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PubMed1987

Stability of coil emboli: an in vitro study.

Gianturco stainless steel coils were discharged into clear plastic tubes of varying sizes and subjected to pulsatile flow in order to study their behavior in a controlled, in vitro environment. When coils are too small for a given vessel, they tend to migrate distally or even proximally. Coils that are too large tend not to reform completely, limiting their cross-sectional area and potentially affecting their occlusive potential. Thus, each coil was tested in tubes of varying sizes and evaluated with regard to positional stability and extent of reformation.

Embolization, Therapeutic↗
PubMedDate not supplied

Experimental analysis of fluid mechanical energy losses in aortic valve stenosis: importance of pressure recovery.

Current methods for assessing the severity of aortic stenosis depend primarily on measures of maximum systolic pressure drop at the aortic valve orifice and related calculations such as valve area. It is becoming increasingly obvious, however, that the impact of the obstruction on the left ventricle is equally important in assessing its severity and could potentially be influenced by geometric factors of the valve, causing variable degrees of downstream pressure recovery. The goal of this study was to develop a method for measuring fluid mechanical energy losses in aortic stenosis that could then be directly related to the hemodynamic load placed on the left ventricle. A control volume form of conservation of energy was theoretically analyzed and modified for application to aortic valve stenosis measurements. In vitro physiological pulsatile flow experiments were conducted with different types of aortic stenosis models, including a venturi meter, a nozzle, and 21-mm Medtronic-Hall tilting disc and St. Jude bileaflet mechanical valves. The energy loss created by each model was measured for a wide range of experimental conditions, simulating physiological variation. In all cases, there was more energy lost for the nozzle (mean = 0.27 J) than for any other model for a given stroke volume. The two prosthetic valves generated approximately the same energy losses (mean = 0.18 J), which were not statistically different, whereas the venturi meter had the lowest energy loss for all conditions (mean = 0.037 J). Energy loss correlated poorly with orifice pressure drop (r2 = 0.34) but correlated well with recovered pressure drop (r2 = 0.94). However, when the valves were considered separately, orifice and recovered pressure drop were both strongly correlated with energy loss (r2 = 0.99, 0.96). The results show that recovered pressure drop, not orifice pressure drop, is directly related to the energy loss that determines pump work and therefore is a more accurate measure of the hemodynamic significance of aortic stenosis.

Aortic Valve Stenosis↗
PubMedDate not supplied

Alteration of hemodynamics in aneurysm models by stenting: influence of stent porosity.

Recent developments in minimally invasive approach to cerebrovascular diseases include the placement of stents in arteries for treatment of aneurysms. Preliminary clinical observations and experimental studies have shown that intravascular stents traversing the orifice may lead to thrombosis and subsequent occlusion of the aneurysm. The alterations in vessel local hemodynamics due to the introduction of a stent are not yet well understood. We investigated changes in local hemodynamics resulting from stent implantation. Pulsatile flow patterns in an experimental flow apparatus were visualized using laser-induced fluorescence of rhodamine dye. The test cells were constructed in a rectangular shape to facilitate an undisturbed longitudinal view of flow patterns in parent vessel and aneurysm models with and without porous stents. Woven nitinol stents of various porosities (76%, 80%, 82%, and 85%) were investigated. The selected fluid dynamic similarity parameters (Reynolds and Womersley numbers) represented conditions usually found in high-flow, larger arteries in humans (such as the carotid artery) and low-flow, smaller arteries (such as the vertebral artery). The mean Reynolds number for the larger arteries was 180, with maximum/minimum values of 490/-30 and the Womersley number was 5.3. The mean Reynolds number for the smaller arteries was 90, with maximum/minimum values of 230/2, and the Womersley number was 2.7. For the larger arteries modeled, placement of a stent of the lowest porosity across the aneurysm orifice resulted in reduction of aneurysmal vortex speed and decreased interaction with parent vessel flow. For smaller arteries, a stent of the same porosity led to a substantial reduction of parent vessel/aneurysmal flow interaction and the appearance of a nonrecirculating crescent of fluid rich in rhodamine dye in the aneurysm dome. Our results can help explain in vivo thrombus formation within an aneurysm after placement of a stent that is compatible with local hemodynamics.

Fluorescent Dyes↗
PubMed2001

In vitro validation of tissue Doppler left ventricular regional wall velocities by using a novel balloon phantom.

To investigate the validity and accuracy of tissue Doppler imaging (TDI) using a novel balloon phantom, validation of TDI myocardial velocity measurements has been carried out indirectly from conventional M-mode images. However it is not a true and independent gold standard. We described a new TDI validation method by using a specially developed left ventricular balloon model mounted in a water bath and constructed using two pear-shaped balloons. It was connected to a pulsatile flow pump at 8 stroke volumes (50-85 ml/beat). The displacement and velocity of the balloon walls were recorded simultaneously by video imaging and TDI on a GE-Vingmed System Five with a 5 MHz phased array probe at the highest frame rates available. Conventional M-mode and 2-D imaging verified that our balloon model mimicked the shape and wall motion of left ventricle. There was a good correlation and agreement between the maximum video excursion of the anterior and posterior walls of the phantom and the results of the temporal integration of digital distance data by TDI (Anterior wall: r = 0.97, SEE = 0.24 mm, mean +/- s = 0.04 +/- 0.24 mm; Posterior wall: r = 0.95, SEE = 0.22 mm, mean +/- s = 0.03 +/- 0.24 mm). Analysis of the velocity profile by the TDI method showed that the velocity at each measured point was correlated well with the velocity obtained from the video images (Anterior wall: r = 0.97, SEE = 0.30 mm, mean +/- s = -0.04 +/- 0.28 mm; Posterior wall: r = 0.97, SEE = 0.30 mm, mean +/- s = 0.04 +/- 0.28 mm). Our balloon model provided a new independent method for the validation of TDI data. This study demonstrated that the present TDI system is reliable for measuring wall motion distance and velocity.

Echocardiography, Doppler↗
PubMed2002

Performance of long J-shaped coils in large and giant intracranial aneurysms: an in vitro study.

We evaluated the performance of long straight coils (Detach-18 J-shaped coils) in large and giant in-vitro aneurysms. The coils consisted of a distal semicircular part 7 or 15 mm in diameter and a proximal 70 cm straight part having three types of stiffness: soft, standard, and stiff. We first investigated the ease of passage through a microcatheter in a realistic cerebral vessel model. Second, we made silicone models simulating lateral-type aneurysms of various spherical dome diameters (12, 15, 20 and 30 mm) and neck sizes (3-10 mm; dome-to-neck ratio approximately 3:1) and connected them to a pulsating circulatory pump. We evaluated the anchoring and folding patterns of the coils, stability of the microcatheter and coils in the aneurysm, and smoothness of delivery and retrieval of coils. Third, we compared the conformability of a coil in a large, irregular aneurysm with that of a spiral coil. The long J-shaped coils were easily advanced and retrieved through a microcatheter in a tortuous vessel model. In 12 mm spherical aneurysms, each coil made a complex framework, and knot formation or damage to the coil during withdrawal was often observed. In 15 mm aneurysms, the coils were all easily delivered and retrieved; standard-stiffness coils adapted best to this size. In 20 mm aneurysms, frameworks were less complex but still good with a standard or stiff coil, but those with soft coil were unstable and changed significantly within 3 min of detachment due to gravity and pulsatile flow. In 30 mm aneurysms, soft coils filled only the lower part during introduction, whereas a stiff coil still made a favourable framework. Conformability of a long J-shaped coil was superior to that of a spiral coil in a large, irregular aneurysm. Long J-shaped coils conform well to various configurations of large and giant aneurysms and can shorten procedures since a larger implant volume can be delivered with a single coil. Their principle of action may promote more favourable occlusion of irregular and large aneurysms by improved conformability and stability.

Embolization, Therapeutic↗
PubMed2002

Combined stent implantation and embolization with liquid 2-polyhydroxyethyl methacrylate for treatment of experimental canine wide-necked aneurysms.

The purpose of the study was the evaluation of 2-polyhydroxyethyl methacrylate (2-P-HEMA) for endovascular liquid embolization of experimental side-wall aneurysms following stent protection in a canine model. The swelling behaviour and polymerization characteristics of 2-P-HEMA in different solutions were investigated in vitro. Different methods for applications were tested in a latex aneurysm model under pulsatile flow conditions. Twenty broad-based carotid side-wall aneurysms were microsurgically produced in five dogs. Four weeks after surgery self-expandable nitinol stents were placed, covering the orifice of the aneurysms. 2-P-HEMA was injected via a microcatheter, which was positioned through the meshwork of the stent. Control angiography was performed immediately after treatment and after 1, 6 and 9 months. In-vivo stent placement succeeded in all but one case. Two aneurysms occluded spontaneously after stent placement. Combined embolization of 17 aneurysms using a stent and 2-P-HEMA was performed. Eleven aneurysms could be primarily completely occluded (65%). A small remaining neck was evident in six aneurysms. Efflux of 2-P-HEMA during the process of embolization was observed in seven aneurysms, due to an excess volume of 2-P-HEMA. The excessive 2-P-HEMA led to significant vessel stenosis in two cases. Two carotid arteries (three treated aneurysms) occluded after 1 month, due to insufficient anticoagulation management. Histological examination of embolized aneurysms revealed no foreign-body or inflammatory reaction. A smooth neo-intimal layer covered the stented vessel segment. Liquid embolization of side-wall aneurysms with 2-P-HEMA is technically feasible. Embolotherapy of aneurysms with liquid agents still has the risk that embolic material will exit even when it is stent-protected. To avoid this problem, stents with smaller strut diameter and/or additional balloon-protection are required. The inert 2-P-HEMA seems to be a promising agent for combining techniques of aneurysm treatment.

Aneurysm↗
PubMed2006

Preclinical testing of a new clot-retrieving wire device using polyvinyl alcohol hydrogel vascular models.

INTRODUCTION: Cerebral embolism is the principal cause of cerebral infarction. Recently, mechanical embolectomy has been proposed as an effective method. We performed a preclinical evaluation of a new mechanical clot-retrieving wire. METHODS: This clot-retrieving wire consisted of three nitinol loops at the tip of a microguidewire. These three loops could be collapsed into a 0.018-inch wire compatible microcatheter. Each loop was 8 mm long and 3.5 mm wide. For simulation, polyvinyl alcohol (PVA) vascular anatomical models of the human carotid (eight models) and vertebrobasilar (three models) circulation were constructed. A pulsatile flow circulation system was used. Embolic clots were produced using pig blood plasma. The microcatheter and the microguidewire were advanced beyond the clot. The wire was then exchanged for the retrieving wire. The microcatheter was then pulled slightly back to open the loops. The clot was then caught by withdrawal of the system. Once caught, the clot was retrieved to the guiding catheter tip. We investigated the following points: ease of device deployment, clot capture ability, clot removal against blood flow and removal of the clot out of the introducer system. RESULTS: A total of 104 procedures were performed in 11 PVA models and evaluated. The drop rate was 19%. We succeeded in partial and total recanalization in 51.0% of the procedures (53/104) within 30 minutes. CONCLUSION: This new clot-retrieving wire could be useful for mechanical clot extraction in stroke.

Embolectomy↗
PubMedDate not supplied

Splenic artery aneurysm: value of color Doppler and the limitation of gray-scale ultrasonography.

BACKGROUND: To reevaluate the advantages and limitations of gray-scale and color Doppler sonography in the diagnosis of splenic artery (Sp-A) aneurysm. METHODS: We reviewed the gray-scale and color Doppler sonograms of five cases with Sp-A aneurysm (four patients with portal hypertension and one patient without portal hypertension). Color Doppler sonography was performed in all five patients, and power Doppler sonography was performed in three. RESULTS: Gray-scale sonography failed to detect the aneurysm in four of five cases because of a surrounding splenorenal (Sp-R) shunt in three patients and marked calcification of the aneurysmal wall in one patient. Pulsed Doppler sonography showed a slightly turbulent pulsatile flow along the aneurysmal wall, which immediately led to the diagnosis in four cases, including the three cases with Sp-R shunt. In one case, color Doppler sonography failed to detect the aneurysm because of a markedly calcified aneurysmal wall, although power Doppler sonography could visualize the aneurysm. CONCLUSIONS: Gray-scale sonography is not a useful diagnostic tool for Sp-A aneurysm. Clinicians should use color Doppler sonography in the evaluation of the splenic hilus in patients with Sp-R shunt to find a small Sp-A aneurysm. The addition of power Doppler sonography is helpful in visualizing calcified Sp-A aneurysms.

Adult↗
PubMedDate not supplied

Stent-protected carotid angioplasty using a membrane stent: a comparative cadaver study.

PURPOSE: To evaluate the performance of a prototype membrane stent, MembraX, in the prevention of acute and late embolization and to quantify particle embolization during carotid stent placement in human carotid explants in a proof of concept study. METHODS: Thirty human carotid cadaveric explants (mild stenoses 0-29%, n = 23; moderate stenoses 30-69%, n = 3; severe stenoses 70-99%, n = 2) that included the common, internal and external carotid arteries were integrated into a pulsatile-flow model. Three groups were formed according to the age of the donors (mean 58.8 years; sample SD 15.99 years) and randomized to three test groups: (I) MembraX, n = 9; (II) Xpert bare stent, n = 10; (III) Xpert bare stent with Emboshield protection device, n = 9. Emboli liberated during stent deployment (step A), post-dilatation (step B), and late embolization (step C) were measured in 100 microm effluent filters. When the Emboshield was used, embolus penetration was measured during placement (step D) and retrieval (step E). Late embolization was simulated by compressing the area of the stented vessel five times. RESULTS: Absolute numbers of particles (median; >100 microm) caught in the effluent filter were: (I) MembraX: A = 7, B = 9, C = 3; (II) bare stent: A = 6.5, B = 6, C = 4.5; (III) bare stent and Emboshield: A = 7, B = 7, C.=.5, D = 8, E = 10. The data showed no statistical differences according to whether embolic load was analyzed by weight or mean particle size. When summing all procedural steps, the Emboshield caused the greatest load by weight (p = 0.011) and the largest number (p = 0.054) of particles. CONCLUSIONS: On the basis of these limited data neither a membrane stent nor a protection device showed significant advantages during ex vivo carotid angioplasty. However, the membrane stent seems to have the potential for reducing the emboli responsible for supposed late embolization, whereas more emboli were observed when using a protection device. Further studies are necessary and warranted.

Adult↗
PubMed1986

Cognitive stress and cardiovascular reactivity. II. Relationship to atherosclerosis, arrhythmias, and cognitive control.

This is the second of a two-part series on the effects of cognitive stress on cardiovascular disease. This paper reviews the relationship between cognitive stress and cardiovascular reactivity as it relates to the development of atherosclerosis and arrhythmias. In addition, the moderation of cardiovascular reactivity by the opportunity to exercise control over the stressor is discussed. The findings may be summarized as follows. First, recent animal work has suggested that the magnitude of heart rate change in the presence of a conditioned aversive stimulus is positively correlated with the extent of coronary atherosclerosis under diets high and low in atherogenic potential. Second, cardiovascular reactivity in humans may be related to several factors that could have an influence on the pathogenesis of atherosclerosis. These factors include: increased beta-adrenergic driving, increased shearing force on the intimal lining of the vessels, changes in pulsatile flow and the subsequent smooth muscle reparatory process. Cognitive (psychological) stress has also been related to ST segment depression, rate-pressure product changes, and changes in cardiac contractility. Animal studies have shown that the susceptibility to ventricular fibrillation may be enhanced by the presence of a conditioned aversive stimulus and may be reduced through adaptation to the aversive environment. The balance between sympathetic and parasympathetic influences on the myocardium may also play a critical role in the susceptibility of an already diseased heart to succumb to fatal arrhythmias during a behavioral stressor. Finally, studies in which subjects may exercise some control over an aversive stimulus suggest that cardiovascular reactivity may be pronounced and sustained in situations requiring frequent adjustment to changes in the criteria for successful performance, and/or the presence of positive incentives.

Arrhythmias, Cardiac↗
PubMed1975

Perfusion of human ovaries in vitro with artificial medium: metabolism and steroidogenesis.

A study was made of ovaries perfused in vitro with a liquid fluorocarbon that was stabilized in emulsion by a nonionic detergent to which tissue culture medium was added. A pulsatile flow was used in an organ preservation system under aseptic conditions. Glucose was utilized and lactate produced at a fairly constant rate for as long as 20 hours of perfusion. 14-C-progesterone and 14-C-17alphaOH-progesterone were synthesized from 14-C-acetate and estradiol was secreted. The production of these steroids by the perfused ovary appears to be responsive to gonadotropins.

Acetates↗
PubMed1979

Management of acute aortic occlusion.

Acute aortic occlusion is most often seen in elderly patients with advanced cardiac disease. The management of these patients has been facilitated by the use of extraanatomic bypass. Over the past 2 years, six patients aged 55 to 87 years presented to our medical center with acute aortic occlusion, three after major operative procedures. One patient had a thrombosed abdominal aortic aneurysm; in the other five patients differentiation between saddle embolus and thrombosis of the distal aorta was impossible. There was one operative death. Four of the other five patients underwent axillobifemoral bypass and one underwent aortofemoral thrombectomy. All survived, and none required amputation. Two of the three patients who underwent preoperative aortography developed transient renal failure postoperatively. Aortography is of little value in diagnosis and is probably contraindicated in acute aortic occlusion. Our recommendation for operative management includes (1) preparation of the patient for possible axillobifemoral bypass, (2) angiography of distal runoff via both femoral arteries, (3) attempt at bilateral aortofemoral embolectomy with Fogarty catheters, and (4) axillobifemoral bypass if embolectomy fails to restore normal pulsatile flow.

Acute Disease↗
PubMed1985

Eversion endarterectomy of the superficial femoral artery and end-to-side anastomosis to the deep femoral artery. An alternative to extended profundoplasty.

The success of aortofemoral reconstruction in patients with superficial femoral artery occlusion depends on the restoration of a satisfactory pulsatile flow to the deep femoral artery. In 18 patients with multilevel disease, widespread involvement of the deep femoral artery, and poor distal outflow, we performed an eversion endarterectomy of the proximal segment of the superficial femoral artery and constructed an end-to-side anastomosis between this segment and the distal deep femoral artery. In 10 patients, the reconstruction was performed after thrombectomy of the occluded aortofemoral graft, and in 8 the two reconstructions were simultaneous. The actuarial patency rate was 93.5 percent at 1 year and 75.2 percent at 5 years. Four late femorodistal bypasses were performed that gave an actuarial limb salvage rate of 68.8 percent at 1 year and 61.6 percent at 5 years. In selected cases, this technique is a valid alternative to an extended profundoplasty or to a femorodistal bypass.

Aged↗
PubMed1996

Cora valveless pulsatile rotary pump: new design and control.

For decades, research for developing a totally implantable artificial ventricle has been carried on. For 4 to 5 years, two devices have been investigated clinically. For many years, we have studied a rotary (but not centrifugal) pump that furnishes pulsatile flow without a valve and does not need external venting or a compliance chamber. It is a hypocycloidal pump based on the principle of the Maillard-Wankel rotary compressor. Currently made of titanium, it is activated by an electrical brushless direct-current motor. The motor-pump unit is totally sealed and implantable, without noise or vibration. This pump was implanted as a left ventricular assist device in calves. The midterm experiments showed good hemodynamic function. The hemolysis was low, but serious problems were encountered: blood components collecting on the gear mechanism inside the rotor jammed the pump. We therefore redesigned the pump to seal the gear mechanism. We used a double system to seal the open end of the rotor cavity with components polished to superfine optical quality. In addition, we developed a control system based on the study of the predicted shape of the motor current. The new design is now underway. We hope to start chronic experiments again in a few months. If the problem of sealing the bearing could be solved, the Cora ventricle could be used as permanent totally implantable left ventricular assist device.

Animals↗
PubMed1987

Maintenance of complex neural function during perfusion of the mammalian brain.

A perfused brain preparation was developed utilizing non-pulsatile flow of artificial blood. Cortical electrical activity and respiratory motor output were maintained for as long as 7-8 h. This preparation permits stable intracellular recordings from CNS neurons displaying ongoing respiratory activity, and should permit analysis of synaptic and intrinsic cellular mechanisms involved in producing the respiratory output. A similar approach may be useful for electrophysiology throughout the CNS, and for other fields in which control of the blood composition and/or mechanical stability are required.

Animals↗
PubMed1994

Failure of pulse oximetry in the assessment of raised limb intracompartmental pressure.

Pulse oximetry has been proposed as an aid to monitoring raised intracompartmental pressures (ICPs). ICP and percentage haemoglobin oxygen saturation in the affected limb were studied in 10 consecutive patients with raised ICP. Compartment pressures ranged from 28 to 64 mmHg (mean 40.9 mmHg). In two patients with absent pulses, pulse oximetry failed to detect pulsatile flow and recorded 0 per cent saturation. The remaining eight patients, including four with absent peripheral pulses, all had percentage haemoglobin saturations within 2 per cent of the opposite normal limb. Arterial haemoglobin desaturation was not associated with raised ICP. The presence of an oximeter signal and a normal reading does not necessarily imply adequacy of tissue perfusion. Pulse oximetry does not appear to be a reliable aid in the diagnosis or monitoring of impaired perfusion due to raised ICP.

Adolescent↗
PubMed1981

Correlation between intimal thickness and fluid shear in human arteries.

A realistic pulsatile flow was passed through a cast of the aortic bifurcation of a 63-year-old male with mild atherosclerosis, and a laser Doppler anemometer was used to measure fluid velocities in the cast at 15 selected sites near the lateral and medial walls. Intimal, medial and adventitial thickness were measured, and sudanophilia was scored, at corresponding sites in the vessel from which the cast had been made. A negative correlation was found between intimal thickness (IT) and wall shear rate (i.e., the velocity gradient at the blood-artery interface). The strongest negative correlation (P less than 0.005) was between IT and "pulse shear rate" (PSR), defined by analogy with pulse pressure. Sudanophilia also correlated negatively with PSR (P less than 0.01). These results suggest that large excursions of interfacial shear, at levels too low to cause damage, may inhibit intimal thickening.

Arteries↗
PubMed1994

Fluid wall shear stress measurements in a model of the human abdominal aorta: oscillatory behavior and relationship to atherosclerosis.

Clinically significant atherosclerosis in the human aorta is most common in the infrarenal segment. This study was initiated to test the hypothesis that flowfield properties are closely related to the localization of plaques in this segment of the arterial system. Wall shear stress was calculated from magnetic resonance velocity measurements of pulsatile flow in an anatomically accurate model of the human abdominal aorta. The wall shear stress values were compared with intimal thickening from 15 post-mortem aortas measured by quantitative morphometry of histological cross sections obtained at standard locations. Wall shear stress oscillated in direction throughout most of the infrarenal aorta, most prominently in the distal region. The time-averaged mean wall shear stress (-1.7 to 1.4 dyn/cm2) was lowest near the posterior wall in this region. These hemodynamic parameters coincided with the locations of maximal intimal thickening. Statistical correlation between oscillatory shear and intimal thickness yielded r = 0.79, P < 0.00001. Low mean shear stresses correlated nearly as well (r = -0.75, P < 0.00005). Comparison of our data with surface maps of Sudan Red staining and early lesions as reported by others revealed similar conclusions. In contrast, pulse and maximum shear stresses did not correlate with plaque localization as has been shown for other sites of selective involvement by atherosclerosis (r < 0.345). Simulated exercise conditions markedly changed the magnitude and pattern of wall shear stress in the distal abdominal aorta. These results demonstrate that in the infrarenal aorta, regions of low mean and oscillating wall shear stresses are predisposed to the development of plaque while regions of relatively high wall shear stress tend to be spared.

Adult↗