ISSN:0009-7322    

出版商:OVID    

年代:1999

数据来源: OVID

ISSN:0009-7322    

出版商:OVID    

年代:1999

数据来源: OVID

ISSN:0009-7322    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

BackgroundUnprocessed ultrasound radiofrequency (RF) signal analysis has been shown to distinguish different tissue structures more reliably than gray-scale interpretation of conventional ultrasound images.Methods and ResultsThe objective of this study was to test the feasibility of in vivo intravascular ultrasound (IVUS) RF signal analysis in an animal model of allograft rejection. Six cynomolgus monkeys underwent transplantation of 3-cm aortic allograft segments distal to the renal arteries from immunologically mismatched donors. IVUS imaging with a 30-MHz system was performed 84 to 105 days after the operation. RF signals were acquired from cross sections of the recipient and the allograft aortas in real time with a digitizer at 500 MHz with 8-bit resolution. Sixty-five cross sections and 68 regions of interest (31 in host aorta and 37 in allograft) were analyzed in the adventitial layer with a total number of 8568 vectors processed. For each region of interest, a weighted-average attenuation was calculated on the basis of the attenuation and length for each individual vector. Histological examination was performed at every cross section imaged by IVUS. When the gray-scale images of conventional IVUS scored by an independent observer were compared, no distinction between adventitia of the native aorta and allograft was possible. Analysis of the average RF backscatter power also showed no significant difference (70.32±3.55 versus 70.72±3.38 dB). However, the average attenuation of allografts was significantly lower than that of the host aortas (2.64±1.38 versus 4.02±1.16 dB/mm,P<0.001). Histology demonstrated a marked adventitial inflammatory response in all allografts, with no inflammation observed in the host aortas.ConclusionsIn vivo IVUS tissue characterization can be performed during routine imaging. In this model of transplant vasculopathy, RF attenuation measurements were more sensitive than visual or quantitative gray-scale analysis.

ISSN:0009-7322    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

BackgroundHypercholesterolemia causes an upregulation of vascular angiotensin II type 1 (AT1) receptor expression in cell culture and animal models. The presented studies were undertaken to examine AT1 receptor overexpression in hypercholesterolemic men and therapeutic interventions thereof by HMG CoA reductase inhibitors (statins).Methods and ResultsEffects of AT1 receptor activation were measured by assessing the blood pressure increase after infusion of angiotensin II in normo- (cholesterol 181±11 mg/dL) and hypercholesterolemic (cholesterol 294±10 mg/dL) men (n=19 and 20, respectively). AT1 receptor expression was assessed on isolated platelets. Some patients were investigated before and after cholesterol-lowering therapy with statins. Hypercholesterolemia led to a significant increase of angiotensin II-induced blood pressure elevation. AT1 receptor expression was significantly enhanced in hypercholesterolemic individuals (Bmax=5.2±1.2 fmol/mg protein) compared with normocholesterolemic men (Bmax=2.1±0.2 fmol/mg protein). Cholesterol-lowering treatment with statins reversed the elevated blood pressure response to angiotensin II infusion (P<0.05) and downregulated AT1 receptor density (P<0.05).ConclusionsHypercholesterolemia induces AT1 receptor overexpression and enhances biological effects of angiotensin II in men. These findings provide novel insights into the pathogenesis of hypertension and atherosclerosis and may initiate rational and new therapeutic concepts.

ISSN:0009-7322    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

BackgroundMonocytes are constitutively activated in unstable angina (UA), resulting in the production of IL-6 and the upregulation of acute phase proteins. Underlying mechanisms are not understood. To explore whether the production of the potent monocyte activator IFN-γ is altered in UA, we compared cytokine production by T lymphocytes in patients with UA (Braunwald's class IIIB) and with stable angina (SA).Methods and ResultsPeripheral blood lymphocytes were collected at the time of hospitalization and after 2 and 12 weeks. Cytokine-producing CD4+and CD8+T cells were quantified by 3-color flow cytometry after stimulation with phorbol myristate acetate and ionomycin. UA was associated with an increased number of CD4+and CD8+T cells producing IFN-γ, whereas patients with SA had higher frequencies of IL-2+and IL-4+CD4+T cells. Expansion of the IFN-γ+T-cell population in UA persisted for at least 3 months. Increased production of IFN-γ in UA could be attributed to the expansion of an unusual subset of T cells, CD4+CD28nullT cells.ConclusionsPatients with UA are characterized by a perturbation of the functional T-cell repertoire with a bias toward IFN-γ production, suggesting that monocyte activation and acute phase responses are consequences of T-cell activation. IFN-γ is produced by CD4+CD28nullT cells, which are expanded in UA and distinctly low in SA and controls. The emergence of CD4+CD28nullT cells may result from persistent antigenic stimulation.

ISSN:0009-7322    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

BackgroundThe appropriate management of patients with intermediate-risk Duke treadmill scores is not established. The purpose of this study was to determine the long-term risk of subsequent cardiovascular events in patients with an intermediate-risk treadmill score who do not have myocardial perfusion defects on radionuclide imaging.Methods and ResultsThe existing databases of the nuclear cardiology laboratories of 4 academic institutions were searched retrospectively. A total of 4649 patients were identified who had intermediate-risk Duke treadmill scores (−10 to 4), normal or near-normal exercise single photon-emission computed tomographic myocardial perfusion images using either thallium-201 or technetium-99m sestamibi, and no previous coronary revascularization. Follow-up was 95% complete. Cardiovascular survival was 99.8% at 1 year, 99.0% at 5 years, and 98.5% at 7 years. Cardiac survival free of myocardial infarction was similarly high at 96.6% at 7 years. Cardiac survival free of myocardial infarction or revascularization was 87.1% at 7 years. Near-normal scans and cardiac enlargement were independent predictors of time to cardiac death. Seven-year cardiac survival was still high at 97.0% in the 357 patients with near-normal scans and normal cardiac size and somewhat lower, at 89.0%, in the 167 patients with cardiac enlargement.ConclusionsPatients with an intermediate-risk treadmill score but with normal or near-normal exercise myocardial perfusion images and normal cardiac sizes are at low risk for subsequent cardiac death and can be safely managed medically until their symptoms warrant revascularization. The appropriate management of patients with cardiac enlargement will remain a matter of clinical judgment.

ISSN:0009-7322    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

BackgroundThis study was done to elucidate mechanisms by which newer cardiopulmonary resuscitation (CPR) techniques, including interposed abdominal compression (IAC), active compression-decompression (ACD), and Lifestick CPR, augment systemic perfusion pressure and forward flow and to compare the 3 techniques in the same test system.Methods and ResultsMathematical models describing hemodynamics of the adult human circulation during cardiac arrest and CPR were created and exercised by use of spreadsheet software. Assumptions of the models are limited to normal human anatomy and physiology, the definition of compliance (volume change/pressure change), and Ohm's law (flow=pressure/resistance). Standard CPR generates 1.3 L/min forward and 25 mm Hg systemic perfusion pressure. In otherwise identical models, IAC-CPR generates 2.4 L/min and 45 mm Hg; ACD-CPR, 1.6 L/min and 30 mm Hg; and Lifestick CPR, which combines IAC and ACD, 3.1 L/min and 58 mm Hg. Augmented CPR techniques work by enhanced priming of either chest or abdominal pump mechanisms.ConclusionsAdjunctive maneuvers, combined with conventional chest compression, can produce substantial hemodynamic benefit in CPR by credible physiological mechanisms.

ISSN:0009-7322    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

BackgroundThe surgical approach to aortic root aneurysm and/or dissection remains controversial. The use of valve-sparing operations, which are thought to have many advantages, is increasing. We hypothesized that the particular technique and type of surgery could influence valve motion characteristics and function. Therefore, we studied the instantaneous opening and closing characteristics of the aortic valve after the main 2 types of valve-sparing surgery.Methods and ResultsIn 20 patients (10 with tube replacement of the aortic root, group A; and 10 with separate replacement of the sinuses of Valsalva, group B) and 10 controls (group C), transthoracic and transesophageal studies on aortic valve dynamics were performed. Three distinct phases of aortic valve motion were identified. They were as follows: (1) a rapid opening, with a velocity of 20.9±4.2 cm/s in group C, 27.1±10.9 cm/s in group B (P=NS), and 58.3±18.4 cm/s in group A (group A versus group C,P<0.001; group A versus group B,P=0.001); (2) a slow systolic closure, with 12.5±6.6% and 10.8±2.2% of maximal opening in groups C and B, respectively (P=NS), and 3.8±1.6% in group A (group A versus group C,P=0.001; group A versus group B,P<0.001); and (3) a rapid closing movement, with a velocity of 26.3±5.6 cm/s in group C, 32.4±11.4 cm/s in group B (P=NS), and 21.8±3.5 cm/s in group A (group A versus group C,P=NS; group A versus group B,P=0.008). The pressure strain of the elastic modulus was different in groups C and B only at the commissures (682±145 g/cm2versus 1896±726 g/cm2, respectively;P<0.001). At all root levels, the distensibility was reduced in group A (P<0.001). Systolic contact of aortic cusps and wall occurred only in group A.ConclusionsNear-normal opening and closing characteristics can be achieved by a technique that preserves the shape and independent mobility of the sinuses of Valsalva.

ISSN:0009-7322    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

BackgroundValve regurgitation has been associated with dexfenfluramine, but its prevalence and severity are uncertain. Additional factors that may contribute to valve regurgitation in patients exposed to this drug are poorly understood.Methods and ResultsEchocardiography was performed on subjects recruited from 26 prescribing sites in 15 states. The total sample of 412 subjects included 172 dexfenfluramine patients and 172 unexposed controls matched for age, sex, and body mass index and 68 unmatched subjects meeting the same entry criteria (51 dexfenfluramine patients and 17 controls). Mean treatment duration was 6.9 months; mean interval from treatment discontinuation to echocardiogram was 8.5 months. Each echocardiogram was interpreted independently by 3 echocardiographers. FDA-grade regurgitation (at least mild aortic regurgitation or at least moderate mitral regurgitation) was significantly more frequent in dexfenfluramine patients (7.6% versus 2.1% for controls;P=0.01; odds ratio, 3.82). This difference was primarily due to more frequent mild aortic regurgitation in dexfenfluramine patients (6.3% versus 1.6% in controls;P<0.02; odds ratio, 4.15). No differences were found in sclerosis or mobility for either the aortic or mitral valve. Factors independently related to FDA-grade regurgitation or any grade of aortic regurgitation were older age, higher diastolic blood pressure at the time of echocardiography, and shorter time from drug discontinuation to echocardiogram.ConclusionsDexfenfluramine use is associated with an increase in the prevalence of abnormal valve regurgitation. Age and blood pressure may also affect the prevalence of regurgitation. Dexfenfluramine-related valve regurgitation may regress after drug discontinuation.

ISSN:0009-7322    

出版商:OVID    

年代:1999

数据来源: OVID