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At least 721 records · Page 40Linked to original sources
PubMed1997

Biocompatibility of alumina ceramic and polyethylene as materials for pivot bearings of a centrifugal blood pump.

The double pivot bearings in the Gyro C1E3 centrifugal blood pump incorporate a high-purity alumina (Al2O3) ceramic and an ultra-high-molecular-weight polyethylene (UHMWPE). This centrifugal pump has been developed as a completely sealless pump for long-term usage. The combination of Al2O3 and UHMWPE are the materials of choice for the acetabular bearing in artificial joints, which have proven to be clinically reliable for over 10 years. Previous studies have examined the biocompatibility of Al2O3 and UHMWPE as bulky implant materials. The present study investigated this material as a blood-contacting material using a standard assessment in vitro and in vivo analysis. The examined items were systemic toxicity, sensitization (guinea pig maximization test), cytotoxicity (elution test), mutagenicity (Ames test), direct contact hemolysis, and thrombogenicity. The studies were performed according to the United States Pharmacopoeia and published previous studies. The samples of both Al2O3 and UHMWPE demonstrated no differences from the negative controls in all tests. These findings indicate that both Al2O3 and UHMWPE are biocompatible materials for double-pivot bearings in the centrifugal blood pump.

Aluminum Oxide↗
PubMed2000

Estimation of plasma serotonin using isopycnic centrifugation.

The valid measurement of the concentration of serotonin (5-HT) in blood plasma is important when using the platelet as a model for the serotonergic neuron. The assay is hampered by the release of 5-HT by (residual) platelets during the preparation for assay. We developed an isopycnic method that separates cells gently and completely from plasma by centrifuging a diluted Percoll density-gradient to which whole blood was added. In this study this method was compared with the usual differential centrifugation method. The isopycnic method on average resulted in nine times lower levels of plasma 5-HT. This difference was linearly related to the number of residual platelets in plasma after differential centrifuging. The proportion of intra-individual variation decreased three-fold. Therefore, the use of a Percoll density-gradient may lead to a more precise and more accurate estimate of the level of plasma 5-HT. Copyright 2000 John Wiley & Sons, Ltd.

Journal Article↗
PubMed1995

A novel drug delivery system for osteomyelitis using porous hydroxyapatite blocks loaded by centrifugation.

A novel drug delivery system for osteomyelitis was developed using porous hydroxyapatite blocks (HA-b) loaded with antibiotics by centrifugation. In the study, 10 mm3 HA-b was placed in a container and mixed with antibiotic solution; the antibiotic was then loaded into the pores of the HA-b by centrifuging at 1500 rpm for 15 min. Slow release of HA-b in both moist form and dried form (by heating at 160 degrees C) was tested after loading with the antibiotic arbekacin sulfate (ABK), 1-N-(S)-4 amino-2-hydroxybutyryl dibekacin. To estimate the concentration of antibiotic, both forms of HA-b were placed in 3 mL of phosphate buffered saline (PBS), which was replaced every 48 h. In both groups, which were loaded with 70 mg ABK per one block of HA (concn 0.5 microgram/mL) which is sufficiently high to control most pathogens, was maintained for 21 exchanges of PBS (after 42 days). Minimum inhibitory concentration for methicillin-resistant Staphylococcus aureus (MRSA), 3.13 micrograms/mL, was maintained until nine exchanges took place (after 18 days). The centrifugation method is simple, and dried ABK produced by heating loaded HA-b is particularly useful in clinical applications for osteomyelitis.

Anti-Bacterial Agents↗
PubMed2000

The Sextic Centrifugal Distortion Terms for an Open-Shell Complex Consisting of a Diatomic Molecule in a (2S+1)Sigma Electronic State and a Closed-Shell Partner.

An effective Hamiltonian for calculating rotational energy levels of an open-shell diatomic molecule, in a (2S+1)Sigma electronic state, weakly bonded to a closed-shell partner was presented (W. M. Fawzy, J. Mol. Spectrosc. 191, 68-80 (1998)). The Hamiltonian was given as H = H(ev) + H(rot) + H(sr) + H(ss) + H(cd) + H(srcd) + H(sscd), where all the quartic centrifugal distortion correction terms were included in the Hamiltonian term H(cd) but the sextic centrifugal distortion terms were ignored. This Hamiltonian is useful in cases where the complex has a well-defined equilibrium geometry and if the barrier to large-amplitude motion is large compared to the rotational constant of both the closed-shell molecule and its paramagnetic partner; if the barrier to large-amplitude motion is small compared to the rotational constant of one or both of the fragments, then a different treatment is required. In this paper, we introduce the new Hamiltonian terms H(sex(A))(cd) and H(sex(S))(cd), which represent the sextic centrifugal distortion correction terms for an asymmetric rotor. We also introduce all the nonvanishing matrix elements of each of the H(sex(A))(cd) and H(sex(S))(cd) operators. These operators and their matrix elements are required for calculating the rotational energy levels of relatively high J values in the described type of weakly bonded open-shell complexes. The terms H(sex(A))(cd) and H(sex(S))(cd) and their matrix elements are also valid for any stable asymmetric rotor in a nondegenerate electronic state. A brief discussion of the new Hamiltonian terms and their matrix elements is given. Copyright 2000 Academic Press.

Journal Article↗
PubMed1994

Blood coagulability and hematological changes in calves with chronic centrifugal biventricular bypass pumps.

A Hemadyne centrifugal pump was used to determine the effects of long-term circulatory assist on platelet number and aggregability. Five calves were supported on biventricular bypass with a pair of Hemadyne centrifugal pumps. On the 7th postoperative day (POD), the heart was fibrillated after pump flow rates were increased to compensate for the total cardiac output. The animals were anticoagulated with heparin throughout the study and adjustments were made to maintain the activated clotting time at between 180 and 220 sec. To maintain the activated clotting time level in the therapeutic range, it was necessary to gradually increase the heparin dose with time due to the developing heparin tolerance. Fibrinogen levels increased significantly on the 3rd postoperative day when compared to the preoperative control value. Platelet aggregation was measured using a whole blood impedance method with adenosine diphosphate and collagen as agonists. Platelet function was found to be significantly depressed following the biventricular bypass procedure (P < 0.05 on the 7th, 14th, and 21st POD). Platelet numbers were significantly decreased compared to the preoperative control values, being the lowest on the 1st and 3rd POD, recovering to 76% of the control values by the 7th POD, and then gradually decreasing to the 55% level by the 28th POD. These results show that, when tested for up to 4 weeks following surgery, both platelet number and function in calves supported with centrifugal pumps remain depressed. Despite the progressive heparin tolerance and suppressed platelet number and function, none of the animals showed abnormal bleeding tendencies on biventricular bypass.

Adenosine Diphosphate↗
PubMed1979

Relationship between photoreceptor terminations and centrifugal neurons in the optic lobe of octopus.

Retinal bundles, connecting the retina of the octopus to the ipsilateral optic lobe, contain both retinal photoreceptor axons that terminate in the optic lobe and centrifugal axons whose cell bodies lie within the lobe. Staining axonal elements in proximal stubs of individual retinal bundles by cobalt diffusion and subsequent sulphide treatment reveals the topographic relationship between afferent terminals and centrifugal cell bodies. At the outer border of the plexiform layer, stained terminal bags (photoreceptor axon enlargements), an indicator of photoreceptor terminal spread within this layer, overlap stained centrifugal cell bodies located within the inner granule layer. The details of this overlap indicate a dorsoventral representation of each retinal bundle within the optic lobe cortex.

Animals↗
PubMed1988

Centrifugal regulation of neuronal activity in the olfactory bulb of the waking rabbit as revealed by reversible cryogenic blockade.

The influences of centrifugal projections to the olfactory bulb were examined on the bulbar EEG and mitral-tufted cell activity in waking rabbits. Each of 6 rabbits was implanted, under surgical anesthesia, with fine wire electrodes for recording of the EEG and mitral-tufted cell unit activity and for stimulating the lateral olfactory tract. Two cooling probes, for reversible cryogenic blockade, were implanted on either side of the left olfactory peduncle. Records of EEG and unit activity were taken for 200 s before, during and after cooling of the probes to 3 degrees centigrade. Antidromic evoked potentials were used to assess the efficacy of the blockade. During the cryogenic blockade bursts of EEG activity, evoked in the bulb by inspiration through the nose, were augmented in amplitude and reduced in frequency. Mitral-tufted cell unit activity was reduced in rate but was more highly correlated with the phase and amplitude of the EEG bursts. Analysis of individual EEG bursts revealed that the variance in frequency of bulbar activity was significantly reduced in the isolated state. The data demonstrate that oscillatory bursting activity in the olfactory bulb is intrinsically maintained within a relatively fixed frequency range during receptor input and does not depend on centrifugal projections for its electrogenesis. Changes in EEG frequency, amplitude and correlation with unit activity support the hypothesis that centrifugal projections act in part to inhibit mitral-tufted cell output by direct excitation of granule cells. These findings are supported by a theoretical model in which distributed feedback to the granule cells from more central olfactory structures acts to regulate the coherency of bulbar activity.

Action Potentials↗
PubMed1997

Flow characteristics and required control algorithm of an implantable centrifugal left ventricular assist device.

As the clinical application of LVADs has increased, attempts have been made to develop smaller, less expensive, more durable and efficient implantable devices using rotary blood pumps. Since chronic circulatory support with implantable continuous-flow LVADs will be established in the near future, we need to determine the flow characteristics through an implantable continuous-flow LVAD. This study describes the flow characteristics through an implantable centrifugal blood pump as a left ventricular assist device (LVAD) to obtain a simple non-invasive algorithm to control its assist flow rate adequately. A prototype of the completely seal-less and pivot bearing-supported centrifugal blood pump was implanted into two calves, bypassing from the left ventricle to the descending aorta. Device motor speed, voltage, current, flow rate, and aortic blood pressure were monitored continuously. The flow patterns revealed forward flow in ventricular systole and backward flow in diastole. As the pump speed increased, an end-diastolic notch became evident in the flow profile. Although the flow rate (Q [l/min]) and rotational speed (R [rpm]) had a linear correlation (Q = 0.0042R - 5.159; r = 0.96), this linearity was altered after the end-diastolic notch was evident. The end-diastolic notch is considered to be a sign of the sucking phenomenon of the centrifugal pump. Also, although the consumed current (I [A]) and flow rate had a linear correlation (I = 0.212Q + 0.29; r = 0.97), this linearity also changed after the end-diastolic notch was evident. Based upon the above findings, we propose a simple algorithm to maintain submaximal flow without inducing sucking. To maintain the submaximal flow rate without measuring flow rate, the sucking point is determined by monitoring consumed current according to gradual increases in voltage.

Algorithms↗
PubMed2005

Centrifugal regulation of task-relevant somatosensory signals to trigger a voluntary movement.

Many previous papers have reported the modulation of somatosensory evoked potentials (SEPs) during voluntary movement, but the locus and mechanism underlying the movement-induced centrifugal modulation of the SEPs elicited by a task-relevant somatosensory stimulus still remain unclear. We investigated the centrifugal modulation of the SEPs elicited by a task-relevant somatosensory stimulus which triggers a voluntary movement in a forewarned reaction time task. A pair of warning (S1: auditory) and imperative stimuli (S2: somatosensory) was presented with a 1 s interstimulus interval. Subjects were instructed to respond by moving the hand ipsilateral or contralateral to the somatosensory stimulation which elicits the SEPs. In four experiments, the locus and selectivity of the SEPs' modulation, the contribution of cutaneous afferents and the effect of contraction magnitude were examined, respectively. A control condition where subjects had no task to perform was compared to several task conditions. The amplitude of the frontal N30, parietal P30, and central P25 was decreased and that of the long latency P80 and N140 was increased when the somatosensory stimuli triggered a voluntary movement of the stimulated finger compared to the control condition. The N60 decreased with the movement of any finger. These results were considered to be caused by the centrifugal influence of neuronal activity which occurs before a somatosensory imperative stimulus. The present findings did not support the hypothesis that the inhibition of afferent inputs by descending motor commands can occur at subcortical levels. A higher contraction magnitude produced a further attenuation of the amplitude of the frontal N30, while it decreased the enhancement of the P80. Moreover, the modulation of neuronal responses seems to result mainly from the modulation of cutaneous afferents, especially from the moved body parts. In conclusion, the short- and long-latency somatosensory neuronal activities evoked by task-relevant ascending afferents from the moved body parts are regulated differently by motor-related neuronal activities before those afferent inputs. The latter activities may be associated with sensory gain regulation related to directing attention to body parts involved in the action.

Acoustic Stimulation↗
PubMed2006

Centrifugal regulation of a task-relevant somatosensory signal triggering voluntary movement without a preceding warning signal.

A warning signal followed by an imperative signal generates anticipatory and preparatory activities, which regulate sensory evoked neuronal activities through a top-down centrifugal mechanism. The present study investigated the centrifugal regulation of neuronal responses evoked by a task-relevant somatosensory signal, which triggers a voluntary movement without a warning signal. Eleven healthy adults participated in this study. Electrical stimulation was delivered to the right median nerve at a random interstimulus interval (1.75-2.25 s). The participants were instructed to extend the second digit of the right hand as fast as possible when the electrical stimulus was presented (ipsilateral reaction condition), or extend that of the left hand (contralateral reaction condition). They also executed repetitively extension of the right second digit at a rate of about 0.5 Hz, irrespective of electrical stimulation (movement condition), to count silently the number of stimuli (counting condition). In the control condition, they had no task to perform. The amplitude of short-latency somatosensory evoked potentials, the central P25, frontal N30, and parietal P30, was significantly reduced in both movement and ipsilateral reaction conditions compared to the control condition. The amplitude of long-latency P80 was significantly enhanced only in the ipsilateral reaction condition compared to the control, movement, contralateral reaction, and counting conditions. The long-latency N140 was significantly enhanced in both movement and ipsilateral reaction conditions compared to the control condition. In conclusion, short- and long-latency neuronal activities evoked by task-relevant somatosensory signals were regulated differently through a centrifugal mechanism even when the signal triggered a voluntary movement without a warning signal. The facilitation of activities at a latency of around 80 ms is associated with gain enhancement of the task-relevant signals from the body part involved in the action, whereas that at a latency of around 140 ms is associated with unspecific gain regulation generally induced by voluntary movement. These may be dissociated from the simple effect of directing attention to the stimulation.

Adolescent↗
PubMed1978

Centrifugal influence on olfactory bulb activity in the rabbit.

(1) Regions which exert centrifugal influences on the olfactory bulb activity were studied by applying systematic stimulation to various areas of the ipsilateral telencephalon in the rabbit. By delivering electric stimuli to the anterior commissure (AC), the deep lying structures in the projection areas of the lateral olfactory tract (LOT) and the medial forebrain bundle situated between the lateral hypothalamic area and the lateral preoptic area, negative field potentials were evoked in the granule cell layer (GCL) of the bulb. (2) Intracellular recordings from the mitral cells and the GCL neurons in the olfactory bulb were performed in order to clarify the modes of the centrifugal influences on the olfactory bulb neurons. (3) EPSPs were recorded in the GCL neurons by stimulation of the deep-lying structure of the prepiriform cortex as well as by stimulation of the AC. The onset time and duration of the EPSPs corresponded well to those of the negative field potentials in the GCL. Thus, it was suggested that these negative potentials were caused by the EPSPs of the number of granule cells. (4) In almost all of the mitral cells, IPSPs were recorded by stimulation of the AC and the deep-lying structures of the LOT projection areas. The onsets of the IPSPs were found with delays of several milliseconds from those of the negative field potentials in the GCL. (5) It was postulated that the excitation of the centrifugal system mainly exerts a depressive influence on the activity of the mitral cell, and that the GCL neuron (presumably the granule cell) seems to be an inhibitory interneuron interpolated between the extrinsic fibers from the telencephalon and the mitral cell.

Animals↗
PubMed1996

Odour-induced c-fos expression in the rat olfactory bulb: involvement of centrifugal afferents.

Expression of the proto-oncogene c-fos is known to increase in granule cells of the olfactory bulb following a sustained olfactory stimulation. Most granule cells displaying high levels of Fos accumulation are located in the bulbar columns defined by the odour-induced foci of high 2-deoxyglucose glomerular uptake. The present studies were undertaken in order to assess the possible involvement of centrifugal afferents in the modulation of odour-induced patterns of either 2-deoxyglucose accumulation or c-fos expression in the olfactory bulb. A unilateral olfactory peduncle section had no effect on the odour-induced 2-deoxyglucose foci but induced a significant decrease in the number of Fos-containing neurons in odour-selective areas of both olfactory bulbs, ipsilateral and contralateral to the lesion. This suppressive effect was much more pronounced in the side ipsilateral to the peduncle section. It is concluded that c-fos expression induced by a sustained stimulation with propionic acid vapours is not only determined by the olfactory peripheral input but also by afferents of central origin. In order to estimate the contingent involvements of the cholinergic and noradrenergic afferents in this control of c-fos expression, we attempted to mimic the effects of the surgical deafferentation on odour-induced c-fos expression by using a pharmacological approach with selective cholinergic and noradrenergic antagonists. The beta-adrenergic antagonist propanolol induced a suppression of the odour-related patterns of Fos accumulation similar to the one caused by the surgical deafferentation of the olfactory bulb. The muscarinic antagonist scopolamine did not alter c-fos expression in the odour-selective area but increased significantly Fos labelling in the other bulbar aspects. Pharmacological investigations indicate that the noradrenergic and cholinergic centrifugal systems are likely involved in the central modulation of c-fos expression in the OB. The Fos protein could be expressed as an early nuclear signal triggering further long-term modifications of the neuronal phenotype, in certain conditions of sensory stimulation involving the activation of centrifugal systems.

Adrenergic beta-Antagonists↗
PubMed1991

Cortical potentials preceding centrifugal and centripetal self-paced horizontal saccades.

Cortical potentials preceding self-paced centrifugal and centripetal saccades were recorded in 15 subjects from F3, Fz, F4, C3, Cz, C4, P3, Pz and P4 versus linked mastoid electrodes. A negative potential starting about 1.0 sec prior to saccade onset, reaching a peak amplitude of 6.8 microV on average, preceded centrifugal saccades. In contrast the negativity preceded centripetal saccades by only 500 msec, and its peak amplitude was smaller (4.6 microV). We conclude that these differences reflect the fact that less 'effort' is needed with centripetal as compared to centrifugal saccades.

Adult↗
PubMed1994

Preparative separation of naphthyltetrahydroisoquinoline alkaloids from Ancistrocladus korupensis by centrifugal partition chromatography.

Crude extracts of Ancistrocladus korupensis contain a complex mixture of naphthyltetrahydroisoquinoline alkaloids, including the human immunodeficiency virus-inhibitory dimeric alkaloids michellamines A and B and the antimalarial monomeric korupensamines A-D. The efficient separation of michellamines A and B from these extracts has been accomplished by centrifugal partition chromatography. The chromatographic conditions used on a multi-channel cartridge unit (Sanki LLN) have been successfully scaled up with a newly developed, stacked-disk type centrifugal partition chromatography unit (Sanki NMF) for separating larger amounts of alkaloid mixtures with similar resolution. A refined, three-step process (solvent-solvent partitioning, centrifugal partition chromatography and HPLC) has been developed and applied to the scaled-up production of michellamine B for preclinical drug development.

Alkaloids↗
PubMed1984

Bacterial air counts obtained with a centrifugal (RCS) sampler and a slit sampler--the influence of aerosols.

Samples of air collected from an air-conditioned hospital room with a 'Biotest RCS' centrifugal air sampler yielded (assuming a sampling rate of 40 l/min) air counts that were approximately twice those obtained with a modified conventional ' Casella ' slit sampler. However, for samples taken during the generation of an aerosol of spores of Bacillus globigii, the slit sampler gave counts that were apparently three- to tenfold higher than those with the centrifugal sampler. For a few minutes after switching off the nebulizer, higher counts were still obtained with the slit sampler, but then the centrifugal sampler again gave consistently higher counts. Our results illustrate that attempts to measure the number of bacteria in air are influenced by the size of the bacterial particles and the sampler that is used.

Aerosols↗
PubMed1984

Effects of centrifugal force on functional and structural integrity of rat liver ribosomes.

The ability of rat liver ribosomes to support in vitro protein synthesis was not adversely affected, and generally tended to increase as the centrifugal force at which they were isolated increased. Polysomal material tended to decrease while 40S and 60S ribosomal subunits apparently increased at progressively higher centrifugal forces. Ribosomal "purity", revealed by u.v. spectrophotometric analysis, deteriorated as centrifugal force increased. Contamination by material that absorbed at 230 nm was particularly evident.

Animals↗
PubMed1987

Topography of centrifugal acetylcholinesterase-positive fibres in the olfactory bulb of the rat: evidence for original projections in atypical glomeruli.

An original pathway of centrifugal acetylcholinesterase-positive fibres is described in the olfactory bulb of the rat. A dense network of positive fibres spreads out superficially at the boundaries of the lateral olfactory tract and the glomerular layer. These labelled fibres converge towards atypical glomerular structures lying close to the classical olfactory glomeruli. The atypical glomeruli are located dorsally at the medial border of the accessory olfactory bulb, in the area previously described as the "modified glomerular complex", and in the ventrolateral bulbar area. They structurally differ from typical glomeruli, as suggested by observations on semithin sections. The ultrastructural distribution of acetylcholinesterases into axonal and dendritic profiles, around and inside atypical glomeruli, is consistent with the hypothesis of centrifugal modulatory influences at this level. This study illustrates several new aspects of morphofunctional heterogeneity in the olfactory system. The glomerular layer of the main olfactory bulb can no longer be considered as morphologically and functionally uniform. Atypical glomeruli located in the mediodorsal and the ventrolateral boundaries of the glomerular layer are characterized by both structural features and an uncommonly high convergence of acetylcholinesterase-positive centrifugal fibres. Such areas might be involved in the processing of specific olfactory signals as demonstrated elsewhere for the "modified glomerular complex".

Acetylcholinesterase↗
PubMed1990

Contribution of centrifugal innervation to choline acetyltransferase activity in the cat cochlear nucleus.

Using a quantitative microchemical mapping approach combined with surgical cuts of fiber tracts, the contributions of centrifugal pathways to choline acetyltransferase activity were mapped three-dimensionally in the cat cochlear nucleus. Large reductions of choline acetyltransferase activity, averaging 70%, were measured in almost all parts of the lesion-side nucleus following transection of virtually all its centrifugal connections. More superficial cuts, penetrating just through the olivocochlear bundle, also led to significant reductions of enzyme activity, especially most rostrally in the anteroventral cochlear nucleus and superficial granular region, where the reductions were similar to those following the complete cuts. Lesions encroaching upon the superior olivary complex gave bilateral effects. Transverse cuts between rostral and caudal parts of the cochlear nucleus gave some small effects. The results suggest that, as in rats, most choline acetyltransferase activity in the cat cochlear nucleus is associated with its centrifugal innervation. However, unlike the situation in rats, the enzyme activity in cats is related more to olivocochlear branches than to ventral fibers in the trapezoid body region. Also, the choline acetyltransferase activity related to olivocochlear collateral innervation is much less uniformly distributed within the cochlear nucleus in cats than in rats.

Animals↗