PubMed Health⌕ Search

Biomedical subjects

J M Tobis

Publications and source records attributed to J M Tobis.

72 records · Page 4Linked to original sources
PubMed1990

Assessment of normal and atherosclerotic arterial wall thickness with an intravascular ultrasound imaging catheter.

A prototype intravascular ultrasound imaging catheter with a 20 MHz transducer was used to obtain 59 cross-sectional images in 14 segments of human atherosclerotic arteries. Three distinct components of the arterial wall were visualized on the ultrasound images: a highly reflective intima, an echolucent media, and a moderately reflective adventitia. Images were obtained at 1 mm increments in vitro and were compared with histologic sections at the same levels. Measurements of the arterial layers showed a close correlation between ultrasound images and histologic sections for the thickness of the intimal plaque (r = 0.91), the media (r = 0.83), and the total wall thickness (r = 0.85). The ultrasound images overestimated the mean intimal and total wall thickness by 0.3 mm and 0.7 mm compared to measurements in histologic sections (p less than 0.001). Intravascular imaging with high-frequency ultrasound is an accurate method for measuring microanatomic arterial dimensions and the extent of atheromatous involvement of the arterial wall. This method could represent an important adjunct to traditional angiographic techniques for assessing the severity of atherosclerosis.

Arteries↗
PubMed1990

Intravascular ultrasonic imaging.

Because conventional imaging methods are inadequate for evaluating human coronary arteries in vivo, an intravascular ultrasonic imaging catheter was developed that allows the arterial wall to be studied in cross-section from within the artery. The catheter incorporates a mechanically rotating 20-MHz transducer, which is designed so that the ringdown occurs within the catheter and imaging is permitted up to the catheter's surface. The device rotates at 1800-rpm within a plastic sleeve and provides real-time cross-sectional images at 30 frames/sec. Preliminary experimental and clinical studies indicate that the intravascular ultrasonic imaging catheter could play a valuable role in providing preoperative information concerning arterial wall thickness and tissue characteristics, in distinguishing normal from diseased arterial wall structures during therapeutic intervention, and in assessing the results of intervention.

Journal Article↗
PubMed1989

Intravascular ultrasound cross-sectional arterial imaging before and after balloon angioplasty in vitro.

A prototype ultrasound imaging catheter was evaluated in vitro using 17 human atherosclerotic artery segments before and after balloon dilatation angioplasty. The catheter was 1.2 mm in diameter and incorporated a single 20-MHz ultrasound transducer to obtain cross-sectional images of the arterial lumen. In 15 of the 17 (88%) arteries, high quality images were obtained, which demonstrated clear demarcation between the lumen and the endothelium, the atheroma plaque, the muscular media, and the adventitia. Qualitative characteristics of plaque disruption, dissection, and residual flaps were readily visible. In addition, quantitative information about cross-sectional lumen area was obtained before and after balloon dilatation. The mean cross-sectional lumen area increased from 8.7 to 15.1 mm2 (p less than 0.01) following balloon dilatation. The lumen area measured from the ultrasound images following dilatation correlated closely with the area measured from histologic sections (r = 0.88). The results from this study indicate that a small-diameter ultrasound imaging catheter can be developed that will provide high-resolution qualitative and quantitative information during peripheral and coronary angioplasty.

Angioplasty, Balloon↗
PubMed1985

Superiority of two-dimensional measurement of aortic vessel diameter in Doppler echocardiographic estimates of left ventricular stroke volume.

Attempts to measure left ventricular stroke volume utilizing the Doppler aortic flow method have found varying correlations between invasive thermodilution and non-invasive Doppler methods. Because stroke volume is the product of the Doppler flow velocity integral (that is, the area under the flow velocity curve) and the cross-sectional area of the vessel through which blood flows, both variables are potential sources of error. Previous studies have shown that the Doppler flow velocity integral can be measured with acceptable reproducibility in the ascending aorta. Consequently, in this study an attempt was made to determine empirically the optimal method for measuring aortic diameter and area. The diameter of the ascending aorta was measured utilizing four M-mode and seven two-dimensional echocardiographic conventions. Doppler aortic flow velocity patterns were recorded with a 2.25 MHz M-mode echocardiographic transducer from the suprasternal notch by mapping the ascending aorta until aortic peak flow velocity was recorded. In 19 adult patients undergoing cardiac catheterization for clinical indications, Doppler stroke volume estimates utilizing the various echocardiographic conventions for measuring aortic root diameter and area were compared with simultaneous measurements of stroke volume by the thermodilution technique. The best correlation (r = 0.87) with thermodilution stroke volume was obtained by estimating aortic area from the two-dimensional parasternal long-axis images with the aortic dimension measured distal to the aortic sinuses from the inner to inner wall. The data were related by the equation: Thermodilution stroke volume = (0.73) X (two-dimensional Doppler stroke volume) + 17 cc.(ABSTRACT TRUNCATED AT 250 WORDS)

Aorta↗
PubMed1983

Correlation of 10-milliliter digital subtraction ventriculograms compared with standard cineangiograms.

Left ventriculograms were obtained with the use of 10 ml of contrast media by passing fluoroscopic video images through a video image processor. The low concentration of dye in the left ventricle was enhanced by the technique of mask mode subtraction, and the images were postprocessed to increase visibility by manipulation of the gray scale and contrast levels. These digital subtraction angiograms were compared to standard cineangiograms by means of 40 ml of contrast media. Of 30 patients studied, six (20%) had runs of ventricular tachycardia during the cineangiogram and had to be excluded. In the remaining 24 patients, there was a good correlation between the two techniques for left ventricular end-diastolic volume (r = 0.77, end-systolic volume (r = 0.95), and ejection fraction (r = 0.97). Spatial resolution in the digital studies was adequate to appreciate wall motion abnormalities that were visualized on the cineangiograms. Left ventricular end-diastolic pressure (LVEDP) did not change after the 10 ml injection, but the mean LVEDP rose 6.0 mm Hg after the 40 ml cineangiograms (p less than 0.01). Digital subtraction angiography can be used to obtain left ventriculograms with one-fourth the amount of contrast media and one-fourth the x-ray exposure compared to standard cineangiograms. This technology will permit multiple left ventriculograms to be obtained which, in turn, will allow intervention studies to be performed in the catheterization laboratory.

Adult↗
PubMed1981

Cardiotoxicity of amitriptyline and doxepin.

The cardiotoxicity of the tricyclic antidepressants amitriptyline and doxepin were compared in an animal with acute overdose. The mean repetitive extrasystole threshold (RET) decreased 71.5% with amitriptyline and 27.5% with doxepin (mean blood levels 933 ng/ml and 1889 ng/ml). Physostigmine reversed these effects. Sodium bicarbonate had a variable effect on the lowered RET. The toxic arrhythmogenic effects of the tricyclic antidepressants can be measured by RET and are partly autonomic tone manipulation. In the same blood level range, doxepin is less toxic than amitriptyline.

Amitriptyline↗
PubMed1980

Effect of amitriptyline antidotes on repetitive extrasystole threshold.

The effect of amitriptyline that leads to ventricular tachycardia was evaluated by the repetitive extrasystole threshold (RET) technique in 18 dogs. The RET was 28.8 +/- 7.9 mamp before and 8.2 +/- 5.3 mamp after amitriptyline, p less than 0.001. Physostigmine, propranolol, sodium bicarbonate, and left stellate ganglionectomy reversed the effect of amitriptyline on RET. We conclude that amitriptyline overdose predisposes to sudden death by lowering the ventricular fibrillation threshold. This cardiotoxic effect is mediated partly through the central nervous system and can be inhibited by increased plasma binding (bicarbonate), cholinergic stimulation (physostigmine), beta adrenergic blockade (propranolol), and sympathetic denervation (left stellate ganglionectomy).

Amitriptyline↗
PubMed1979

Effects of isosorbide dinitrate on pulmonary hypertension in chronic obstructive pulmonary disease.

Eighteen patients with chronic obstructive pulmonary disease with pulmonary hypertension were studied to assess the hemodynamic response to acute oxygen administration and to oral isosorbide dinitrate (ISDN). All 18 patients had baseline hemodynamic measurements and hemodynamic measurements during low-flow nasal oxygen. Following a second baseline measurement, patients received either oral ISDN (11 patients) or placebo (7 patients) in a randomized, double-blind protocol. Heart rate decreased with oxygen administration but there were no other significant hemodynamic changes. With oral ISDN, there was a significant fall in pulmonary artery and brachial artery pressure. Cardiac output, right atrial pressure, pulmonary wedge pressure, and pulmonary vascular resistance all fell but not significantly. We conclude that oral ISDN is effective in reducing pulmonary hypertension in patients with chronic obstructive pulmonary disease.

Blood Pressure↗
PubMedDate not supplied

Lessons from intravascular ultrasonography: observations during interventional angioplasty procedures.

This article reviews many of the applications of intravascular ultrasonic imaging for coronary and peripheral arterial disease. In vitro studies demonstrate an excellent correlation between ultrasound measurements of lumen and plaque cross-sectional area compared with histologic sections. In vivo clinical studies reveal the enhanced diagnostic capabilities of this technology compared with angiography. Ultrasonic imaging also permits visualization of the atherosclerotic plaque itself for the first time in vivo. In addition to accurately describing the plaque morphology, ultrasonography can identify some of the tissue characteristics of the plaque. During interventional procedures, ultrasonic imaging has been shown to be beneficial for enhanced diagnosis as well as improvement of our understanding of the mechanism of newer interventional devices such as directed atherectomy, rotational or TEC atherectomy, or excimer laser. Initial studies suggest that ultrasound guidance of intravascular stent deployment may be critical for optimizing stent placement. Randomized studies are currently in progress to determine whether the guidance provided by intravascular ultrasonic imaging will alter the results of interventional procedures so that the restenosis rate can be improved.

Angioplasty↗
PubMedDate not supplied

Limitations of coronary angiography compared with intravascular ultrasound: implications for coronary interventions.

The use of intravascular ultrasound catheters to produce images of lumen and plaque cross-sectional areas has had a profound effect on the practice of interventional cardiology. This imaging modality provides, for the first time, a low-power microscopic view of vascular anatomy within a living patient. This article will review some of the advantages of intravascular ultrasound imaging compared with angiography when used for diagnostic or interventional therapeutic procedures.

Atherectomy, Coronary↗
PubMedDate not supplied

The reproducibility of intravascular ultrasound imaging in vitro.

To determine which factors may affect the image quality when an intravascular ultrasound catheter is used in vivo, the influence of blood, temperature change, and contrast media were evaluated. In addition, to confirm the reproducibility of intravascular ultrasound imaging to measure cross-sectional lumen area, intraobserver and interobserver variability were determined. The findings indicated that ultrasound images in blood are mildly attenuated, that changes from room temperature to body temperature do not have a significant impact on the image quality, that contrast media attenuates the image intensity in a dose-dependent manner, and that the intravascular ultrasound imaging catheter provides a reproducible method for measuring arterial lumen area with excellent intraobserver and interobserver correlation.

Arteriosclerosis↗
PubMedDate not supplied

Comparison of noninvasive with hemodynamic data in patients with pulmonary hypertension due to chronic obstructive pulmonary disease.

Twenty-one patients with chronic obstructive pulmonary disease were studied with right heart catheterization. The mean pulmonary artery pressure (PAP) was compared with several noninvasive tests. The pulmonary lobar diameter/thoracic ratio correlated with the PAP, r = 0.677, P less than 0.01. The oxygen saturation and pH were used to derive a calculated value for PAP. The calculated PAP correlated with PAP values measured below 40 mm Hg, r = 0.787, P less than 0.01 but correlated very poorly with PAP values measured above 40 mm Hg. The electrocardiogram revealed at least one criterion for right ventricular abnormality in all 18 patients with pulmonary hypertension, but was too nonspecific to correlate with PAP. The hemoglobin concentration did not correlate with PAP. There was such wide variation between the measured PAP and the various noninvasive tests that these noninvasive tests could not be used to accurately predict the PAP in an individual patient.

Blood Gas Analysis↗
PubMedDate not supplied

ECMO assisted angioplasty for cardiomyopathy patients with unstable angina.

Patients who are otherwise unsuitable candidates for coronary bypass surgery or standard coronary angioplasty (PTCA) may be successfully treated with PTCA during ECMO. Five patients (3 men, 2 women), with a mean age of 57 years, are reported on here. They were not considered good candidates for standard therapy because of poor left ventricular function (mean EF, 24; range, 16 to 28%). Patients were supported by percutaneous femoral bypass using a BARD CPS machine, and underwent successful PTCA of either two vessels (three patients) or three vessels (two patients); in addition, one patient had dilatation of a stenotic aortic valve. Patients were supported with ECMO for 26 to 140 (mean 104) minutes, and required transfusion with 0 to 4 (mean 2) units of blood during or after the procedure. Complications included groin hematoma in two patients. All were discharged within 4 days of the procedure. Follow-up of the patients has been completed (4-7 mo) with no further hospitalizations for unstable angina. All patients remain in NYHA Class II or III. These data suggest that ECMO-assisted angioplasty is a safe and effective method of palliation of unstable angina associated with cardiomyopathy.

Adult↗