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At least 649 records · Page 36Linked to original sources
PubMed2001

[Usefulness of the Centrifuge Accommodation Module for analyzing gravity responses in plant seedlings].

Onboard centrifuges are indispensable tools for clarifying the effects of microgravity on various physiological processes in plant seedlings. Centrifuges are basically attached to the incubators designed for the International Space Station (ISS). However, because of the limitation in size, that loaded to the Cell Biology Experiment Facility (CBEF) is usable only to some small seedlings such as Arabidopsis. The Centrifuge Accommodation Module (CAM) has great advantages in the size and the amounts of plant materials feasible to load, the quality of acceleration produced, and the easiness of operation on it. The CAM is an apparatus that characterizes the ISS most and its construction on schedule is highly expected.

Centrifugation↗
PubMed1975

Effect of centrifugation on amniotic fluid phospolipid recovery.

Amniotic fluid lecithin and sphingomyelin were determined quantitatively in 33 samples obtained throughout the last trimester. Each sample was divided into three parts and each part was centrifuged at different relative forces prior to extraction. It is shown that centrifugation always removes considerable amounts of both lecithin and sphingomyelin from the supernatant towards the end of pregnancy, but very little at the beginning of the last trimester. The fatty acid composition of amniotic fluid lecithin, studied by gas liquid chromatography, indicate that surface active lecithin is lost by centrifugation of the fluid prior to extraction.

Amniotic Fluid↗
PubMed1981

Effects of shaking and centrifugation on human sperm motility.

Fresh seminal specimens from 48 normospermic donors were subjected to shaking and centrifugation at various intensities and durations, and their effect on sperm motility was determined objectively by the multiple exposure photography (MEP) method. Shaking for 15 sec by mechanical vibrator did not induce any drop in serum percentage of motility, while shaking for 30 to 180 sec was followed by immediate drop of this parameter. Sperm velocity increased for a short duration in all shaken specimens, after which it dropped considerably in most cases. Following centrifugation below 330 g for 10-20 min, sperm motility was almost unaffected. However, there was a significant drop in sperm motility after specimens were subjected to rates above 580 g for the same time duration. Intensive shaking and centrifugation significantly increased the percentage of dead spermatozoa, as confirmed from the combined supravital staining and MEP technique.

Centrifugation↗
PubMedDate not supplied

Centrifugation on Percoll gradient enhances fluorescent lectin binding on human sperm: a flow cytometric analysis.

Centrifugation on a Percoll gradient is commonly used to enrich sperm preparations in mobile forms prior to in vitro fertilization attempts. It has been suggested that this method also induces the capacitation of sperm, a step preceding the acrosomal reaction allowing egg fertilization. The modifications of the acrosomal membrane involved in these physiological events likely include alterations of glycosylation patterns. This hypothesis was investigated by comparing the membrane binding of 15 fluorescein-conjugated lectins on 60 samples of sperm, before and after Percoll centrifugation. The numbers of labeled sperm and their mean fluorescence intensity, recorded in flow cytometry, significantly increased for 10 and 14 of the 15 lectins tested. Microscopic examination of the labeled sperm showed that the acrosome and equatorial plates were more often labeled after Percoll centrifugation, confirming the hypothesis that this method modifies the glycosylation pattern of structures important for egg fertilization.

Centrifugation, Density Gradient↗
PubMed1988

Ultrastructural characterization of isolated human head and neck squamous carcinoma cells. Assessment of isopycnic centrifugation.

In an experiment to evaluate the merit of isopycnic centrifugation as a method of separating cell types in human head and neck squamous cell carcinomas, cells have been isolated from four specimens of these tumors and subjected to isopycnic centrifugation in continuous Percoll gradients. Cell types were identified by electron microscopy. The R- (ribosome-rich), T- (tonofilament-rich), and RT- (intermediate) cell types yielded broad bands overlapping extensively with one another, and partially with the bands of leukocytes. The pattern differed for each tumor studied, so that universal density levels separating given cell types could not be found. Isopycnic centrifugation proves less suitable in analyzing cells dispersed from solid tumors than for cells in suspended culture, blood, effusions, etc., probably because of heterogeneous growth conditions of cells in solid tumors.

Carcinoma, Squamous Cell↗
PubMed2002

Technical note: effect of removal of microbial cells by centrifugation on peptide and alpha-amino nitrogen concentrations in ruminal fluid.

We evaluated the effect of centrifuging rumen fluid prior to analysis on concentrations of alpha-amino N (AAN) and peptides. Rumen fluid was collected from steers fed grain-based diets at either various times after feeding or after dosing the rumens with solubilized casein. Fluid was either directly processed for peptide analysis by acidifying 10 ml of rumen fluid with 0.5 ml of 70% (wt/wt) perchloric acid, or first centrifuged at 500 x g for 20 min to remove protozoa and then at 30,000 x g for 15 min to remove bacterial cells prior to further processing. By removing microbial cells, intracellular AAN and peptides were not included in subsequent analyses. Concentrations of AAN were determinedusing an automated trinitrobenzene sulfonic acid assay, and peptides were determined as the increase in AAN following acid hydrolysis of the samples. When casein was not dosed, removal of microbial cells prior to analysis decreased concentrations of both AAN andpeptides, and the decrease was greater for AAN (2.2 mM)than for peptides (1.2 mM). Dosing with casein led to much higher concentrations of ruminal peptides and AAN. After casein dosing, decreases in AAN and peptidecon-centrations due to prior centrifugation (2.1 mM and 1.0 mM for AAN a nd pept ides, respectively) were similar to the decreases observed before the casein dosing. Results suggest that the contribution of intracellular AAN and peptides to the concentrations in ruminal fluid are relatively constant across broad ranges of dietary protein supply for cattle fed corn-based diets.

Amino Acids↗
PubMed1997

Recovery of Staphylococcus aureus from centrifuged quarter milk samples.

The identification of cows that are positive for mastitis caused by Staphylococcus aureus is difficult under field conditions. The frequency of isolation of S. aureus from quarter milk samples was compared with the frequency of recovery of S. aureus from sediment after centrifugation of those same samples. Overall, 776 quarter milk samples from 194 cows were studied. Cultures that were positive for S. aureus were obtained from 82 samples; 153 sediments from quarter milk samples were also positive for S. aureus. The results of this investigation showed that cultures of the sediment of quarter milk samples increased the number of positive outcomes up to 145.5%, depending on the herd. Using a different group of samples, including samples taken 1 to 5 d or 7 to 10 d after calving and samples taken after intramammary therapy, a 94% increase in cultures that were positive for S. aureus after centrifugation was found compared with cultures of the same quarter milk samples that were not centrifuged. Sedimented cultures may be useful in S. aureus control programs that require the segregation, selective treatment, or culling of cows that are positive for S. aureus.

Animals↗
PubMed2005

Perception of the head transversal plane and the subjective horizontal during gondola centrifugation.

The subjective visual horizontal (SVH) and the subjective head transversal plane (STP) were measured by means of an adjustable luminous line in darkness during centrifuging. Subjects (N = 10) were seated upright, facing forward in a swing-out gondola. After acceleration of the centrifuge to 2G (vectorial sum of the earth's gravity and the centrifugal force; gondola inclination 60 degrees), subjects had to set the line either so that it was perceived as gravitoinertially horizontal (SVH) or so that it was perceived as parallel with the transversal ("horizontal") plane of the head (STP). Initially after acceleration, the SVH was tilted with respect to the gravitoinertial horizontal of the gondola (M = 16.6 degrees). This tilt was compensatory with respect to the gondola inclination. However, the STP was tilted in the opposite direction (M = 12.4 degrees), which might suggest a vestibular-induced distortion of the mental representation of one's own body. Similar results were obtained when measuring the subjective visual vertical (SVV) and the subjective midsagittal plane (SSP) in 5 subjects. The perceived roll angle (obtained as SVH-STP or SVV-SSP) was considerably larger than had previously been reported. Time constants for exponential decay of the tilt of the SVH or SVV were often 2-3 min, indicating a memory for semicircular canal information on changes in head orientation--a position-storage mechanism.

Adult↗
PubMed2005

On the role of otoliths and semicircular canals in spatial orientation: Dynamics of the visually perceived eye level during gondola centrifugation.

The visually perceived eye level (VPEL) was measured during gondola centrifugation. Subjects (N = 11) were seated upright, facing motion in a swing-out gondola The head was adjusted so that Reid's baseline was tilted 10 degrees anterior end up. The subjects were requested to adjust the position of a small luminous dot so that it was perceived as gravitationally at eye level. In the 1-g environment, the VPEL was a few degrees below the true gravitational eye level (M = -1.75 degrees, SD = 1.90 degrees). After rapid acceleration of the centrifuge to 2 G (vectorial sum of the earth gravity force and the centrifugal force), there was an exponentially increasing depression of the VPEL. The initial value was -6.4 degrees +/- 5.2 degrees. During 10 min at 2 G, the VPEL approached an asymptotic value of -24.8 degrees +/- 5.4 degrees. The time constant showed a large interindividual variability, ranging from 59 to 1,000 sec (M = 261 sec, median = 147 sec). The findings are discussed, taking into consideration otolith-semicircular-canal interaction, as well as memory functions of the vestibular system.

Adult↗
PubMed1996

Possible segregation caused by centrifugal titanium casting.

The possibility of the segregation under solidification process using a centrifugal casting machine was investigated using an electron probe microanalyzer with elemental distribution map, line analysis and quantitative analysis. When a very small quantity of platinum was added to local molten titanium during the casting process, macroscopic segregation was observed under conditions of density difference of 0.1 g/cm3 at the most, confirming that the centrifugal force of the casting machine is extremely strong. When a Ti-6Al-4V alloy was cast, however, no macroscopic segregation was observed. The centrifugal force of the casting machine examined in the present study hardly results in the body-force segregation in this titanium alloy.

Alloys↗
PubMedDate not supplied

Evaluation of the importance of centrifugation as a component of zinc sulfate fecal flotation examinations.

Fifty canine fecal samples were evaluated by five flotation procedures to compare the sensitivity of the zinc sulfate (ZnSO4) centrifugation flotation test with ZnSO4 flotation tests using benchtop incubation during the flotation period. One or more parasite species were detected in 40 samples. Results showed that centrifugation with ZnSO4 solution was significantly more likely to detect a positive sample than benchtop procedures. The difference in procedures was due primarily to increased detection of Trichuris eggs and Giardia cysts by centrifugal flotation. No significant difference was seen in the ability of benchtop procedures to detect positive samples when tests sat either for 5 or 10 minutes before examination.

Ancylostoma↗
PubMed1999

Echocardiographic evaluation of female centrifuge subjects for chronic changes in cardiac function.

BACKGROUND: High sustained G exposure as experienced in flying high performance aircraft can affect cardiac function. Numerous studies, mostly on male pilots, have evaluated the chronic effects of exposure to high G. To date, none of these studies has revealed significant positive findings in cardiac function as a result of long-term high G exposure. METHODS: A longitudinal study was conducted on six female centrifuge panel members who did not have a history of significant high +Gz exposure. Baseline echocardiographic studies were conducted prior to any +Gz exposure on the Dynamic Environment Simulator (DES) centrifuge. The echocardiograms were repeated after each panel member completed approximately 100 3-min high G (up to 9 G) exposures over the period of 7 mo. These follow-up echos were performed after all six subjects had been exposed to at least 6 h (cumulative) of sustained acceleration > 3 G. The women were protected with the COMBAT EDGE positive pressure breathing G protection ensemble. Each subject served as her own control. All studies were evaluated independently by a cardiologist who was blinded to the order in which the echos were performed. Although complete echocardiographic studies were performed, only the parameters identified as significant in prior studies were evaluated. RESULTS: No significant differences were found between the initial and follow-up echo parameters. CONCLUSIONS: We found no significant differences in cardiac function after at least 6 and up to 17 h (cumulative) of exposure to G > 3 in women. These subjects will be monitored during a longitudinal study throughout their centrifuge subject career.

Aerospace Medicine↗
PubMed1999

Visual symptoms and G-LOC in the operational environment and during centrifuge training of Turkish jet pilots.

BACKGROUND: High-performance fighter aircraft produce high-sustained +Gz forces with rapid onset rates. Because of this G-producing capability, military jet pilots are subjected to physiological stress, which may lead to visual disturbances and G-induced loss of consciousness (G-LOC). Although visual disturbances are very common in jet flights, G-LOC is relatively rare but more dangerous. The frequency and causes of G-LOC need to be determined in the interest of flight safety. METHODS: Part I. A survey was conducted on Turkish jet pilots to reveal the incidence of symptoms due to +Gz acceleration. Anonymous questionnaires were given to F-16, F-4, and F-5 pilots. They consisted of inquiries about the occurrence of visual symptoms and/or G-LOC during +Gz acceleration in the operational environment. Part II. During the years 1992-1996, 486 F-16, 801 F-4, and 256 F-5 fighter pilots underwent high "G" training at Turkish Aerospace Medical Center and they were assessed in terms of G-LOC rates. RESULTS: Part I. A total of 325 pilots who flew T-37 in undergraduate pilot training (UPT) answered the questionnaire. The pilots were divided into 3 groups according to the types of aircraft, which they fly now: 116 F-16, 182 F-4, and 27 F-5 pilots. A total of 311 pilots (95.7%) reported having experienced greyouts and/or blackouts. With 25 pilots (7.7%) experiencing G-LOC, the G-LOC frequency according to the type of aircraft was: 5.2% (T-37) [in UPT]; 4.3% (F-16), 1.6% (F-4), and 0% (F-5). Part II. In centrifuge training, the incidence of G-LOC in pilots of the various types of aircraft were: 12% (F-16), 6.4% (F-4), and 8.6% (F-5). CONCLUSIONS: Centrifuge training reduces G-LOC rates of subsequent centrifuge training; and it is hoped might reduce the G-LOC rate in the operational environment. Almost all jet pilots reported having experienced +Gz related visual symptoms, but G-LOC seems to be a more common problem for pilots who fly rapid onset rate aircraft than pilots who fly high "G" capable but lower G onset rate aircraft.

Acceleration↗
PubMed1999

Semicircular canal and saccular influence on the subjective visual horizontal during gondola centrifugation.

Measurements of the subjective visual horizontal (SVH) were performed in 11 healthy test persons during an increase of the resultant gravitoinertial force vector in a large swing-out gondola centrifuge. Three levels of hypergravity (1.5 g, 2.0 g, 2.5 g) were used, each with a duration of 4 minutes and with 1-2 minute pauses at 1.0 g in between. The direction of the resultant gravitoinertial force vector was always parallel with the head and body length axis. Hence, there was no roll stimulus to the otolith organs. The swing-out of the gondola during acceleration, however, is sensed by the vertical semicircular canals as a change in roll head position, thus creating an otolith-semicircular canal conflict. After acceleration of the centrifuge there was a tilt of the SVH relative to the resultant gravitoinertial horizontal. This tilt gradually decayed during the 4-minute period of recordings. For a subgroup of seven test subjects who had completely normal ENG-recordings in 1 g environment, the initial offset of SVH and the time constants for exponential decay were determined for each g level; initial offsets: 9.9 degrees (1.5 g), 7.7 degrees (2.0 g), 6.1 degrees (2.5 g); time constants: 89s (1.5 g), 74s (2.0 g), 37s (2.5 g). The offset of SVH is interpreted as being the result of mainly the stimulus to the vertical semicircular canals during acceleration of the centrifuge. The slow decay, however, does not correspond to the dynamics of the semicircular canal system, and is suggested to reflect some kind of central position storage mechanism. A smaller offset and more rapid decay for the higher g loads may be explained by an increasing dominance of graviceptive input, presumably from the saccules. In conclusion, these results might suggest the role of the vertical semicircular canals as well as the sacculus in the formation of SVH. They may also have relevance with regard to the spatial disorientation problem in aviators.

Adult↗
PubMed1975

[Description of a method for the determination of the number and quality of influenza virus antibody molecules by means of equilibrium centrifugation (author's transl)].

The method of equilibrium centrifugation for determining the number of antibody molecules (A) and their equilibrium constant K characterizing the reactivity of antibody with antigen described in this paper is based on the use of virus-coated formaldehyde-treated erythrocytes as immuno-adsorbent. Graded doses of the immuno-adsorbent are mixed with the serum to be tested and the degree of antibody adsorption is measured. By analogy to the formula used in the method of equilibrium filtration, these data can be evaluated in order to determine the concentration of antibody molecules and the equilibrium constant K. Adsorption of virus on formaldehdye-treated erythrocytes results in steric hindrance of a part of the antigenic sites of the virus particles. This was taken into account by measuring sera comparatively both by means of equilibrium centrifugation and by use of equilibrium filtration and establishing correction formulas. Both techniques were found to have the same sensitivity and accuracy. In comparison to equilibrium filtration, equilibrium centrifugation offers the advantage that it can be used with test antigens which are below the minimum size needed in equilibrium filtration.

Adsorption↗
PubMed1984

Core temperature of tailless rats exposed to centrifugation.

Although it comprises only about 5% of the total body surface area of the rat, the tail can dissipate about 17% of the animal's body heat. In the present study, we have investigated the role of the tail in the altered thermoregulation of rats during acute hypergravic exposures (achieved by centrifugation). Such exposures produce a rapid fall in core temperature (Tc) leading to a sustained hypothermia. In addition to the Tc changes, there is a significant, but transient increase of tail temperature, indicative of an accelerated rate of heat loss. To determine the extent to which increased heat loss from the tail affects the hypothermic response, rectal temperature changes were measured in both tailless and intact rats subjected to centrifugation. Results from this study indicate that the increased heat loss from the tail per se does not contribute in a measurable way to the hypothermia induced by centrifugation stress.

Aging↗
PubMed1996

A survey of centrifuge subjects assessing the relationship between repeated +Gz exposures and chronic back pain.

Research using human centrifuges has been done for many years. Long-term follow-up of such subjects has not been carried out previously. To evaluate whether there is an increased incidence of back problems in former centrifuge subjects, we did a retrospective questionnaire survey of 20 subjects with significant centrifuge exposure histories to moderate G levels at least 5 to 10 years ago, and two USAF active duty, age-matched control groups (former hypobaric subjects and naive subjects). The results revealed no increase in back pain or injury in the study group. The only significant indicators for back pain or injury in our study population are a history of tobacco use and increasing height. Moderate G exposures were not a predictor of subsequent back pain. We recommend a larger prospective study controlling for intensity, profile and duration of G exposure.

Adult↗
PubMed2000

[Detecting mycobacteria and their L-forms in peripheral blood from pulmonary tuberculosis patients by cultivation with hemolyzed-centrifugated blood in liquid medium].

OBJECTIVE: To establish a new method of detecting mycobacteria and their L-forms in blood. METHODS: 65 samples of peripheral blood from patients with pulmonary tuberculosis were cultivated directly or cultivated with hemolyzed-centrifugated blood sediments in 92-3TB and 92-3TBL liquid medium, and the cultures were staining with immunoenzyme technique (ABC method). RESULTS: In 65 specimens, the positive rates of mycobacteria and their L-forms were 15%, 26% respectively with total isolation rate of 32%. In cultivating with hemolyzed-centrifugated blood the positive rate was much higher than direct cultural method (P < 0.05). In sputum the positive rates of acid-fast bacilli and their L-forms were 38% and 20% respectively, with total isolation rate of 52%, higher than that in peripheral blood (P < 0.05), and the total positive rate of combinative detection of blood and sputum salmples was 65%. CONCLUSIONS: Mycobacteria and their L-forms exist in peripheral blood of patients with pulmonary tuberculosis, and mainly in L-forms. Cultivation with hemolyzed-centrifugated blood in liquid medium and staining with immunoenzyme technique are valuable in routine detection of mycobacteria and their L-forms in peripheral blood. The positive rate of bacterial culture of pulmonary tuberculosis could be increased in combination with sputum mycobacteria and their L-forms examination.

Adolescent↗