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Biomedical subjects

N Bom

Publications and source records attributed to N Bom.

At least 91 records · Page 5Linked to original sources
PubMed1988

Intra-arterial ultrasonic imaging for recanalization by spark erosion.

Presently several new methods are being developed to recanalize obstructed arteries during catheterization. Intra-arterial high frequency ultrasonic imaging may be used as a guidance for these new techniques. Spark erosion is a new obstruction removal technology. Experiments have shown that this method can be applied in a selective way. An ultrasonic intra-arterial imaging system allows for the proper indication of the spark erosion catheter relative to the obstruction. The first in vitro results of this study illustrate that integration of catheter tip imaging and spark erosion is possible.

Angioplasty, Balloon↗
PubMed1988

The role of intraoperative two-dimensional echocardiography in the assessment of thoracic aorta pathology.

The role of intraoperative two-dimensional echocardiography is discussed in 15 consecutive patients with thoracic aorta pathology undergoing cardiac surgery. A 5 MHz mechanical scanner was used before and immediately after cardiopulmonary bypass. In 5 patients intraoperative two-dimensional studies revealed crucial morphologic information which, consequently, had a marked influence on their planned surgical procedure. In 3 patients the findings provided additional information whereas in the remaining patients the intraoperative echocardiographic findings confirmed the preoperative diagnosis. Following surgery the adequacy of cardiac repair was assessed and, in one patient, epicardial echocardiography indicated the necessity for reoperation. The application of intraoperative two-dimensional echocardiography leads to a better understanding of the pathology involved and facilitates a more appropriate decision concerning the surgical procedure.

Adolescent↗
PubMed1988

The value of transoesophageal echocardiography for diagnosis of thoracic aorta pathology.

The potential of transoesophageal echocardiography for preoperative diagnosis of thoracic aorta pathology was evaluated in 15 patients with aortic dissection and 15 patients with aortic aneurysm. The transoesophageal echocardiographic findings were compared with 14 computed tomograms and 21 angiograms. Six patients underwent only transoesophageal echocardiography. All patients were operated upon and the surgical findings were used as a reference for these diagnostic methods. Transoesophageal echocardiography established a complete and correct diagnosis in 27 patients. The diagnosis was partially correct in three patients, all having an aortic dissection. A complete and correct diagnosis was obtained by computed tomography and angiography in 8 and 17 patients, respectively. The results indicated that transoesophageal echocardiography is a sensitive and convenient method for the definitive diagnosis of pathology of the thoracic aorta. It could become the technique of choice in patients suspected of having acute aorta pathology as it enables a rapid and definitive diagnosis at the bedside.

Adult↗
PubMed1988

The first derivative as a means of synchronizing pulsatile flow velocity and vessel diameter waveforms in the fetal descending aorta.

In order to calculate volume flow, blood flow velocity and pulsatile vessel diameter waveforms in the lower thoracic part of the descending aorta of the fetal lamb and human fetus were matched for identical cardiac cycle length by fetal ECG and the first derivative of these waveforms. Volume flow values were not essentially different using either method. There is simultaneous onset of the blood flow velocity and pulsatile vessel diameter waveforms. The first derivative can reliably replace the fetal ECG as a means of synchronizing blood flow velocity and pulsatile vessel diameter waveforms in the fetal descending aorta.

Animals↗
PubMed1988

Monitoring aspects of an ultrasonic esophageal transducer. Initial experience.

A method of semi-automatic contour detection is described using a commercial (Kontron) image analysis instrument. Input data consists of high-quality transesophageal echocardiograms of short-axis left ventricular cross-sections. The purpose of the study is to evaluate the feasibility of such a method for the quantitative monitoring of the dynamic behaviour of the left ventricle during high risk surgery. From the first experience it is authors' impression that the automatically derived contour depends strongly on the selected algorithm parameters. Therefore derivation of absolute measurements from these contours seems problematic. Automatic contour detection seems much better fit for monitoring situations, where the patient acts as his own reference and there is no need to change the algorithm parameters.

Echocardiography↗
PubMed1988

Design and construction of an esophageal phased array probe.

The clinical urge for echocardiographic data from patients with inadequate image quality at the precordial examination has initiated the development of transesophageal scanning techniques. The orientation of heart structures with respect to the transducer position in the esophagus, the absence of interfering structures in the soundbeam and the constraints imposed by the anatomy of the esophagus result in a different set of parameters for the optimization of the transducer and its assembly. In this article, the design and construction of a miniaturized 5 MHz phased array transducer optimized for transesophageal scanning is described. Relevant parameters and their influence on the design will be discussed, such as: bandwidth, sensitivity, resolution (in three dimensions), focal depth and the production method.

Echocardiography↗
PubMed1987

Limits of reproducibility of blood flow measurements by Doppler echocardiography.

This study evaluates the variability of a quantitative Doppler echocardiographic method for blood flow calculation at the mitral and tricuspid orifice. Four subjects underwent 2-dimensional Doppler echocardiography during normal respiration and nonrespiration. Doppler recordings were integrated to determine mean temporal velocity (MTV) for each cardiac cycle separately. MTV during inspiration and expiration were compared, as were MTVs of 20 consecutive cycles during nonrespiration. Diameters of mitral and tricuspid orifice and interception angles were measured in 10 consecutive cycles at 4 predetermined moments. All results were averaged to a mean subject situation. MTVs were significantly (p less than 0.001) higher during expiration than during inspiration (12.4 and 11.0 cm-2) for the mitral orifice and lower (9.2 and 11.0 cm-2) for the tricuspid orifice. MTV at both orifices showed a significantly smaller variability (7.7% and 9.0%) during nonrespiration than during respiration (14.5% and 13.2%). Diameters of mitral orifice and tricuspid orifice were significantly (p less than 0.001) larger during diastole than during systole whereas standard error of the mean for both was 5.0%. Interception angles measured at mitral orifice are all close to 0 degrees and show minimal variability, while at the tricuspid orifice the angle varied from 15 degrees in diastole to 25.5 degrees in systole, constituting a significant difference in cosine (0.96 to 0.90).

Adult↗
PubMed1987

A simplified mitral valve method for two-dimensional echo Doppler blood flow calculation: validation in an open-chest canine model and initial clinical studies.

Quantitative two-dimensional Doppler echocardiography is increasingly used for the calculation of cardiac blood volumes. This study evaluates a simplified method for measuring volume flow at the mitral valve orifice. In four open-chest dogs the simplified mitral valve method was compared to a previously described mitral orifice method for Doppler volume flow calculation and to data obtained by electromagnetic flow measurement. Cardiac output varied from 1.4 to 7.7 L/min. Correlation for both the Doppler method and the electromagnetic meter volume flows was r = 0.98 to 0.99, and there was no significant difference between the two methods. In a clinical pilot study, 10 children were studied in the catheterization laboratory, and the simplified Doppler flow method was compared to thermodilution cardiac output measurements with good results. The study indicates that the simplified mitral valve method provides acceptable accuracy for Doppler cardiac output measurement.

Animals↗
PubMed1987

[A method of intraluminal echoarteriography].

Interventional cardiology and new recanalisation methods have pressed the need for high frequency intra-arterial imaging to visualize obstructions. In a first in-vitro set-up it is shown that intra-arterial echo imaging is possible. Ideas to further integrate this with spark erosion are presented and serve for further study.

Cardiac Catheterization↗
PubMed1987

Spark erosion of arteriosclerotic plaques.

For the recanalization of occluded arteries by means of plaque ablation an electrical technique, called spark erosion, has been developed. In vitro tests have shown that well-defined holes can be produced easily in fibrous, collagenous and lipid plaques, with minimal thermal side effects. As the method is not, by its nature, selective in vivo application will require an additional guidance technique to avoid arterial perforation. For this purpose, the potential use of tissue impedance as a sensing parameter has been tested. Main advantages of spark erosion are that it is a well controllable, low cost and highly effective tissue ablation technique.

Animals↗
PubMed1986

Effects of nifedipine on left ventricular performance in unstable angina pectoris during a follow-up of 48 hours.

In 1981, a large, double-blind, randomized, multicenter trial was started in The Netherlands to evaluate the therapeutic effects of nifedipine or metoprolol in patients with unstable angina. This study, called the Holland Interuniversity Nifedipine Trial (HINT), included several hundred patients to establish potential therapeutic effects. From December 1982 until January 1984 the effects of nifedipine on left ventricular (LV) performance in a subgroup of 37 HINT patients were studied using radionuclide techniques. All patients (18 treated with nifedipine, 19 with placebo) underwent radionuclide angiography and 33 underwent thallium-201 scintigraphy just before and 48 hours after the start of treatment with the experimental medication. Radionuclide angiographic studies were also performed 1 hour (29 patients) and 4 hours (31 patients) after the start of treatment. The thallium-201 images showed defects in 24 (73%) of the baseline images and in 21 (64%) of the 48-hour images. No significant differences were seen between patients receiving nifedipine or placebo in the incidence of new defects or in the disappearance of defects at 48 hours. Changes in thallium-201 images were not related to recurrence of myocardial ischemia or the development of acute myocardial infarction. Nineteen of the 37 patients (51%) with baseline blood pool images had a reduced LV ejection fraction (EF) (38 +/- 10%) and 18 patients (49%) had a normal LVEF of 56 +/- 5%. LVEF improved after 48 hours in 8 patients receiving nifedipine and in only 1 patient receiving placebo (p less than 0.02). This effect was not present at 1 and 4 hours after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Angina Pectoris↗
PubMed1986

Influence of nifedipine on left ventricular perfusion and function in patients with unstable angina: evaluation with radionuclide techniques.

In 1981, a large, double-blind, randomized trial was started in The Netherlands to evaluate the therapeutic effects of nifedipine and/or metoprolol in patients with unstable angina. This study has been called the Holland Interuniversity Nifedipine/metoprolol Trial (HINT) and required several hundred patients to establish potential therapeutic effects. From December 1982 to January 1984 the effects of nifedipine on left ventricular (LV) performance in a subgroup of 52 HINT patients were studied using radionuclide techniques. All patients (23 on nifedipine, 29 controls) underwent thallium-201 scintigraphy or radionuclide angiography just before and 48 h after the start of experimental medication. The radionuclide angiographic studies were also performed at 1 and 4 h after treatment. Nifedipine did not influence the incidence or disappearance of perfusion defects on the 48-h thallium images. No significant differences in overall LV ejection fraction (EF) were seen at any time between nifedipine-treated patients and controls. However, paired observations in 37 patients showed improvement of LVEF after 48 h in 8 patients on nifedipine and in only 1 control patient. Scintigraphic measurements on admission were not related to clinical outcome after 48 h. Concomitant administration of metoprolol did not influence LVEF in either group. It is concluded that nifedipine improves LVEF after 48 h in a subset of patients with unstable angina without affecting myocardial perfusion. This finding indicates that nifedipine has a predominant effect on afterload reduction in patients with unstable angina. However, early scintigraphic measurements had no significant predictive value for subsequent cardiac events.

Angina Pectoris↗
PubMed1986

Transducers in medical ultrasound. Part 4: Transducer safety.

Transducer safety encompasses a wide spectrum of topics. It may range from mechanical construction reliability to biological effects created by ultrasound radiation. In this Paper the electrical and acoustical safety aspects are summarized and initial experience with sterilization of echocardiographic transducers for peroperative cardiac scanning is mentioned.

Echocardiography↗
PubMed1985

Transducers in medical ultrasound: Part Two. Vibration modes, matching layers and grating lobes.

The performance of transducers used for medical diagnosis depends to a great extent on matching layer, backing impedance and geometry of the active surface. In this paper special attention is given to the element vibrational modes, the optimum matching, the grating lobe and change of the real acoustic impedance into an imaginary impedance as a function of the product of the width and wavelength. Grating lobes on the echo image and the effect of a mismatch of the matching layer are illustrated. Suggestions are made for the design of linear and phased array transducers considering the above-mentioned aspects.

Humans↗
PubMed1985

Transducers in medical ultrasound: Part One. Ferro-electric ceramics versus polymer piezoelectric materials.

A wide variety of transducer shapes and applications exists in the field of diagnostic ultrasound. As a basic material ferro-electric ceramics are used almost exclusively, but polymer piezoelectric material seems a new alternative. By comparing in a qualitative way the most relevant parameters of these materials, a state of the art judgement may be made about their applicability in diagnostic ultrasound.

Ceramics↗
PubMed1985

Left ventricular performance in unstable angina: assessment with radionuclide techniques.

In a clinical trial we studied left ventricular performance at rest in 50 patients with unstable angina by radionuclide techniques. Thallium-201 scintigraphy was performed on admission in 38 patients and repeated after 48 hr in 32 patients. Also dynamic blood pool scintigraphy was performed in 37 patients on admission and in 45 patients after 48 hr. Of the 50 patients, 27 (54%) had no recurrent episodes of myocardial ischemia, but 23 (46%) patients showed recurrent ischemic episodes of whom 11 (22%) patients developed a myocardial infarction. The thallium-201 images showed perfusion defects in 27 (71%) of the 38 patients studied on admission and in 20 (63%) of the 32 patients studied at 48 hr. No relation between clinical outcome and presence or absence of defects was observed. Left ventricular ejection fraction was abnormal (less than 50%) in 19 (51%) of the 37 patients on admission and in 29 (64%) of the 45 patients studied at 48 hr. As with thallium-201, no relation could be established between clinical outcome and left ventricular ejection fraction. It is concluded that radionuclide techniques are useful to provide insight into the pathophysiological mechanism of unstable angina, but they are not helpful for the short-time assessment of clinical outcome.

Angina Pectoris↗