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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↗
PubMed1991

Chest wall motion during epidural anesthesia in dogs.

To determine the relative contribution of rib cage and abdominal muscles to expiratory muscle activity during quiet breathing, we used lumbar epidural anesthesia in six pentobarbital sodium-anesthetized dogs lying supine to paralyze the abdominal muscles while leaving rib cage muscle motor function substantially intact. A high-speed X-ray scanner (Dynamic Spatial Reconstructor) provided three-dimensional images of the thorax. The contribution of expiratory muscle activity to tidal breathing was assessed by a comparison of chest wall configuration during relaxed apnea with that at end expiration. We found that expiratory muscle activity was responsible for approximately half of the changes in thoracic volume during inspiration. Paralysis of the abdominal muscles had little effect on the pattern of breathing, including the contribution of expiratory muscle activity to tidal breathing, in most dogs. We conclude that, although there is consistent phasic expiratory electrical activity in both the rib cage and the abdominal muscles of pentobarbital-anesthetized dogs lying supine, the muscles of the rib cage are mechanically the most important expiratory muscles during quiet breathing.

Anesthesia, Epidural↗
PubMed1990

Fast computed tomography for quantitative cardiac analysis--state of the art and future perspectives.

Two fast computed tomographic scanners, designed primarily for imaging cardiac structures and function, have been in use since the early 1980s. The technical aspects of both systems have been described previously in detail, and a considerable body of scientific literature now documents the biomedical capabilities of these scanners. This review examines these biomedical capabilities as applied to quantitative analysis of the heart and pulmonary circulations. On the basis of this overview, some speculations about the current strengths and possible further developments of the fast computed tomographic approach in these applications are made.

Coronary Angiography↗
PubMed1990

Detection of mild coronary stenoses using the Dynamic Spatial Reconstructor.

The accuracy of the Dynamic Spatial Reconstructor (DSR) in the detection of moderate coronary artery stenoses was examined in 20 closed-chest dogs. Twenty-eight hollow plastic cylinders were embolized into the left coronary arteries and produced 25% to 56% reductions in arterial lumina diameter. For each dog, one three-dimensional (3-D) image of the heart was reconstructed from each DSR scan recorded during injection of contrast into the aortic root. Analysis involved blinded visual analysis by four independent observers of multiview projection images computed from the single 3-D image. Postmortem coronary angiograms of the isolated heart were considered definitive for location of the stenoses. Overall sensitivity of detection by DSR was 89% and specificity 81%. Sensitivity of detecting stenoses greater than or equal to 50% was 98%. Receiver operating characteristics (ROC) analysis showed that detection of stenoses in the left coronary arteries is of equal sensitivity and specificity.

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↗
PubMed1989

Significance of Doppler indices of diastolic filling of the left ventricle: comparison with invasive hemodynamics in a canine model.

Doppler measurements of mitral flow velocity curves have been proposed as a method for characterizing diastolic filling of the left ventricle. Different velocity curves have been empirically described in different disease states and under differing loading conditions in humans, but relating these various Doppler parameters to hemodynamic measurements of ventricular diastolic properties has not been fully elucidated. The effect of differing loading conditions (preload reduction, preload increase, afterload increase) on the Doppler mitral flow velocity and high-fidelity left atrial-left ventricular pressures was examined in seven closed-chest, anesthetized dogs. Preload reduction by balloon inflation in the inferior vena cava resulted in significant decreases in E velocity (early diastolic velocity) from 0.39 +/- 0.09 m/sec to 0.29 +/- 0.10 m/sec (p less than 0.01) and prolongation of deceleration time from 131 +/- 18 msec to 165 +/- 60 msec (p less than 0.05). Preload increase by infusion of fluids resulted in a significant increase in E velocity from 0.39 +/- 0.09 m/sec to 0.49 +/- 0.10 m/sec (p less than 0.001) and shortening of the deceleration time from 131 +/- 18 msec to 95 +/- 15 msec (p less than 0.001). The effect of afterload increase was variable and was dependent upon the left atrial pressure. Significant but weak positive correlations were noted between E velocity and maximal left atrial-left ventricular pressure gradient (r = 0.47, p less than 0.001) and total change in left ventricular pressure (r = 0.68, p less than 0.001), with inverse relationships between the deceleration time and these parameters. There was no overall relationship between the time constant tau and the E velocity, but an inverse relationship emerged when the data were examined according to different filling pressures. These results indicate that none of the mitral velocity measurements should be directly equated with other measurements of diastolic function. However, distinct velocity curves emerged under differing loading conditions that help in interpreting the meaning of these curves.

Animals↗
PubMed1989

Position and motion of the human diaphragm during anesthesia-paralysis.

Regional motion of the human diaphragm was determined by high-speed, three-dimensional x-ray computed tomography. Six healthy volunteers were studied first while awake and breathing spontaneously and again while anesthetized-paralyzed and their lungs ventilated mechanically. Tidal volume (VT) and respiratory frequency were similar during both conditions. Three subjects were studied while they were supine and three while they were prone. During spontaneous breathing, movement of dependent diaphragm regions was greater than that of nondependent regions in four of six subjects. In five of the six subjects, dorsal diaphragm movement exceeded ventral movement regardless of body position. The volume displaced by the diaphragm (delta Vdi) was similar to VT in supine subjects but tended to be less than VT in prone subjects. After induction of anesthesia-paralysis, the end-expiratory position of the diaphragm did not change consistently in supine subjects, whereas a consistent cephalad volume shift occurred in prone subjects. During anesthesia-paralysis and mechanical ventilation, delta Vdi was reduced to approximately 50% of VT in both body positions. In the supine position, the pattern of diaphragm motion during mechanical inflation was nearly uniform. By contrast, in the prone position, the motion was nonuniform, with most motion occurring in the dorsal (nondependent) regions. It is concluded that the dominant influence on diaphragm motion may be some anatomical difference between the crural and costal diaphragm regions rather than the abdominal hydrostatic pressure gradient.

Adult↗
PubMed1989

Chest wall motion during spontaneous breathing and mechanical ventilation in dogs.

We measured the volume change of the thoracic cavity (delta Vth) and the volumes displaced by the diaphragm (delta Vdi) and rib cage (delta Vrc) in six pentobarbital-anesthetized dogs lying supine. A high-speed X-ray scanner (dynamic spatial reconstructor) provided three-dimensional images of the thorax during spontaneous breathing and during mechanical ventilation with paralysis. Tidal volume (VT) was measured by integrating gas flow. Changes in thoracic liquid volume (delta Vliq, presumably caused by changes in thoracic blood volume) were calculated as delta Vth - VT. Absolute volume displaced by the rib cage was not significantly different during the two modes of ventilation. During spontaneous breathing, thoracic blood volume increased during inspiration; delta Vliq was 12.3 +/- 4.1% of delta Vth. During mechanical ventilation, delta Vliq was nearly zero. Configuration of the relaxed chest wall was similar during muscular relaxation induced by either pharmacological paralysis or hyperventilation. Expiratory muscle activity produced 50 +/- 11% of the delta Vth during spontaneous breathing. We conclude that at constant VT the volume displaced by the rib cage is remarkably similar during the transition from spontaneous breathing to mechanical ventilation, while both diaphragmatic volume displacement and changes in intrathoracic blood volume decrease by a similar amount.

Animals↗
PubMed1988

Three-dimensional canine renovascular structure and circulation visualized in situ with the dynamic spatial reconstructor.

The dynamic spatial reconstructor--a unique, high speed, volume-scanning, X-ray computed tomographic imaging system--was utilized to examine canine renovascular anatomy and renal circulation in situ. In each of the four kidneys examined in this study initial scans were done during bolus injections of angiographic contrast material into the renal artery. A subsequent scan was then performed following an injection of methyl-methacrylate-based casting compound that had been contrast enhanced with ethiodol. After the scans, each kidney was removed, and its parenchyma was digested in potassium hydroxide to expose the vascular cast. Comparison of casts with their reconstructed images and with images obtained during injection of contrast material showed that interlobar arteries and occasionally arcuate arteries could be clearly detected. Although discrete vessels less than 1 mm in diameter could not be resolved, dynamic changes in parenchymal distribution of density during passage of contrast material allowed interpretation of flow through the multiple capillary beds of the kidney. Such analysis indicated that maximal density was in the outer-middle zone of the cortex throughout the duration of the scan. Analysis of artery-to-vein transit time showed arrival of contrast material in the renal vein as soon as 3 sec, and continuation for longer than 8 sec, after the renal artery bolus. In conclusion, renal circulation in the dog can be discretely visualized with the dynamic spatial reconstructor up to the level of the arcuate arteries; however, capillary flow as a whole can be followed through the cortex, and the results suggest the presence of both rapid and slow components of peritubular circulation.

Animals↗
PubMed1988

Blood velocity measurements during selective coronary angiography before and after percutaneous transluminal coronary angioplasty.

The velocity of blood flowing down a coronary artery may provide an index of myocardial perfusion, independent of the need for measuring the amount of myocardium supplied by a vessel. The velocity of the leading edge of contrast material was therefore measured before and after percutaneous transluminal coronary angioplasty in 15 patients utilizing digitized images from routine coronary angiography. The velocity (mean +/- SD) before percutaneous transluminal coronary angioplasty in the 15 patients was 11.9 +/- 6.0 cm/s, increasing to 21.7 +/- 8.7 cm/s after (P less than 0.01). There was a correlation between the percent change in velocity and the change in percent stenosis before and after percutaneous transluminal coronary angioplasty (r = 0.65; P less than 0.001). The mean absolute interobserver and intraobserver variabilities for the velocity measurements were 2.1 and 1.8 cm/s, respectively. Measurement of coronary flow velocity from data obtained at the time of routine coronary angiography is an easily performed reproducible technique, which may be used to assess the results of an intervention such as percutaneous transluminal coronary angioplasty.

Absorptiometry, Photon↗
PubMed1988

Volume quantification of chest wall motion in dogs.

We employed high-speed multisliced X-ray-computed tomography to determine the relative volume contributions of rib cage (delta Vrc) and diaphragmatic motion (delta Vdi) to tidal volume (VT) during spontaneous breathing in 6 anesthetized dogs lying supine. Mean values were 40 +/- 6% (SE) for delta Vrc and 62 +/- 8% of VT for delta Vdi. The difference between VT and changes in thoracic cavity volume was taken to represent a change in thoracic blood volume (2 +/- 3% of VT). To estimate how much of delta Vrc was caused by diaphragmatic contraction and how much of delta Vdi was caused by rib cage motion, delta Vrc and delta Vdi were determined during bilateral stimulation of the C5-C6 phrenic nerve roots in the apneic dog and again during spontaneous breathing after phrenicotomy. Thoracic cavity volume (Vth) measured during hypocapnic apnea was consistently larger than Vth at end expiration, suggesting that relaxation of expiratory muscles contributed significantly to both delta Vrc and delta Vdi during spontaneous inspiration. Phrenic nerve stimulation did not contribute to delta Vrc, suggesting that diaphragmatic contraction had no net expanding action on the rib cage above the zone of apposition. Spontaneous breathing after phrenicotomy resulted in small and inconsistent diaphragmatic displacement (8 +/- 4% of VT). We conclude that the diaphragm does not drive the rib cage to inflate the lungs and that rib cage motion does not significantly affect diaphragmatic position during spontaneous breathing in anesthetized dogs lying supine.

Abdomen↗
PubMed1988

Regional pulmonary perfusion estimated by high-speed volume scanning CT.

Three pigs with surgically created aortopulmonary shunts and two pigs who had sham operation were scanned in a fast computed tomography (CT) scanner, the dynamic spatial reconstructor (DSR). Each pig was scanned during injection of a bolus of roentgen contrast medium in the right atrium and during injection into the left ventricle. In addition to these DSR scans, radiolabeled, 15-micron-diameter microspheres were injected into the right atrium and into the left ventricle. The quantitative distribution of roentgen contrast agent was used to estimate regional pulmonary blood flow independently from the right and left circulations using analysis of the indicator dilution curves derived from the DSR images (Y). These values were compared to the regional values of pulmonary perfusion based on the microsphere distribution (X). The correspondence between the two methods (for all pigs together) was Y = 0.83X + 0.52 with r = 0.964. The less than unity slope is attributed to the partial collapse of the lung at the time of sectioning (for counting of tissue radioactivities). As regional air content of the lung also was measured from the DSR images, these data support the contention that regional ventilation and perfusion can be estimated from a fast CT scan of the thoracic contents during the passage of a bolus of contrast medium.

Animals↗