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Biomedical subjects

J R Kramer

Publications and source records attributed to J R Kramer.

At least 37 records · Page 2Linked to original sources
PubMed1991

Cardiac catheterization 1990: a report of the Registry of the Society for Cardiac Angiography and Interventions (SCA&I).

This report presents the first year's experience of a totally computerized cardiac catheterization laboratory reporting system, including the results and complications of invasive and interventional procedures. Sixty-three laboratories reported a total of 71,916 patients studied between January 1 through December 31, 1990. Two previous registry reports have been published. Compared with data acquired by previous methods, in spite of an older and sicker population, the mortality for diagnostic procedures has remained remarkably constant (0.11%). The computerized format facilitates data collection and analysis, helps resolve new issues as they arise and serves as a method of monitoring quality of laboratories and individuals.

Adult↗
PubMed1991

476 nm excited laser-induced fluorescence spectroscopy of human coronary arteries: applications in cardiology.

We have shown that normal coronary arteries and noncalcified and calcified atherosclerotic plaque can be differentiated on the basis of the 476 nm excited fluorescence spectra, providing the basis of a spectroscopic guidance system for coronary artery laser angiosurgery. This discrimination is based on extraction of parameters from tissue fluorescence spectra, which are proportional to the tissue concentrations of structural proteins (collagen and elastin) and ceroid via a model of tissue fluorescence. We use these parameters to calculate the likelihood that an area of interest in a coronary artery is normal, noncalcified, or calcified plaque. This method of diagnosing atherosclerosis provides information about the histochemical composition of atherosclerotic lesions and is thus fundamentally different from the diagnostic methods currently used. It may ultimately have bearing on a number of pertinent clinical problems. We have discussed applications to studying initiating factors in formation and progression of plaque, healing after interventional treatments, and the likelihood of restenosis after PTCA.

Algorithms↗
PubMed1990

Ten-year survival of patients with mild angina or myocardial infarction without angina: a comparison of medical and surgical treatment.

Ten-year survival percentages were calculated for groups of 407 initially medically treated patients and for 390 patients who had early coronary bypass surgery; all had either mild angina pectoris or myocardial infarction without subsequent angina pectoris. Uncensored actuarial survival was 77% for medical patients and 83% for the surgical group. For 179 patients who had internal thoracic (mammary) artery grafting as part of their procedures, survival was 91% in contrast to 76% for those who had vein grafts only. A sharp drop of the survival curve for the vein graft group after the seventh year was not shown for those who had internal thoracic artery grafts. Survival was 71% for 280 patients treated medically only.

Angina Pectoris↗
PubMed1989

Alteration of spectral characteristics of human artery wall caused by 476-nm laser irradiation.

Fluorescence spectroscopy is a promising new technique for discrimination of normal and atherosclerotic arterial tissues. It has been suggested that this technique be used as a guidance system for laser angiosurgery catheters; however, irradiation by 476-nm light can change the spectroscopic properties of arterial tissue. We present studies that establish intensity levels and exposure times at which alterations in tissue spectral properties are minimal. We also investigate the nature of spectral alterations following exposure of normal human aorta to high intensities of 476-nm laser light. Changes in laser-induced fluorescence (LIF) are characterized by two prominent features: the peak fluorescence intensity decreases permanently, and the fluorescence lineshape changes in a largely reversible way. We relate these changes to alterations in individual tissue chromophores: permanent changes in absolute fluorescence intensity are due to irreversible changes in tissue fluorophores, reversible changes in fluorescence lineshape are due alterations in tissue absorbers. A simple kinetic model is used to describe the decrease in absolute fluorescence intensity.

Aorta↗
PubMed1989

Late follow-up of 781 patients undergoing percutaneous transluminal coronary angioplasty or coronary artery bypass grafting for an isolated obstruction in the left anterior descending coronary artery.

Seven hundred eighty-one patients with isolated left anterior descending coronary atherosclerosis treated with either coronary artery bypass grafting or percutaneous transluminal coronary angioplasty between January 1980 and December 1984 were studied to determine late survival and event-free survival. Follow-up was complete in 775 patients (99.4%). Actuarial survival at 5 years was 98% for surgical patients and 95% for angioplasty patients (p = 0.02). Five-year event-free survival (freedom from myocardial infarction, bypass grafting, angioplasty, and death) was 93% for surgical patients and 62% for angioplasty patients. This study suggests that the higher initial cost and complexity of bypass surgery may be justified by superior long-term results.

Angioplasty, Balloon, Coronary↗
PubMed1989

Spectral diagnosis of atherosclerosis using an optical fiber laser catheter.

This communication demonstrates that fluorescence spectra of human aorta with good S/N ratios can be collected using an optical fiber laser catheter. The performance of this catheter is compared to a non-fiber optic collection system with an equivalent delivery/collection geometry. For a given sample, fluorescence lineshapes obtained using the two systems are identical; differences in peak fluorescence intensity are related to the different collection efficiencies of the two systems. It is shown that the fluorescence lineshape of arterial tissue depends on the delivery/collection geometry of the detection system, and that this is due to the interaction of absorption and fluorescence within the artery wall. This effect is investigated systematically using a specially designed collection system. Results are analyzed qualitatively using a simple, one-dimensional model of tissue fluorescence. With this analysis, we present design requirements for a collection system in which such geometric effects are eliminated, and show that our optical fiber laser catheter satisfies these requirements.

Aortic Diseases↗
PubMed1989

Argon ion laser-excited autofluorescence in normal and atherosclerotic aorta and coronary arteries: morphologic studies.

Argon ion laser-excited autofluorescence was studied in unstained frozen sections of 47 normal and atherosclerotic human aortas and coronary arteries by means of a bright-field microscope modified for fluorescence microscopy with 476 nm argon ion laser epillumination, and compared to morphology in serial sections stained with H & E, Movat pentachrome, and oil red O. Normal artery autofluorescence correlated morphologically with the structural protein fibers elastin and collagen in the intima, media, and adventitia. Atherosclerotic plaque autofluorescence correlated morphologically with lipid or calcified deposits in the atheroma core. The autofluorescence of these deposits differed from that of elastin and collagen in distribution, intensity, and color, and increased with the severity of the plaque. We conclude that argon ion laser-excited autofluorescence in normal and atherosclerotic arteries correlates with morphology and has diagnostic potential in laser angiosurgery.

Adult↗
PubMed1989

The dynamics of progression of coronary atherosclerosis studied in 168 medically treated patients who underwent coronary arteriography three times.

To study the dynamics of progression of coronary atherosclerosis we analyzed findings in 168 patients who underwent coronary arteriography three times without undergoing coronary surgery or percutaneous transluminal coronary angioplasty. Of 66 patients who had progression in interval 1 (from first to second coronary arteriogram), 32 also had progression in interval 2 (from second to third coronary arteriogram); of 102 patients who had no progression in interval 1, 37 had progression in interval 2. In only 9 of the 32 patients who had progression during both intervals was the same lesion involved, and in six of these patients other lesions were also involved. Progression correlated with the duration of the interval between catheterizations, an increase in symptoms, and the occurrence of myocardial infarction. Analysis of variance showed no significant differences in mean values for age, blood pressure, total serum cholesterol, and serum triglycerides in the four main progression groups. Progression of coronary atherosclerosis is a highly unpredictable process. It follows a nonlinear course, and information derived from sequential coronary arteriograms is of little value in predicting future progression.

Angiography↗
PubMed1989

A one-layer model of laser-induced fluorescence for diagnosis of disease in human tissue: applications to atherosclerosis.

This paper describes a general model of tissue fluorescence which can be used both to: 1) determine chemical and physical properties of the tissue, and 2) design an optimal algorithm for clinical diagnosis of tissue composition. This model is based on a picture of tissue as a single, optically thick layer, in which fluorophores and absorbing species are homogeneously distributed. As a specific example, the model is applied to the laser induced fluorescence (LIF) of normal and atherosclerotic human aorta using 476 nm excitation. Methods for determining the relevant attenuation and fluorescence lineshapes are detailed, and these lineshapes are used to apply the model to data from 148 samples. The model parameters are related to the concentrations of the major arterial chromophores: structural proteins, hemoglobin and ceroid. In addition, the model parameters are used to derive diagnostic algorithms for the presence of atherosclerosis. Utilizing a binary classification scheme, the presence or absence of pathology was determined correctly in 88 percent of cases.

Algorithms↗
PubMed1988

Remote biomedical spectroscopic imaging of human artery wall.

We discuss a general technique, laser spectroscopic imaging (LSI), remote acquisition of spectroscopic images of biological tissues and tissue conditions. The technique employs laser-induced spectroscopic signals, collected and transmitted via an array of optical fibers, to produce discrete pixels of information from which a map or image of a desired tissue characteristic is constructed. We describe a prototype LSI catheter that produces spectral images of the interior of human arteries for diagnosis of atherosclerosis. The diagnostic is based on the fact that normal artery wall and atherosclerotic plaque exhibit distinct fluorescence spectra in the 500-650 nm range when excited by 476-nm laser light; the fluorescence from blood is minimal. The catheter is composed of 19 optical fibers enclosed in a transparent, protective shield. Argon ion laser radiation is used for excitation, and an optical multichannel spectral analyzer is used for detection. Sequential sampling is used to minimize crosstalk among fibers and reduce blurring of the image. Computer-processed 19-pixel spectroscopic images are produced of fresh cadaver artery in vitro. Regions of normal tissue, plaque, and blood are identified, and the diagnoses are confirmed histologically and by direct spatial correlation. The results demonstrate the concept of using this laser catheter system for real-time imaging.

Arteriosclerosis↗
PubMed1988

Effects of varying argon ion laser intensity and exposure time on the ablation of atherosclerotic plaque.

Using continuous wave (CW) argon ion laser light, a total of 253 laser exposures of varying power (1.5, 3, 5, 8 or 10 W) and duration (20-1,333 ms) were delivered to four segments of human atheromatous aorta obtained at autopsy. Exposure conditions were controlled by using an optically shielded laser catheter that provided a 500 micron spot of light of known power. Two thresholds for consistently reproducible ablation could be defined-an intensity threshold at 25.5 W/mm2 and a fluence threshold at 3.2 J/mm2. Above threshold, a fluence of 5.1 J/mm2 was found to produce the most efficient ablation, ie, removed the greatest volume (mm3) per energy delivered (J) compared to other fluence levels employed (p less than 0.0001). Between aortic segments, however, considerable variability in efficiency (mm3/J) was observed, possibly owing to different optical properties and/or plaque composition. Low-intensity laser radiation produced inconsistent ablation and extensive coagulation effects to surrounding tissue. When a fluence of 5.1 J/mm2 was constructed with a high-intensity laser beam and a short exposure time, consistent and efficient tissue removal resulted without histologic evidence of coagulation necrosis.

Angioplasty, Balloon↗
PubMed1988

Gas volume quantitation during argon ion laser ablation of atheromatous aorta in blood and 0.9% saline media with an optically shielded catheter.

Using an optically shielded fiber optic laser catheter, the amount of gas produced when firing an argon ion laser into 0.9% saline solution or blood alone and into atheromatous aorta in either a blood or 0.9% saline medium was quantitated. Energies from 0.25 to 4 joules (J) were used at powers of 2, 5, and 8 W. We found that total volume of gas produced is small not only at equilibrium (0.3 +/- 0.1 microliter/J when firing in blood alone and also when ablating aorta in blood or saline media) but also at peak (2.5 +/- 0.2 microliters/J firing in blood alone and 1.0 +/- 0.1 microliter/J or 0.9 +/- 0.1 microliter/J when ablating aorta in saline or blood, respectively). Because these volumes are small, a clinically significant event from a gas embolus is unlikely during intravascular laser ablation of atheromatous plaque in the energy and power range studied. No gas was quantitated when firing the argon ion laser into 0.9% saline solution alone. The peak gas volume when firing in blood alone was significantly greater than that produced in the other chamber environments. This is thought to be due to increased absorption of argon laser light by hemoglobin. The gas volumes produced by lasing aorta in 0.9% saline or blood were not statistically different.

Angioplasty, Balloon↗
PubMed1988

Survival of patients with mild angina or myocardial infarction without angina: a comparison of medical and surgical treatment.

A group of 390 patients with mild angina pectoris or myocardial infarction without subsequent angina had early coronary bypass operation. Five year survival was significantly higher (95.4%) than in a similarly selected medically treated group (88.5%) reported before. One death occurred in the 30 day postoperative period. Five year survival in the 179 patients who had internal mammary artery grafts was 98.9%. Survival for patients with mild angina and satisfactory left ventricular function (96.2%) was significantly higher than in the medical subset (91.3%). In the patient population studied, five year survival was higher in patients who had early bypass operations than in those who did not.

Adult↗
PubMed1988

Removal of surgically induced fibrous arterial plaques by argon ion laser angiosurgery using a multifiber delivery system. An experimental study in the dog.

Removal of intravascular atherosclerotic obstructions by laser irradiation has gained the attention of many investigators, but has proven to be considerably more difficult to accomplish than initially envisioned. We tested, in an animal model, an argon ion laser delivery system that permits control of (1) laser power, (2) exposure time, and (3) laser beam spot size. The study was conducted on surgically, induced focal fibrous plaques in the carotid arteries of nine dogs. Plaque removal, vessel patency, and healing were evaluated angiographically and by light and electron microscopy at intervals up to 60 days after treatment. Results showed that intravascular obstructions could be removed, healing occurred, and vessels remained patent for up to 60 days.

Animals↗
PubMed1987

A model for thermal ablation of biological tissue using laser radiation.

We present a theory of thermal laser ablation based on the heat equation and on an energy balance equation derived from it. Ablation is assumed to be brought about by the heating and evaporation of tissue water. The model is three-dimensional, and scattering and the water-steam phase transition are explicitly taken into account. The model predicts threshold parameters and a steady-state ablation velocity in terms of the optical and thermal properties of the tissue and the laser beam intensity and spot diameter.

Biophysical Phenomena↗
PubMed1987

The use of lasers in vascular and cardiac surgery. Clinical review.

Use of lasers is routine in medical fields such as ophthalmology and dermatology, but in spite of intensive research in recent years, its role in cardiac and vascular surgery still remains to be determined. Laser energy can vaporize atherosclerotic plaques in human arteries obtained at necropsy. Fiberoptic catheters have been constructed to deliver the laser energy to atheromas at a distance from the arteriotomy. The healing of the arterial wall after laser treatment is rapid and results in complete reendothelialization. Lasers have been used in patients undergoing coronary surgery as well as peripheral vascular reconstructions. In some cases, the percutaneous approach has also been used. In these clinical series, the laser treatment was in almost all cases followed by either transluminal balloon angioplasty or by-pass operation. Complications after laser treatment include vessel perforation, reocclusions, thrombosis, or aneurysm formation. The development of more advanced fiberoptic catheters and better understanding of dosimetric parameters are promising features to avoid these complications as well as development of methods for steering of the laser catheter itself and means for "real time" diagnosis (e.g. angioscopes, spectroscopic diagnosis). The future use of lasers in cardiac and vascular surgery seems promising, especially as an alternative to balloon angioplasty.

Cardiac Surgical Procedures↗