Size Of Emboli Research Articles

Comparative evaluation of clinically available inferior vena cava filters with an in vitro physiologic simulation of the vena cava.

A physiologic in vitro model of the human inferior vena cava (IVC) was developed to evaluate the clot-trapping efficiency of various IVC filters. The flow model closely simulates the physical parameters of the human IVC in fluid viscosity, specific gravity, temperature, and pulsatility; blood flow velocity, volume, and inherent turbulence; and vein orientation, wall compliance, and clot composition. Five filters--Greenfield (G), Bird's Nest (BN), Vena Tech (VT), Simon nitinol (SN), and titanium Greenfield (TG)--were compared by using two vena cava and blood clot sizes and horizontal and vertical orientation of the model. Each filter varied significantly in its clot-capturing efficiency, depending on vena cava size and orientation and emboli size. Overall, decreasing rank order in filter clot-trapping efficiency was SN, BN, VT, TG, and G. The in vitro model of the human IVC is an alternative to multicenter clinical trials in evaluating the relative clot-trapping efficiency of various IVC filters.

Venous air embolism during cesarean section: more common than previously thought.

To confirm the incidence of venous air embolism (VAE), we simultaneously monitored expired nitrogen concentration (FEN2) and precordial Doppler in 30 patients undergoing cesarean delivery during general anesthesia. Patients were randomized into two groups and the effect of a 10 degrees reverse Trendelenburg tilt versus the horizontal position was evaluated. Forty-two episodes of VAE, defined by an increase in FEN2 of 0.1%, were detected in 97% (29/30) of patients. Doppler ultrasound failed to detect 9 of the episodes and 23 (41%) changes in Doppler tones were not associated with an increase in FEN2. These spurious Doppler signals were synchronous with compression of retroperitoneal structures, suggesting turbulent venous return to be the cause. The reverse Trendelenburg position did not reduce the incidence of VAE. Compared with the preinduction baseline, mean arterial blood pressure decreased by 31.5 +/- 10.1 mm Hg in this position and 22.6 +/- 13.4 mm Hg in the supine position after hysterotomy. We conclude that VAE in cesarean delivery during general anesthesia occurs very frequently, and that changes in Doppler tones may not be reliable indicators of this complication. Measures to reduce the size and effect of air emboli therefore should be applied routinely in all patients.

Transcranial Doppler detection of circulating cerebral emboli. A review.

The identification of gaseous emboli using Doppler ultrasound was described as early as the 1960s. Recently it has been demonstrated that this method can also detect solid emboli such as thrombi and platelet aggregates. This may make this technology useful in a large number of patients with, or at risk of, embolic stroke. Emboli appear as short-duration, high-intensity signals in the Doppler spectrum. The intensity of the Doppler signal from an artery containing an embolus depends on the density difference between the embolic material and blood. This difference is greatest for gaseous emboli, which are therefore the most easy to detect. Gaseous emboli have been demonstrated during deep-sea diving, and their presence correlates with the occurrence of decompression sickness. Similar signals have been detected during cardiopulmonary bypass. A relation has been demonstrated between the number of emboli detected by transcranial Doppler and a decline in neuropsychological function after cardiopulmonary bypass. Solid emboli such as thrombi and platelet aggregates result in less intense signals than air emboli. Their detection, using Doppler ultrasound, has recently been described in patients with prosthetic heart valves, atrial fibrillation, and carotid artery disease. It may also help in the detection and localization of embolic sources in patients with stroke. Studies in in vitro and in vivo models demonstrate that this technique provides information on the size and type of emboli. Larger emboli produce signals of greater intensity and duration. Practical patient monitoring will require automatic emboli detectors incorporated into the Doppler machine; such programs are being developed. Detection of solid emboli using Doppler techniques offers an exciting new diagnostic tool. It has been demonstrated that the technique can detect solid emboli. The prognostic significance of such emboli remains to be determined. It is hoped that the technique will allow detection of patients at high risk of embolic stroke in whom appropriate prophylactic treatment can then be instituted.

Embolus size affects gas exchange in canine autologous blood clot pulmonary embolism.

Embolic pulmonary hypertension is associated with alterations in gas exchange of variable severity, which we hypothesized to be related to embolus size. We therefore examined the effects of different-size autologous blood clot embolization on pulmonary arterial pressure-cardiac output relationships (Ppa/Q) and on the distribution of ventilation-perfusion ratios (VA/Q) in 18 intact anesthetized and ventilated (inspired fraction of O2 0.4) dogs. Multipoint Ppa/Q plots were generated by a manipulation of venous return before and 60 min after sufficient amounts of small (1 mm, n = 6 dogs), medium (5 mm, n = 6 dogs), or large (10 mm, n = 6 dogs) clots to increase Ppa to 50 mmHg. The distribution of VA/Q was determined by the multiple inert gas elimination technique at the same intermediate Q in each of these experimental conditions. All three sizes of emboli resulted in an 82-92% mean angiographic pulmonary vascular obstruction and increased both the extrapolated pressure intercepts and the slopes of the linear Ppa/Q plots. Gas exchange was altered the most after large clots, which were associated with lower arterial pH, higher physiological and inert gas dead spaces, higher dispersion of ventilation, and also lower mean VA/Q of perfusion distributions. In contrast, inert gas dead space was decreased after small clots. We conclude that, in autologous blood clot embolic pulmonary hypertension, Ppa/Q characteristics are unaffected by embolus size but that gas exchange is affected differently, mainly in high-VA/Q regions and most often after the largest clots.

Differentiation between different pathological cerebral embolic materials using transcranial Doppler in an in vitro model.

The detection of circulating particulate cerebral emboli using transcranial Doppler ultrasonography has been recently reported. It has been suggested that this method might allow discrimination between different embolic materials; this would be very useful for selecting specific pharmacological treatment in individual patients. This study was designed to identify those parameters of the Doppler signal that might prove useful in discriminating between different types and sizes of particulate cerebral emboli. An extracorporeal circuit filled with a saline/Tween solution and driven by a peristaltic pump was used. The tubing was placed in a skull in the position of the middle cerebral artery. Using transcranial Doppler ultrasound, flow was insonated via the transtemporal window. The following embolic materials of measured sizes (range of maximum dimension, 0.5-5.0 mm) were introduced into the circuit: thrombus (n = 20), platelet-rich aggregates (n = 15), atheromatous material (n = 20), and fat (n = 20). The Doppler signal was recorded during the passage of each embolus. Off-line analysis was performed to measure the maximum amplitude and duration of the signal. For all embolic materials there was a highly significant relation between embolus size and maximum amplitude of the Doppler signal. The closest correlation was obtained when the logarithm of maximum amplitude was used (for thrombi, r = 0.74; for platelet, r = 0.87; for atheroma, r = 0.46; and for fat, r = 0.68). The slope of the regression line differed for the different embolic materials and was significantly steeper for platelets than for atheroma (p < 0.01). Platelet emboli of maximum dimension < or = 1.5 mm resulted in a significantly lower maximum amplitude than similarly sized atheroma emboli (157 dB versus 206.7 dB, p < 0.01). For larger emboli (> 2 mm) there was little further increase in maximum amplitude with increases in embolus size. For all embolic materials there was a highly significant linear relation between embolus size and duration of the high-amplitude (> 150 dB) signal (for thrombi, r = 0.75; for platelet, r = 0.90; for atheroma, r = 0.77; and for fat, r = 0.86). Platelet emboli result in lower-amplitude signals, and therefore analysis of maximum amplitude may provide information on the type of embolic material. However, it may be difficult to determine whether a given signal is associated with a large platelet embolus or a small atheroma embolus. Duration of the high-amplitude signal will allow accurate estimation of the size of emboli, particularly where the emboli are all of the same material.

Effect of ventilation with soluble and diffusible gases on the size of air emboli

Pulmonary hypertension resulting from venous air embolism is known to increase after ventilation with highly soluble and diffusible gases. Exacerbation of the hypertension could be due to further blockage of the circulation if the bubbles enlarge as a result of ingress of gas by diffusion. This mechanism has been frequently cited but lacks direct proof. To determine directly whether intravascular air bubbles actually enlarge when highly soluble and diffusible gases are inspired, we used microscopy to measure the size of gas emboli in vivo. When air bubbles were injected into the right atrium, the bubbles that appeared in pulmonary arterioles were larger during ventilation with helium or nitrous oxide than with air. Air bubbles injected into the pulmonary artery enlarged when the inspired gas was changed to helium or nitrous oxide. The direction, magnitude, and timing of changes in bubble size were consistent with a net diffusion of gas into the bubbles. These data support the idea that venous air emboli enlarge during ventilation with soluble and diffusible gases and thereby cause further vascular obstruction.

Effects of embolus size on hemodynamics and gas exchange in canine embolic pulmonary hypertension

We examined the effects of different-sized glass-bead embolization on pulmonary hemodynamics and gas exchange in 12 intact anesthetized dogs. Pulmonary hemodynamics were evaluated by multipoint pulmonary arterial pressure (Ppa)/cardiac output (Q) plots before and 60 min after sufficient amounts of 100-microns (n = 6 dogs) or 1,000-microns (n = 6 dogs) glass beads to triple baseline Ppa were given and again 20 min after 5 mg/kg hydralazine in all the animals. Gas exchange was assessed using the multiple inert gas elimination technique in each of these experimental conditions. Embolization increased both the extrapolated pressure intercepts (by 6 mmHg) and the slopes (by 5 mmHg.l-1.min.m2) of the linear Ppa/Q plots, together with an 80% angiographic pulmonary vascular obstruction. These changes were not significantly different in the two subgroups of dogs. However, arterial PO2 was most decreased after the 100-microns beads, and arterial PCO2 was most increased after the 1,000-microns beads. Both bead sizes deteriorated the distribution of ventilation (VA)/perfusion (Q) ratios, with development of lung units with higher as well as with lower than normal VA/Q. Only 100-microns beads generated a shunt. Only 1,000-microns beads generated a high VA/Q mode and increased inert gas dead space. Hydralazine increased the shunt and decreased the slope of the Ppa/Q plots after 100-microns beads and had no effect after 1,000-microns beads. We conclude that in embolic pulmonary hypertension, Ppa/Q characteristics are unaffected by embolus size up to 1,000 microns.(ABSTRACT TRUNCATED AT 250 WORDS)

An application of a quantitative analytical system for the grading of pulmonary fat embolisms

The severity of pulmonary fat embolism in 5 autopsied cases has been measured using a quantitative image analytical system. With reference to the mean size of the fat emboli, the cases were divided into 2 groupings regardless of the number of the emboli. The mean sizes of the emboli in 3 cases of the first group were significantly larger (about 490–600 μm 2) than those found in the 2 cases of the other group (about 220 and 235 μm 2). An investigation into the localization of fat emboli revealed that more were lodging in the small arteries and artelioles in the first group than in the second. Our results have indicated that a reliable grading of pulmonary fat embolism can not be established without a quantitative image analysis of the size and localization of the fat emboli, and that this quantitative analytical method is useful in achieving this reliable grading.

The effect of Coumadin upon thrombus forming on foreign surfaces.

Experience with the Stagnation Point Flow Experiment has revealed the earliest microscopic events surrounding thrombus inception and growth on foreign surfaces in a perfectly defined flow field. Using 40 and 80 X magnification, the effects of Coumadin upon these events was studied. These events include leukocyte adherence, fibrin deposition and platelet aggregation, deviation of flow streamlines around these aggregates, and subsequent downstream thrombus growth. Surface density of leukocytes was measured as a function of time and shear, and served as an index of the quantity of thrombus on the surface, which in turn, allowed direct comparisons of thrombus growth rate between experiments. Coumadin decreases the adhesive force between leukocytes or thrombi and the foreign surface. Emboli are more frequent with Coumadin, but are smaller. Thrombus inception is not altered. These results suggest that clinical benefit obtained from use of Coumadin derives from reduction in size of emboli.

PULMONARY BONE MARROW EMBOLISM: A REVIEW OF 350 NECROPSY CASES

Of a total of 350 necrospy cases, 71 were instances of pulmonary bone marrow embolism. The number of emboli did not vary significantly depending on whether the destruction of bone marrow was observed or not. However, the size of emboli and the number of nucleated cells increased in cases in which the destruction of bone marrows was observed. In other words, when the bones and bone marrows were destroyed to some extent, the size of emboli increased. In contrast with this, the number of emboli did not vary significantly depending on the magnitude of the destruction of bones and bone marrows. Of a total of 62 cases of which clinical histories were available, 60 were instances in which cardiac massage was carried out. The numbers and sizes of emboli varied significantly depending on whether cardiac massage was carried out or not. In other words, the number of bone marrow emboli was significantly high in cases in which cardiac massage was carried out. We suggested that cardiac massage was the most important of all predisposing factors of bone marrow embolism.

Entrapment of sized emboli by the KMA-Greenfield intracaval filter.

Clinical studies demonstrating the effectiveness of the Kim-Ray Greenfield vena caval filter in the management of pulmonary emboli have stimulated efforts to accurately define this filter's capability to entrap sized emboli and maintain caval patency. Twenty-three dogs had filters inserted and positioned distal to the renal veins. Radiopaque emboli measuring 2 to 5 mm were introduced via the femoral vein. Cineradiography allowed direct observation of emboli capture and filter flow dynamics. Probability of entrapment was found to be related to (1) emboli size, (2) depth of filling of the conical-shaped filter by prior entrapment of emboli, and (3) absence of distal venous hypertension. The geometric design of the filter, which allows progressive vertical filling while maintaining circumferential blood flow, is thought to be responsible for entrapment of emboli and avoidance of venous thrombosis and hypertension.

Computerized discrimination of microemboli in extracorporeal circuits

A computerized ultrasonic particle detection system is capable of identifying microemboli in the 10 to 350 μ range. Data show that appropriate computer analysis of the reflected signals allows discrimination of size and type of emboli. All extracorporeal circuits have microemboli with a large variation in size and number, depending upon the apparatus and how it is run.

Organic fragmentation in pulmonary thrombo-emboli.

Organic fragmentation is a cell-mediated process whereby the periphery of thrombo-emboli is broken up into multiple tiny fragments lined by flat cells and separated by endothelialised clefts and spaces. The process was looked for in 238 lung emboli from 107 subjects and was observed in 45 emboli (41 subjects). The true incidence is much higher since fragmentation is preceded by the surfacing of emboli by flat endothelial cells. Among such emboli its frequency was 41%. Fragmentation can involve emboli of all sizes though it is most frequent and extensive in small ones. The process is important for the resolution of emboli and helps the canalisation of the embolised arteries. It reduces the size of emboli and may also undermine mural attachments and thereby lessen the extent of anchoring to the vessel wall. The mechanism of fragmentation and the origin of the cells responsible are discussed.

Observations in anticoagulant and thrombolytic therapy in pulmonary embolism

A LL PATIENTS with clinically recognized pulmonary embolism have the constant threat of a recurrent episode which may prove fatal, making it imperative that treatment be give, n to prevent this development. In fact, autopsy studies indicate that in more than two-thirds of cases with fatal pulmonary embolism, evidence is found of prior emboli having occurred in the days or weeks preceding the fatal episode, and it has been suggested that untreated, more than one-third of patients will have recurrence. 1-3 Contrariwise, if recurrence is prevented, significant resolution of the pulmonary obstruction occurs over a period of weeks or months which returns the pulmonary circulation to preembolic condition in most cases. 4 Thus, in the majority of patients with pulmonary embolism, the primary objective of therapy is to prevent recurrence, and therefore, a course of anticoagulants is the only therapy indicated, and outlook for recovery is excellent. In a few cases, either because of the size or number of emboli, or presence of preexisting abnormality of the pulmonary circulation, there is severe compromises of cardiopulmonary dynamics which threaten survival. In such patients, it is desirable to accelerate removal of the obstruction of the pulmonary circulation as well as to prevent recurrence, and in those cases thrombolytic therapy may be of value.

Renal trauma. Treatment by angiographic injection of autologous clot.

The safety of treatment of renal hemorrhage from trauma with angiographic injection of autologous clot was investigated in rats by demonstrating the effect of various sizes of clot emboli on renal survivial. A large amount of clot injected into the entire distal part of the renal arterial tree (equivalent to 20 cu cm in the human) was required to produce a 15% infarction. This large safety range is possibly due to the endogenous fibrinolytic capability of normal vascular endothelium.

Behavior of gas emboli subjected to pressure variation in biological systems

Abatraet- Dynamic behavior of gas emboti in a quiescent liquid having the rheological properties of human or animal blood subject to pressure variations is studied. Consideration is given to step and sinusoidal changes in the system pressure. It is disclosed that in the study of dynamic behavior of gas emboli, a Newtonian model may be used to approximate the rheological behavior of human or animal blood in which the emboli are situated. The instantaneous embolus size in blood under pulsating pressure change may be determined by the equilibrium condition of instantaneous static pressures.

POSTMORTEM ARTERIOGRAPHIC STUDIES OF THE HUMAN LUNG IN PULMONARY EMBOLIZATION.

PULMONARY EMBOLISM is now the most common lethal pulmonary disease in adults seen at necropsy in the general hospital population. It is the third most common nonlethal pulmonary lesion after pneumonia and emphysema. In 1960, it was the third most common cause of death in this hospital; it was the main cause of death in 15% of the patients autopsied, and it was a major contributory cause in an additional 19%. These findings promoted the study of the number, size, and distribution of pulmonary emboli, and of the pulmonary parenchymal and circulatory alterations resulting from them. Previous reports have considered particular aspects of the physiology or pathology of pulmonary embolism, but without detailed correlation of one approach with others. The methods used have not identified smaller emboli, or delineated the extent of anatomic alterations. Moreover, there has been no method for estimating the number of emboli or the reduction in

Further evidence for a critical vessel caliber in experimental coronary shock.

New experiments confirm previous observations that production of protracted coronary shock in the closed-chest dog following microsphere embolization is a critical function of the embolus size. The vessels occluded by the critical emboli have been located by a plastic coronary injection-tissue corrosion technic, and a definite relationship has been demonstrated between vessel caliber and anatomic type, in a dog heart, for the gradient from epicardium through endocardium.