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Biomedical subjects

E L Ritman

Publications and source records attributed to E L Ritman.

At least 91 records · Page 5Linked to original sources
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↗
PubMed1987

Some technical considerations in tomographic coronary arteriography.

Coronary artery anatomy can be visualized using high-speed, volume scanning x-ray CT. A single scan during a bolus injection of contrast medium provides image data for display of all angles of view of the opacified coronary arterial tree. Due to the tomographic nature of volume image data, the superposition of the vessels on themselves and on other contrast filled coronary arteries, such as would occur in an aortic root injection of contrast agent, can be eliminated. To achieve the goal of coronary arteriography using a single angiographic injection, the tomographic scanner must scan the entire volume encompassing the coronary arteries synchronously and within a brief period of time. The volume must be scanned so that the thickness of the scanned slices is less than the diameter of the smallest vessel desired to be visualized quantitatively. Preliminary results from a fast volume scanning CT scanner (the Dynamic Spatial Reconstructor) used to scan experimental animals are used to indicate the quantitative and qualitative impact of such variables as scanned slice thickness, scanned slice separation and angle between the vessel and the plane of the scanned slices.

Animals↗
PubMed1987

Heart-lung interaction: effect on regional lung air content and total heart volume.

To study the interactions between and within the heart and lungs, end-diastolic (ED) and end-systolic (ES) volumes and intrathoracic location of the heart, and the regional air content, volume and geometry of the lungs, were measured from three-dimensional image data generated with the Dynamic Spatial Reconstructor (DSR). The DSR was used to scan the full thoracic extent of anesthetized dogs and sloths at selected transpulmonary pressures. The results show that the dependent to nondependent gradient of regional lung opacity (or conversely regional air content) in the supine animal was not present in the prone animals. While the rib cage and diaphragm of the dog deformed markedly, the shape of the sloth's rib cage and diaphragm remained essentially constant with change in body orientation. As a consequence of these findings, we deduce that the observed change in gradient of regional lung air content in both dog and sloth are in response to changes in the intrathoracic position of the heart which alter ventral lung geometry and not a response to changes in rib cage or diaphragm geometry. In a second series of studies we reconstructed the 3-D extent of the heart at ED and ES in supine anesthetized dogs and demonstrated that the total heart volume (THV) (i.e. contained by the pericardial sac) during sinus rhythm differs by less than 5% between ED and ES. The DSR image data show that this is achieved by the epicardial apex remaining essentially fixed and that the plane containing the atrio-ventricular valves moves like a plunger towards the apex in systole. When atrial fibrillation is present, the THV no longer remains constant and decreases during systole, presumably because of increased stiffness of the atrial myocardium. We conclude from the experimental results that the heart plays an important role in determining regional differences in alveolar expansion, and that by maintaining a constant THV, the heart minimizes energy expenditure which would be caused by moving the lung.

Animals↗
PubMed1987

Measurement of three-dimensional anatomy and function of pulmonary arteries with high-speed x-ray computed tomography.

Pulmonary arterial geometry was quantitatively evaluated in five dogs. One was a control dog, two were subjected to monocrotaline administration, and two had a subclavian-to-pulmonary artery shunt. Measurements of pulmonary arterial anatomy were made with the dynamic spatial reconstructor (DSR), a high-temporal-resolution, volumetric, roentgenographic, computed tomographic scanner. In the control dog, pulmonary arterial cross-sectional areas and segment lengths were measured both from images generated from DSR scans obtained during injection of contrast medium and from a methylmethacrylate cast of the same vascular tree. The correlations between the DSR and cast-based measurements of cross-sectional area and segment lengths were 0.98 and 0.97, respectively. Over periods of eight and 11 months' observation, the pulmonary arterial pressure in the two dogs with surgically created left-to-right shunts increased from 29/15 to 42/17 mm Hg and 19/12 to 25/16 mm Hg, respectively. The cross-sectional areas increased progressively in the proximal portion of the main lobar arteries, remained unchanged in the midportion, and decreased in the distal portion of these arteries. Similar changes occurred in one of the two dogs treated with monocrotaline injections, while in the other the taper of the distal vessels did not change significantly. Pulmonary vascular resistance, computed from cardiac output and pulmonary artery pressure, increased proportionately to the decrease of the cross-sectional areas of distal vessel in both the monocrotaline administration dogs; the resistance decreased proportionately to the increase of the pulmonary arterial cross-sectional areas in both of the surgical dogs.

Animals↗
PubMed1987

Three-dimensional imaging of the stomach: role of pylorus in the emptying of liquids.

Using the dynamic spatial reconstructor and manometry, we measured gastric emptying, pyloric size, and antral contractile activity in three anesthetized dogs in the prone position. Our objective is to evaluate the effect of intestinal perfusion of equicaloric, neutral, and isosmolar nutrients (Maltose 32.5 mg/ml, casein hydrolysate 32.5 mg/ml, and oleic acid 15.5 mg/ml) at a constant rate of 10 ml/min in the proximal jejunum on the dynamics of the antropyloric region. Isotonic saline perfusion was used as a control solution. Test meal in the stomach was 600 ml of isotonic Gastrograffin. Antral phasic pressure activity was recorded using an antroduodenal six-channel (ports 5 mm apart) perfused probe (2 mm OD). Gastric emptying in response to intestinal perfusion of fat was significantly slower (P less than 0.02) in comparison to other nutrients or isotonic saline. There was no significant difference in the maximum or minimum pyloric diameter in response to the four intestinal perfusates. However, the pylorus was closed for a significantly longer duration (P less than 0.05) during the perfusion of fat in the upper intestine. Antral contractions were related to pyloric opening in an "antral contraction followed by pyloric opening" sequence. This study suggests that the presence of fat in the upper intestine delays gastric emptying and that this effect is regulated in part by increased resistance to flow offered by the pylorus.

Animals↗
PubMed1987

Dynamic three-dimensional anatomy of pulmonary arteries in pigs with aorto-to-pulmonary artery shunts.

Accurate quantitation of three-dimensional pulmonary arterial geometry is difficult in vivo by the usual clinical imaging techniques. We have used a fast, multislice, computed tomography (CT) scanner, the dynamic spatial reconstructor (DSR), to obtain such measurements. After one injection of contrast medium into the right atrium, all major pulmonary arteries were imaged in three dimensions at 60 per second intervals throughout several cardiac cycles. Computer-generated pseudothree-dimensional displays were generated to show the arteries from several views so that superposition of arteries could be avoided. Using this technique, we have quantitated pulmonary arterial geometry in five pigs, three of them with surgically created aortopulmonary shunt and two with sham shunts. Pulmonary arterial cross-sectional areas (CSA) along the length of the left and right pulmonary arteries as they course through the lower lobes of the lungs were measured at peak-systole and end-diastole. From these image data, the systolic to diastolic change in CSA was measured. The regression line relating the CSA at these two phases had slopes in the five pigs ranging from 0.41 to 0.85. The magnitude of this slope corresponded closely with pulmonary arterial pressure, which ranged from 20 to 92 mm Hg.

Animals↗
PubMed1986

Angiography for delineation of systemic-to-pulmonary shunts in congenital pulmonary atresia: evaluation with the dynamic spatial reconstructor.

In patients with pulmonary valve atresia, the arterial supply to the lungs is derived entirely from the aorta or its major branches. The anatomic detail of this arterial supply is usually identified by obtaining multiple selective arteriograms involving numerous injections of contrast material and x-ray exposures. In this study, we demonstrated that the information obtained from conventional diagnostic angiography in two patients with congenital pulmonary atresia was also clearly evident on scans from the dynamic spatial reconstructor (DSR), a high-speed three-dimensional computed tomographic system. Thus, numerous shunts, stenoses, and systemic collateral arteries were demonstrated by DSR scanning, which involved only one or two nonselective injections of a contrast agent and less x-ray exposure than that normally necessitated by angiographic study.

Aorta↗
PubMed1986

Branching pattern of pulmonary arterial tree in anesthetized dogs.

The geometry of the pulmonary arterial tree of six adult dogs was measured by a high-speed, volume-scanning, X-ray tomographic technique. After the dogs were anesthetized a catheter was advanced to the right ventricular outflow tract and 2 mL/kg Renovist contrast agent injected rapidly. During the subsequent pulmonary arterial phase of the angiogram the dogs were scanned. Three-dimensional geometry of the pulmonary arterial tree was measured in terms of vessel segment cross-sectional area, branching angles and interbranch segment lengths along axial pathways. The effect of lung inflation and phase of the cardiac cycle on geometry was shown to be most marked on vessel cross-sectional area. The geometric branching patterns in all dogs were similar. The observed, in-vivo branching pattern behaved somewhat like the branching pattern predicted from optimized models proposed by Murray, Zamir, and Uylings.

Animals↗
PubMed1986

Regional myocardial volume perfused by the coronary artery branch: estimation in vivo.

Seven closed-chest dogs were anesthetized with intramuscular Innovar and a N2O/O2 gas mixture. Maximal coronary vasodilation was induced by intra-aortic injection of nitroglycerin (200 micrograms/kg) and continuous infusion of adenosine (1 mg/kg/min) into the main pulmonary artery. Superselective coronary arteriograms were obtained at varying distances along the left circumflex and left anterior descending coronary arteries during scans using the dynamic spatial reconstructor rapid tomographic x-ray scanner. At end-diastole the images of the coronary arteries and opacified myocardium were analyzed for cross-sectional area (CSA) of the coronary artery lumen and regional myocardial volume (Vdsr) perfused by that coronary artery. Postmortem regional myocardial volume (Vpath) was related to the volume perfused by the same artery measured in vivo by the dynamic spatial reconstructor as follows: Vdsr = 4.56 + 0.93 Vpath (r = .98, p less than .001). In addition, the cross-sectional area of the coronary artery supplying a volume of myocardium was related to that volume as follows: Vdsr = - 1.95 + 6.34 CSAmax (r = .88, p less than .001). This suggests that a maximally dilated coronary artery luminal cross-sectional area is linearly related to the volume of muscle it perfuses. We speculate that this relationship may be useful in expressing the physiologic significance of coronary arterial narrowing.

Adenosine↗
PubMed1986

Accuracy of pulmonary vascular dimensions estimated with the dynamic spatial reconstructor.

Measurements of pulmonary artery conduit dimensions were obtained in two children after first-stage right ventricular outflow tract reconstruction for congenital pulmonary atresia. These conduits provide an opportunity for evaluation of measurement accuracy of intrathoracic vascular structures that is not possible with the same objectivity in the native vascular tree. Patients were scanned in the dynamic spatial reconstructor (DSR), a high-speed CT scanner, during injection (0.7-1.2 ml/kg) of contrast agent into the pulmonary artery conduit. As the DSR is a volume imaging system, all angles of view are always available from one angiogram, and it can provide images of oblique planes through the structure of interest. In the patient with the 12-mm diameter conduit (113 mm2 area), the cross-sectional area of DSR measurement was 115 +/- 5 mm2 (mean value +/- SD), the roll film value was 84 +/- 6 mm2, and the cineangiogram value was 97 +/- 3 mm2. In the patient with the 8-mm diameter conduit (50 mm2 area), the cross-sectional area of DSR measurement was 47 +/- 5 mm2, the roll film value was 36 +/- 3 mm2, and the cine film value was 35 +/- 4 mm2. The DSR scan (8 s) involved 0.63-0.95 R/s exposure at the sternum, whereas the biplane cineangiogram (3-5 s) involved 0.8 R/s. Based on these data, we conclude that a single DSR scan provides accurate measurements of pulmonary anatomy and vessel dimensions.

Child↗
PubMed1985

Renal cortical perfusion--preliminary experience with the dynamic spatial reconstructor (DSR).

The three-dimensional image data generated by the Dynamic Spatial Reconstructor (DSR) enables measurement of the three-dimensional distribution of blood supply in organs. We have applied this imaging technique to evaluate renal cortical blood flow distribution and compare it with distribution of radiolabeled microspheres. The DSR, a high temporal resolution volumetric roentgenographic computed tomographic scanner, was used to scan the volume containing a kidney in 0.13-0.26 s and repeating this scan 8-4 times per s for six s during a renal arteriogram. Five anesthetized dogs were studied in the prone position with the left kidney exteriorized through a flank incision. An electromagnetic flowmeter was placed around the renal artery and a needle placed retrograde into the artery for injection of a 2 cc bolus of contrast agent. During the scan the contrast agent was injected over a four s period during which radioactively labelled microspheres were injected into the left atrium. The tomographic images of approximately 10 parallel, 5 mm thick sagittal slices corresponding to the slices of the kidney used for counting microspheres in the cortical layers were displayed and analyzed. The time point chosen for analysis was the one in which peak brightness (i.e., concentration of contrast agent) was detected in the cortex. The spatial distribution of peak brightness values was compared to the number of microspheres at the same sampling locations. The microsphere-based value of regional cortical blood flow fell below the regression line for the juxtamedullary cortex and above for the outer cortex. This result is consistent with the preferential distribution of microspheres to the outer cortex whereas the contrast agent distributed more uniformly throughout the cortex.

Animals↗
PubMed1985

Three-dimensional cardiac anatomy and function in heart disease in adults: initial results with the dynamic spatial reconstructor.

The dynamic spatial reconstructor, or DSR, is a unique high-speed volume-imaging x-ray scanner based on computed tomographic principles. In this report, we present data obtained from the first feasibility DSR studies of adult patients with heart disease. Information from three patients--one with hypertrophic obstructive cardiomyopathy, one with calcific aortic valvular disease, and one with a left ventricular aneurysm--is described in detail. The mean DSR scanning time for each patient was 20 seconds, and the mean total irradiation to the sternum was 15.3 R. Transverse cross sections were reconstructed and then retrospectively reformatted to provide operator-selected oblique sections in space (for example, long-axis and short-axis sections of the left ventricle), to follow these sections through time (such as from end-diastole through end-systole), and to create three-dimensional displays (for instance, of the left ventricular chamber). Unique quantitative measurements of structure and function were made by using these images. For generation of most imaging data, only one injection of contrast material into the right side of the heart is necessary. Clinically useful three-dimensional dynamic imaging data can be acquired from adult patients with heart disease by using the DSR. Compared with conventional angiocardiography, DSR studies can provide information with less x-ray exposure and fewer angiographic injections.

Adult↗
PubMed1985

Anatomy and function of the heart and intrathoracic vessels in congenital heart disease: evaluation with the Dynamic Spatial Reconstructor.

The Dynamic Spatial Reconstructor is a unique high speed volume imaging X-ray scanner based on computed tomographic principles. It has several potential advantages over conventional angiographic methods, including reduced invasion, reduced rate of false negative results and increased accuracy of measurements of structure and function. To evaluate the utility of the Dynamic Spatial Reconstructor in the investigation of congenital heart disease, scanning was performed in several pediatric patients with pulmonary valve atresia. Early results show that three-dimensional images of the cardiac chambers and intrathoracic vessels can be acquired and displayed with the system. All the information necessary for quantitative analysis of the pulmonary arteries can be obtained with a single scan involving injection of 0.6 to 2.0 cc/kg of contrast agent and radiation exposure of 0.54 to 0.95 rad/s over 5 to 8 seconds.

Angiography↗
PubMed1985

Shape and dimensions of cardiac chambers: importance of CT section thickness and orientation.

Three-dimensional (3D) computed tomography (CT) scan data were used to quantitate the geometry of all heart chambers. The Dynamic Spatial Reconstructor (DSR) was used to scan dogs with in situ casts of the cardiac chambers. Chamber volumes estimated from DSR images were accurate within 5% of water displacement volume measurements of the actual casts for chambers greater than 11 ml and within 10% of water displacement volumes for chambers less than 11 ml. Anatomic features of the actual cast correlated closely with anatomy visible in computer-generated surface images of the 3D DSR image data. The important effect of reconstructed section thickness and orientation on the fidelity of 3D cardiac geometry is demonstrated.

Animals↗
PubMed1985

Invariant total heart volume in the intact thorax.

Fast multisliced computerized tomography (Dynamic Spatial Reconstructor or DSR) was used to study the change in total heart volume (content of the pericardial sac) between end diastole (ED) and end systole (ES) with lungs held at 0 and 15 cmH2O airway inflation pressure (Paw). Nine dogs were anesthetized and scanned in the DSR. At 0 cmH2O airway pressure, mean total heart volume changed, on the average, only 2.7 +/- 0.6% (SE) of its ED volume comparing ED with ES. With lungs inflated to 15 cmH2O Paw, total heart volume decreased 12 +/- 0.5%. However, at this new heart volume, the change in total heart volume between ED and ES was only 1.7 +/- 0.5%. The data indicate that the epicardial apex of the heart remains relatively stationary while the atrioventricular groove moves toward the apex during systole and away from the apex during diastole. Thus the atria and ventricles empty and fill reciprocally even when the pericardial contents do not fully distend the pericardial sac. The invariant total heart volume observed in these species would minimize the work of the heart by maximizing the percentage of work expended to move blood and minimizing the work expended to move tissue (i.e., lung).

Animals↗