patients with idiopathic dilated cardiomyopathy.

UNLABELLED: The objective of this study was to assess noninvasively the microvascular reactivity to sympathetic stimulation in patients with idiopathic dilated cardiomyopathy (IDC) and in healthy volunteers, who underwent cardiac catheterization for exclusion of coronary artery disease. METHODS: Myocardial flow was quantified with 13N-ammonia PET and tracer kinetic modeling at rest and in response to cold pressor testing (CPT). Ten healthy volunteers (8 men, 2 women; mean age +/- SD, 50.7 +/- 15 y) and 10 matched patients (8 men, 2 women; mean age, 52.5 +/- 14 y) with IDC (mean left ventricular ejection fraction, 0.30 +/- 0.12) were included in the study. RESULTS: Myocardial perfusion at rest was not significantly different between the groups. However, myocardial vascular resistance (MVR) was significantly lower in IDC patients at rest than in healthy volunteers. In response to CPT a significant decrease in MVR was found in healthy volunteers (1.9 +/- 0.4 to 1.5 +/- 0.4 mm Hg x 100 g/mL; 22% decrease) but not in IDC patients (1.5 +/- 0.4 to 1.4 +/- 0.3 mm Hg x 100 g/mL; 9% decrease). Consequently, the increase of the myocardial blood flow in response to CPT was significantly lower (P < 0.008) in IDC patients (56 +/- 17 to 66 +/- 18 mL/100g/min; 20% increase) compared with healthy volunteers (52 +/- 12 to 80 +/- 30 mL/100 g/min; 52% increase), whereas both showed comparable hemodynamic reactions. CONCLUSION: The data indicate that CPT in combination with 13N PET imaging is a valuable noninvasive tool for assessment of coronary microvascular reaction to sympathetic stimulation in IDC patients. Lower coronary vascular resistance was found in IDC patients at rest compared with healthy volunteers, suggesting possible exhaustion of sympathetically induced dilation of the coronary microvasculature in IDC patients at rest. This mechanism may explain the impaired flow response to cold in IDC patients in the present study.

Blood Pressure↗
PubMed1999

Oxidative metabolism of the transplanted human heart assessed by positron emission tomography using C-11 acetate.

For investigation of the metabolic profile of the transplanted human heart, positron emission tomography with C-11 acetate was performed to compare global and regional oxidative metabolism in 14 transplant patients with that in 10 healthy volunteers. Because no difference between transplants and normals could be observed, the results suggest that oxidative metabolism remains stable after transplantation, whereas cardiac work remains the major determinant.

Carbon Radioisotopes↗
PubMed1999

Serial assessment of sympathetic reinnervation after orthotopic heart transplantation. A longitudinal study using PET and C-11 hydroxyephedrine.

BACKGROUND: Little is known about the progressiveness of sympathetic reinnervation late after cardiac transplantation (HTX). The aim of the present study was to describe individual growth of sympathetic terminals after HTX by a longitudinal quantitative assessment. METHODS AND RESULTS: In 20 patients after HTX, dynamic PET with C-11 hydroxyephedrine (HED) was performed twice within 3.0+/-0.5 years. According to the time interval between HTX and first PET, subgroups of patients early (group A, <1.5 years; n=7), intermediate (group B, 1.5 to 7 years; n=7) and late (group C, >7 years; n=6) after HTX were defined. At the time of first HED PET, 10 patients were completely denervated (7 in group A, 2 in group B, and 1 in group C). Only 3 remained denervated at second PET. A significant increase of reinnervated myocardium between first and second PET was found in all 3 groups (0% to 9+/-9% of left ventricle for group A, P<0.05; 13+/-12% to 23+/-17% for group B, P<0.05; 21+/-21% to 37+/-23% for group C, P<0.05). The magnitude of increase was similar between groups. Reinnervation was first surveyed in the basal anterior region, then toward apex, septal, and lateral wall. Inferior wall remained denervated. The largest reinnervated area surveyed in an individuum was 66% of the left ventricle. CONCLUSIONS: The present data confirm the low likelihood of sympathetic reinnervation within 18 months after HTX. Once the reinnervation process is initiated, a continuous growth is observed even late after HTX, suggesting a progressive nature of reinnervation. Reinnervation, however, remained regionally heterogeneous, and a complete restoration was not found until 15 years after HTX.

Adult↗
PubMed1999

Kinetics of 123I-MIBG after acute myocardial infarction and reperfusion therapy.

UNLABELLED: Metaiodobenzylguanidine (MIBG) washout from the myocardium has been thought to reflect sympathetic nerve tone. After acute myocardial infarction, however, little is known about this parameter. The aim of this study was to determine the significance of cardiac washout after myocardial infarction and early reperfusion by investigating MIBG kinetics and correlating those kinetics to clinical parameters. METHODS: Sixty patients with acute myocardial infarction underwent planar MIBG and thallium imaging within 14 d of early reperfusion therapy. Global uptake and washout in myocardium, lungs and liver were calculated from early and delayed images. A regional analysis of myocardial kinetics in normal and infarcted myocardium and in an infarct border zone was also performed. Scintigraphic data were correlated with heart-rate variability as an electrophysiologic marker for autonomic tone and prevalence of arrhythmia in 52 patients. Heart-rate variability was described by time-domain indices from long-term electrocardiogram recordings. An age-matched normal control group for MIBG consisted of 10 individuals without heart disease. RESULTS: The infarct patients had preserved left-ventricular ejection fraction (LVEF) (56% +/- 17%). Although late myocardial uptake was expectedly lower in infarct patients compared with healthy volunteers (2.36 +/- 0.66 versus 2.80 +/- 0.55; P = 0.04), global myocardial MIBG washout was faster (11.6% +/- 7.9% versus 0.2% +/- 10.2%, respectively; P = 0.002). Lung and liver kinetics did not differ in patients and healthy volunteers. Global MIBG washout showed a weak but significant positive correlation with the baseline heart rate (r = 0.28, P = 0.03) and an inverse correlation with LVEF (r = -0.28, P = 0.04). Washout was faster in a subgroup of 8 patients with reduced heart-rate variability (16.5% +/- 9.9% versus 10.3% +/- 8.3%; P = 0.04). Regional analysis revealed similar degrees of enhanced MIBG washout for infarcted (low perfusion, low MIBG uptake) and remote myocardium (normal perfusion, high MIBG uptake), whereas the border zone (normal perfusion, low MIBG uptake) showed a nonsignificant trend toward higher washout. CONCLUSION: After myocardial infarction, changes in MIBG kinetics occur specifically in the myocardium, whereas kinetics in lung and liver remain unchanged. Even in patients with left-ventricular function preserved by reperfusion therapy, MIBG washout is abnormal and globally increased. Enhanced washout may reflect increased sympathetic nerve tone and represent increased catecholamine turnover or impaired reuptake in the subacute phase of myocardial infarction.

3-Iodobenzylguanidine↗
PubMed1998

Nuclear medicine studies of the heart.

Nuclear imaging techniques are well established diagnostic tools in clinical cardiology, providing noninvasive information about myocardial perfusion, function and metabolism. The cost-effectiveness of radionuclide imaging in the diagnostic work-up of patients with coronary artery disease has been demonstrated. Additionally, the documented prognostic value of scintigraphic parameters is of clinical importance to guide decision making. Advances in technology, new radiotracers and new applications contribute to continuous growth in the field of nuclear cardiology. Multi-headed gamma camera systems lead to higher spatial resolution and sensitivity of cardiac single photon emission tomography (SPECT), and they also provide the opportunity for attenuation correction or electrocardiographic gating of SPECT images. Objective quantitative values of perfusion, function and metabolism are derived from scintigraphic data by use of improved software and hardware. With the latest developments in tracer technology, imaging of myocardial necrosis, receptor systems and autonomic innervation has become a reality and will lead to new clinical applications in the future.

Autonomic Nervous System↗
PubMed1998

Myocardial blood flow and coronary flow reserve late after anatomical correction of transposition of the great arteries.

OBJECTIVES: Myocardial blood flow (MBF) in children late after arterial switch operation (ASO) was investigated quantitatively by positron emission tomography (PET). BACKGROUND: In children with transposition of the great arteries (TGA), ASO is widely accepted as the management of choice. The long-term patency of coronary arteries after surgical transfer to the neo-aorta, however, remains a concern. METHODS: Twenty-two normally developed, symptom-free children were investigated by PET with nitrogen-13 ammonia at rest and during adenosine vasodilation 10+/-1 years after ASO. A subgroup of 15 children (9+/-1 years; group A) had simple TGA and underwent ASO within 20 days after birth while 7 (13+/-3 years; group B) had complex TGA and underwent ASO and correction of associated anomalies later after birth. Ten young, healthy adults (26+/-6 years) served as the control group. RESULTS: Resting MBF was not different between groups. After correction for the rate-pressure product as an index of cardiac work, younger children of group A had significantly higher MBF at rest compared to healthy adults (102+/-29 vs. 77+/-6 ml/100 g/min; p = 0.012) while flow in group B was not different from the other groups (85+/-22 ml/100 g/min; p = NS). Hyperemic blood flows were significantly lower in both groups after ASO compared to normals (290+/-42 ml/100 g/min for group A, 240+/-28 for group B, 340+/-57 for normals; p < 0.01); thus, coronary flow reserve was significantly lower in both groups after ASO compared to healthy adults (3.0+/-0.6 for group A, 2.9+/-0.6 for group B, 4.6+/-0.9 for normals; p < 0.01). CONCLUSIONS: Blood flow measurements suggest decreased coronary reserve in the absence of ischemic symptoms in children late after arterial switch repair of TGA. The global impairment of stress flow dynamics may indicate altered vasoreactivity; however, the prognostic significance of these findings needs to be determined.

Adolescent↗
PubMed1997

Whole-body positron emission tomography in clinical oncology: comparison between attenuation-corrected and uncorrected images.

The clinical need for attenuation correction of whole-body positron emission tomography (PET) images is controversial, especially because of the required increase in imaging time. In this study, regional tracer distribution in attenuation-corrected and uncorrected images was compared in order to delineate the potential advantages of attenuation correction for clinical application. An ECAT EXACT scanner and a protocol including five to seven bed positions, emission scans of 9 min and post-injection transmission scans of 10 min per bed position were used. Uncorrected and attenuation-corrected images were reconstructed by filtered backprojection. In total, 109 areas of focal fluorine-18 fluorodeoxyglucose (FDG) uptake in 34 patients undergoing PET for the staging of malignancies were analysed. To measure focus contrast, a ratio of focus (target) to background average countrates (t/b ratio) was obtained from transaxial slices using a region of interest technique. Calculation of focus diameters by a distance measurement tool and visual determination of focus borders were performed. In addition, images of a body phantom with spheres to simulate focal FDG uptake were acquired. Transmission scans with and without radioactivity in the phantom were used with increasing transmission scanning times (2-30 min). The t/b ratios of the spheres were calculated and compared for the different imaging protocols. In patients, the t/b ratio was significantly higher for uncorrected images than for attenuation-corrected images (5.0+/-3.6 vs 3.1+/-1.4; P<0.001). This effect was independent of focus localization, tissue type and distance to body surface. Compared with the attenuation-corrected images, foci in uncorrected images showed larger diameters in the anterior-posterior dimension (27+/-14 vs 23+/-12 mm; P<0.001) but smaller diameters in the left-right dimension (19+/-11 vs 21+/-11 mm; P<0.001). Phantom data confirmed higher contrast in uncorrected images compared with attenuation-corrected images. It is concluded that, although distortion of foci was demonstrated, uncorrected images provided higher contrast for focal FDG uptake independent of tumour localization. In most clinical situations, the main issue of whole-body PET is pure lesion detection with the highest contrast possible, and not quantification of tracer uptake. The present data suggest that attenuation correction may not be necessary for this purpose.

Female↗
PubMed1997

Myocardial damage assessed by indium-111-antimyosin: correlation with persistent enteroviral ribonucleic acid in dilated cardiomyopathy.

The persistence of enteroviral ribonucleic acid (RNA) in the myocardium has been implicated as a pathogenetic factor in idiopathic dilated cardiomyopathy. Enteroviral persistence may lead to myocardial cell membrane damage, resulting in increased uptake of antimyosin antibodies. To further evaluate this hypothesis, a direct comparison of myocardial antimyosin uptake with the presence of enteroviral RNA was performed in ten patients (one female, nine male; 53+/-8 years) with chronic dilated cardiomyopathy. Planar antimyosin images were obtained 48 h after the injection of indium-111-labelled antimyosin Fab. Using a region of interest technique, the heart to lung uptake ratio (HLR) was calculated as a semiquantitative parameter of myocardial tracer uptake. Cardiac catheterization was performed to assess left ventricular function and to obtain myocardial biopsy samples. In the biopsy samples, gene amplification by polymerase chain reaction (PCR) was used to specifically detect enteroviral RNA. In the ten patients, the left ventricular ejection fraction was 39%+/-11% and the end-diastolic volume 131+/-46 ml/m2. The HLR was 1.72+/-0.21 and showed no correlation with functional parameters. In two patients with a positive PCR consistent with persisting enteroviral RNA, the HLR was not higher than that in eight patients with a negative PCR (1.46+/-0. 18 vs 1.78+/-0.18, respectively). These results suggest that increased uptake of 111In-antimyosin in chronic idiopathic dilated cardiomyopathy cannot be explained by pure persistence of enteroviral RNA. Other pathogenetic factors such as myocardial autoantibodies or microvascular spasm may be responsible for myocyte membrane damage detected by antimyosin.

Antibodies, Monoclonal↗