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Biomedical subjects

E L Ritman

Publications and source records attributed to E L Ritman.

At least 55 records · Page 3Linked to original sources
PubMed1997

Quantitative evaluation of regional myocardial perfusion using fast X-ray computed tomography.

Clinical quantitation of regional myocardial perfusion using a minimally invasive and easily applied technique could allow for ready quantitation of the functional significance of coronary disease, allow for further understanding of flow reserve in various cardiomyopathic and hemodynamic overload (pressure versus volume) conditions, and possibly provide basic information needed regarding the development and clinical significance of coronary collateral vessels and diseases of the myocardial microcirculation. Electron beam CT (EBCT) is a unique cardiac imaging modality that allows for rapid acquisition tomographic slices of the heart with excellent spatial resolution. It has been demonstrated to provide accurate measurements of cardiac anatomy, biventricular function, myocardial mass, and estimates of mural atherosclerotic plaque burden via quantification of coronary calcium. The application of classical indicator techniques for use by fast x-ray computed tomography techniques such as electron beam CT has been shown to allow quantitative analysis of regional myocardial perfusion throughout the myocardium. Initial studies using central intravenous contrast injection in experimental animals showed a close correlation of regional myocardial perfusion as quantitated by electron beam CT with measurements using radiolabeled microspheres at resting and moderately increased flow states. At high flow states, however, electron beam CT significantly underestimated absolute myocardial perfusion and thus myocardial flow reserve. Using another fast CT device, the Dynamic Spatial Reconstructor (DSR), concepts of intramyocardial vascular blood volume and its relation to myocardial flow have been established. By adapting these concepts to electron beam CT scanning and accounting for the increase in intramyocardial vascular blood volume at vasodilatation, the ability to correctly quantitate perfusion states up to approximately 400 mL.min-1. 100 g-1 using central intravenous contrast administration was demonstrated. This implies that studies can be done with intravenous injection methods for characterization of regional myocardial perfusion up to the normal flow reserve of approximately 4:1. Important physiologic and clinical abnormalities in flow reserve generally result in a ratio < 3:1. Electron beam CT offers the capability to quantitate regional myocardial perfusion in both the clinical and research setting. Of particular interest is the ability to provide quantitative regional myocardial perfusion which can be coupled to the evaluation of cardiac anatomy and function as well as mural coronary atherosclerotic calcium burden during the same scanning session. Thus, electron beam CT has the potential to become a valuable, minimally invasive clinical tool for comprehensive analysis of cardiac function and coronary status.

Cardiomyopathies↗
PubMed1997

Technetium-99m MIBI to assess coronary collateral flow during acute myocardial infarction in two closed-chest animal models.

UNLABELLED: Collateral flow is an independent determinant of infarct size in both animal and clinical studies of myocardial infarction. The purpose of this study was to quantitatively evaluate, in a closed-chest animal model, a noninvasive method of measuring coronary collateral flow over a wide spectrum of collateral flow rates from a tracer that can be injected during occlusion but measured after reperfusion. METHODS: Fourteen animals underwent 40 min of coronary occlusion using a closed-chest technique. Two closed-chest models representing different rates of collateral flow were used: canine and porcine. Coronary blood flow was measured by radiolabeled microspheres. Collateral blood within the risk zone was estimated from the severity of 99mTc-sestamibi tomographic perfusion defect. RESULTS: Collateral blood flow was significantly higher in the canine model than it was in the porcine model. There was close agreement (r = 0.90) between absolute collateral flow by microspheres and the severity of the tomographic perfusion defect. CONCLUSION: These results suggest that an accurate noninvasive estimate of collateral blood flow can be provided by an intravenous injection of 99mTc-sestamibi.

Animals↗
PubMed1996

Mechanical significance of respiratory muscle activity in humans during halothane anesthesia.

BACKGROUND: Prior human studies have shown that halothane attenuates activity in the parasternal intercostal muscle and enhances phasic activity in respiratory muscles with expiratory actions. This expiratory muscle activity could contribute to reductions in the functional residual capacity produced by anesthesia. Termination of this activity could contribute to the maintenance of inspiratory rib cage expansion. The purpose of this study was to estimate in humans the mechanical significance of expiratory muscle activity during halothane anesthesia and to search for the presence of scalene muscle activity during halothane anesthesia that might contribute to inspiratory rib cage expansion. METHODS: Six subjects (3 males, 3 females) were studied while awake and during 1.2 MAC halothane anesthesia, both during quiet breathing and during carbon dioxide rebreathing. Respiratory muscle activity was measured using fine-wire electromyography electrodes. Chest wall configuration was determined using images of the thorax obtained by three-dimensional, fast computed tomography and respiratory impedance plethysmography. Functional residual capacity was measured by a nitrogen dilution technique. Measurements were obtained after paralysis with 0.1 mg/kg vecuronium and mechanical ventilation. RESULTS: Phasic inspiratory activity was present in the scalene muscle of four anesthetized subjects during quiet breathing and all anesthetized subjects during rebreathing. Phasic inspiratory activity was present in the parasternal intercostal muscle during halothane anesthesia in only the three female subjects and was enhanced by rebreathing; parasternal intercostal muscle activity was never present in anesthetized males. During anesthesia with quiet breathing, phasic expiratory activity was observed in the transversus abdominis muscles of only the three male subjects. Despite these differences in the pattern of respiratory muscle use, the pattern of chest wall responses to rebreathing was similar between males and females. When expiratory muscle activity was present, paralysis increased the end-expiratory thoracic volume by expanding the rib cage, demonstrating that this activity reduced thoracic volume in these subjects. Changes in thoracic blood volume were significant determinants of the change in functional residual capacity produced by paralysis. CONCLUSIONS: In humans anesthetized with 1.2 MAC end-tidal halothane, there are marked interindividual differences in respiratory muscle use during quiet breathing that may be related to sex; phasic inspiratory scalene muscle and parasternal intercostal muscle activity may contribute to inspiratory rib cage expansion in some subjects; and when present, expiratory muscle activity significantly constricts the rib cage and contributes to reductions in functional residual capacity caused by halothane anesthesia.

Adult↗
PubMed1996

Atelectasis and chest wall shape during halothane anesthesia.

BACKGROUND: Anesthesia produces atelectasis in the dependent areas of the lungs by mechanisms that remain unknown. It has been proposed that anesthesia produces a cephalad shift in the end-expiratory position of the diaphragm, which compresses the lungs and produces atelectasis. This study tested the hypothesis that the extent of atelectasis is correlated with the cephalad displacement of the dependent portion of the diaphragm produced by halothane anesthesia in healthy young human subjects. METHODS: Twelve volunteers (mean age 34 yr) were studied while awake and during approximately 1.2 minimum alveolar concentration halothane anesthesia. Chest wall configuration was determined using images of the thorax obtained by three-dimensional fast computed tomography. Functional residual capacity was measured by a nitrogen dilution technique. Measurements were performed during quiet breathing in all subjects and after paralysis with 0.1 mg/kg vecuronium and mechanical ventilation in six subjects. Atelectasis was assumed to be present in regions of the lung that showed radiographic attenuation values similar to solid organs such as the liver. RESULTS: Atelectasis in dependent lung regions was not apparent in scans performed while the subjects were awake. Anesthesia with spontaneous breathing increased the volume of atelectasis measured at end-expiration by more than 1 ml in 9 of 12 subjects. For all subjects, the volume of atelectasis was 29 +/- 10 ml (M +/- SE), representing 0.67 +/- 0.23% of the total thoracic volume. The distribution of atelectasis varied along the cephalocaudal axis, with less atelectasis in more cephalad transverse sections. Paralysis and mechanical ventilation significantly decreased the volume of atelectasis present at end-expiration. There was no correlation between the average amount of cephalad displacement of the most dependent region of the diaphragm and the amount of atelectasis, nor was there any correlation between the amount of atelectasis and anesthesia-induced changes in the end-expiratory position of any chest wall structure. CONCLUSIONS: The dependent lung atelectasis produced by halothane anesthesia does not appear to be related to changes in the position of any single chest wall structure in these healthy young subjects, but rather to an interaction of several factors that remain to be identified.

Adult↗
PubMed1996

Human chest wall function during epidural anesthesia.

BACKGROUND: Although epidural anesthesia (EA) can significantly disrupt the function of the respiratory system, data concerning its effects on respiratory muscle activity and the resulting motion of the chest wall are scarce. This study aimed to determine the effects of lumbar EA on human chest wall function during quiet breathing. METHODS: Six persons were studied while awake and during mid-thoracic (approximately a T6 sensory level) and high (approximately a T1 sensory level) lumbar EA produced by either 2% lidocaine (two persons) or 1.5% etidocaine (four persons) with 1:200,000 epinephrine. Respiratory muscle activity was measured using fine-wire electromyography electrodes. Chest wall configuration during high EA was determined using images of the thorax obtained by three-dimensional, fast computed tomography. The functional residual capacity was measured using a nitrogen dilution technique. RESULTS: High EA abolished activity in the parasternal intercostal muscles of every participant but one, whereas the mean phasic activity of the scalene muscles was unchanged. High EA significantly decreased the inspiratory volume displacement of the rib cage compared with intact breathing but did not have a significant effect on diaphragm displacement. Therefore, high EA decreased the percentage contribution of rib cage expansion to inspiratory increases in thoracic volume (delta Vth) (from 27 +/- 2 [MSE] to 10 +/- 11% of delta Vth). Paradoxic rib cage motion during inspiration (i.e., a net inward motion during inspiration) developed in only one participant. High EA substantially increased the functional residual capacity (by 295 +/- 89 ml), with a significant net caudad motion of the end expiratory position of the diaphragm. In addition, high EA significantly decreased the volume of liquid in the thorax at end expiration in five of the six participants, a factor that also contributed to the increase in functional residual capacity in these persons. CONCLUSIONS: Rib cage expansion continues to contribute to tidal volume during high EA in most subjects, even when most of the muscles of the rib cage are paralyzed; the mean phasic electrical activity of unblocked respiratory muscles such as scalenes does not increase in response to rib cage muscle paralysis produced by EA; and high EA increases the functional residual capacity, an increase produced in most participants by a caudad motion of the diaphragm and a decrease in intrathoracic blood volume.

Adult↗
PubMed1995

Impact of acute pulmonary rejection on cardiac function.

BACKGROUND: Experiments were designed to define cardiac function in dogs with single lung allografts during acute rejection of the allografted lung. METHODS AND RESULTS: Left lungs were either autotransplanted (n = 4) or allotransplanted (n = 8) in adult male mongrel dogs. All allotransplanted animals were maintained on triple-drug immunosuppression (cyclosporine, azathioprine, and steroids) for 5 days after the operation. In 4 allotransplanted animals, treatment was discontinued, allowing the animals to reject (usually after a further 3 days; rejecting group); 4 other allotransplanted animals were maintained on immunosuppression for an additional 3 days (immunosuppressed group). Another group of dogs were not operated on but were maintained on the same immunosuppression as the rejecting group (controls). All experimental animals underwent fast computed tomographic scanning with measurement of left ventricular pressure and calculation of ventricular chamber volumes, cross-sectional areas of coronary arteries, myocardial perfusion, and intramyocardial blood volume. Neither cardiac output, left ventricular mass, left ventricular pressure, nor myocardial oxygen consumption was altered during acute rejection of lung allografts. However, left ventricular contractility (systolic elastance, Emax) and ejection fraction were depressed to approximately one half (P < .05) in acutely rejecting animals compared with other groups. The cross-sectional area of the coronary arteries was less in autotransplanted and allotransplanted treated animals than in animals that were not operated on. Cross-sectional area of the coronary arteries was decreased by an additional 30% in the rejecting group (P < .05). CONCLUSIONS: The results of this study indicate that acute rejection of a single lung allograft decreases cardiac performance and reduces diameter of coronary arteries in the recipient. Alterations of circulating humoral factors and activated leukocytes may contribute to these changes.

Animals↗
PubMed1995

Myocardial microcirculation as evaluated with CT.

This study explores use of whole-body CT imaging to separately quantitate the physiological behavior of the nonrecruitable (e.g., arterioles) and recruitable (mostly capillary) components of the intramyocardial microcirculation. In two groups of dogs, one with microembolization and one with epicardial artery stenosis, we demonstrate that intramyocardial blood volume (rho) and blood flow (F) follow the relationship rho = AF + BF1/2 where A represents the transit time of the recruitable and BF-1/2 is the transit time of the nonrecruitable components. These transit times are shown to change in different, but characteristic, patterns.

Animals↗
PubMed1995

Computed tomography evaluation of regional increases in microvascular permeability after reperfusion of locally ischemic myocardium in intact pigs.

RATIONALE AND OBJECTIVES: I evaluated how well fast computed tomography (CT) scanning could quantify altered myocardial microvascular function resulting from transient ischemia and subsequent reperfusion. METHODS: A major epicardial coronary artery of anesthetized pigs was occluded for either 0, 15, 30, 60, or 120 min. Fast X-ray CT scan sequences were performed before and during occlusion and 30, 60, and 90 min after onset of subsequent reperfusion. Regional myocardial perfusion, intramyocardial blood volume, and myocardial microcirculatory permeability-surface area product were estimated from the CT scan sequences. RESULTS: With the increasing duration of ischemia, the permeability-surface area product remained unchanged during reperfusion (p > .05), but an index of myocardial microvascular permeability increased with the progressive duration of ischemia and of reperfusion (p < .05). CONCLUSION: These CT-based findings are consistent with published, more invasive demonstrations that capillary permeability is increased during postischemic reperfusion in proportion to the duration of the preceding ischemia.

Animals↗
PubMed1995

Human chest wall function while awake and during halothane anesthesia. I. Quiet breathing.

BACKGROUND: Data concerning chest wall configuration and the activities of the major respiratory muscles that determine this configuration during anesthesia in humans are limited. The aim of this study was to determine the effects of halothane anesthesia on respiratory muscle activity and chest wall shape and motion during spontaneous breathing. METHODS: Six human subjects were studied while awake and during 1 MAC halothane anesthesia. Respiratory muscle activity was measured using fine-wire electromyography electrodes. Chest wall configuration was determined using images of the thorax obtained by three-dimensional fast computed tomography. Tidal changes in gas volume were measured by integrating respiratory gas flow, and the functional residual capacity was measured by a nitrogen dilution technique. RESULTS: While awake, ribcage expansion was responsible for 25 +/- 4% (mean +/- SE) of the total change in thoracic volume (delta Vth) during inspiration. Phasic inspiratory activity was regularly present in the diaphragm and parasternal intercostal muscles. Halothane anesthesia (1 MAC) abolished activity in the parasternal intercostal muscles and increased phasic expiratory activity in the abdominal muscles and lateral ribcage muscles. However, halothane did not significantly change the ribcage contribution to delta Vth (18 +/- 4%). Intrathoracic blood volume, measured by comparing changes in total thoracic volume and gas volume, increased significantly during inspiration both while awake and while anesthetized (by approximately 20% of delta Vth, P < 0.05). Halothane anesthesia significantly reduced the functional residual capacity (by 258 +/- 78 ml), primarily via an inward motion of the end-expiratory position of the ribcage. Although the diaphragm consistently changed shape, with a cephalad displacement of posterior regions and a caudad displacement of anterior regions, the diaphragm did not consistently contribute to the reduction in the functional residual capacity. Halothane anesthesia consistently increased the curvature of the thoracic spine measured in the saggital plane. CONCLUSIONS: The authors conclude that (1) ribcage expansion is relatively well preserved during halothane anesthesia despite the loss of parasternal intercostal muscle activity; (2) an inward displacement of the ribcage accounts for most of the decrease in functional residual capacity caused by halothane anesthesia, accompanied by changes in diaphragm shape that may be related to motion of its insertions on the thoracoabdominal wall; and (3) changes in intrathoracic blood volume constitute a significant fraction of delta Vth during tidal breathing.

Adult↗
PubMed1995

Chest wall responses to rebreathing in halothane-anesthetized dogs.

BACKGROUND: The pattern of respiratory muscle use during halothane-induced anesthesia differs markedly among species breathing quietly. In humans, halothane accentuates phasic activity in rib cage and abdominal expiratory muscles, whereas activity in the parasternal intercostal muscles is abolished. In contrast, halothane abolishes phasic expiratory muscle activity during quiet breathing in dogs, but parasternal muscle activity is maintained. Respiratory muscle responses to CO2 rebreathing were measured in halothane-anesthetized dogs to determine if species differences present during quiet breathing persist over a wide range of central respiratory drive. METHODS: Chronic electromyogram electrodes were implanted in three expiratory agonists (the triangularis sterni, transversus abdominis, and external oblique muscles) and three inspiratory agonists (the parasternal intercostal muscle, costal and crural diaphragm) of six mongrel dogs. After a 1-month recovery period, the dogs were anesthetized in the supine position with halothane. The rebreathing response was determined by Read's method during anesthesia with stable 1 and 2 minimum alveolar end-tidal concentrations of halothane. CO2 concentrations were measured in the rebreathing bag using an infrared analyzer. Chest wall motion was measured by fast three-dimensional computed tomographic scanning. RESULTS: Halothane concentration did not significantly affect the slope of the relationship between minute ventilation (VE) and PCO2 (0.34 +/- 0.04 [M +/- SE] and 0.28 +/- 0.05 l.min-1.mmHg-1 during 1 and 2 minimum alveolar concentration anesthesia, respectively). However, 2 minimum alveolar concentration anesthesia did significantly decrease the calculated VE at a PCO2 of 60 mmHg (from 7.4 +/- 1.2 to 4.0 +/- 0.6 l.min-1), indicating a rightward shift in the response relationship. No electromyographic activity was observed in any expiratory muscle before rebreathing. Rebreathing produced electromyographic activity in at least one expiratory muscle in only two dogs. Rebreathing significantly increased electromyographic activity in all inspiratory agonists. Rebreathing significantly increased inspiratory thoracic volume change (delta Vth), with percentage of delta Vth attributed to outward rib cage displacement increasing over the course of rebreathing during 1 minimum alveolar concentration anesthesia (from 33 +/- 6% to 48 +/- 2% of delta Vth). CONCLUSIONS: Rebreathing did not produce expiratory muscle activation in most dogs, demonstrating that the suppression of expiratory muscle activity observed at rest persists at high levels of ventilatory drive. Other features of the rebreathing response also differed significantly from previous reports in halothane-anesthetized humans, including (1) an increase in the rib cage contribution to tidal volume during the course of rebreathing, (2) recruitment of parasternal intercostal activity by rebreathing, (3) differences in the response of ventilatory timing, and (4) the lack of effect of anesthetic depth on the slope of the ventilatory response. These marked species differences are further evidence that the dog is not a suitable model to study anesthetic effects on the activation of human respiratory muscles.

Anesthetics, Inhalation↗
PubMed1995

Microvascular blood volume-to-flow relationships in porcine heart wall: whole body CT evaluation in vivo.

The goal of this study was to evaluate the functional behavior of recruitable (mostly capillary) and nonrecruitable (mostly arterioles and venules) components of the intramyocardial microvasculature in the in situ heart of intact experimental animals. For this purpose fast X-ray computerized tomography (CT) scans were performed in a group of anesthetized pigs. Each scan was performed during an aortic root angiogram and was repeated after sequential injections of a suspension of nonradioactive microspheres into a selected coronary artery. Regional myocardial perfusion (F, ml.g-1.min-1) and intramyocardial blood volume (rho, ml/g) were estimated from the dynamic CT image sequences. For the intramyocardial microcirculation, rho = AF + B square root of F [where A = 0.016 min and B = 0.076 (ml.min/g)1/2] was shown to describe the rho-to-F relationship over the entire range of flows observed. With increasing embolization with 15-microns diameter microspheres, the coefficients A and B changed in a way consistent with A describing the transit time through the functionally recruitable component and B/ square root of F describing the transit time through the functionally nonrecruitable component of the microcirculation.

Animals↗
PubMed1995

Pressure dependency of canine intrarenal blood flow within the range of autoregulation.

The mechanism of pressure-induced natriuresis remains controversial. To assess whether intracortical or medullary renal blood flows (RBF) change with changes in renal perfusion pressure (RPP), global and regional RBFs were measured using the dynamic spatial reconstructor, a fast computed tomography scanner, in eight anesthetized dogs (group B) within the range of RBF autoregulation (RPP of 153.5 and 114.4 mmHg). Similar measurements were obtained in seven control dogs (group A) in which RPP was not manipulated. In group B, only inner medullary perfusion decreased (from 0.84 to 0.51 ml/min per cm3 of tissue, P = 0.03) with reduction of RPP, whereas global renal, intracortical, and outer medullary perfusions remained unaltered. In group A there was no change in global or regional renal perfusion. The change in inner medullary perfusion in group B (-34.7%) was significantly different (P = 0.021) from that in group A (+27.4%). Global, cortical, and total medullary RBFs (ml/min) and volumes did not change in either group. These results suggest that with changes in RPP, the only detectable change in intrarenal perfusion occurs in the inner medulla.

Animals↗
PubMed1994

Myocardial capillary permeability to iohexol. Evaluation with fast x-ray computed tomography.

RATIONALE AND OBJECTIVES: The accuracy and sensitivity of fast x-ray computed tomography (CT) for estimating myocardial capillary permeability to iohexol was evaluated. The long-term goal is to quantitate capillary integrity. METHODS: Anesthetized pigs were scanned during coronary infusion of adenosine and an aortic root injection of iohexol. The CT images were used to compute myocardial perfusion (F) and capillary extraction factor (E). The permeability-surface area product (PS) was calculated as follows: PS = -F.ln(1-E). Accuracy of the PS value was evaluated with catheter-sampled dual-dilution curves (DDC) resulting from simultaneous injection of cobalt-58 EDTA and iodine-125 albumin. A second group of pigs was scanned while bradykinin (5, 10 or 20 ng/kg/min) was infused into the coronary artery. RESULTS: The DDC and CT-based PS values (mean +/- standard deviation) were as follows: 0.149 +/- 0.107, 0.125 +/- .067; 0.127 +/- 0.072, 0.129 +/- 0.053; and 0.132 +/- 0.043, 0.190 +/- 0.111 for 350, 230, and 175 mg iodine/mL, iohexol respectively. The regression was PS = 0.22 [bradykinin] + 0.083, r = .845. CONCLUSIONS: Dual-dilution curve-obtained and CT-obtained PS values are well correlated. The data show that concentration of iohexol has little (P > .1) impact on the calculated PS value and the bradykinin data suggest good sensitivity.

Adenosine↗
PubMed1994

Anesthesia and chest wall function in dogs.

Three anesthetics (pentobarbital, halothane, and isoflurane) were studied in six mongrel dogs to systematically compare their effects on chest wall function during spontaneous breathing. Each dog received each anesthetic on separate occasions. Electrical activities of several respiratory muscles were measured with chronically implanted electrodes, and chest wall motion was assessed by high-speed three-dimensional computed tomography scanning. Phasic expiratory muscle activity was markedly depressed by volatile anesthetics halothane and isoflurane compared with pentobarbital. In contrast, inspiratory activity in parasternal intercostal muscles was relatively well preserved during anesthesia with these volatile agents. The contribution of expiratory muscles to tidal volume was diminished during halothane and isoflurane compared with pentobarbital anesthesia. As anesthesia was deepened, expiratory muscle activity was unchanged during pentobarbital anesthesia, enhanced in some dogs during isoflurane anesthesia, and remained absent during halothane anesthesia. Activity in parasternal intercostal muscle was depressed as inspired concentration of halothane or isoflurane was increased, whereas diaphragmatic activity was unchanged. Depression of expiratory muscle activity by halothane persisted when breathing was stimulated by positive end-expiratory pressure, with significant mechanical consequences for chest wall configuration. Many of these findings are in contrast with previous observations in humans and suggest that the dog is not a suitable model for the study of the effects of anesthetic drugs on the pattern of human respiratory muscle activity.

Abdominal Muscles↗
PubMed1994

Measurement of renal perfusion and blood flow with fast computed tomography.

Fast computed tomography (CT) is one of the few methods available to measure cortical and medullary renal blood flow (RBF) directly. Because these measurements are complicated by passage of the contrast medium into extravascular compartments, we used the residual opacity following the vascular blush as an index to account for extravascular iohexol. Kidneys of anesthetized dogs were examined in situ by fast CT following intra-aortic injections of iohexol. Perfusion was analyzed during a control period and three subsequent periods in which RBF was reduced by 10%, 30%, and 50%. Cortical microvascular distribution volume changed from 19.7 +/- 2.8% to 19.8 +/- 1.7%, 15.3 +/- 1.2%, and 9.9 +/- 1.7%, respectively, without significant alterations in cortical mean transit time. Microvascular distribution volume was divided by mean transit time to determine tissue perfusion. Cortical perfusion changed from 3.8 +/- 0.7 to 3.9 +/- 0.6, 3.1 +/- 0.5, and 2.2 +/- 0.5 mL.min-1.mL tissue-1. Total cortical blood flow (cortical perfusion multiplied by cortical volume) decreased from 164 +/- 32 to 159 +/- 31, 117 +/- 20, and 86 +/- 22 mL/min, respectively. Medullary microvascular distribution volume, mean transit time, perfusion, and total blood flow remained unchanged. Fast CT-determined total RBFs (cortex plus medulla) were similar to simultaneous electromagnetic flow measurements. These results indicate that renal regional perfusion is more dependent on the microvascular distribution volume than mean transit time and that variations in renal tissue perfusion with reduction of RBF are more apparent in the cortex than in the medulla.

Analysis of Variance↗
PubMed1993

In vivo myocardial microcirculation: evaluation with a whole-body x-ray CT method.

The detailed anatomic geometry of the myocardial microvasculature is unresolvable by current "whole body" imaging techniques. An index of microvascular patency can however be provided by monitoring the intramyocardial blood content by whole body imaging methods. Both spatial distribution and intracyclic changes of regional intramyocardial blood volume can be estimated by whole-body imaging techniques such as x-ray CT and SPECT. Examples of how these methods can be used are provided.

Animals↗
PubMed1993

Antral volume and propulsion-retropulsion in response to upper intestinal nutrients in a canine model.

We measured antral volumes and propulsion-retropulsion for individual peristaltic cycles using the dynamic spatial reconstructor in three female mongrel dogs. Our aim was to quantify the effect of intestinal perfusion of equicaloric, isotonic, and isomolar nutrients (maltose, 32.5 mg/100 ml; casein hydrolysate, 32.5 mg/100 ml; and oleic acid 15.5 mg/100 ml) at a rate of 10 ml/min in the upper small intestine on total antral volume and the propulsion-retropulsion function of the "antral pump." Isotonic saline was used as a control solution. Isotonic gastrografin (600 ml) was instilled intragastrically as a meal. A 6-channel perfused manometric assembly was used to record antral phasic pressure activity. Antral volume was significantly lower (P < 0.05) in response to fat perfusion compared with other nutrients or isotonic saline. The propulsion-retropulsion ratio was also significantly reduced (P < 0.05) in response to fat perfusion in the upper small intestine. Our study, therefore, indicates that the fraction of a liquid meal delivered to the antrum is determined, at least in part, by the upper small intestinal nutrients and also that the presence of fat in the small intestine alters the propulsion-retropulsion function of the antrum.

Animal Nutritional Physiological Phenomena↗