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Biomedical subjects

R Bach

Publications and source records attributed to R Bach.

At least 19 recordsLinked to original sources
PubMed1995

Differential characterization of blood flow, velocity, and vascular resistance between proximal and distal normal epicardial human coronary arteries: analysis by intracoronary Doppler spectral flow velocity.

To characterize coronary blood flow velocity parameters and to determine the relation among velocity, volumetric flow, and vascular resistance in awake human beings, we performed paired proximal and distal velocity measurements in 28 angiographically normal coronary arteries. Mean velocity, peak velocity, diastolic-to-systolic velocity ratio, and diameter and cross-sectional area of proximal and distal arteries were determined and coronary flow and vascular resistance computed. Mean velocity and coronary vasodilator reserve were similar for all three native arteries and were preserved from proximal to distal segments. Volumetric flow decreased from proximal to distal segments. The demonstrated inverse and curvilinear (polynomial) relation between volumetric flow and vascular resistance agrees with theoretical and animal models of coronary physiologic characteristics and suggests a nadir of coronary vascular resistance below which coronary flow no longer increases.

Adult↗
PubMed1994

Factors affecting the restenosis rate after percutaneous transluminal coronary angioplasty.

In an open study follow-up angiographies were performed independently from the clinical course on altogether 131 consecutive patients (99 men, 32 women) six months after percutaneous transluminal coronary angioplasty (PTCA). During this period patients received at least 320 mg of aspirin daily. Possible factors affecting the restenosis rate included age, sex, diabetes mellitus, arterial hypertension, abnormal lipid metabolism, smoking, dosage of aspirin administered, degree of stenosis shown by affected vessels before dilatation, number of vascular segments dilated and platelet reactivity. Restenosis was defined as a renewed narrowing of the dilated segment by 50% or more, with an increase in stenosis by at least 20%. In the present study the following restenosis rates were found six month after a primarily successful PTCA: 30% for the entire sample (39 out of 131 patients); 25% in patients with normal platelet function, 50% in those with mildly abnormal platelet function, and 60% in those with frankly abnormal platelet function; 24% in non-diabetic patients and 45% in diabetics. Analysis of the findings showed that abnormal platelet function and the presence of diabetes mellitus were the most important factors in the subsequent development of restenosis after angioplasty. The same also applied in a more restricted manner to the degree of stenosis present before angioplasty.

Aged↗
PubMed1994

Intraaortic balloon pump support during high-risk coronary angioplasty.

Intraaortic balloon pump support has been demonstrated to be of clinical benefit when used therapeutically and prophylactically in high-risk patients undergoing percutaneous transluminal coronary angioplasty (PTCA). Afterload reduction and post-PTCA-enhanced coronary blood flow afforded by diastolic augmentation during intraaortic balloon pumping provides hemodynamic stabilization, attenuates clinical perturbations of myocardial ischemia, and may provide an important 'bridge' to emergent coronary bypass surgery following abrupt vessel closure complicating PTCA. Recent studies demonstrate a reduction in cardiac morbidity and improved coronary artery patency among patients receiving prophylactic intraaortic balloon pumping after establishing infarct artery reperfusion during acute cardiac catheterization for acute myocardial infarction. A modest increase in cardiac output (20-30%), the requirement of a stable, regular cardiac rhythm, peripheral vascular disease and aortic insufficiency limits the use of intraaortic balloon pump support in relatively few patients. These studies demonstrate that intraaortic balloon counterpulsation provides an effective and safe form of mechanical support in many high-risk patients undergoing PTCA.

Angioplasty, Balloon, Coronary↗
PubMed1994

A monoclonal antibody against rabbit tissue factor inhibits thrombus formation in stenotic injured rabbit carotid arteries.

Tissue factor (TF) is a transmembrane protein that binds factor VII/VIIa, thus activating the extrinsic blood coagulation pathway. Since this pathway appears to be involved in the formation of intravascular thrombi, the anti-rabbit TF monoclonal antibody, AP-1, was produced and tested as an antithrombotic agent in a rabbit model of recurrent intravascular thrombosis. In this model, a plastic constrictor is positioned around the injured rabbit carotid arteries, and flow is monitored with a Doppler flow probe. This produces cyclic flow variation (CFV) in the carotid artery, which is caused by recurrent formation and dislodgment of thrombi at the site of the stenosis. After monitoring CFV pattern for 30 minutes, AP-1 was infused intravenously into nine rabbits at doses of 0.05 to 1.5 mg/kg body weight, and a control monoclonal antibody that does not react with rabbit TF was infused into four additional rabbits. In all rabbits receiving AP-1, CFV was abolished, and a steady normal blood flow was restored, indicating that thrombus formation had been blocked by AP-1. By contrast, in all rabbits that received the control monoclonal antibody, CFV continued unaltered. There was no change in the partial thromboplastin time and ex vivo platelet aggregation to several different agonists after infusion of AP-1, indicating an absence of systemic effects on the coagulation process. We conclude that activation of the extrinsic coagulation pathway has a key role in triggering intravascular thrombosis and that an anti-TF monoclonal antibody is an effective antithrombotic agent that could have therapeutic potential for humans.

Animals↗
PubMed1994

Efficacy and quality in clinical trials. Requirements to the investigator site. European Economic Community.

Guidelines and recommendations to conduct clinical trials have been defined for Europe since 1st July 1991 to ensure high quality standards. Thus, cost and speed of clinical trials are becoming more and more important in clinical research. The article tries to summarize specific requirements to the investigator site considering the aspects of quality and data evaluation. Furtheron a model is proposed to optimize realization of clinical trials in hospital institutions. Realization of "Good Clinical practice" (GCP) at the sponsor and the investigator site will improve the quality of clinical trials for the sake of the patients and finally leads to the acceptance of European clinical trials abroad.

Clinical Trials as Topic↗
PubMed1993

[Complications after coronary angiography and balloon dilatation].

All major complications within four weeks after diagnostic cardiac catheterization (DCCA; n = 4,778) or percutaneous transluminal coronary angioplasty (PTCA; n = 3,073) were analysed prospectively in 7,851 patients (5,769 men, 2,082 women; mean age 59.4 [16-88] years). There were 116 such complications in 114 patients, 46 (0.9%) after DCCA, 70 (2.3%) after PTCA. 76% of all complications occurred during the first two days after the procedure: bleeding in 29 patients, false aneurysms in 15, arterial occlusions in 12, venous ones in three, cerebral ischaemia in 12, fulminant pulmonary emboli in three, cardiac complications in 27, and others in 15. There were five deaths in connection with a DCCA, 18 with PTCA. Complications were twice as common in women as in men (DCCA: 1.5% vs 0.7%, P < 0.05; PTCA: 4.2% vs 1.7%, P < 0.001). Complications after DCCA were more frequent in those aged over 55 years (1.2% vs 0.3%, P < 0.05); after PTCA they were more frequent in those aged over 65 years (4.1% vs 1.3%, P < 0.05). Other risk factors for complications were: peripheral arterial occlusive disease for arterial occlusion (P < 0.001), high heparin dosage with DCCA (P < 0.05), and additional venous puncture with DCCA (P < 0.01).

Adolescent↗
PubMed1993

Chronic hypoxic pulmonary hypertension. Is thrombin involved?

Thrombin contracts vascular smooth muscle and stimulates its proliferation. Using a specific thrombin inhibitor, hirudin, we studied whether thrombin contributes to the pulmonary vasoconstriction and vascular proliferation that occurs in pulmonary hypertension. Hirudin was infused intravenously (0.2 mg/h/kg) by minipumps in nine rats during a 3-wk exposure to hypobaric hypoxia (HH). Vehicle (normal saline) was infused in eight hypoxic control (HC) and seven normoxic control (NC) rats. Sufficient hirudin delivery was confirmed by a failure of undiluted plasma from HH, but not from NC and HC, to clot in response to thrombin. When the plasma samples were diluted 1:10, the thrombin time was significantly prolonged in HH when compared with that in both NC and HC. Although hirudin slightly reduced mean pulmonary arterial pressure in open-chest rats, there was no significant difference between the hypoxic groups in total pulmonary resistance, right ventricle weight, morphologic remodeling of lung vessels, or the perfusion pressure-flow relationship in isolated lungs. Vasoconstrictor responses of isolated lungs to angiotensin II and acute hypoxic challenges were not affected by hirudin treatment. We conclude that hirudin, in a dose sufficient to reduce thrombin's catalytic effect on fibrinogen, does not significantly prevent the development of chronic hypoxic pulmonary hypertension.

Animals↗
PubMed1992

Long-acting angiotensin-converting enzyme inhibition: once-daily lisinopril versus twice-daily captopril in mild-to-moderate heart failure.

Once-daily lisinopril (5-20 mg) was compared with twice-daily captopril (12.5-50 mg) in a double-blind, randomized, parallel-group study of angiotensin-converting enzyme (ACE) inhibition conducted in 31 centers for 12 weeks in patients with heart failure (New York Heart Association class II-III) who were currently receiving digitalis and/or diuretics. The drugs were compared with regard to their effects on exercise duration, measured with bicycle ergometry, and on ectopic activity, measured using Holter monitoring. Both drugs significantly increased exercise duration after both 6 and 12 weeks of randomized treatment. Neither ACE inhibitor had any significant impact on the hourly rate of either ventricular ectopic counts or couplets, nor was there any difference between treatments with regard to the proportions of patients in whom ventricular ectopic counts were reduced. Both drugs were well tolerated, with no differences observed between treatments. Potassium, urea, and creatinine levels remained stable for both treatments throughout the study.

Adult↗
PubMed1992

[Cardiac function and the skin microcirculation in acromegaly].

The microcirculation was measured by nail-fold capillary video microscopy in 21 patients (12 men, 9 women; mean age 54.7 [29-74] years) with acromegaly. Levels of growth hormone (12.0-71.7 microU/ml) and of somatomedin C (2.4-10.5 IU/ml) were elevated in 10 patients, despite preceding treatment. Eleven patients had an increase in myocardial thickness and nine had impairment of left ventricular function, although only slight in most. Left ventricular hypertrophy was demonstrable even in the absence of hypertension. No patient had evidence of coronary heart disease. Nail-fold capillary video microscopy (capillary density, torque index, reactive hyperaemia, epidermal blood flow) failed to distinguish between successfully treated patients and those with persistently elevated growth hormone concentrations or disease duration of over 5 years. There was no evidence of inadequate capillary blood flow as a cause of abnormal function in hypertrophied organs.

Acromegaly↗
PubMed1992

Interpretation of cardiac pathophysiology from pressure waveform analysis: coronary hemodynamics, Part III: Coronary hyperemia.

Basal patterns (systolic/diastolic components) of coronary flow velocity as previously described are generally maintained during hyperemia and can be easily recorded in the catheterization laboratory during pharmacologic stimulation. The interpretation of the clinical significance of coronary vasodilatory reserve may be complicated by both coronary and myocardial diseases. Distal coronary artery hyperemic responses measured with ultrasound Doppler-tipped guidewires will provide new information on traditional observations of coronary physiology in humans.

Adenosine↗
PubMed1992

The usefulness of a tracking catheter in complex coronary angioplasty.

Complex lesion angioplasty, such as chronic total occlusions, coronary vessels with right angle take-offs, tortuous vessels, and tortuous internal mammary artery or saphenous vein grafts is a continuing challenge. The complex problems have been successfully managed with novel guiding catheter shapes and ultralow profile balloons. However, on occasion steerable guidewire placement remains extremely difficult, despite significantly improved means of intracoronary manipulations.

Aged↗
PubMed1992

[Excimer laser coronary angioplasty after primary unsuccessful PTCA].

Excimer laser coronary angioplasty is a new technique for ablation of coronary stenosis, however, the indications for its application are still controversial. We describe two male patients, 60 and 65 years old, who underwent unsuccessful balloon PTCA with a short, concentric and calcified coronary stenosis, although balloon inflation pressure was increased to a maximum in both cases. Excimer laser angioplasty following the failed procedures showed no evidence for tissue ablation angiographically, but a repeat attempt with balloon angioplasty was successful in both cases. Thus, laser angioplasty may be considered as an adjunct technique to balloon angioplasty after a failed PTCA in resistant, non-inflatable lesions.

Aged↗
PubMed1991

Treatment of unstable angina pectoris (European experience).

Unstable angina pectoris is used to describe accelerated angina, new onset of angina, or prolonged angina. The natural history of the angina varies according to clinical presentation. The 1-year mortality rate ranges from 2% to nearly 40%. Specific therapy includes nitrates, beta-adrenergic blockers, and/or calcium antagonists as well as antithrombotic therapy in the form of aspirin. Patients with severe angina at rest and ST- and T-wave changes should be admitted to a coronary care unit where full-dose heparin is administered. Coronary angiography should be performed in individuals who fail to respond to the conventional therapy in order to evaluate other therapeutic options, including percutaneous transluminal coronary angioplasty (PTCA) and coronary bypass surgery. In some cases, especially in patients with intracoronary thrombus, thrombolytic therapy may be beneficial.

Angina, Unstable↗
PubMed1991

Molecular cloning, characterization and expression of cDNA for rabbit brain tissue factor.

Tissue factor (TF) is a membrane anchored glycoprotein that initiates blood coagulation by forming a complex with circulating factor VII or VIIa. TF has been identified in atherosclerotic plaques and may possibly trigger thrombosis after spontaneous plaque rupture as seen in acute myocardial infarction or angioplasty. We have previously developed an atherosclerotic rabbit model for study of the acute and chronic outcomes following angioplasty. As a first step in developing inhibitors of TF, we have isolated and characterized a rabbit cDNA coding for the mature TF. The sequence comparison of rabbit TF cDNA with those of human and mouse TFs show considerable similarity at both the nucleotide and amino acid levels. The TF cDNA when expressed in E. coli demonstrates a procoagulant activity comparable to that of native rabbit brain TF. The TF activity can be blocked by a polyclonal antibody against rabbit TF.

Animals↗