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Biomedical subjects

E L Ritman

Publications and source records attributed to E L Ritman.

At least 19 recordsLinked to original sources
PubMed1992

Myocardial volume perfused by coronary artery branches--a three-dimensional x-ray CT evaluation in human cadaver hearts.

The volume of myocardium perfused by coronary arterial branches and cumulative length of the main feeder branches perfusing that volume were measured from multislice computed tomography images of human cadaver hearts with barium sulfate gel injected into the coronary arteries. Previously we have shown in in vivo pig hearts that the relationship between the volume (V), in mL, of perfused myocardium and the length (L), is well conveyed by V = M x 10(-aL) where M is total mass of myocardium perfused by a major epicardial artery and a is constant congruent to 0.01 mm-1. In the nine human hearts studied, this relationship was V = 115 x 10(-0.006L), r = -0.894 for the LAD; V = 48 x 10(-0.009L), r = -0.7663 for the LCX and V = 103 x 10(-0.004L), r = -0.673 for the RCA. These results suggest that the angiographically delineated volume of myocardium at risk of infarction, due to acute blockage along a coronary artery, could possibly be estimated from the 3D branching geometry of the epicardial coronary arterial tree.

Adolescent↗
PubMed1992

Bending and twisting of an in vivo coronary artery at a bifurcation.

Dynamic changes in the geometric shape and dimensions of a left coronary artery tree were extracted from the computer-tomographically reconstructed three-dimensional images of an in situ beating heart of an anesthetized dog. Wireframe models of the left coronary artery tree at 16 different instants of a cardiac cycle were constructed for the study of its flexing motion. For quantifying the local bending and twisting of the left coronary artery tree, the anatomic landmarks of the bifurcation points are selected as focussed locations. At these points, the space curves of the tree at different cardiac instants were first derived in parametric forms. Curvature and torsion expressions are next obtained in terms of the derivatives with respect to the parameter. This analysis revealed that during the initial contraction of the heart wall, a 2% reduction per millisecond in the radius of curvature occurred near the bifurcation point where the left circumflex coronary artery descends toward the apex of the heart. When the left ventricular chamber reached a maximum value, the radius of curvature was found to decrease at a rate of 2.3% ms-1. At the end of diastole, an increase in the radius of curvature at a rate of 5.7% ms-1 was observed. The twisting rates per unit length of artery near the bifurcation point of the selected artery were found to range from -0.62 to 0.63 degrees ms-1.

Animals↗
PubMed1992

Myocardial volume perfused by coronary artery branches. A three-dimensional X-ray computed tomographic evaluation in pigs.

RATIONALE AND OBJECTIVES: The authors tested the hypothesis that the cumulative length of arterial branches is related to the volume of tissue they perfuse. This experiment investigates the potential value of this approach for assessing the volume of myocardium at risk in cases of coronary occlusion. METHODS: The volume of myocardium perfused by coronary arterial branches and the cumulative length of the main feeder branches perfusing that volume were measured in vivo in pig hearts from multislice computed tomographic (CT) images of the heart, recorded during an aortic root injection of nonionic contrast agent. RESULTS: The relationship between the volume (V, in milliliters) of perfused myocardium and the length (L, in millimeters) of the left anterior descending artery was V = 42.4 x 10(-0.011L) (r = -0.892); for the right coronary artery, V = 37.0 x 10(-0.008L) (r = -0.888); and for the left circumflex coronary artery, V = 27.7 x 10(-0.011L) (r = -0.883). CONCLUSIONS: These results suggest that the maximum volume of myocardium at risk of infarction due to blockage along a coronary artery could possibly be estimated from the three-dimensional geometry of the epicardial coronary arterial tree.

Animals↗
PubMed1992

Dynamic intramyocardial blood volume: evaluation with a radiological opaque marker method.

In this study the change of intramyocardial blood volume within one cardiac cycle was deduced from the time sequence of the volume delineated by radiopaque markers attached to the left ventricular wall. These data were compared with the change in the volume of the same region of myocardium estimated from the change in angiographic opacification of the heart wall. Five dogs were anesthetized, and four pairs of 2-mm-diameter lead beads were attached to the epicardial and endocardial regions. Two scans using the dynamic spatial reconstructor (a high-speed computed tomographic scanner) were performed during aortograms, one under control conditions and the other during adenosine infusion. The results have shown that the increases of myocardial volume defined by the beads (delta Vbead, % of volume at control) were comparable to the increase of intramyocardial blood volumes estimated by the increase in wall opacity (delta Vblood, % of muscle); delta Vblood = 0.93 delta Vbead + 1.54%; r = 0.987.

Animals↗
PubMed1992

In vivo relation of intramyocardial blood volume to myocardial perfusion. Evidence supporting microvascular site for autoregulation.

BACKGROUND: The goal of this study was to explore the role of several factors that affect intramyocardial blood volume by using minimally invasive computed tomography. Anesthetized dogs were scanned with the dynamic spatial reconstructor, a high-speed tomographic scanner, during injection of a bolus of iohexol into the aortic root. METHODS AND RESULTS: In control dogs, it is indicated that the fraction of myocardium that is blood (FMB, %) relates to myocardial perfusion (F, milliliters per gram per minute) in that region as FMB congruent to a.F1/2, where a = 9.5 +/- 1.2% (milliliters times minute per gram)1/2 (mean +/- SD) in the subendocardium and a = 9.6 +/- 1.1% in the subepicardium. In another group of dogs, for the myocardium perfused by a stenosed epicardial artery, a increased to approximately 10 for a 25-43% stenosis (or pressure gradient of 9 mm Hg across narrowing) and to greater than 11 for a 50-55% stenosis (or pressure gradient of 40 mm Hg across narrowing). In these dogs, flow was not impaired under control hemodynamic conditions, but the usual increase of flow (i.e., flow reserve) observed under maximum vasodilation conditions was impaired. In another group of dogs, progressive embolization (using 15-microns-diameter microspheres) of the left ventricular myocardial microcirculation caused the value of a to remain at approximately 9.5 with embolization up to 50% of the fatal dose of microspheres, but it then decreased progressively with embolization to 4.6 at the fatal dose. CONCLUSIONS: We conclude that the FMB/F relation reflects hemodynamic conductance at the microvascular level.

Animals↗
PubMed1991

LV oxygen consumption and pressure-volume area: role of norepinephrine and verapamil.

The effect of norepinephrine or verapamil on the relationship of left ventricular (LV) myocardial oxygen consumption (MVO2) and systolic pressure-volume area (PVA) was investigated in hearts within the never-opened thorax of dogs with blocked baroreceptor reflex. LV chamber volumes and myocardial blood flow were measured using a fast computed tomography scanner. At 10 micrograms/min delivery rate of norepinephrine, MVO2 (mJ.g-1.cycle-1) equals (2.30 +/- 0.48) PVA + (20.60 +/- 4.24) (n = 11; 1 mJ.g-1.cycle-1 is equivalent to 0.563 ml O2.100 g-1.min-1 at 112 beats/min). With verapamil infusion, MVO2 equals (2.57 +/- 1.33)PVA + (10.73 +/- 3.16) (n = 17). The regression slopes did not differ (P greater than 0.25) for any of the conditions. At comparable PVA values the norepinephrine group showed an increase of MVO2 compared with the prenorephrine baseline state (P less than 0.01), and the verapamil group showed a reduction of MVO2 compared with the preverapamil baseline state (P less than 0.05). We conclude that the MVO2 to LVPVA relationship in the in situ heart, within the never-opened thorax, conveys that the oxygen-wasting effect of catecholamines is quantifiable using the shift in this relationship.

Animals↗
PubMed1990

LV pressure-volume area and oxygen consumption: evaluation in intact dog by fast CT.

The relationship between left ventricular (LV) myocardial oxygen consumption (MVO2) and LV systolic pressure-volume area (PVA) was investigated in anesthetized closed-chest dogs with intact reflexes and subsequently with beta-adrenergic blockade, with or without simultaneous muscarinic blockade. LV chamber volumes were measured using a fast computerized tomography (CT) scanner (dynamic spatial reconstructor, DSR) at 33-ms intervals. Myocardial blood flow was measured from the DSR scans of aortic root angiograms. With intact reflexes, LV MVO2 (Y) related to PVA (X) values as Y = (4.28 +/- 1.81)X + (1.94 +/- 6.0) (n = 24) (mJ.g-1.cycle-1). With beta-adrenergic blockade, LV MVO2 (Y) related to PVA (X) value as Y = (4.24 +/- 1.03)X - (6.43 +/- 6.5), (n = 9) (mJ.g-1.cycle-1). With beta-adrenergic and muscarinic blockade, LV MVO2 (Y) related to PVA (X) value as Y = (2.84 +/- 1.72)X + (3.51 +/- 5.15), (n = 13) (mJ.g-1.cycle-1). The slopes of these regressions are higher than the slopes demonstrated by others in isolated ventricles but very similar to those demonstrated in open-chest dogs.

Adrenergic beta-Antagonists↗
PubMed1979

Right and left ventricular function after the Mustard procedure in transposition of the great arteries.

Right and left ventricular function was assessed at cardiac catheterization in 33 asymptomatic patients 0.5 to 11 years (mean 4.6) after the Mustard operation for complete transposition of the great arteries. Ages at operation had ranged from 0.5 to 16 years (mean 4.2 years). Right ventricular function was assessed using videodensitometric determination of ejection fraction and ventricular volume data. Ventricular volumes were obtained by computerized video analysis utilizing Simpson's rule. The right ventricular ejection fraction was 37 +/- 11 percent (standard deviation), as assessed with videodensitometry and 42 +/- 10 percent as assessed with ventricular volume--both values less than normal (P less than 0.001). Right ventricular end-diastolic volume was significantly greater than normal (P less than 0.001) and averaged 202 +/- 70 percent, but left ventricular end-diastolic volume averaged only 125 +/- 53 percent. These observations after the Mustard operation indicate that right ventricular function is seriously decreased with relatively preserved left ventricular function. They support efforts for surgical correction utilizing the left ventricle as the systemic ventricle.

Age Factors↗
PubMed1979

Application of optimized parallel processing digital computers and numerical approximation methods to the ultra high-speed three-dimensional reconstruction of the intact thorax.

In order to achieve the computational capability to carry out many thousands of cross-sectional reconstructions, necessary to support a prototype high temporal and spatial resolution cylindrical scanning multiaxial tomographic unit, a series of design, software simulation, and fabrication studies is underway to develop a special-purpose high-speed reconstruction computer. This processor will rely upon integrated circuit arithmetic components of advanced design, and highly parallel architecture to execute X-ray based transaxial reconstruction algorithms at the rate of hundreds of cross sections/sec.

Computers↗
PubMed1979

Display and visualization of three-dimensional reconstructed anatomic morphology: experience with the thorax, heart, and coronary vasculature of dogs.

A new method, termed reprojection, is used to visualize anatomic morphology contained within three-dimensional reconstructions made up of images of multiple parallel cross sections. This method involves the projection, either orthographically into a plane or radially onto a cylinder, of the volume picture elements (voxels) of the reconstruction. Orthographic reprojection images, formed by mathematically summing the magnitudes of the voxels along selected parallel paths through the reconstructed volume, are analagous to conventional radiographs formed by the passage of an X-ray beam through the volume. The reprojection image is a two-dimensional array of picture elements that is displayed on a television monitor using a digital-to-video scan converter. Also described are the techniques of noninvasive selective tissue dissolution and numerical dissection, whereby obscuring portions of the reconstructed volume are either partially "dissolved" or totally eliminated before reprojection. Utilizing these methods, anatomic information present in a three-dimensional reconstruction but not clearly seen in a reprojection image is rendered visible after removal of superposed structures. The usefulness of these methods is demonstrated utilizing three-dimensional reconstructions of the thorax, heart, and coronary arteries of dogs.

Animals↗
PubMed1979

High speed synchronous volume computed tomography of the heart.

A new generation, fully electronic high-speed whole-body computed tomography system is being developed to provide accurate dynamic visualization and measurement of the vital functions of the heart based on rapid changes in its shape, dimensions, and perfusion. This Dynamic Spatial Reconstruction System (DSR) will provide stop-action (1/100 sec.), rapidly sequential (60/sec.) synchronous volume (240 simultaneous, 1mm-thick cross sections) reconstructions and display of the full anatomic extent of the internal and external structures of the heart throughout successive cardiac cycles, and will permit visualization of the three-dimensional vascular anatomy and circulation throughout the myocardium.

Animals↗
PubMed1979

Assessment of left ventricular function in secundum atrial septal defect by computer analysis of the M-mode echocardiogram.

Left ventricular function in 53 patients with secundum atrial septal defect was assessed by computer-assisted analysis of the left ventricular echocardiogram and by cardiac catheterization. The patients were divided into two groups, those younger and those older than 60 years, to investigate the effect of aging on left ventricular function. Cavity size was significantly smaller than normal (p less than 0.01) and septal motion was abnormal in 86%, but values for cardiac index, left ventricular end-diastolic pressure, velocity of circumferential fiber shortening, left ventricular filling rate, and duration of rapid filling were normal in both groups. Regional dynamics assessed in terms of peak rates of systolic thickening and diastolic thinning of the septum and posterior wall were also normal in both groups. We concluded that, although left ventricular minor dimensions are small, and septal motion is reversed in the majority of patients with atrial septal defect, left ventricular function is normal, and it does not appear to deteriorate with increased age, pulmonary hypertension, or the presence of right ventricular failure. The abnormal septal motion appears to be compensated for by enhanced septal and posterior wall percentage thickening.

Adolescent↗
PubMed1979

Emission-computed tomography and its application to imaging of acute myocardial infarction in intact dogs using Tc-99m pyrophosphate.

The techniques of emission-computed tomography have been used to obtain in vivo quantitative estimates of the three-dimensional distribution of gamma-emitting radionuclides in dog hearts. Conjugate views, obtained for 60 equiangular projections around 360 degrees by rotating the object in front of a gamma camera, were used to reconstruct multiple-level emission transaxial images for various test objects, and for dogs with surgically induced acute myocardial infarcts. Corrections for attenuation were performed in the backprojection step of the convolution algorithm used for reconstruction. Quantitative estimates of the spatial extent and concentration of activity were obtained to within 10--15% rms error. Correlations were obtained between the radionuclide and histopathologic estimates of the extent and location of infarction.

Animals↗
PubMed1978

Spatial distribution of pulmonary blood flow in dogs in increased force environments.

Spatial distribution of pulmonary blood flow (SDPBF) during 2- to 3-min exposures to 6-8 Gy acceleration was studied, using radioactive microspheres in dogs, and compared to previously reported 1 Gy control distributions. Isotope distributions were measured by scintiscanning individual 1-cm-thick cross sections of excised, fixed lungs. Results indicate: 1) the fraction of cardiac output traversing left and right lungs did not change systematically with the duration and magnitude of acceleration; but 2) the fraction is strongly affected by the occurrence or absence of fast deep breaths, which cause an increase or decrease, respectively, in blood flow through the dependent lung; and 3) Gy acceleration caused a significant increase in relative pulmonary vascular resistance (PVR) in nondependent and dependent regions of the lung concurrent with a decrease in PVR in the midsagittal region of the thorax. Result 3 may be mediated primarily by changes in regional alveolar volume and geometry in the nondependent hemithorax conbined with hydrostatic effects of extravascular fluid and active hypoxic response in the dependent region and is superimposed on, and may override, hydrostatic effects of perfusion pressures on SDPBF during acceleration.

Adaptation, Physiological↗
PubMed1978

Regional myocardial wall thickening response to nitroglycerin. A predictor of myocardial response to aortocoronary bypass surgery.

The peak rate of systolic wall thickening (p +/- dTw/dt) in regions of the left ventricle (LV) was determined preoperatively by biplane roentgen videometry in 18 patients before and after sublingual administration of nitroglycerin (NTG) and 3-23 months (median 12) after aortocoronary bypass surgery. The regional LV response to NTG was a reliable predictor for postoperative improvement in regional wall dynamics after successful aortocoronary bypass grafting. The ejection fraction response to NTG or surgery will not predict the regional myocardial response to NTG or surgery, nor will the regional response predict the global response. Subendocardial myocardial infarction is another cause of unimproved regional myocardial function after NTG and aortocoronary bypass surgery.

Adult↗
PubMed1978

Cardiac function in the normal newborn: additional information by computer analysis of the M-mode echocardiogram.

Computer analysis of the M-mode echocardiogram in 50 normal newborns provided measurements of wall thicknesses and chamber size and, in addition, assessment of right and left ventricular wall, septal, and cavity dynamics throughout the cardiac cycle. Data obtained with this new technique indicated that (1) right and left ventricular cavity functions are similar in the normal newborn, (2) right and left ventricular cavity filling and emptying vary directly with peak rates of septal and ventricular wall thinning and thickening, respectively, and (3) there is a close time relationship among maximum left atrial dimension, minimum left ventricular dimension, and mitral valve opening. This analysis, which is the first complete analysis of the echocardiogram in the newborn, provides a normal range of septal and ventricular wall dynamics as well as right and left ventricular and left atrial function and has clinical implications in that it may allow early recognition of both congenital and perinatal myocardial disease.

Atrial Function↗