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PubMed1976

Physiological changes associated with long-term increases in acceleration.

The long-term retention of organisms in increased acceleration fields is an experimental approach towards understanding the biological consequences of earth gravity. Such treatment, called chronic acceleration, simulates a change in gravity and requires exposed organisms to adapt physiologically to the new environment. Information from chronic acceleration supplements that from space physiology in understanding gravitational physiology. Many of the responses in long-term exposure to increased acceleration are those which would be anticipated from the imposed symmetrical loading. For example, increased requirements for posture and locomotion induce appropriate changes in musculo-skeletal organs. Displacement of body fluids and increased hydrostatic pressures lead to greater blood volumes and increased tissue hydration. However, there are also specific acceleration effects which cannot be so directly interpreted. Among these are decreases of mature body size and of depot fat, which are proportional in degree to field strength. The role of chronic acceleration research in the development of gravitational biology and its relationship to earth-orbital experiments are considered. The applicability of chronic acceleration studies with human subjects towards planning of deep space exploration is also discussed.

Acceleration↗

PubMed1999

Influence of postural changes on nystagmic elicitation induced by linear acceleration.

Functional nystagmic eye movements are compensatory responses meant to stabilize the gaze during head movement. Niven et al. (1966) have reported that otolithic nystagmus can be elicited by linear acceleration in humans only along interaural (Y-axis) acceleration (Gy), but not along occipitonasal (X-axis) or head-to-foot (Z-axis) acceleration. This result was reexamined in the present study in normal subjects who elicited lateral (Gy) nystagmus frequently. The nystagmic elicitation was examined by EOG in 4 healthy subjects who were fastened tightly in the chair of a linear accelerator and instructed to look straight ahead at an imaginary target in the dark. The stimulation was five oscillations of a constant 10-m stroke at two different acceleration levels of 0.3 and 0.5 G in a step mode. The X- and Z-axis accelerations did not induce any horizontal or vertical nystagmus, while the Y-axis acceleration did, in agreement with the above report. However, it was found that nystagmic elicitation due to Gy loading tended to be lower in the supine than in the upright sitting position. The present finding that nystagmic slow-phase velocity (SPV) increased with an increase in the G-load also contradicted the above report. Upright subjects who showed G-directional preponderance (DP) in nystagmic elicitation did not always maintain DP when supine. No relation could be seen between DP and SPV, suggesting that DP might be generated by a central mechanism different from SPV control.

Acceleration↗

PubMed2004

The locking and unlocking characteristics of a seat belt inertial locking system due to acceleration.

An inertial locking mechanism of a seatbelt is designed to prevent further seatbelt extension when it exceeds an acceleration threshold. The acceleration threshold varies with the orientation of the mechanism and direction of acceleration. A setup and procedure were created to test the acceleration threshold of the inertial locking mechanism of a seatbelt in various orientations. For an example of an inertial locking mechanism a 1984 Ford Mustang seatbelt mechanism was used. During testing, the mechanism was put into an orientation that simulated accelerations that could be seen in normal collisions. The mechanism responded by locking with an average acceleration of 2.535 g. The mechanism was then tested in orientations that would simulate those seen by a vehicle in a rollover situation. In certain orientations, the mechanism was locked while at rest, but became unlocked when accelerated.

Acceleration↗

PubMed1992

The relationship between head and neck anthropometry and kinematic response during impact acceleration.

Research on the effects of impact acceleration on the body, primarily the head and neck, has been conducted at the U.S. Naval Biodynamics Laboratory for nearly two decades. Over 150 Navy enlisted men have been subjected to impact acceleration on a sled propelled by a nitrogen-powered horizontal accelerator. Their head and neck kinematic responses during the experimental impact were measured and stored in automated data bases. Similarly, anthropometric measurements were recorded for these subjects. To investigate the relation between head and neck anthropometry and response to impact acceleration, tests involving 15 subjects were selected. A strong relation was found between head and neck anthropometry and linear acceleration of the head along the Z axis. Lesser correlations were determined between the anthropometric measurements and linear acceleration along the X axis and angular acceleration about the Y axis. These findings are potentially applicable to areas such as aircrew selection, physical training and protective equipment development.

Acceleration↗

PubMed2002

[Experimental study of taxol combining accelerated radiation on laryngeal carcinoma cells].

OBJECTIVE: To investigate the effect of taxol combining accelerated radiation on the human laryngeal squamous cell carcinoma Hep-2 cell lines in vitro, and to provide the experimental basis for the usage of these two combined theraputic methods. METHOD: Using techniques of tumor cells culture in vitro, the suppressive and time-dependency effects of taxol (1 x 10(-8) mol/L) combine 2 Gy X-rays generated by accelerator on the human laryngeal squamous cell carcinoma Hep-2 cell lines were observed. RESULT: Cell growth is obviously suppressed in group taxol combined accelerated radiation and it's livability is 11.11%, much lower than accelerated radiation combined taxol. After adding taxol 12 h or 24 h then combined accelerated radiation, the two groups were no difference statistically. Cell livability of group taxol is lower than group accelerated radiation. CONCLUSION: Cell growth is obviously suppressed in the human laryngeal squamous cell carcinoma Hep-2 cell lines after given 1 x 10(-8) mol/L taxol combined 2 Gy X-rays generated by accelerator. Taxol acts as a radiation sensitizer.

Antineoplastic Agents, Phytogenic↗

PubMedDate not supplied

Effects of +Gz acceleration on human body systems as a form of training based of physiological data evaluation.

Twenty-five men with decreased acceleration tolerance limits were subjected to two weeks centrifuge training, in which selected characteristics of +Gz acceleration (head-feet directed) were applied. The training loads were controlled basing on the responses of blood flow velocity and heart rate. The results show that the human centrifuge training in which the graded loads are based on measurement of these parameters, increases acceleration tolerance limits. It is also demonstrated that the human centrifuge training methods can be used in pilots after convalescence period or on finding lowered acceleration tolerance produced by other causes. The physical and physiological methods of increasing acceleration tolerance limits (ATL) consist some of the most important and urgent problems of today to be solved in modern military aviation. This demand is produced not only by the systematically increasing requirements as to the highest health performance of the military pilot, but also by the enormous costs of the flying equipment and training. In the group of different methods of increasing ATL, the human centrifuge training is an open problem. The available literature presents only a few reports in which the +Gz acceleration (i.e. head-pelvis directed) was used as the loading stimulus in pilots' training. The reasons for the lack of interest in this direction of examination include: easily developed decompensation of the circulatory system; cummulated effects of acceleration, and lack of optimal criteria to evaluate the body systems loads. Moreover, the positive effects of training could be baffled by the above mentioned factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗

PubMed1984

Comparative analysis: effects of positive and negative lateral acceleration on isometric fatigue in the forearm.

UNLABELLED: The purpose of this investigation was to determine the difference, if any, produced by +/- Gy acceleration on forearm fatigue. The Dynamic Environment Simulator (DES) at the USAF Aerospace Medical Research Laboratory was used to create a lateral acceleration environment. The experiment was designed to measure the forearm strength, endurance, recovery from fatigue, and surface electrical activity of six subjects during +/- 2 Gy acceleration. THE RESULTS: isometric performance was degraded during -2 Gy acceleration compared to + 2 Gy acceleration. The percentage drop in center frequency of the EMG signal was determined to be unreliable as a fatigue index during lateral acceleration. When head and shoulder restraints were used during lateral maneuvers, they were a factor in pilot performance, with + 2 Gy being superior to -2 Gy. This study suggested a way of analyzing the EMG signals that may permit quantification of isometric fatigue during lateral acceleration.

Acceleration↗

PubMed1993

Two-dimensional spatiotemporal coding of linear acceleration in vestibular nuclei neurons.

Response properties of vertical (VC) and horizontal (HC) canal/otolith-convergent vestibular nuclei neurons were studied in decerebrate rats during stimulation with sinusoidal linear accelerations (0.2-1.4 Hz) along different directions in the head horizontal plane. A novel characteristic of the majority of tested neurons was the nonzero response often elicited during stimulation along the "null" direction (i.e., the direction perpendicular to the maximum sensitivity vector, Smax). The tuning ratio (Smin gain/Smax gain), a measure of the two-dimensional spatial sensitivity, depended on stimulus frequency. For most vestibular nuclei neurons, the tuning ratio was small at the lowest stimulus frequencies and progressively increased with frequency. Specifically, HC neurons were characterized by a flat Smax gain and an approximately 10-fold increase of Smin gain per frequency decade. Thus, these neurons encode linear acceleration when stimulated along their maximum sensitivity direction, and the rate of change of linear acceleration (jerk) when stimulated along their minimum sensitivity direction. While the Smax vectors were distributed throughout the horizontal plane, the Smin vectors were concentrated mainly ipsilaterally with respect to head acceleration and clustered around the naso-occipital head axis. The properties of VC neurons were distinctly different from those of HC cells. The majority of VC cells showed decreasing Smax gains and small, relatively flat, Smin gains as a function of frequency. The Smax vectors were distributed ipsilaterally relative to the induced (apparent) head tilt. In type I anterior or posterior VC neurons, Smax vectors were clustered around the projection of the respective ipsilateral canal plane onto the horizontal head plane. These distinct spatial and temporal properties of HC and VC neurons during linear acceleration are compatible with the spatiotemporal organization of the horizontal and the vertical/torsional ocular responses, respectively, elicited in the rat during linear translation in the horizontal head plane. In addition, the data suggest a spatially and temporally specific and selective otolith/canal convergence. We propose that the central otolith system is organized in canal coordinates such that there is a close alignment between the plane of angular acceleration (canal) sensitivity and the plane of linear acceleration (otolith) sensitivity in otolith/canal-convergent vestibular nuclei neurons.

Acceleration↗

PubMed2001

Estimation of steady-state culture characteristics during acceleration-stats with yeasts.

Steady-state culture characteristics are usually determined in chemostat cultivations, which are very time-consuming. In contrast, acceleration-stat (A-stat) cultivations in which the dilution rate is continuously changed with a constant acceleration rate are not so time-consuming, especially at high acceleration rates. Therefore, the A-stat could be advantageous to use instead of the chemostat. However, the highest acceleration rate, meaning the fastest A-stat that can be applied for estimating steady-state culture characteristics, is not known yet. Experimental results obtained with Zygosaccharomyces rouxii, an important yeast in soy sauce processes, showed that the culture characteristics during the A-stat with an acceleration rate of 0.001 h(-2) were roughly comparable to those of the chemostat. For higher acceleration rates the deviation between the culture characteristics in the A-stat and those in the chemostat obtained at the same dilution rate generally started to increase. The source of these deviations was examined by simulation for Saccharomyces cerevisiae. The simulations demonstrated that this deviation was not only dependent on the metabolic adaptation rate of the yeast, but also on the rate of change in environmental substrate concentrations during A-stats. From this work, it was concluded that an A-stat with an acceleration rate of 0.001 h(-2) is attractive to be used instead of chemostat whenever a rough estimation of steady-state culture characteristics is acceptable.

Adaptation, Physiological↗

PubMed1993

Decreased levels of the high molecular weight subunit of neurofilaments and accelerated neurofilament transport during the recovery phase of 2,5-hexanedione exposure.

The neurotoxicant 2,5-hexanedione (HD) causes the accumulation of neurofilaments in the distal axon and an acceleration of neurofilament transport proximal to the site of their accumulation. It has been proposed that the acceleration of transport is due to the direct reaction of HD with neurofilament proteins and, conversely, that this acceleration is a secondary response to the axon to injury. The objective of this study was to determine whether the response of axons to HD intoxication includes acceleration of neurofilament transport. Pulse labelling was used to analyze neurofilament transport in age-matched rats exposed to HD or PBS. The animals receiving HD were exposed either throughout the period of radiolabel transport, or prior to the pulse labeling of neurofilament proteins. If acceleration of the rate of neurofilament transport was due to the direct reaction of HD with proteins, then neurofilaments synthesized after the exposure period should travel at control rates, since these proteins would not have been exposed to the toxicant. After 28 days of transport, optic nerve proteins were examined using SDS-PAGE, fluorography, and computerized densitometry. In both HD-treated groups, neurofilament transport was accelerated relative to age-matched control animals. In addition, the amount of NFH was decreased relative to other neurofilament subunits. The combination of accelerated transport and a diminished proportion of NFH is similar to the observations of neurofilament axonal transport during growth and development. These observations suggest that this persistent, secondary effect is a reparative response to injury that recapitulates axonal growth and development.

Animals↗

PubMed1989

Differential effect of the autoimmune Yaa and lpr genes on the acceleration of lupus-like syndrome in MRL/MpJ mice.

The Yaa gene (Y chromosome-linked autoimmune acceleration), linked to the BXSB/MpJ Y chromosome, and the autosomal recessive lpr (lymphoproliferation) gene have been shown to accelerate the progression of the lupus-like autoimmune syndrome in the BXSB and MRL strains, respectively. To compare more directly the role of the Yaa and lpr genes in the development of the autoimmune syndrome, the Y chromosome of BXSB mice was transferred to MRL mice by backcross procedures, and the effect of the Yaa gene on the autoantibody formation and the development of lupus-like nephritis in MRL mice was investigated in comparison with those bearing the lpr mutation. The Yaa gene as well as the lpr gene were able to shorten the life span of MRL mice as a result of the accelerated development of lethal lupus-like nephritis. However, the acceleration promoted by the Yaa gene (50% mortality rate: 12 months) was less severe than that induced by the lpr gene (50% mortality rate: 7 months). This may be related to the finding that the lpr gene enhanced the production of a large spectrum of autoantibodies, including anti-DNA, rheumatoid factors and anti-gp70, and of cryoglobulins, whereas only anti-gp70 production among the autoantibodies studies was markedly enhanced by the Yaa gene. The selective autoimmune accelerating effect of the Yaa gene was similarly observed in (NZW X MRL)F1 hybrid mice. Our results suggest that the Yaa gene, unlike the lpr gene, exhibits selective autoimmune accelerating activity, but as a result of increased formation of certain nephritogenic autoantibodies such as anti-gp70 antibodies, the Yaa gene is able to accelerate the progression of lupus-like nephritis in lupus-prone mice.

Animals↗

PubMed2006

Can accelerated aqueous aging simulate in vivo oxidation of gamma-sterilized UHMWPE?

Oxidation of ultrahigh molecular weight polyethylene (UHMWPE) gamma-sterilized arthroplasty components occurs in vivo. Though accelerated in vitro protocols have been developed to test the relative oxidation resistance of various types of UHMWPE, it is desirable to develop an accelerated aging protocol that more closely approximates the in vivo environment. The goal of this study was to investigate the effects of temperature, solute, and oxygen partial pressure in aqueous media on the oxidation of gamma-sterilized UHMWPE, as the basis for the development of improved accelerated aging protocols. The accelerated oxidation behavior of gamma-sterilized GUR 1150 was studied at 60 and 70 degrees C in an open vessel filled with distilled water or PBS in equilibrium with a controlled partial pressure of oxygen. The extent of oxidation was assessed using standardized mechanical and chemical evaluation techniques (small punch and Fourier transform infrared spectroscopy). Accelerated oxidation of UHMWPE was achieved in aqueous environments; however, both clinically relevant and nonrelevant oxidation species (e.g., aldehydes) were observed for long aging times at 60 degrees C, and for all aging times at 70 degrees C. These findings point the way to the development of an accelerated aging protocol. The current data, considered in conjunction with real-time aging studies, suggest that a temperature between body temperature and 60 degrees C may accelerate oxidative degradation without altering the oxidative patterns encountered in vivo.

Biocompatible Materials↗

PubMed1984

Acceleration of epithelial keratinization by carcinogens in fetal rat forestomach in organ culture.

Epithelial keratinization in fragments of fetal rat forestomach in organ culture was significantly accelerated by treatment with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) for 1 h (Fukamachi and Takayama 1979). In this paper, we examined whether acceleration of epithelial keratinization may be characteristic for some carcinogens, and also the mechanism of acceleration of epithelial keratinization by treatment with MNNG. Forestomach epithelial keratinization was accelerated by treatments with 4-nitroquinoline-1-oxide, N-acetoxy-2-acetylaminofluorene, 1-methyl-1-nitrosourea, 7,12-dimethylbenzanthracene, methyl methanesulfonate, and MNNG, but not with 2-acetylaminofluorene, pyrene, or dimethylsulfoxide, indicating that carcinogens may specifically accelerate epithelial keratinization. Chemicals that accelerated epithelial keratinization inhibited epithelial mitotic activity on day 1 in culture, but the mitotic rate was restored to the control level from day 2 onwards. The epithelial keratinization was completely inhibited by adding 5 micrograms/ml of retinoic acid (RA) to the culture medium, irrespective of treatment with MNNG. Addition of 1 microgram/ml of RA suppressed epithelial keratinization in control explants more than in MNNG-treated explants. One possible explanation is that the epithelial cells become less sensitive to RA after MNNG-treatment. A mechanism is proposed assuming that carcinogens induce some qualitative changes in epithelial cells by inhibiting cell proliferation on day 1 in culture, and consequently the epithelial keratinization is accelerated.

4-Nitroquinoline-1-oxide↗

PubMed2001

The accelerator hypothesis: weight gain as the missing link between Type I and Type II diabetes.

Blood glucose concentrations are controlled by a loop incorporating two components, the beta cells which secrete insulin and the insulin-sensitive tissues (liver, muscle, adipose) which respond to it. Loss of blood glucose control might result from failure of the beta cells to secrete insulin, resistance of the tissues to its action, or a combination of both. The distinctions between Type I (insulin-dependent) and Type II (non-insulin-dependent) diabetes mellitus are becoming increasingly blurred both clinically and aetiologically, where beta-cell insufficiency is the shared characteristic. The 'Accelerator Hypothesis' identifies three processes which variably accelerate the loss of beta cells through apoptosis: constitution, insulin resistance and autoimmunity. None of the accelerators leads to diabetes without excess weight gain, a trend which the 'Accelerator Hypothesis' deems central to the rising incidence of both types of diabetes in the industrially developed world. Weight gain causes an increase in insulin resistance, which results in the weakening of glucose control. The rising blood glucose (glucotoxicity) accelerates beta-cell apoptosis directly in all and, by inducing beta-cell immunogens, further accelerates it in a subset genetically predisposed to autoimmunity. Rather than overlap between two types of diabetes, the 'Accelerator Hypothesis' envisages overlay. Body mass is central to the development and rising incidence of all diabetes. Only tempo distinguishes the 'types'. The control of weight gain, and with it insulin resistance, could be the means of minimising both.

Apoptosis↗

PubMed2004

Accelerated dynamic Fourier velocity encoding by exploiting velocity-spatio-temporal correlations.

OBJECTIVE: To describe how the information content in a Fourier velocity encoding (FVE) scan can be transformed into a very sparse representation and to develop a method that exploits the compactness of the data to significantly accelerate the acquisition. MATERIALS AND METHODS: For validation, fully sampled FVE datasets were acquired in phantom and in vivo experiments. Fivefold and eightfold acceleration was simulated by using only one fifth or one eighth of the data for reconstruction in the proposed method based on the k-t BLAST framework. Reconstructed images were compared quantitatively to those from the fully sampled data. RESULTS: Velocity spectra in the accelerated datasets were comparable to the spectra from fully sampled datasets. The detected peak velocities remained accurate even at eightfold acceleration, and the overall shape of the spectra was well preserved. Slight temporal smoothing was seen in the accelerated datasets. CONCLUSION: A novel technique for accelerating time-resolved FVE scan is presented. It is possible to accelerate FVE to acquisition speeds comparable to a standard time-resolved phase-contrast scan.

Algorithms↗

PubMed2006

MDM2 SNP309 accelerates familial breast carcinogenesis independently of estrogen signaling.

A single nucleotide polymorphism (SNP309T>G) in the intronic promoter of MDM2 was recently found to accelerate carcinogenesis in early-onset cancer cases. This cancer acceleration presumably was due to increased SP1 binding, resulting in enhanced MDM2 transcriptional activation by estrogens. We evaluated MDM2 SNP309 in 343 familial breast cancer cases with known mutation status for CHEK2 1100delC, BRCA1 and BRCA2. Cancer acceleration was indeed observed in early-onset familial breast cancer cases (diagnosed <or= 51 years), with 16% of cases carrying the MDM2 SNP309 GG genotype as compared to 4% of late-onset cases (P = 0.029). The cancer acceleration was even more pronounced in the non-mutant familial breast cancer cases, with 17% of early-onset cases carrying MDM2 SNP309 GG as compared to 2% of late-onset cases (n = 214; P = 0.015). There was no evidence for an influence of estrogen signaling in the cancer acceleration by MDM2 SNP309, as there were no differences in the prevalence of MDM2 SNP309 GG among CHEK2 1100delC and BRCA2 mutant cases (with 90% ER-positive cancers) or BRCA1 mutant cases (10% ER-positive cancers). Nor did we observe differences in MDM2 SNP309 frequencies among 75 familial breast cancer cases of our cohort with known ER status. Overall, our data suggest that MDM2 SNP309 accelerates familial breast carcinogenesis, but that this acceleration is not influenced by estrogen signaling.

Adult↗

PubMed1988

Serial evaluation of left ventricular function in congestive heart failure by measurement of peak aortic blood acceleration.

Peak acceleration of blood in the ascending aorta, an index of global systolic left ventricular (LV) function, can be measured noninvasively using a continuous wave Doppler velocimeter applied suprasternally. The feasibility of this approach as a tool for detecting improvement of LV function was studied in 16 patients with congestive heart failure (CHF). Measurements were made daily for 6 consecutive days. The daily variability of peak acceleration examined in 11 normal subjects was +/- 2 m/s/s. In 11 of 16 patients with CHF, peak acceleration increased more than 2 m/s/s by day 6 compared with day 1 (group 1). In 5 of 16 patients, peak acceleration remained unchanged (group 2). In group 1, peak acceleration was 11 +/- 1 m/s/s on day 1 and increased to 16 +/- 1 m/s/s on day 6 (p less than 0.001). In this group, CHF resolved by day 6 in 9 of 11 patients. In group 2, peak acceleration was 9 +/- 1 m/s/s on day 1 and remained unchanged through day 6. In these 5 patients, the signs and symptoms of CHF persisted through day 6. The results suggest that peak acceleration measured noninvasively with continuous wave Doppler can detect improvement of LV function in patients with CHF. The approach provides a simple and reliable bedside means for serial evaluation of LV systolic function.

Adult↗

PubMed1991

Ventricular tachycardia and accelerated ventricular rhythm presenting in the first month of life.

Fourteen infants aged less than 1 month presented to our institution during the last 22 years with ventricular tachycardia (VT) or accelerated ventricular rhythm and a structurally normal heart. In 2, VT was associated with long QT syndrome. Both are alive on beta-blocker therapy, 1 with an implanted pacemaker. Twelve infants had accelerated ventricular rhythm, and 2 of these died in the first 2 months of life of unrelated conditions. The other 10 are alive at a median age of 4 years (range 2 months to 11 years), and none were lost to follow-up. Hemodynamic compromise did not occur with accelerated ventricular rhythm. The ventricular rate was very close to the sinus rate in all 12, less than 12% above the sinus rate. The mean QRS duration during accelerated ventricular rhythm was 92.5 ms, and averaged twice the QRS duration during sinus rhythm. Fusion beats were seen in all 12, and there was atrioventricular dissociation with capture beats in 10. In 2, ventriculoatrial conduction was present. Treatment was attempted in 5 of the 10 survivors with accelerated ventricular rhythm, and was thought to be successful in 4. Treatment was later successfully withdrawn in all 5, so that all 10 survivors were free of accelerated ventricular rhythm and were not receiving antiarrhythmic medications at last follow-up. Because of the excellent long-term outcome and the lack of hemodynamic compromise during the rhythm, it seems reasonable to withhold antiarrhythmic therapy in infants with accelerated ventricular rhythm and await resolution of the rhythm.

Anti-Arrhythmia Agents↗