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PubMed2005

Critical concentration for colloidal crystallization determined with microliter centrifuged suspensions.

We report an elegant method using centrifugal sedimentation for determining the critical particle concentration for colloidal crystallization. A small amount of a dilute suspension of monodispersed particles stored in a flat capillary cell was centrifuged to temporarily generate a nonequilibrium gradient of the particle concentration including a crystalline-noncrystalline phase boundary in the cell. In the recovering process after the centrifugation, the particle concentration of the crystalline phase at the boundary was found to always have the equilibrium value, although the global concentration distribution evolved with time. The critical concentration was determined based on spatially resolved spectrometry. The present method requires only one batch of a suspension of the order of microliters and is applicable up to high concentration regions near the closest packing without the effect of the particle aggregation.

Journal Article↗
PubMed1998

In vivo evaluation of the miniaturized Gyro centrifugal pump as an implantable ventricular assist device.

A miniaturized Gyro centrifugal pump has been developed to be incorporated into a totally implantable artificial heart. The Gyro PI (permanently implantable) model is a pivot bearing supported centrifugal pump with a priming volume of 20 ml. With the miniaturized actuator, the pump-actuator package has a height of 53 mm, a diameter of 65 mm, and a displacement volume of 145 ml. To evaluate the hemocompatibility and efficiency of the Gyro PI pump system, a plastic prototype (Gyro PI-601) was implanted into a bovine model as a left or right ventricular assist device (LVAD or RVAD), bypassing from the left ventricular apex to the descending aorta or from the right ventricular infundibulum to the main pulmonary artery. The calves were anticoagulated with heparin to maintain activated clotting times from 150 to 200 s. Four calves were supported for 23, 24, and 50 days in the LVAD studies, and 40 days in the RVAD study. The first calf died due to intrathoracic bleeding associated with sepsis. The second calf was euthanized for a low flow rate less than 2 L/min due to an obstructed inflow with growing pannus. The third and fourth calves were euthanized as scheduled. Renal and hepatic functions remained normal, and plasma free hemoglobin values were less than 8 mg/dL throughout the experiments. The fourth case showed flow rates of 4.83 +/- 0.57 L/min, input power of 6.16 +/- 0.49 W, and the inside temperature of the actuator of 43.5 +/- 0.52 degrees C. The pumps implanted in the fourth calf demonstrated no thrombus formation at the autopsy. These in vivo experiments revealed that the Gyro PI pump can provide adequate flow as an easily implantable, efficient, antithrombogenic, and nonhemolytic centrifugal LVAD or RVAD with miniaturized actuators.

Animals↗
PubMed1999

Flow visualization analysis for evaluation of shear and recirculation in a new closed-type, monopivot centrifugal blood pump.

Flow visualization has great potential in analyzing flow patterns of centrifugal blood pumps to locate possible hemolysis and thrombus formation sites. This study focused on the said phenomena thought to correlate with areas of high shear velocity and stagnation and analyzed a new closed-type centrifugal blood pump. As a result of analyzing the flow of inlet and front gap of the impeller, flow in the front gap was approximately 30% of the external flow. Visualization in the back gap showed sufficient exchange also. Analysis in the volute area and around the washout holes revealed high shear locations and quantified the highest shear velocity. Maximum shear on the volute wall was found to be 9,000-19,000 s-1 and was located in the 0.2-mm vicinity of the wall. Based on these results, previous hemolysis tests, and small pump size, one concludes that the analyzed closed-type centrifugal pump has a relatively smooth flow suitable for a totally implantable artificial heart.

Algorithms↗
PubMed1999

Analysis of optimal design configurations for a multiple disk centrifugal blood pump.

A multiple disk centrifugal pump was analyzed as a blood pump for use in cardiac assistance or as a bridge to transplant device. The original configuration consisted of 6 parallel disks with 0.016 inch spacing between disks. This pump suffered from a degradation of flow with increasing afterload. A study was conducted to analyze flow performance as a function of afterload, preload, and motor speed. Configurations were examined including 4, 5, and 6 disks each with spacings of 0.15, 0.20, and 0.25 inches. Flow rates were examined for variations in afterload from 60-130 mm Hg, in preload from 0-20 mm Hg and for motor speeds of 1,250, 1,500, and 1,750 rpm. Analyses of afterload effects were intended to determine those configurations that produced less flow degradation with increasing afterload. Analyses of motor speed effects were intended to determine any configurations that produced greater flow increases with increasing motor speed. A hemolysis study was also performed. Both plasma free hemoglobin and the index of hemolysis were compared to data reported for other centrifugal blood flow devices. Results indicated that a 5 disk configuration with a 0.15 inch spacing produced optimal flow results with minimal degradation at higher afterloads. No optimal configuration based upon motor speed was indicated. Preload effects on pump performance were minimal. Hemolysis results indicated minimal blood damage with levels below those of many other centrifugal blood pump designs.

Animals↗
PubMed2000

Transaortic inflow and outflow cannula for centrifugal mechanical assistance.

A specific cannula allowing single site transaortic inflow and outflow cannulation for centrifugal assist devices is described. The cannula is inserted through a straight 18 mm collagen coated Dacron tube anastomosed to the anterior aspect of the ascending aorta. The inflow conduit of the cannula is positioned into the left ventricle through the aortic valve, and the end hole of the outflow conduit is positioned in the ascending aorta. The cannula was evaluated in vivo in 3 adult pigs by the institution of a centrifugal pump for left ventricular support. Optimal flow varied between 5 and 6 L/min and mean aortic pressure between 55 and 70 mm Hg throughout the 3 days of left ventricular support. Recently, we employed this cannula in a patient who was not able to be weaned from cardiopulmonary bypass for the institution of left ventricular support using a centrifugal pump. The cannula provided effective inflow and outflow drainage with an optimal flow of 5.2 L/min throughout the 72 h of support. The patient was successfully weaned from support on the fourth postoperative day. This rational transaortic approach of cannulation using this specific cannula is a refined implantation technique which allows direct left ventricular inflow drainage, reduces the time of implantation, spares left ventricular myocardium, avoids bleeding that is sometimes encountered at other cannulation sites, and avoids compression of the heart by cannulas.

Aged↗
PubMed2001

Design and evaluation of a single-pivot supported centrifugal blood pump.

In order to develop a centrifugal blood pump that meets the requirements of a long-term, implantable circulatory support device, in this study a single-pivot bearing supported centrifugal blood pump was designed to evaluate its basic performance. The single-pivot structure consisted of a ceramic ball male pivot mounted on the bottom surface of the impeller and a polyethylene female pivot incorporated in the bottom pump casing. The follower magnet mounted inside the impeller was magnetically coupled to the driver magnet mounted on the shaft of the direct current brushless motor. As the motor rotated, the impeller rotated supported entirely by a single-pivot bearing system. The static pump performance obtained in the mock circulatory loop revealed an acceptable performance as a left ventricular assist device in terms of flow and head pressure. The pump flow of 5 L/min against the head pressure of 100 mm Hg was obtained at rotational speeds of 2,000 to 2,200 rpm. The maximum pump flow was 9 L/min with 2,200 rpm. The maximum electrical-to-hydraulic power conversion efficiency was around 14% at pump flows of 4 to 5 L/min. The stability of the impeller was demonstrated at the pump rpm higher than 1,400 with a single-pivot bearing without an additional support at its top. The single-pivot supported centrifugal pump can provide adequate flow and pressure as a ventricular assist device, but its mechanical stability and hemolytic as well as thrombotic performances must be tested prior to clinical use.

Equipment Design↗
PubMedDate not supplied

The surge technique: a method to increase purity of platelet concentrates obtained by centrifugal apheresis.

A surge technique has been developed to increase the purity of high-yield platelet concentrations prepared on a blood processor with the Latham bowl. The surge technique combines elutriation with centrifugal separation, utilizing plasma recirculated from the plasma/air bag back into the centrifuge bowl to elute platelets from the red cell mass. Platelet concentrates prepared by surge collection with six separation cycles (n = 22), contained an average of 3.9 +/- 1.4 X 10(11) platelets, with 0.15 +/- 0.11 X 10(9) leukocytes, and red cells below the level of detection. The surge technique reduces collection time by 4 minutes per cycle and eliminates the need for a secondary centrifugation; thus, 96 minutes donor processing time would permit eight separation cycles. Platelets collected by the surge technique exhibited unaltered morphology and capacity to take up radioactively labeled serotonin in vitro compared to pre-apheresis controls. Results from in vitro functional studies also indicate that the capacity of platelets collected with the surge technique to respond to various concentrations of adenosine diphosphate, collagen, and thrombin by aggregation and secretion of both serotonin (dense bodies) and beta-thromboglobulin (alpha-granules) was not significantly different (p less than or equal to 0.05) from that of pre-apheresis controls.

Adenosine Diphosphate↗
PubMedDate not supplied

Effect of delayed centrifugation or reading on the detection of ABO incompatibility by the immediate-spin crossmatch.

The immediate-spin (IS) crossmatch is a method that detects ABO incompatibility. However, under certain circumstances, this test may show unwanted negative or weak results, even though the red cells (RBCs) and serum being tested are ABO incompatible with each other. The present study investigated the potential effect of delayed centrifugation or reading on the IS crossmatch test performance. When the centrifugation step of the IS crossmatch between group O sera and group A1 RBCs was delayed for 2 minutes, 5 of 200 crossmatches showed no agglutination with only trace (n = 2) or moderate (n = 3) hemolysis, and one crossmatch showed only weak, macroscopic agglutination, but moderate hemolysis. All six sera contained A antibodies that were lytic in vitro and, therefore, probably were capable of causing in vivo hemolysis of transfused A1 RBCs. Delaying the reading of the IS crossmatch test for 2 minutes had no apparent effect on test performance. These data demonstrate the importance of technologists' recognition of hemolysis as a positive result on IS crossmatches, especially if the performance of the centrifugation step of the test is delayed. Furthermore, the unwanted negative agglutination results were abolished by suspending the group A1 RBCs in saline containing EDTA. The authors' laboratory has modified its IS crossmatch procedure so that donor RBCs are routinely suspended in saline containing EDTA before testing. This procedural change should increase the safety of the IS crossmatch.

ABO Blood-Group System↗
PubMed2001

Blood loss in elective coronary artery surgery: a comparison of centrifugal versus roller pump heads during cardiopulmonary bypass.

OBJECTIVES: To compare the effects of centrifugal pumps versus roller pumps for cardiopulmonary bypass (CPB) in routine cardiac surgery on hematologic parameters in the context of modern practice. DESIGN: Prospective, randomized, partially blinded. SETTING: University teaching hospital. PARTICIPANTS: Elective coronary artery surgery patients (n = 113) INTERVENTION: Patients were randomized to be perfused with either a roller head (group R, n = 56) or a centrifugal head (group C, n = 57) pump. Patients received epsilon-aminocaproic acid before and during CPB. Core body temperatures were allowed to drift down to approximately 32 degrees C. MEASUREMENTS AND MAIN RESULTS: Postoperative chest tube blood loss, blood product requirements, hemoglobin, and platelet counts were assessed. There were no significant differences in preoperative or intraoperative parameters, including CPB time, complexity of procedure, and minimum core temperature. There were the expected reductions in hemoglobin and platelet levels post-CPB in both groups to a similar extent. Chest tubes remained in situ for similar durations, and the final volume of drainage was not significantly different (group C, 1300 +/- 92 mL; group R 1117 +/- 83 mL; p = 0.14). Allogeneic blood was given to 23% of patients in group C and 18% in group R (p = 0.63). Aspirin was associated with an increase in early chest tube drainage. CONCLUSIONS: In this surgical and perfusion environment, the authors were unable to show an advantage, from the hematologic point of view, in the routine use of a centrifugal pump head in elective coronary artery surgical patients. The use of antifibrinolytic agents and mild hypothermia may have effects on hemostasis that overshadow the influence of pump head design in this type of surgery.

Aged↗
PubMedDate not supplied

[Body traction using centrifugal force in the treatment of spinal diseases].

In self treatment bodystretching centrifugal force was used in order to diminish backbone pains after discektomy L3/L4. After 13 minutes of treatment with up to 1.5 G centrifugal force related to the lumbal region on a centrifuge of the Max-Planck-Institut für Verhaltensphysiologie Seewiesen the author felt free of pains in the back. The pains have not returned for 18 months yet.

Back Pain↗
PubMed1999

A centrifugal particle concentrator for use in inhalation toxicology.

Epidemiologic studies have provided strong evidence that episodic exposure to ambient particulate matter is associated with increases in morbidity and mortality. These adverse effects have been demonstrated at concentrations far below the National Ambient Air Quality Standard (NAAQS), and thus, the biological plausibility of these effects has been questioned. For the purpose of exposing test animals to relevant and reproducible exposure concentrations of ambient particulate matter (PM), we have developed a simple and inexpensive concentrator system that can concentrate ambient particles 10-fold. A high-volume blower is used to deliver ambient air to the inlet manifold of a centrifugal concentrator and the entrained particles travel along a concentric annulus formed by a stationary solid outer cylinder and a porous inner cylinder rotating at high speed (up to 12,500 rpm). Suction applied at one end of the porous shaft causes the dispersion medium (air) to pass through the porous cylinder and into the shaft. Since the rotational velocity of airborne particles is comparable to that of the rotating cylinder near its surface, the particles move radially outward due to the centrifugal force, in addition to their motion laterally along the cylinder and inward due to the suction of air into the rotating porous cylinder. The particles reach their highest concentration near the outlet manifold, where they enter the exposure chamber under positive pressure ( approximately 0.4 cm H2O). Except for coarse particle loss due to impaction and diffusional loss of ultrafine particles in the concentrator, the increase in particle concentration is the ratio of the flow rates for the inlet air and the air delivered to the exposure chamber. We have used the centrifugal concentrator to deliver concentrated ambient urban PM to a nose-only exposure chamber and examined the concentrating effect across ambient particle sizes.

Air↗
PubMed1968

Rabbit skeletal muscle glycogen. A morphological and biochemical study of glycogen beta-particles isolated by the precipitation-centrifugation method.

Glycogen in its particulate beta-form is localized in the sarcoplasm close to the sarcoplasmic reticulum. Some particles are in close contact with the membranes, on the outer side of the vesicles. The mild technique of differential precipitation-centrifugation has been adapted to the preparation of glycogen from adult skeletal muscle. A preliminary low-speed centrifugation which eliminates the contractile protein structures and the cell debris is followed by a high-speed centrifugation which produces pellets containing glycogen mixed with smooth-walled vesicles, the glycogen-sarcovesicular fraction. The glycogen obtained after treatment of this fraction with deoxycholate and two washings contains 3% protein. A similar protein content contaminates glycogen banded in a linear sucrose gradient. The glycogen-sarcovesicular fraction and the purified glycogen have been examined, under the electron microscope, in sections of fixed and embedded material or with the negative staining technique. The glycogen beta-particles in negatively stained preparations have an average diameter of 39.4 mmicro. The largest particles present irregular outlines, suggesting the presence of conglomerated subunits, about 20 mmicro in diameter. These subunits seem to fall apart under the influence of concentrated potassium hydroxide. The mean sedimentation coefficients calculated for infinite dilution vary from 115 to 135S. The spectrophotometric analysis of the glycogen-iodine complex indicates the presence of long end-chains in the molecule.

Animals↗
PubMedDate not supplied

Effect of stationary guiding vanes on improvement of the washout behind the rotor in centrifugal blood pumps.

In centrifugal pumps, there always exists an area of stagnation between the rear of the rotor and the rear housing wall that promotes thrombus formation around the axle. Some current devices overcome the problem by using holes in the rotor plane, leading to increased hydrodynamic losses and shear stress. In this study, a simple apparatus was developed to overcome this problem. Guiding vanes were fixed to the rear housing wall. These vanes decrease the tangential velocity of the fluid and thus the centrifugal force, leading to an increased secondary flow toward the axle. The effect of such vanes was studied in videographic and ultrasound studies. An increase of washout and mixing between the flow layers could be demonstrated (stay time < 200 msec versus several seconds without vanes). In the first animal experiment using nonoptimized vanes, there was no thrombus at the back plane or the seal, and only a small thrombus at the transition between axle and rotor. Hemolysis was slightly elevated (3.2 mg/dl versus 2.5 mg/dl in control experiments). In conclusion, it is highly likely that this simple system will improve the flow characteristics in centrifugal pumps.

Animals↗
PubMedDate not supplied

Blood damage related to cardiopulmonary bypass: in vivo and in vitro comparison of two different centrifugal pumps.

Cardiopulmonary bypass (CPB) induces hemolysis and the activation of the inflammatory and coagulation systems. Several components of the CPB equipment may contribute to such phenomenon. We tested the effects of two differently designed centrifugal pumps (Bio-Pump, Medtronic and Revolution, Cobe) on several markers of hemolysis, coagulation, and inflammation: plasma free hemoglobin,prothrombin fragment 1.2, platelet factor 4, and P-selectin. Twenty patients requiring coronary artery bypass grafting were randomized to undergo CPB with one of the study centrifugal pumps, and 10 experiments (5 for each pump) were performed with a closed loop circuit to assess pumps' performances over 6 circulation hours using human blood. CPB induced a significant elevation of all the tested markers. Neither in the in vivo nor in the in vitro study were significant differences observed between the groups. Because the Revolution centrifugal pump, which was recently designed and distributed, produced results comparable with those obtained with the BioPump, it should be considered as safe as the Bio-Pump to perform clinical CPB.

Aged↗
PubMedDate not supplied

Advantages of temporary venoatrial shunt using centrifugal pump during bidirectional cavopulmonary shunt.

Single-ventricle palliation without the use of cardiopulmonary bypass carries advantages that reduce systemic edema and inflammatory responses; however, simple clamping of the superior vena cava (SVC) without a temporary shunt leads to increase in cerebral venous pressure and subsequent decrease in cerebral blood flow during bidirectional cavopulmonary shunt (BCPS). We report our experience of BCPS, using a centrifugal pump-assisted temporary shunt. The criteria included an unrestrictive interatrial communication, the absence of atrioventricular valve regurgitation, and the existence of an antegrade pulmonary blood flow. From August 2000, 14 children with single-ventricle physiology met the criteria. The mean age was 1.0 +/- 0.9 years, and the mean weight was 8.4 +/- 2.6 kg. A temporary shunt was established between the SVC and the right atrium with right-angle cannulae, which were connected to a centrifugal pump to accelerate the blood flow from the SVC to the right atrium. All patients tolerated the procedure. Mean central venous pressure was 17 +/- 4 mm Hg, and transcutaneous oxygen saturation was maintained at 77 +/- 8% during anastomosis. No patients required blood transfusion. There were no postoperative neurological complications. The centrifugal pump-assisted temporary shunt offered safer and more effective circulatory support than other shunt systems, with excellent venous drainage in pediatric patients undergoing BCPS.

Assisted Circulation↗
PubMed2002

Plasma instability of a vacuum arc centrifuge.

Ever since conception of the vacuum arc centrifuge in 1980, periodic fluctuations in the ion saturation current and floating potential have been observed in Langmuir probe measurements in the rotation region of a vacuum arc centrifuge. In this work we develop a linearized theoretical model to describe a range of instabilities in the vacuum arc centrifuge plasma column, and then test the validity of the description through comparison with experiment. We conclude that the observed instability is a "universal" instability, driven by the density gradient, in a plasma with finite conductivity.

Journal Article↗
PubMed1976

Morphology of Arabidopsis Grown under Chronic Centrifugation and on the Clinostat.

Morphological measurements were made on populations of Arabidopsis thaliana grown from seed for 21 days under essentially constant environmental conditions except for the influence of gravitational or centrifugal accelerations. Growth conditions were what had been proposed for experiments in an artificial satellite. Observations are reported for plants grown at normal 1-g upright or on horizontal clinostats and for plants grown on a centrifuge. Increased g-force, up to 15 times normal, was found to have significant but small effects on some morphological end points. The plants' sensitivity to the magnitude of the g-force was much less than to its vector direction.Data from centrifuge experiments (which determined the g-functions for particular characters) were extrapolated to zero-g to predict a set of morphological characteristics of a plant developing in the satellite environment. As an alternative means of predicting properties of a zero-g plant, characteristics of plants grown on horizontal clinostats were measured. The results of these two predictive methods were not in agreement.Clinostat grown plants were morphologically distinct from upright stationary controls. When plants were grown while rotating in the upright position on vertical clinostats they were similar to stationary plants also grown upright, but there were small differences some of which were statistically significant.

Journal Article↗
PubMed1981

Soluble Cell Wall Polysaccharides Released from Pea Stems by Centrifugation : I. EFFECT OF AUXIN.

The metabolism of polysaccharides by pea stem segments treated with and without auxin was investigated using a centrifugation technique for removing solution from the free space of the cell wall. Glucose is the predominant sugar in both the ethanol-soluble and ethanol-insoluble fractions of the cell wall solution extracted with water. In the water-soluble, ethanol-insoluble polysaccharides, arabinose, xylose, galactose, and glucose make up 9.5, 23.8, 23.9, and 39.9%, respectively, of the neutral sugars, while rhamnose, fucose, and mannose are present at concentrations between 0.5 and 2.0%.Auxin treatment enhances the levels of xylose and glucose in ethanol-insoluble polysaccharides relative to controls, and this difference can be detected within 30 minutes of auxin treatment. Cellulose-binding experiments show that the enhanced levels of xylose and glucose are in a polymer having the cellulose-binding properties of xyloglucan. (3)H-glucose labeling experiments confirm the auxin-enhanced metabolism of the xyloglucan fraction; however, increased labeling of arabinose is also observed in auxin-treated sections. Auxin treatment also causes a marked increase in the level of uronic acids centrifuged from pea internode sections. Thus, after 3 hours of incubation in indoleacetic acid, the level of uronic acids in the ethanol-insoluble polysaccharides which can be recovered by centrifugation is increased 2- to 3-fold over sections incubated in water. These auxin-enhanced changes in xylose, glucose, and uronic acids are correlated with enhanced rates of section growth.Incubation of excised pea internode sections in acidic buffers also enhances the rate of xyloglucan and polyuronide metabolism. This acid-enhanced metabolism of xyloglucan and polyuronide is inhibited by low temperature, suggesting that it is enzyme-mediated.Extraction of the cell wall solution with CaCl(2) increases the yield of all neutral sugars. Arabinose and mannose are increased 4- and 3-fold, respectively, and xylose and glucose by about 20%, while galactose levels are 40% higher in cell wall solution extracted with CaCl(2) than in that extracted with water. Although calcium increases the amount of neutral sugars extracted, it does not affect the auxin-induced changes in neutral sugars. Extraction of the cell wall solution with ethyleneglycol-bis-(beta-aminoethyl ether)-N,N'tetraacetic acid enhances the yield of uronic acids and also increases the difference due to auxin treatment.

Journal Article↗