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The terminals of centrifugal fibers to the olfactory bulbs of goldfish were studied by electron microscopy after transection of the medial, lateral or entire olfactory tract. The centrifugal fibers originate in the telencephalic hemisphere, pass through both the medial and the lateral olfactory tract, and form synaptic contacts with dendrites in the granule cell layer.
Liver parenchymal cells from the periportal and centrilobular zones differ in their morphological, biochemical and functional characteristics. In an effort to obtain fractions enriched in either periportal or centrilobular cells, isolated rat liver parenchymal cells were separated into five subpopulations by centrifugal elutriation. The mean diameters of the cells present in fractions I-V were 19.6, 21.1, 21.8, 22.7 and 23.5 micron, respectively. The content of cytochrome P-450 as well as benzphetamine N-demethylase and 7-ethoxyresorufin O-deethylase activities were higher in the larger parenchymal cells than in the smaller ones. After administration of phenobarbital the content of cytochrome P-450 was approximately two-fold greater in the cells present in fractions 3-5, when compared to the same subpopulations isolated from untreated rats; the activity of benzphetamine N-demethylase was enhanced to a similar extent in all five fractions. 3-Methylcholanthrene treatment resulted in a significant increase of cytochrome P-450 content and 7-ethoxyresorufin O-deethylase activity in all five fractions: both parameters were slightly higher in fractions 4 and 5 than in fractions 1 and 2. In conclusion, the elutriated liver parenchymal cells seem to preserve the biochemical heterogeneity observed in the intact liver; the potential enrichment of periportal and centrilobular cells in the different fractions by centrifugal elutriation is discussed.
Electron microscopic views of centrifugal nerve fibers in the optic nerve stump of a 56-year-old man are presented. These nerve fibers had survived for 16 days after removal of the corresponding eyeball and exhibited terminal swellings pointing in a distal direction and indicating axoplasmic flow towards the removed eye. The centrifugal nerves in this adult lack any evidence of attempted regeneration that has earlier been observed under similar conditions in the optic nerve stump of a child.
Patients with reduced left ventricular function do have an increased risk of inability to be weaned off bypass after open heart surgery despite maximal pharmacologic support and intraaortic balloon counter-pulsation. Centrifugal pumps used for extracorporeal circulatory assist can maintain a patient in low cardiac output up to days without anticoagulation. We used a centrifugal pump in 3 patients: as a left ventricular assist device (LVAD) in 2 patients and right ventricular assist device (RVAD) in 1 patient. One LVAD-patient became a long-term survivor after 20 h of assist, another was bridged successfully to an open heart procedure for 2 h after papillary muscle rupture. One RVAD patient died on the operating table due to massive tracheal bleeding probably caused by pulmonary hypertension.
Haematocrits were measured as a function of ultrafiltration in a simulated haemodialysis circuit using bovine blood (plasma conductivity 12 mS cm-1) and hypotonic (8.6 mS cm-1) or hypertonic (16 mS cm-1) dialysates as well as in the absence of dialysate. A comparison was made between measurements by light absorption due to haemoglobin, by impedance in the blood line at 5 kHz using Hanai's model of blood conductivity, by conductivity measurements of blood samples at 1.2 kHz using a conductimeter, by centrifugation of blood samples and by calculations using fluid conservation. The validity of Hanai's model was verified to be satisfactory by direct blood and plasma conductivity measurements. In the absence of ionic transfer the impedance device underestimated the haematocrit by 5 to 7%. This underestimation reached 18% in the case of hypertonic dialysate, but this effect can be minimised if the haematocrit necessary for calibration is measured by centrifugation after 15 min of dialysate circulation when ionic balance is achieved. It was found that the optical method monitors haemoglobin concentration rather than red cell volume changes and is not affected by osmotic red cell swelling in the case of hypotonic dialysate. It can be concluded that the light absorption technique is both more accurate and more convenient to use than impedance.
OBJECTIVE: We developed "EVAHEART": a compact centrifugal blood pump system as an implantable left ventricular assist device for long-term circulatory support. The 55 x 64 mm pump is made from pure titanium, and weighs 370 g. The entire blood-contacting surface is covered with an anti-thrombogenic coating of diamond like carbon (DLC) or 2-methacryloyloxyethyl phosphorylcholine (MPC) to improve blood compatibility. Flows exceeding 12 L/min against 100 mmHg pressure at 2600 rpm was measured. A low-temperature mechanical seal with recirculating cooling system is used to seal the shaft. EVAHEART demonstrated an acceptably low hemolysis rate with normalized index of hemolysis of 0.005 +/- 0.002 g/100L. METHODS: We evaluated the pump in long-term in-vivo experiments with seven calves. Via left thoracotomy, we conducted left ventricular apex-descending aorta bypass, placing the pump in the left thoracic cavity. RESULTS: Pump flow rates was maintained at 5-9 L/min, pump power consumption remained stable at 9-10 W in all cases, plasma free Hb levels were less than 15 mg/dl, and the seal system showed good seal capability throughout the experiments. The calves were sacrificed on schedule on postoperative day 200, 222, 142, 90, 151, 155, and 133. No thrombi formed on the blood contacting surface with either the DLC or MPC coating, and no major organ thromboembolisms occurred except for a few small renal infarcts. CONCLUSION: EVAHEART centrifugal blood pump demonstrated excellent performance in long-term in-vivo experiments.
In this study, we investigated the somatosensory evoked potentials (SEPs) during the preparatory period of self-initiated plantar flexion at different force levels of muscle contraction and elucidated the mechanism behind the centrifugal gating effect on somatosensory information processing. We recorded SEPs following stimulation of the tibial nerve at the popliteal fossa during the preparatory period of a 20% maximal voluntary contraction (MVC) and 50% MVC. The preparatory period was divided into two sub-periods based on the components of movement-related cortical potentials, the negative slope (NS sub-period) and the Bereitschaftspotential (BP sub-period). The subjects were instructed to concentrate on the movement and not to pay attention to the continuous electrical stimulation. Pre-movement SEPs were averaged separately during the two sub-periods under each MVC condition. The mean amplitudes of BP and NS were larger during the 50% MVC than the 20% MVC. As for the components of SEPs, during the NS sub-period the amplitude of P30 under the 50% MVC and N40 under both conditions were significantly smaller than that in the stationary sequence, and N40 amplitude was significantly smaller during the 50% MVC than the 20% MVC. During the BP sub-period, the amplitude of P30 and N40 during the 50% MVC was significantly smaller than during the stationary sequence, while it was not significantly different between the 20% and 50% MVCs. In conclusion, the extent of the centrifugal gating effect on SEPs was dependent on the activities of motor-related areas, which generated the NS and BP.
Continuous venovenous hemofiltration/hemodiafiltration (CVVH/D) is commonly used to provide renal replacement therapy for critically ill patients who are hemodynamically unstable. Occasionally, the addition of plasmapheresis therapy is necessary for some conditions, including immune-mediated acute renal failure, sepsis, fulminant hepatic failure, and thrombotic thrombocytopenic purpura/hemolytic uremic syndrome. Most tertiary care facilities provide centrifugation plasmapheresis instead of membrane plasmapheresis, because of the requirement for both therapeutic plasma exchange and pheresis of cellular blood products. We report a new technique where centrifugation plasmapheresis and CVVHD (P-CVVHD) are combined and used concurrently. Blood from the patient was concurrently filtered utilizing a Hospal BSM 22 machine with a Multiflow 60 hemofilter and a Cobe Spectra continuous cell separator in a parallel configuration. P-CVVHD is technically possible and can be used for long periods of time with limited risks. There may be advantages to P-CVVHD compared with discontinuous combined CVVH/D and plasmapheresis therapy.
The ultracentrifuge provides several techniques for the quantitative characterization of reversible small molecule-macromolecule and macromolecule-macromolecule interactions in solution. The nature of the association to be studied determines the preferred technique. High speed centrifugation is the method of choice for characterizing reversible heteroassociations between species of greatly different mass (i.e., sedimentation coefficient). This technique provides a relatively rapid, artifact-free, and thermodynamically rigorous means of quantifying the amount of nonsedimenting or slowly sedimenting free ligand in equilibrium with rapidly sedimenting acceptor-bound ligand at one particular solution composition. Results obtained over a broad range of ligand and/or acceptor concentrations lead to model-independent binding isotherms that may subsequently be analyzed in the context of models for ligand-acceptor association. Lower speed centrifugation to sedimentation equilibrium is the method of choice for characterizing reversible selfassociations and for characterizing heteroassociations between components that cannot be well separated on the basis of sedimentation velocity. In the dilute limit, this technique can provide model-free information about the dependence of weight-average molecular weight of each component upon solution composition, which can subsequently be analyzed in the context of equilibrium models for self- or heteroassociation. At higher concentrations, the models must be generalized to allow for the effect of nonspecific (nonideal) interactions upon sedimentation and association. The use of tracers provides a means for greatly extending the range of solute concentrations and solution compositions over which both types of measurements may be applied, providing enhanced ability to discriminate between alternative proposed mechanisms for self- or heteroassociations.
Since January 1985, the Heart Transplant Program at Washington University Medical Center, St. Louis, has performed 89 heart transplantations in 86 patients. Twenty patients (23%) have required preoperative mechanical support of circulation or respiration prior to transplantation. The Bio-Medicus centrifugal pump (Bio-Pump) formed the basis of our circulatory support system during the period of this report. Nine patients were placed on the Bio-Pump with the intention of bridging them to transplantation. Six patients required left ventricular assistance; in 2, the device was inserted because they could not be weaned from cardiopulmonary bypass. Two patients required biventricular assistance, 1 because she could not be weaned from cardiopulmonary bypass at the end of a cardiac operation. Extracorporeal membrane oxygenation was necessary in 1 patient for right ventricular decompensation and cardiac arrest four hours after orthotopic cardiac transplantation. One of these 9 patients died on circulatory support, and in another, a complication developed that precluded transplantation. The remaining 7 patients (78%) underwent a successful transplant procedure after an average of 1.6 days of circulatory support (range, 0.5 to three days), and all are long-term survivors of transplantation. There has been 1 late death at 17 months from a cerebrovascular hemorrhage. In summary, the centrifugal pump provides excellent short-term circulatory support for individuals who would otherwise die before cardiac transplantation.
From August 1979 through August 1991, 91 patients were supported with centrifugal mechanical ventricular assist. Major indications for its use were postcardiotomy ventricular failure (79) or as a bridge to cardiac transplantation (12). In postcardiotomy use (0.2% of all cardiac procedures), there were 54 male (68.4%) and 25 female patients (31.6%) with a mean age of 54.8 years and a mean duration of use of 3.56 days (range, 1 hour to 19 days). Forty-nine patients (62%) were successfully weaned, and 20 (25.3%) were hospital survivors. In 57 patients the device was inserted to wean from cardiopulmonary bypass, whereas in 22 it was employed later in the postoperative period because of low cardiac output or sudden arrest. Thirty-four (59.6%) of the 57 patients in the former group were weaned, and 15 (26.3%) were discharged, results similar to those in the latter group with 15 (68.2%) weaned and 5 (22.7%) discharged. Morbidity associated with use of centrifugal blood pumps included bleeding (87.3%; mean transfusion requirement, 53.2 units), renal failure (46.8%), cerebrovascular accident (12.7%), thromboembolism (12.7%), and hepatic insufficiency (12.7%). After a mean follow-up of 45.4 months (range, 2 to 142 months), 7 patients had died (35% late mortality), 1 patient is in functional class IV, and all others are in functional class I or II. Lower survival was associated with biventricular failure and renal failure but not with age or sex of the patient.
Previous investigations with roller pumps and pneumatic pulsatile assist devices have demonstrated that nearly complete capture of normal left ventricular end-diastolic volume was necessary for appreciable reductions in oxygen consumption and stroke work. We tested the hypothesis that a centrifugal pump would decrease left ventricular stroke work and oxygen consumption as a function of pump flow. Ten sheep (35 to 50 kg) were instrumented and placed on left atrium-to-descending aorta bypass with a small, lightweight (112 g), implantable centrifugal pump. The relations between pump flow as a percent of cardiac output (% bypass), left ventricular stroke work, and oxygen consumption were studied. Left ventricular stroke work was calculated from the pressure-volume loops obtained with micromanometer and conductance catheters and was indexed per 100 g of left ventricular wet weight. Oxygen consumption was calculated from left main coronary artery blood flow and the arterial-coronary sinus oxygen content difference, normalized to 100 g of left ventricular wet weight and a heart rate of 100 beats/min. Measurements were made in stepwise increments of pump flow from zero to the maximum obtainable and then reversed in similar decrements. Analyses were made for 27 complete runs. Our data demonstrate that reductions in left ventricular stroke work and oxygen consumption were achieved from zero to maximal bypass. There was an approximate 66% and 50% reduction in left ventricular stroke work and oxygen consumption, respectively, at 60% bypass.(ABSTRACT TRUNCATED AT 250 WORDS)
BACKGROUND: The data presented are a brief summary of The International Registry for Mechanical Ventricular Assist Pumps and Artificial Hearts and a summary of the personal experience of the Minnesota Thoracic Associates at the Minneapolis Heart Institute with the use of the Sams centrifugal pump from May 1985 to September 1994. METHODS: Ventricular support with the use of centrifugal pumps for postcardiotomy shock consisted of cannulation of the left atrium and aorta for left ventricular support and the right atrium and pulmonary artery for right ventricular support, or the combination of the two for biventricular support. RESULTS: The average survival and discharge rate recorded by the National Registry for postcardiotomy syndrome was 25.3%. Our experience at Minnesota Thoracic Associates was 54%. The National Registry reported 45.7% of the patients being weaned from the device or receiving transplants and 25.3% of the patients ultimately discharged from the hospital. Sixty-five percent of the patients in our experience either were weaned from the device or received a transplant for an overall discharge rate of 42%. The average effective hospital cost per survivor was almost $400,000.00. CONCLUSIONS: It is our belief that when considering the cost analysis of temporary devices, one must conclude that a more economical approach for the treatment of end-stage cardiac disease would be aggressive development of a permanent ventricular assist device.
The projection areas of mitral cell axons in the lateral (LOT) and medial (MOT) olfactory tracts and the pathways of two groups of centrifugal fibers (with fast and slow conduction velocities) to the olfactory bulb were studied in the carp using the field potential method. Mitral cell axons of the LOT and those of the MOT projected to the overlapping areas in the bilateral telencephalon and preoptic area (POA), the contralateral MOT, and the nucleus posterior tuberis (NPT) in the diencephalon. However, the precommissural, ventromedial part of the ipsilateral telencephalon received the projection only from mitral cell axons of the MOT, not from those of the LOT. No projection was detected in the contralateral LOT and the contralateral olfactory bulb. The distribution of the fast and slow centrifugal fibers and/or their cells of origin were similar to each other. They were distributed bilaterally in the telencephalon and POA, in the NPT, and contralateral LOT and MOT. These areas overlapped with the projection areas of the mitral cell axons considerably. The results support and extend those obtained from anatomical studies.
Centrifugal modulation from the midbrain, pons and medulla of the spinal nociceptive tail flick (TF) reflex evoked by graded noxious heating of the tail was studied in lightly pentobarbital-anaesthetized rats. In initial experiments, the relationship between the intensity of the noxious thermal stimulus and the TF latency was characterized. The thermal stimulus was provided by a lamp focused on the ventral surface of a rat's tail. Five different rates of heating of the tail were varied systematically by altering the voltage supplied to the lamp and were characterized using a thermocouple to measure the temperature of tissue exposed to the radiant heat. A linear stimulus-response function relating the inverse of the latency of the TF to the rate of heating of the tail was established. However, the mean cutaneous tissue temperature of the exposed tail at the time of the TF was found to be invariant and independent of the rate of heating. Focal electrical stimulation in the midbrain, pons and medulla modulated the TF reflex in two different ways, analogous to modulations of stimulus-response functions of single-cell recordings of spinal dorsal horn neurons. A Type I modulation, analogous to the parallel shift in response threshold seen in spinal dorsal horn neurons, was an absolute increase in the thermal threshold of the TF reflex. A Type II modulation, analogous to a change in slope or gain seen in spinal dorsal horn neurons, was a linear increase in the thermal threshold of the TF reflex as a function of the rate of heating. Type I modulations were produced by electrical stimulation in the ventromedial medulla (n. raphe magnus and n. reticularis gigantocellularis) and lateral periaqueductal gray of the midbrain. Type II modulations were produced by electrical stimulation in the dorsolateral pons, locus coeruleus-subcoeruleus and in the medial periaqueductal gray. This experimental approach has shown itself to be useful in the characterization of descending inhibition of nociception. Much simpler and less invasive than analogous spinal dorsal horn single cell electrophysiologic studies, it can be used to study the mechanisms of centrifugal modulation of nociceptive flexion reflexes and further establishes the utility of the lightly anaesthetized rat preparation for studies of nociception-antinociception.
We describe the assessment of an enzymatic method, with colorimetric detection, for the determination of triglyceride. Two commercial single vial reagent sets were evaluated, by manual and centrifugal analyzer techniques, and compared to a method which had attained standardized status from the Center for Disease Control (CDC). Precision and accuracy obtained on analysis of CDC reference materials, and precision obtained on analysis of plasma samples, did not fulfill the criteria of CDC. The precision met the criteria of the College of American Pathologists based upon intra-individual variation. Good correlation between the reagent set method and a continuous-flow method with prior extraction was evident but proportional and constant biases were found. The method would be suitable for routine use particularly if a centrifugal analyzer was employed. If a manual method was used it is recommended that blanks be performed on samples. The method had acceptable linearity. Use of a constant relationship between concentration and absorbance did not lead to improved performance characteristics.
We have examined the effects of enucleation and of inhibitors of mRNA synthesis (actinomycin D and cordycepin) on protein turnover of HeLa cells. Enucleation markedly inhibited the rate of protein degradation for short-lived proteins. However, cells centrifuged in the absence of cytochalasin B at the speed required to obtain cytoplasts showed protein degradation rates identical to those of cytoplasts, while inhibitors of mRNA synthesis did not affect the process. Although enucleation may affect degradation of specific proteins, these results suggest that centrifugation is largely responsible for the inhibition of protein degradation in cytoplasts.
A study was undertaken to evaluate two techniques for casting accuracy on removable partial denture frameworks: centrifugal casting and vacuum-pressure casting. A standard metal die with predetermined reference points in a horizontal plane was duplicated in refractory investment. The casts were waxed, and castings of nickel-chrome alloy were fabricated by the two techniques. Both the casts and the castings were measured between the reference points with a measuring microscope. With both casting methods, the differences between the casts and the castings were significant, but no significant differences were found between castings produced by the two techniques. Vertical measurements at three designated points also showed no significant differences between the castings. Our findings indicate that dental laboratories should be able to use the vacuum-pressure method of casting removable partial denture frameworks and achieve accuracy similar to that obtained by the centrifugal method of casting.