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PubMed1998

A new clinical technique for demonstrating changes in eye acceleration during horizontal saccades in patients with partial internuclear ophthalmoplegias.

The eyelid-mounted accelerometer can pick up the acceleration waveform of the eye during horizontal eye movements. The acceleration profile comprises high-amplitude pulsatile activity in the saccade and changes in the level of background ocular microtremor related to eye position. Adducting saccades of 20 degrees were recorded in eight patients with partial internuclear ophthalmoplegias caused by multiple sclerosis and in eight age-matched healthy subjects. The initial pulse of acceleration activity was reduced by 85% in the patients. In the worst-affected cases, adducting saccades were associated only with an increase in the level of background ocular microtremor in the acceleration trace. The results confirm the hypothesis that an internuclear ophthalmoplegia is due to the loss of the pulse signal to ocular motor neurons, with preservation of the step signal in an adducting saccade.

Adult↗

PubMed1999

Biomedical applications of accelerator mass spectrometry-isotope measurements at the level of the atom.

Accelerator mass spectrometry (AMS) is a nuclear physics technique developed about twenty years ago, that uses the high energy (several MeV) of a tandem Van de Graaff accelerator to measure very small quantities of rare and long-lived isotopes. Elements that are of interest in biomedicine and environmental sciences can be measured, often to parts per quadrillion sensitivity, i.e. zeptomole to attomole levels (10(-21)-10(-18) mole) from milligram samples. This is several orders of magnitude lower than that achievable by conventional decay counting techniques, such as liquid scintillation counting (LSC). AMS was first applied to geochemical, climatological and archaeological areas, such as for radiocarbon dating (Shroud of Turin), but more recently this technology has been used for bioanalytical applications. In this sphere, most work has been conducted using aluminium, calcium and carbon isotopes. The latter is of special interest in drug metabolism studies, where a Phase 1 adsorption, distribution, metabolism and excretion (ADME) study can be conducted using only 10 nanoCurie (37 Bq or ca. 0.9 microSv) amounts or less of 14C-labelled drugs. In the UK, these amounts of radioactivity are below those necessary to request specific regulatory approval from the Department of Health's Administration of Radioactive Substances Advisory Committee (ARSAC), thus saving on valuable development time and resources. In addition, the disposal of these amounts is much less an environmental issue than that associated with microCurie quantities, which are currently used. Also, AMS should bring an opportunity to conduct "first into man" studies without the need for widespread use of animals. Centre for Biomedical Accelerator Mass Spectrometry (CBAMS) Ltd. is the first fully commercial company in the world to offer analytical services using AMS. With its high throughput and relatively low costs per sample analysis, AMS should be of great benefit to the pharmaceutical and biotechnology industries as well as other life science areas.

Biotechnology↗

PubMed1991

Accelerated idioventricular rhythm detected during elective surgery in a healthy man.

Accelerated idioventricular rhythm (AIVR) is found most commonly in the presence of underlying heart disease. It is characterized by acceleration of a latent pacemaker that normally depolarizes slowly. We describe a 30-year-old man who was found to have episodes of accelerated idioventricular rhythm (AIVR) on cardiac monitoring during elective orthopedic surgery. Noninvasive evaluation including two-dimensional echocardiography was unremarkable. No late potentials were detected on a signal-averaged electrocardiogram. During an exercise tolerance test, AIVR was suppressed as heart rate increased. A 24-h Holter monitor revealed that the AIVR rate was consistently 73-76 beats/min, which appeared whenever the sinus rate slowed to this level. The patient has been asymptomatic, and the rhythm has persisted at least through a 5-month follow-up period.

Accelerated Idioventricular Rhythm↗

PubMed2001

Precision of magnetic resonance velocity and acceleration measurements: theoretical issues and phantom experiments.

Magnetic resonance (MR) sequences have been developed for acquiring multiple components of velocity and/or acceleration in a reasonable time and with a single acquisition. They have many parameters that influence the precision of measurements: NS, the number of flow-encoding steps; NEX, the number of signal accumulations; and ND, the number of dimensions. Our aims were to establish a general relationship revealing the precision of these measurements as a function of NS, ND, and NEX and to validate it by experiments using phantoms. Previous work on precision has been restricted to two-step (NS = 2) or 1D (ND = 1) MR velocity measurements. We describe a comprehensive approach that encompasses both multistep and multidimensional strategies. Our theoretical formula gives the precision of velocity and acceleration measurements. It was validated experimentally with measurements on a rotating disk phantom. This phantom was much easier to handle than fluid-based phantoms. It could be used to assess both velocity and acceleration sequences and provided accurate and precise assessments over a wide, adjustable range of values within a single experiment. Increasing each of the three parameters, NS, ND, and NEX, improves the precision but makes the acquisition time longer. However, if only one parameter is to be assessed, maximizing the number of steps (NS) is the most efficient way of improving the precision of measurements; if several parameters are of interest, they should be measured simultaneously. By contrast, increasing the number of signals accumulated (NEX) is the least efficient strategy.

Acceleration↗

PubMed2005

Calculation of left ventricle relative pressure distribution in MRI using acceleration data.

Measurements of pressure variations within the cardiac chambers could provide important information for clinical assessments of cardiovascular function. In this work an MRI method for evaluating spatial distributions of intracardiac relative pressure is presented. We first calculated pressure gradients from MR maps of blood acceleration by applying the NS equation. We then used an original algorithm to compute pressure distribution in a region of interest (ROI) by minimizing the pressure gradient curl so that the result in a given pixel is independent of the integration path. The method was assessed in five healthy volunteers by means of MR 2D maps of the blood acceleration in the left ventricle (LV) during ejection and filling phases. The pressure variations calculated from acceleration mapping fit the known physiological variations better than those based on velocity maps acquired in the same volunteers. Furthermore, the optimization algorithm presented here produced the same results as iterative algorithms proposed by other authors, but in much less time and without requiring adjustable parameters or boundary conditions.

Acceleration↗

PubMed1990

An experimental study of the moderator assembly for a low-energy proton accelerator neutron irradiation facility for BNCT.

An accelerator-based neutron irradiation facility (ANIF), which has been proposed for BNCT, is based on a 2.5-MeV proton beam bombarding a thick lithium target. Neutrons which are emitted from the lithium target are too energetic for BNCT and must be moderated. A calculational study, which was done previously on the moderator assembly for an ANIF, shows that, with an optimized moderator assembly, an ANIF can produce a neutron flux which has quality and intensity sufficient for BNCT. In order to verify our previous calculational study, a lithium target and a non-optimized moderator assembly (a cylindrical tank of D2O) have been constructed and tested at the Ohio State University Van de Graaff proton accelerator. The neutron spectrum was measured for neutrons emerging from the moderator assembly. The measured neutron spectrum agrees reasonably well with that obtained from Monte Carlo calculations, except for neutrons with energies above 100 keV. For those neutrons, the measured spectrum is lower by a factor of two than the calculated one. In addition to the neutron spectrum measurement, the boron-10 absorbed dose was measured on the axis of the neutron field in a 20 cm x 20 cm x 20 cm water phantom, and the result agrees quite well with that obtained from calculation. This experiment confirms that the calculated optimized moderator assembly, consisting of a 22.5-cm thick, 25-cm diameter cylinder of beryllia (BeO) surrounded by a 30-cm thick jacket of alumina (Al2O3), produces an epithermal neutron flux of 3.12 x 10(7) n/cm2-s per mA of protons. For an accelerator delivering 30 mA of 2.5-MeV protons, the irradiation time for a single-session treatment can be as short as 50 minutes. The calculated ratio of absorbed neutron dose to fluence for the optimized moderator assembly is 4.9 x 10(-11) cGy-cm2/n, which is equal to that of a 5-keV neutron beam. Our experimental measurements indicate that the ratio of absorbed neutron dose to fluence may in fact be lower (better) than calculated.

Boron↗

PubMed1992

The cerebrovascular response to experimental lateral head acceleration.

A number of microvascular changes, such as the development of astrocyte lucency, increased endothelial pit/vesicle activity, development of crater like lesions, and endothelial microvilli have been reported after injury to the brain. Lateral head acceleration in the non-human primate, however, still provides the best experimental model for human diffuse axonal injury. No attempt has yet been made to document the spatial extent or time course of the microvascular response to acceleration injury to the head. We have examined the brains of baboons 1, 4, 6, and 12 h and 7 days after acceleration injury to the head to analyse the microvascular response. In the experimental animals there was a short-term rise in intracranial pressure followed by a long-term resolution, and a reduction in both mean arterial blood pressure and cerebral perfusion pressure which, however, never dropped below 75% of baseline for more than 5 min after injury in any animal. We found evidence for extravasation of blood in a small number of blood vessels in all parts of the brain. Interendothelial tight junctions are not disrupted. Pit/vesicle activity rises in the 1st h in the occipital cortex, but not until 4 h in the frontal cortex, and remains elevated for at least 7 days. There is little change in the thalamus. Development of microvilli is most rapid in the frontal cortex with peak values at 1 h, but slower in the thalamus and occipital cortex where peak values are only obtained at 6 h. Highest numbers of microvilli occur in parasagittal regions of the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗

PubMed2004

Linear accelerator output variability.

The Wellington Cancer Centre is equipped with two matched linear accelerators (Varian 2100CD) linear accelerators (identified as SN1027 and SN42). Each morning, before treatments commence, a radiation therapist carries out an output constancy check of the radiation output and every fortnight a physicist measures, in a phantom, the delivered radiation dose to check on the machine calibration. The daily output checks have been recorded into a database (Argus QA for Radiation Oncology) since August 1997 and in June 1998 the fortnightly calibration measurements were added. The information in the database, up to April 2003, has been analysed to consider the quality of the daily constancy checks as compared with the fortnightly calibration measurements and whether the data contains useful information on machine performance. After allowance for the effects of machine recalibration the fortnightly calibration measurements had an average standard deviation of 0.4% and the daily constancy checks 0.8%. The daily constancy checks had a greater number of large deviations than would be expected assuming a normal distribution and were not a good predictor of the need for a recalibration. The fortnightly calibration measurements with a much lower spread give a reliable indication of the need for a recalibration allowing the adoption of a +/- 1% tolerance. Over the period analysed one accelerator (SN42) was relatively stable with the output generally drifting between +/- 1% while the other (SN1027) had a consistent increase in the average output of about 2.5% per year.

Calibration↗

PubMed2001

[Otolith-ocular reflex in linear acceleration of low frequencies].

BACKGROUND: During constant velocity rotation about the earth's vertical axis, eccentric displacement of the head can be used to generate adequate stimulation of the otolith organs. More recently, studies have been performed with a variable radius rotatory chair, which permits a controlled modulation of the centripetal or radial acceleration, to achieve linear acceleration frequencies much lower than with a conventional linear sled. METHODS: In the present study, frequency response and threshold testing was performed using sinusoidal modulation of the chair radius. Three-dimensional eye movements were recorded with binocular video-oculography. RESULTS: The gain (0.09 degree/degree at 0.03 Hz, 0.009 degree/degree at 1 Hz) and phase relationships of the otolith-ocular response (OOR) show a low-pass characteristic over the measured range of 0.03-1.0 Hz. In comparison to the flat response of neurophysiological recordings from the otolith afferent, our findings support the idea that any low-pass filtering of otolith afferents occurs at the level of the vestibular nuclei. CONCLUSION: The OOR could be detected at acceleration levels of 0.03 m/s2, much lower than the subjective threshold for the perception of 0.08 m/s2.

Acceleration↗

PubMed2000

Analysis of the significance of the measurement of acceleration with respect to lateral laxity of the anterior cruciate ligament insufficient knee.

The purpose of this study was to assess dynamically the lateral thrust of anterior cruciate ligament (ACL) insufficient knees, and from the findings determine any relationship between ACL insufficiency and the later development of osteoarthritis (OA). We investigated 80 knees in 40 patients awaiting ACL reconstruction and 25 knees of 25 patients, which had undergone ACL reconstruction. An acceleration sensor was fixed to the anterior tibial tubercle and this 'acted' in two directions--medial lateral and perpendicular. The peak value of the lateral acceleration immediately after heel strike was significantly greater in the ACL insufficient knees when compared to their opposite normal knees. When the periods from injury were compared, the lateral thrust of the injured side after 3 years or more was significantly greater than in the first 3 years. There was no significant difference between the normal knees and the ACL reconstructed knees. The results indicated that the lateral acceleration peak value was significantly greater in the ACL insufficient knees than in their opposite normal knees.

Acceleration↗

PubMed2000

Dynamic visual acuity during linear acceleration along the inter-aural axis.

We investigated visual-vestibular interactions during linear acceleration along the inter-aural axis. Eighteen healthy volunteers and two patients with central neurological diseases were subjected to transaural linear acceleration in the direction of gravity force (frequency: 0.5-1.5 Hz; amplitude: 5 cm). During linear acceleration, eye movements were recorded under three test conditions: eyes closed (EC), while staring at an imaginary target (IT) and during the testing of dynamic visual acuity (DVA). As parameters of evaluation we used the amplitude of horizontal eye movements, phase shift and the decrease of DVA threshold (DVAT). Under all test conditions, eye amplitude increased with rising stimulus frequency and exceeded, especially in the higher frequency range, a hypothetically calculated eye amplitude for smooth pursuit. The combination of a visual and vestibular input (DVA and IT) led to a better compensation (lower phase shift) than under vestibular stimulation alone (EC). Eye movements during low-frequency stimulation depended more on the visual system while responses in the higher frequency range were mainly triggered by the otolith organ. At 1.5 Hz the compensatory function of the visual-vestibular system was limited (rising phase shift) and DVAT decreased even in a significant number of healthy subjects. Patients with diseases of the central nervous system showed a higher phase shift and thus a stronger decrease of DVAT (two levels) already at a stimulus frequency of 1.25 Hz.

Acceleration↗

PubMed2003

Optical acceleration cancellation: a viable interception strategy?

Interception of fly balls requires active locomotion toward the point where catching can take place; as a result, the visual information guiding interception is affected by the catcher's own movement. The only interception theory currently available for a catcher standing in the plane of motion of the ball is Optical Acceleration Cancellation (OAC); in this strategy, the pseudo-optical variable "optical acceleration" (OA), if nonzero, specifies how the catcher should adjust his current velocity. We formulate a precise implementation of OAC where the catcher strives to maintain OA zero at all times and analyze its implications in terms of the catcher's interception behavior for different ball trajectories under air-friction-free, low-friction, and friction-dominated conditions. We conclude that the point in the ball trajectory where first visual contact (FVC) takes place determines to a large extent the ensuing interception behavior of the catcher. Conventional trajectories (FVC slightly above eye level, ball coming toward the catcher) result in fast acceleration to a constant velocity and successful interception. Trajectories with FVC below eye level typically result in unsatisfactory behavior of the catcher, who runs away from rather than toward the point of interception. In addition, ball trajectories are identified for which the OA equals zero even though the catcher is not on an interception course.

Acceleration↗

PubMed1983

Dysrhythmia comparison in apparently healthy males during and after treadmill and acceleration stress testing.

Maximal treadmill exercise stress testing and centrifuge +Gz-acceleration stress testing are both known to be dysrhythmogenic. A comparison of the effects of these two stresses on 60 healthy men was performed. The 60 individuals were divided into three groups of 20 each. One group was made up of healthy volunteer members from the United States Air Force School of Aerospace Medicine acceleration stress panel. The other two groups were asymptomatic USAF aircrewmen undergoing aeromedical evaluation for newly discovered dysrhythmias (dysrhythmia group) and for other aeromedical abnormalities (nondysrhythmia group). The effect of these two stresses on the poststress cardiac rate and rhythm were also evaluated by means of 24-hour Holter monitoring. Both stresses were observed to induce dysrhythmias with approximately the same frequency in the two patient groups; but, with the panel members who experienced higher +Gz stress, the centrifuge stress induced more dysrhythmias than did treadmill exercise stress. The stress-induced changes were limited to the period of stress and did not significantly affect cardiac rate or rhythm in the poststress 24-hour period. Certain dysrhythmias were more commonly associated with centrifuge stress. Centrifuge acceleration stress testing apparently is as safe as maximal treadmill exercise testing. For USAF high-performance fighter pilots who are routinely exposed to repeated high sustained +Gz stress during aerial combat, it is imperative to assure that they are not predisposed to +Gz-induced dysrhythmias which could cause sudden inflight incapacitation. Centrifuge stress testing is therefore a valuable tool in the aeromedical evaluation of these aircrewmen.

Acceleration↗

PubMed1978

Human tolerance to impact acceleration.

Tolerance to brief impact is related to the imposed velocity change, whilst in longer impacts it is the level of acceleration which is critical. This behaviour results from the dynamic characteristics of the body which, for practical purposes, can be represented as a simple mass spring system. For any given acceleration vector, and for any given system of body restraint, whole body (primary) tolerance can be defined by two parameters--a critical velocity change and a critical plateau acceleration level. Appropriate figures are given for 14 different posture and restraint conditions. It is stressed that these are best estimates (or in some cases, best guesses) and that secondary or tertiary mechanisms of injury, in particular head strikes, must not be ignored in any real-life conditions of impact.

Acceleration↗

PubMed1984

Tandem Van de Graaff accelerator production of positron labeled radiopharmaceuticals for routine clinical use.

This paper describes a facility to produce positron labeled radiopharmaceuticals with a tandem Van de Graaff accelerator. 11C labeled carbon monoxide (11CO), 15O labeled H2O (H2 15O) and 18F labeled 2-deoxy-2-fluoro-D-glucose ([18F]2FDG), were chosen so that physiological measurements of cerebral blood volume, cerebral blood flow, and the cerebral metabolic rate for glucose could be made routinely in our PET center. This facility uses a tandem Van de Graaff accelerator which is relatively remote from the clinical area. Measurements of radionuclide yield and beam penetration showed that it was feasible to deliver sufficient amounts of radioactivity for the measurements. Both 11CO and H2 15O presented significant delivery problems due to their shorter half-lives. For H2 15O a continuous delivery system for water vapour and an infusion system for the administration of H2 15O in saline were designed and constructed. 11CO and [18F]2FDG were hand carried. This facility has demonstrated that a tandem Van de Graaff accelerator can routinely supply a PET center with adequate quantities of these three radiopharmaceuticals.

Carbon Monoxide↗

PubMed1994

Particulate suspension model for blood flow under external body acceleration.

A mathematical model has been developed to investigate the influence of externally imposed periodic body acceleration on blood flow in aorta and arteriole. The rheological properties of blood has been represented by regarding the blood as a two-phase Newtonian fluid, that is, a suspension of cells in plasma. An exact analytical solution of coupled differential equations, describing the flow of a particle-fluid suspension, is obtained using the Laplace transforms technique. The effects of body acceleration and blood cells concentration on velocity, flow rate, acceleration and shear rates are computed and displayed graphically.

Acceleration↗

PubMed1991

Combining position and acceleration measurements for joint force estimation.

The calculation of joint forces in biomechanics is usually based on the measurements of the kinematics of a given body segment, the estimation of the inertial properties of that segment and the solution of the 'inverse dynamics problem'. Such a process results in estimates of the joint forces and moments needed to sustain the monitored motion. This paper presents a new approach that combines position and acceleration measurements for the purpose of deriving high-quality joint force estimates. An experimental system that is based on an instrumented compound pendulum was designed and tested. The joint forces necessary to maintain a swinging motion of the pendulum were measured by an array of strain gauges, and were compared to the forces estimated by the integrated kinematic segment that measured the position and acceleration of the pendulum. The joint force measurements were also compared to the force estimates that were based on the calculated segmental acceleration generated by the differentiation of the segmental position alone. The results show a high degree of correlation between the forces estimated by the integrated segment and those measured by the strain gauges. The force estimates based on the position measurements alone were less accurate and noisier. The application of the integrated segment to the study of human kinetics is discussed and illustrated by the ankle and knee forces during slow walking. The results suggest that the use of accelerometers is necessary for the estimation of transients and high-frequency components of joint forces.

Acceleration↗

PubMed1988

Concussion. Acceleration limits causing concussion.

Among the many features common to all species of the animal kingdom is the transient loss of function of the nervous system as the result of a jarring blow, a phenomenon known as concussion. Understanding of concussion has been hampered by the lack of a uniform definition, with many authors including cases with gross, irreversible changes. The phenomenon occurs only with a blow that significantly accelerates and thus is best defined as "a transient disturbance of neuronal function as a result of acceleration." There must be a threshold beneath which no loss of function occurs and a ceiling beyond which changes are not reversible. Experiments with nonanesthetized frogs revealed that at 33 g only the occasional frog would be stunned. From 50 to 230 g, consciousness was always lost but rapidly regained and retained, while beyond, the loss was not always reversible. The time of functional loss was increasingly proportional to acceleration.

Acceleration↗