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At least 1,279 records · Page 71Linked to original sources
PubMed1987

Laboratory methods for the diagnosis of disseminated histoplasmosis: clinical importance of the lysis-centrifugation blood culture technique.

Disseminated histoplasmosis, an uncommon disease that is usually fatal if not treated, is being recognized with increasing frequency in immunosuppressed patients. We retrospectively reviewed the laboratory methods used to establish the diagnosis of disseminated histoplasmosis in 28 patients examined at our institution. Tissue stains provided the initial diagnosis in 13 of the patients (46%). Serologic tests (complement fixation or immunodiffusion) were positive in 25 patients (89%); the frequencies of positive serologic results were similar in immunocompetent and in immunosuppressed patients. Blood cultures were positive in 20 of the patients (71%) and provided the initial diagnosis in 7 (25%); 5 of these 7 cases (71%) were detected with use of the lysis-centrifugation method. Furthermore, the recovery time for this blood culture method was less than that for a conventional blood culture method (brain-heart infusion biphasic technique). The lysis-centrifugation blood culture technique is an important laboratory method for the diagnosis of disseminated histoplasmosis.

Adult↗
PubMed2001

Creating porous tubes by centrifugal forces for soft tissue application.

Chemically crosslinked poly(2-hydroxyethyl methacrylate) (PHEMA) tubes were synthesized by applying centrifugal forces to propagating polymer chains in solution. Initiated monomer solutions, with a composition typical for PHEMA sponges, were placed into a cylindrical mold that was rotated about its long axis. As polymerization proceeded, phase separated PHEMA formed a sediment at the periphery under centrifugal action. The solvent remained in the center of the mold while the PHEMA phase gelled, resulting in a tube. By controlling the rotational speed and the formulation chemistry (i.e., monomer, initiator and crosslinking agent concentrations), the tube dimensions and wall morphology were manipulated. Tube manufacture was limited by a critical casting concentration [M]c, above which only rods formed. All tubes had an outer diameter of 2.4 mm, reflecting the internal diameter of the mold and a wall thickness of approximately 40-400 microm. Wall morphologies varied from interconnecting polymer and water phases to a closed cell, gel-like, structure. Concentric tubes were successfully prepared by using formulations that enhanced phase separation over gelation/network formation. This was achieved by using formulations with lower concentrations of monomer and crosslinking agent and higher concentrations of initiator. This technique offers a new approach to the synthesis of polymeric tubes for use in soft tissue applications, such as nerve guidance channels.

Biocompatible Materials↗
PubMed2000

Centrifuge modeling of air sparging - a study of air flow through saturated porous media.

The success of air sparging as a remedial technology for treatment of contaminated aquifers is well documented. However, there is no consensus, to date, on the mechanisms that control the flow of injected air through the saturated ground. Currently, only qualitative results from laboratory experiments are available to predict the zone of influence of a sparging well. Given that the patterns of air flow through the soil will ultimately determine the efficiency of an air sparging treatment, it is important to quantify how sparged air travels through a saturated porous medium. The main objective of this research is to develop a model that describes air transport through saturated porous media. This paper presents results from an ongoing study that employs centrifuge modeling to reproduce in situ air sparging conditions. Centrifuge testing is an experimental technique that allows reduced-scale duplication, in the laboratory, of the stresses and pressure distributions encountered in the field. In situ conditions are critical in the development of actual air flow patterns. Experiments are being conducted in a transparent porous medium consisting of crushed borosilicate glass submerged in fluids of matching indices of refraction. Air is observed as it flows through the porous medium at varying gravitational accelerations. Recorded images of experiments allow the determination of flow patterns, breakthrough velocities, and plume shapes as a function of g-level and injection pressure. Results show that air flow patterns vary from fingering, at low g-levels, to pulsing at higher accelerations. Grain and pore size distribution of the porous medium do not exclusively control air flow characteristics. Injector geometry has a definite effect on breakthrough velocities and air plume shapes. Experiments have been conducted to compare the velocity of air flow through the saturated porous medium to that of air in pure liquids. Results show that the velocity of air through the medium is lower than that in the pure fluid, as expected. At high g-levels however, plume breakthrough velocities are proportional to the velocity of the air in the pure fluid.

Acceleration↗
PubMed2001

Visual feedback of the moving arm allows complete adaptation of pointing movements to centrifugal and Coriolis forces in human subjects.

A classical visuo-manual adaptation protocol carried out on a rotating platform was used to test the ability of subjects to adapt to centrifugal and Coriolis forces when visual feedback of the arm is manipulated. Three main results emerge: (a) an early modification of the initial trajectory of the movements takes place even without visual feedback of the arm; (b) despite the change in the initial trajectory, the new external force decreases the accuracy of the pointing movements when vision is precluded; (c) a visual adaptive phase allows complete adaptation of the pointing movements performed in a modified gravitoinertial field. Therefore vision would be essential for subjects to completely adapt to centrifugal and Coriolis forces. However, other sensory signals (i.e. vestibular and proprioceptive) may constitute the basis for early but partial correction of the pointing movements.

Adult↗
PubMed1998

Preliminary report on fractionation of fucans by ion-exchange displacement centrifugal partition chromatography.

A new method combining ion-exchange displacement chromatography with centrifugal partition chromatography (CPC) was used for the fractionation of partially depolymerized fucans (polysulphated polysaccharides). The ion-exchanger was Amberlite LA2, a high-molecular-mass liquid secondary amine miscible with most common organic solvents and immiscible with aqueous solutions. Ion-exchange displacement centrifugal partition chromatography was performed with LA2 in methyl isobutyl ketone (MiBK) as the stationary phase, water as the mobile phase, Cl- as the carrier and OH- as the displacer. A complex mixture of partially depolymerized fucans was resolved into adjacent families characterized by their peak molecular mass and polydispersity. The Dubois test (sugar) and the azur A test (SO3-) confirmed the displacement mode of the process, and size-exclusion chromatographic controls confirmed its efficiency.

Chemical Fractionation↗
PubMed1998

Centrifugal ventricular assist in children under 6 kg.

OBJECTIVE: The clinical application of centrifugal ventricular assist devices (VAD) has generally been limited to adults and large paediatric patients. In our experience neonates and small paediatric patients requiring ventricular support post-cardiopulmonary bypass are well supported by VAD. In this study we analyse our experience. METHODS: We have examined the records of our VAD patients who weighed less than 6 kg. Thirty-four patients, ranging in age from 2 to 258 days (median 60 days) and weight from 1.9 to 5.98 kg (median 3.7 kg), underwent 35 VAD procedures. One patient was supported on VAD twice. RESULTS: All patients had congenital heart lesions and were placed on VAD either because they could not be weaned from cardiopulmonary bypass after repair or palliation of the lesion (71.5%), or for support in the post-operative period due to refractory low cardiac output (28.5%). Twenty-two of the 35 VAD procedures (0.63, 95% CI: 0.45-0.78) resulted in successful weaning and decannulation, this was similar to the weaning probability for patients greater than 6 kg (P = 0.07). There were 10 late deaths in this group, with a 1-year KM survival of 0.31 (95% CI: 0.17-0.47). Most late deaths were related to irreversible cardiac disease processes as were the elective discontinuance of VAD outcomes. Neither weight, age, VAD duration, CPB duration, X clamp duration, univentricular anatomy or TGA anatomy predicted successful discharge from hospital (P > 0.05)--Weight P = 0.576; Age P = 0.532; VAD duration P = 0.181; CBP duration P = 0.549; X clamp duration P = 0.984; Univentricular anatomy P = 0.481; TGA anatomy P = 0.099. CONCLUSION: We believe centrifugal ventricular assist is a realistic option in very small patients who require post-cardiopulmonary bypass support. It is relatively easy to establish and manage, the results, although showing no factors predictive of successful discharge, are encouraging.

Cardiopulmonary Bypass↗
PubMed1990

Centrifugal pathways to the retina: which way does the "searchlight" point?

This commentary extends the review by Hiroyuki Uchiyama (1989) entitled "Centrifugal pathways to the retina: influence of the optic tectum" Visual Neuroscience 3, 183-206. A further scrutiny is made of the topography of the isthmo-retinal projection of the pigeon, which provides the most fully investigated example of a retinopetal projection. It is suggested that the topographical organization in this system is compatible with it's input being derived from the lower visual field (and upper retina) and it's output being directed to the horizon and lower retina. This is another form of attentional hypothesis for the centrifugal pathway, compatible with a role in ground feeding, and is testable by current tracing techniques in neurobiology.

Animals↗
PubMed1989

Centrifugal directional bias in the middle temporal visual area (MT) of the macaque.

We have examined the distribution of preferred directions of motion for neurons in the middle temporal visual area (MT) of the macaque. We found a marked anisotropy favoring directions that are oriented away from the center of gaze. This anisotropy is present only among neurons with peripherally located receptive fields. This peripheral centrifugal directionality bias corresponds well to the biased distribution of motions characteristic of optic flow fields, which are generated by displacement of the visual world during forward locomotion. The bias may facilitate the processing of this common form of visual stimulation and could underlie previously observed perceptual anisotropies favoring centrifugal motion. We suggest that the bias could arise from exposure of modifiable cortical circuitry to a naturally occurring form of selective visual experience.

Animals↗
PubMedDate not supplied

Centrifugal innervation modulates visual activity of tectal cells in pigeons.

Centrifugal modulation of visual responsiveness of tectal cells by the isthmo-optic nucleus (ION) through the retina was studied in homing pigeons. Visual activity evoked by computer-generated stimuli was reduced by an average of 59% in tectal cells whose receptive fields (RFs) either overlapped with, or were close to, those of isthmo-optic cells whose activity was blocked by the injection of lidocaine through micropipettes. Activity usually recovered to 87% of pre-drug controls in 8-17 min (average 12.3 min) after stopping lidocaine injections. Those tectal cells whose RFs were far from those of ION cells did not show clear-cut changes in their visual responsiveness to isthmo-optic lidocaine application. The spatial relationship between receptive fields of tectal and isthmo-optic cells, saline controls, as well as the specificity, reproducibility and reversibility of effects of ION-injected lidocaine on tectal activity, show that this chemical action is pharmacological, not toxicological. Neuronal circuitry underlying centrifugal modulation of tectal activity by isthmo-optic cells is discussed.

Action Potentials↗
PubMedDate not supplied

Long-range competition among the neurons projecting centrifugally to the quail retina.

Birds have a well-developed centrifugal pathway from the isthmo-optic nucleus to the retina. In the present study, receptive-field properties of the isthmo-optic (IO) neurons and suppressive effect of remote stimuli far beyond the "classical" receptive fields were examined electrophysiologically in the Japanese quail. Receptive fields emitting more than half the maximal ON-OFF response to a small spot of light measured 4.3+/-1.9 deg (n = 37) in diameter. A stationary spot of light was presented at a remote point (35-76 deg) away from the receptive-field center, besides a stimulus for the receptive-field center, with various onset time difference. The peripheral spot, when turned on 50-100 ms before the center spot, maximally suppressed the ON and OFF responses to the center spot. In most of the IO neurons examined (13 out of 15 units), even small remote stimuli (2-5 deg in diameter) significantly suppressed the ON-OFF responses to the center stimulus. The suppressive effects of remote stimuli were seen to be extended to, at least, two thirds of the entire visual field of a single eye. Such wide suppressive fields indicate that the IO neurons may compete with each other for activity in a very long-range scale. Simulation using a simple static model based on three basic principles of processing of the centrifugal visual system-topographical input, long-range competition, and local gain enhancement-suggests that the system could function as an autonomous mechanism for attentional object selection.

Animals↗
PubMed2001

Development of a fully integrated analysis system for ions based on ion-selective optodes and centrifugal microfluidics.

A fully integrated, miniaturized analysis system for ions based on a centrifugal microfluidics platform and ion-selective optode membranes is described. The microfluidic architecture is composed of channels, five solution reservoirs, a measuring chamber, and a waste reservoir manufactured onto a disk-shaped substrate of poly(methyl methacrylate). Ion-selective optode membranes, composed of plasticized poly(vinyl chloride) impregnated with an ionophore, a proton chromoionophore, and a lipophilic anionic additive, were cast, with a spin-on device, onto a support layer and then immobilized on the disk. Fluid propulsion is achieved by the centrifugal force that results from spinning the disk, while a system of valves is built onto the disk to control flow. These valves operate based on fluid properties and fluid/substrate interactions and are controlled by the angular frequency of rotation. With this system, we have been able to deliver calibrant solutions, washing buffers, or "test" solutions to the measuring chamber where the optode membrane is located. An analysis system based on a potassium-selective optode has been characterized. Results indicate that optodes immobilized on the platform demonstrate theoretical responses in an absorbance mode of measurement. Samples of unknown concentration can be quantified to within 3% error by fitting the response function for a given optode membrane using an acid (for measuring the signal for a fully protonated chromoionophore), a base (for fully deprotonated chromoionophore), and two standard solutions. Further, the ability to measure ion concentrations by employing one standard solution in conjunction with acid and base and with two standards alone were studied to delineate whether the current architecture could be simplified. Finally, the efficacy of incorporating washing steps into the calibration protocol was investigated.

Calibration↗
PubMed2004

Development and assessment of a miniaturised centrifugal chromatograph for reversed-phase separations in micro-channels.

This paper describes the micro-fabrication and preliminary assessment of a miniature polydimethylsiloxane (PDMS) device for performing rapid, parallel liquid phase chromatographic separations driven by centrifugal force in microchannels. Device components include a main separating channel, into which a high performance liquid chromatography (HPLC) particulate stationary phase was packed under pressure by application of centrifugal force, in addition to solvent and sample reservoirs. Also described are methods for sealing such devices based upon partial polymerisation of PDMS. The mobile phase flow rate through a typical device was measured and several important chromatographic parameters determined from a test separation. An expression describing mobile phase flow through packed channels was also developed, based upon work on liquid flow in open micro-channels. Good agreement between predicted and measured flow rates were observed. Some predictions for potential uses of such devices and possibilities for further miniaturisation are discussed.

Journal Article↗
PubMed1998

Centrifugal pumps as left ventricular assist for coronary revascularization on a beating heart.

During recent years, coronary bypass surgery has progressed toward minimizing invasiveness. One important feature of this approach is performing surgery on a beating heart. During the crucial phase of such surgery, the mechanical support of the heart with a left ventricular assist device (LVAD) is a possible option. During the period from October 1, 1994 until June 30, 1997, we employed a centrifugal pump system in 118 cases of coronary artery bypass graft (CABG) procedures with LVAD support (mechanically supported CABG [SUPPCAB]). A total of 179 distal anastomoses with an average of 1.5 +/- 0.5 coronary anastomoses per patient was performed. Three types of pumps were used: 23 BioPump, 87 Isoflow, and 8 Capiox systems. The median time on mechanical support was 44 min (range, 16-116 min). The mean flow rate during support time was 3.5 +/- 0.8 L/min, which results in a calculated flow of 1.7 +/- 0.6 L/min/m2 body surface area (BSA). The average flow was 3.2 +/- 0.8 L/min with the BioPump and 3.7 +/- 0.8 L/min with the Isoflow pump, respectively (p < 0.01). The mean arterial pressure during mechanical support was 75 +/- 12 mm Hg. In 2 patients, the pump system was kept running postoperatively in the ICU. Eight of the patients received operations under resuscitation or in cardiogenic shock. Nine (7.9%) of the patients did not survive the early postoperative phase. For coronary revascularization of the anterolateral and diaphragmatic parts of the heart, the SUPPCAB procedure is feasible with excellent mechanical support of the heart by centrifugal pumps. Especially in high risk cases, this procedure can be recommended.

Adult↗
PubMed1999

Detection of suction and regurgitation of the implantable centrifugal pump based on the motor current waveform analysis and its application to optimization of pump flow.

In this study, a detection algorithm for suction and regurgitation of the centrifugal pump during left heart bypass without relying on external flow or pressure sensors was developed and evaluated in acute studies using adult goats. The detection scheme relies on power spectral density (PSD) analysis of the motor current waveform through which the waveform deformation index (WDI) is obtained. This index is defined as the ratio of the fundamental component of the PSD to the higher PSD components, and its value increases with the deformation of the basic waveform. By assuming that the undistorted motor current waveform can be represented by a pure sine waveform, we theoretically synthesized various waveforms which have different second harmonic components. We were able to synthesize the waveform whose shape was close to the distorted motor current waveform under varying suction levels obtained in a mock loop study. From this study, we came to the conclusion that the WDI value of 0.2 can serve as a threshold level in deciding the suction and regurgitation speeds (rpm) during left heart bypass. In the study using adult goats, we were successful in minimizing both regurgitation and suction when the centrifugal pump speed was adjusted based on the WDI algorithm. The resultant bypass flow ranged from 1.5 to 2.0 L/min which was around 60% of the total flow. Further study is underway to evaluate the applicability of the WDI method in optimizing bypass pump flow.

Algorithms↗
PubMed1999

Experimental study on hemolysis in centrifugal blood pumps: improvement of flow visualization method.

To evaluate rotary blood pumps, flow visualization is commonly applied to determine the flow patterns in a centrifugal blood pump, which have a relationship to its hemolytic performance. However, it is very troublesome to visualize the flow near the vanes due to the high rotational speed of the impeller. The rotational speed of the impeller in a centrifugal blood pump is usually several hundred revolutions per minute. In this study, we combined a high-speed video camera based imaging method and an optical system in which the image of the rotating impeller was kept stationary. In the optical system, a prism rotating at half the speed of the impeller reflected the image of the impeller. The resultant reflected image was observed by a high-speed video camera through a half mirror. With this optical setup, the image through the half mirror became stationary, and the path of a specific tracer particle could be traced for a longer duration. A longer duration of measurements and better quality of the obtained images were realized through this improvement. Movement of a specific tracer from the inlet portion to the outlet portion of the impeller could be examined using the developed method.

Acrylic Resins↗
PubMed1999

Computational fluid dynamics analysis to establish the design process of a centrifugal blood pump: second report.

To establish an efficient design process for centrifugal blood pumps, the results of computational fluid dynamics (CFD) analysis were compared to the results of flow visualization tests and hemolysis tests, using the Nikkiso centrifugal blood pump. CFD analysis revealed that the radial gap greatly affected the shear stress in the outlet diffuser. The hemolysis study also indicated a similar tendency. To see the flow behind the impeller, we conducted a comparative study between models with and without washout holes using the CFD technique. CFD analysis indicated that flow and pressure distributions behind the impeller were different between both models, and a particle was observed to remain longer behind the impeller in the model without washout holes. In the future, CFD analysis could be a useful tool for developing blood pumps in comparison to flow visualization tests and hemolysis tests.

Computer Simulation↗
PubMed2000

Development of a centrifugal pump with thick blades.

We have developed a centrifugal blood pump with thick impeller blades (60% of pitch) to obtain a small tip clearance. An unshrouded impeller with 6 backward curved thick blades was used to reduce the dead zone between the shroud and upper casing. A streamline angle in volute was uniform in circumferential direction by continuity and angular momentum conservation. To prove the effectiveness of small tip clearance, performance and hemolysis tests were conducted on pumps with a tip clearance of 0.5, 1.5, and 2.0 mm at exit with the blade thickness of 60% of pitch, and with that of 1.0, 2.0, and 2.5 mm at exit with the thickness of 40% of pitch. The results showed that the smaller the tip clearance, the better the hydrodynamic and hemolytic performance. The best result was seen in the pump with tip clearance of 0.5 mm with a blade thickness of 60% of pitch. These results suggest that a centrifugal pump with thick blades and a small tip clearance can be a promising alternative as a cardiopulmonary bypass pump.

Animals↗
PubMed2000

Analytical investigation of leakage flow in disk clearance of a magnetically suspended centrifugal impeller.

Leakage flow through the disk clearance of a magnetically suspended centrifugal blood pump is essential for a good washout. An analytical approach, based on the theory of lubrication, is used to predict the leakage volume flow rate, nondimensional radial velocity, nondimensional mean pressure distribution, and comparative shear stress distribution for different disk clearance geometry under varying rotational speeds. The results showed that nondimensional mean pressure distribution and nondimensional radial velocity distribution along the clearance are independent of rotational speed. The flow through the gap depends on a nondimensional parameter S that denotes the ratio of centrifugal forces to the head generating capability of the impeller. It was found that an impeller having a lower S has less possibility of flow reversals in the gap, and gap with maximum height at the outside radius also is more susceptible to flow reversals at the impeller surface. The comparative shear stress within the gap reveals that, in general, the scalar stress is below 500 N/m2.

Algorithms↗