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PubMed1997

The acceleration-velocity relationship: identification of normal and spastic upper extremity movement.

This study defines and evaluates a non-invasive technique that will identify a spasm as an uncommanded movement (U) from a normally commanded movement (C). Upper arm function during a tracking task is recognized as non-linear and characterized by a phase plane with acceleration (second derivative of stick position) plotted on the ordinate and velocity (first derivative of stick position) plotted on the abscissa. An acceleration time constant (tau A) is defined as (VA/AM) where AM is the maximal acceleration and VA is the velocity at AM. A deceleration time constant (tau D) is also defined as (VD/DM), where DM is the maximal deceleration and VD is the velocity at DM. Ten spastic subjects (S) were categorized into three groups of mildly spastic (M), intermediately spastic (I), and highly spastic (H) which were compared to five normal subjects (N). The results indicate that for C and U, both VA and AM are significantly lower for S at all three levels as compared to N. tau A is significantly higher for M and I as compared to N. Both VD and tau D are significantly higher for S at all three levels when compared to N. DM is significantly lower for S at all three levels of S when compared to N. Finally, AM and tau A significantly differentiate C vs U for M. VA and tau D significantly differentiate for I. VA, AM as well as DM, tau D significantly differentiate for H. The physical significance of these results is discussed with respect to the time course and magnitude of net muscle moment (M), and the reversal of the agonist-antagonist relationship during the acceleration and deceleration phases. Finally, a spasm identification algorithm is proposed.

Acceleration↗

PubMed2002

Reduced oxygen release from erythrocytes by the acceleration-induced flow shift, observed in an oxygen-permeable narrow tube.

The oxygen release from flowing erythrocytes under accelerational force (0-4 g) was examined using an oxygen-permeable, fluorinated ethylenepropylene copolymer tube (25 microm in inner diameter). The narrow tube was fixed vertically on the rotating disk of a new centrifuge apparatus, and erythrocyte suspension was perfused in the direction of Earth gravity. The accelerational force was applied perpendicularly to the flow direction of cells by centrifugation. The microscopic images of the flowing cells obtained at five different wavelengths were analyzed, and marginal cell-free layer and oxygen saturation of the cells were measured. By lowering oxygen tension around the narrow tube, erythrocytes were deoxygenated in proportion to their traveling distance, and the deoxygenation was enhanced with decreasing flow velocity and hematocrit. With increase of the g-value, the shift of flowing erythrocyte column to the centrifugal side was increased, the column was compressed, and the oxygen release from the cells was suppressed. Qualitatively, similar results were obtained by inducing erythrocyte aggregation with Dextran T-70 (MW = 70,400), without accelerational force. These results conclude that both the accumulation of erythrocytes under accelerational force and the enhancement of erythrocyte aggregation by macromolecules lead to the reduction of oxygen release from the flowing cells.

Acceleration↗

PubMed1999

Impact of the surface slipperiness of grasped objects on their subsequent acceleration.

Seven subjects were asked to reach and grasp an object between the thumb and index finger, lift it about 30 cm high and 25 cm forward from one table to another, at their preferred speed. The perpendicular grip force and the tangential load force applied to the contact surface were digitized at 500 Hz and stored on a laboratory computer. The trajectory of the wrist and of the object was recorded using four infrared cameras tracking the movement of reflective markers attached to the distal styloid process of the radius and on the top of the object. The aim of this study was to demonstrate the influence of low friction (i.e. surface slipperiness) on the acceleration of the wrist. Friction was reduced by coating the smooth brass grasping surface with talc. The seven subjects had skin to surface coefficients of friction which ranged from 0.52-1.18 for dry brass and 0.24 0.34 for talc-coated brass. Two weights (418 and 1070 g) were used with each surface. The results indicated that with the slippery surface the necessary higher grip force/load force ratio was produced by an increase in the grip force and by a decrease in the wrist acceleration and a consequent reduction in the load force. This strategy was observed for both weights over a range of grip strengths between 21-98% of the individual's maximum voluntary contraction (MVC). This implies that even with adequate grip force reserves the reduction in acceleration is an acceptable and probable alternative solution to the force control problem. Our results also suggested that the loading rate and the object acceleration were planned and controlled together which emphasizes the role played by a predictive mechanism in organizing the kinematics of movements involving hand-held objects. This study shows that friction of the grasping surface not only affects the prehensile force dynamics, but it also influences the kinematics of the entire upper limb.

Acceleration↗

PubMed2002

Action-perception dissociation in response to target acceleration.

The purpose of this study was to investigate whether information about the acceleration characteristics of a moving target can be used for both action and perception. Also of interest was whether prior movement experience altered perceptual judgements. Participants manually intercepted targets moving with various acceleration, velocity and movement time characteristics. They also made perceptual judgements about the acceleration characteristics of these targets either with or without prior manual interception experience. Results showed that while aiming kinematics were sensitive to the acceleration characteristics of the target, participants were only able to perceptually discriminate the velocity characteristics of target motion, even after performing interceptive actions to the same targets. These results are discussed in terms of a two channel (action-perception) model of visuomotor control.

Acceleration↗

PubMed2001

Comparison of quality assurance for performance and safety characteristics of the facility for Boron Neutron Capture therapy in Petten/NL with medical electron accelerators.

BACKGROUND AND PURPOSE: The European Council Directive on health protection 97/43/EURATOM requires radiotherapy quality assurance programmes for performance and safety characteristics including acceptance and repeated tests. For Boron Neutron Capture therapy (BNCT) at the High Flux Reactor (HFR) in Petten/NL such a programme has been developed on the basis of IEC publications for medical electron accelerators. RESULTS: The fundamental differences of clinical dosimetry for medical electron accelerators and BNCT are presented and the order of magnitude of dose components and their stability and that of the main other influencing parameter 10B concentration for BNCT patient treatments. A comparison is given for requirements for accelerators and BNCT units indicating items which are not transferable, equal or additional. Preliminary results of in vivo measurements done with a set of 55Mn, 63Cu and 197Au activation foils for all single fields for the four fractions at all 15 treated patients show with < +/- 4% up to now a worse reproducibility than the used dose monitoring systems (+/- 1.5%) caused by influence of hair position on the foil-skull distance. CONCLUSIONS: Despite the more complex clinical dosimetry (because of four relevant dose components, partly of different linear energy transfer (LET)) BNCT can be regulated following the principles of quality assurance procedures for therapy with medical electron accelerators. The reproducibility of applied neutron fluence (proportional to absorbed doses) and the main safety aspects are equal for all teletherapy methods including BNCT.

Acceleration↗

PubMed1998

Consistency in quality control programmes for electron accelerators in radiotherapy centres.

BACKGROUND AND PURPOSE: To gain insight into the current practice of quality control (QC) of medical electron accelerators and to reduce possible variations in test frequencies and test procedures. MATERIALS AND METHODS: An extensive questionnaire on QC procedures of medical electron accelerators was distributed and completed by all (21) radiotherapy institutions in The Netherlands. The questions were related to safety systems, mechanical parameters, beam profiles, beam energy, absolute dosimetry, wedge filters, the dose monitor system and radiation leakage. The data of the questionnaire were compared with recommendations given in national and international reports on QC of electron accelerators. RESULTS: Large variations in time spent on QC exist, especially for accelerators having dual energy photon beams and several electron beam energies. This diversity is mainly due to differences in philosophy with regard to QC and the differences in resources and machine time available. Furthermore, large variations in test frequencies and test methodologies were observed. The staffing level involved in the QC measurements was evaluated and compared with recent recommendations provided by EFOMP-ESTRO. CONCLUSIONS: From these recommendations and the results of the questionnaire, a set of minimum guidelines for a QC programme could be formulated and implemented in all radiotherapy institutions in The Netherlands.

Guidelines as Topic↗

PubMed1980

Responses to step and repeated impulse accelerations in second order vestibular neurons of the cat.

The characteristics of response of 98 vestibular nuclei neurons were investigated in the barbiturate anesthetized cat. All type I and type II neurons (tonic and kinetic) responded to stimulation of the horizontal canals with step and impulse accelerations. Seventy-seven (79 per cent) neurons of all types demonstrated adaptation, while the remaining 21 (21 per cent) neurons showed either reverse adaptation or no adaptation. When the interval between impulses with impulse accelerations reached a critical minimum, the averaged response was remarkably like the response to step acceleration, including the rate of adaptation. A previously undescribed response decline to repetitive impulse acceleration was seen, which, while sharing some characteristics with habituation, appears to be more closely related to adaptation. Furthermore, the data suggest that adaptation seen at the vestibular nuclear level is more likely a central phenomenon rather than a peripheral one.

Acceleration↗

PubMed1999

Muscle sympathetic nerve response to vestibular stimulation by sinusoidal linear acceleration in humans.

To clarify the effects of natural otolith stimulation on muscle sympathetic nerve activity (MSNA) in humans, eight male volunteers were seated in a linear accelerator (sled) during the recording of MSNA from the tibial nerve with microneurography, and also the recording of electrocardiogram, blood pressure measured with a Finapres device and thoracic impedance during movement. Sinusoidal linear acceleration with peak values of +/-0.10, 0.15 and 0.20 Gx were applied to the sitting subjects in the anteroposterior direction. Both the total activity and the burst rate of MSNA decreased during the sinusoidal linear acceleration, whereas the average heart rate, thoracic impedance and mean arterial pressure did not change significantly. These results suggest that moderate sinusoidal linear acceleration in the anteroposterior direction may suppress MSNA in humans.

Acceleration↗

PubMed2003

A noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator-based stereotactic radiotherapy of uveal melanoma.

PURPOSE: To introduce a noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator-based stereotactic radiotherapy for uveal melanoma. METHODS AND MATERIALS: At the Department of Radiotherapy and Radiobiology, University of Vienna, stereotactic radiotherapy is offered to patients with uveal melanoma considered unsuitable for (106)Ru brachytherapy or local resection. For the present feasibility study, 8 patients were carefully selected according to their ability to fixate a small light source with the diseased eye and whether they had a rather small head to meet the limited geometric space available. A polymethyl methacrylate tube was attached to a stereotactic mask system in craniocaudal orientation supporting a 45 degrees mirror, which was placed in front of the diseased eye. At the other end of the tube, the patient was given a small fixation light, and a small camera was positioned beneath, which was shielded for use during MRI. A computer interface calculated and visualized the spatial difference of the actual and a given reference pupil position, which was defined before CT scanning, during the MRI sequences, and during treatment delivery at the linear accelerator. RESULTS: The described system can be attached to a conventional stereotactic mask system with minor modifications. Because of the large distance between the eye and the fixation light, the optical fixation system was well tolerated by all patients, and a stable position of the eye was obtained. The camera system can be used during CT and MRI without interference. Absorption of the 6-MV photon beam by the mirror and the polymethyl methacrylate tube was negligible. The computer interface designed to determine the pupil position uses an image-processing algorithm that correlates a template of the reference image with the actual image of the eye. Provided sufficient illumination of the pupil, the correlation function showed a pronounced minimum at the reference position. The precision of the algorithm was tested by phantom measurements. For a given 1 mm or 2 mm displacement, the interface reported a mean shift of 0.96 +/- 0.18 mm or 2.07 +/- 0.11 mm, respectively. CONCLUSION: The results of this study demonstrated the feasibility of a new optical fixation system for linear accelerator-based stereotaxis. The artifact-free application of the camera system during image acquisition and irradiation and the use of the computer interface, which automatically monitored eye movements with submillimeter precision, provided large improvements compared with existing techniques. Given well-defined interruption criteria and accelerated image processing, the described system has a high potential to perform automatically gated treatment beam delivery in the near future.

Humans↗

PubMed2003

Acceleration patterns of the head and pelvis when walking on level and irregular surfaces.

The aim of this study was to evaluate acceleration patterns at the head and pelvis while subjects walked on a level and an irregular walking surface, to develop an understanding of how the postural control system responds to challenging walking conditions. Thirty young, healthy subjects walked on a level corridor and on artificial grass underlain with foam and wooden blocks placed in an arbitrary manner. Temporo-spatial gait parameters and acceleration patterns at the head and pelvis were measured. The results revealed that when walking on the irregular surface, subjects were able to maintain their velocity, but adopted a slower and more variable cadence and a significantly longer stride length. The magnitude of pelvis accelerations increased, however head accelerations were not affected by the walking surface. When considered as an overall pattern of movement, these findings suggest that one of the primary objectives of the postural control system when walking on irregular surfaces is head control, and that subjects adapt their stepping pattern on irregular surfaces to ensure that the head remains stable.

Acceleration↗

PubMed2001

The feasibility of accelerator-based in vivo neutron activation analysis of nitrogen.

The feasibility of accelerator-based in vivo neutron activation analysis of nitrogen has been investigated. It was found that a moderated neutron flux from approximately 10 microA of 2.5 MeV protons on a 9Be target performed as well as, and possibly slightly better than the existing isotope-based approach in terms of net counts per unit subject dose. Such a system may be an attractive alternative to the widespread use of (238,239)Pu/Be or 252Cf neutron sources, since there is more flexibility in the energy spectrum generated by accelerator-based neutron sources. From a radiation safety standpoint, accelerators have the advantage in that they only produce radiation when in operation. Furthermore, an accelerator beam can be pulsed, to reduce background detected in the prompt-gamma measurement, and such a device has a wide range of additional biological and medical applications.

Body Composition↗

PubMed2000

Measurements of acceleration during videofluorographic evaluation of dysphagic patients.

Accelerometry represents a noninvasive technique for the assessment of the swallowing mechanism. However, the underlying physiological events that give rise to the acceleration signal are poorly understood. In the present study, the acceleration signal was measured simultaneously during videofluorography examination. Preliminary results revealed that the signal occurred during laryngeal elevation and the magnitude of acceleration correlated well with the laryngeal displacement. Acceleration measurements present a potentially useful noninvasive tool.

Acceleration↗

PubMed2004

Rotational acceleration measurements--evaluating helmet protection.

PURPOSE: Current helmet testing standards do not address the rotational components of an impact to the head. We describe a new testing paradigm used to measure the rotational acceleration of a headform and a protective helmet following an impact to the head in the horizontal plane. This impact simulation allows for the testing of currently available head protection devices in conditions thought to be important for the generation of cerebral concussion. The degree to which a particular helmet dampens rotational acceleration, and thus protects against concussion, can be assessed. METHODS: Our testing device consists of a pneumatic piston that provides a measured impact to a standard headform. Four different helmets were tested using the described paradigm. RESULTS: Acceleration curves for each helmet and the corresponding headform are presented. CONCLUSIONS: Clear differences in rotational acceleration were demonstrated. Possible avenues of further investigation are discussed.

Acceleration↗

PubMed2001

The use of the Australian Basic Treatment Equivalent (BTE) workload measure for linear accelerators in Canada.

The Inter Society of Radiation Oncologists of North America (ISRON) workload standard for linear accelerators is the one most widely used; it regards the treatment of 250 or more patients per year as an acceptable limit. Nevertheless, there is concern that this standard does not represent the current workload of linear accelerators, given that the complexity of techniques and equipment has increased significantly since the ISRON model was developed in the late 1980s. Delaney et al. recently validated a workload indicator for Australian (AUS) centres, known as the basic treatment equivalent (BTE). They showed that this was a better predictor of workload and that there was less variation between centres using this model than there would have been by using fields/hour. This centre attempted to validate this model for use in a Canadian centre, by collecting treatment data on all linear accelerator-treated patients during February 1998. The linear accelerators at this centre delivered 2,295 fractions (6,928 fields) in 662 hours during February 1998. When 15 minutes was used as a denominator, the BTE model functioned as a better workload indicator than simple measures such as fields/hour. It also had better performance in reducing variability between machines. A BTE of 3,403 was calculated for these machines. The mean value for fields/hour, BTE/hour and BTE/fraction for this centre fell within the range of values quoted by AUS centres. The BTE/fraction value for this centre was relatively high compared with the AUS mean, indicating this centre's reliance on the use of a high number of complex techniques. We recommend that the model should be further refined for the Canadian context by developing BTE values with the use of local time and motion studies, including factors such as multileaf collimators and enhanced dynamic wedges.

Australia↗

PubMed1976

[Attentions, sensumotoric coordination, and angular acceleration threshold under the influence of small doses of alcohol in relation to aspects of personality (author's transl)].

In a parallel cross-over design 22 male students were examined with 0,6 g alcohol per kg of body weight (0,5 o/oo). The dependent variables were attention, sensumotoric coordination angular acceleration threshold, and mood. A number of personality trait factors (FPI, MPI, habit of alcohol and tobacco consumption, body measures) and state factors (subjective state, psychophysiological state) were also measured, others were helf constant (age, sec, intelligence, standardisized breakfest, duration of drinking time, day time, week time). The accelerated concentration of blood alcohol was connected with neuroticism and subjective bad state on day of examination. The accelerated elimination of blood alcohol varried with bad subjective state. Attention, and sensumotoric coordination were significantly (by a BAC of 0,42 o/oo) diminished and the sensitivity of angular acceleration threshold was strongly (by a BAC of 0,30, 0,44, 0,38 and 0,21 o/oo) diminished, connected with a general brightening of mood. Certain personality traits and states may diminish performances with those slight doses of alcohol.

Acceleration↗

PubMed1997

[Maculo-ocular reflex and visual perception during vertical acceleration].

BACKGROUND: We investigated the effect of vertical acceleration upon the otolithic-ocular reflex of 22 healthy people. The study was performed to obtain standard values for subsequent investigations at patients. METHODS: People sitting on a chair were accelerated in the vertical axis with an amplitude of 4 cm and the frequencies of 0.5 Hz, 1 Hz, 1.5 Hz, 2 Hz, 2.5 Hz and 2.7 Hz. The movements of the ocular globe were initially recorded during vertical acceleration with the eyes closed. Then visual acuity was tested during linear acceleration with the eyes open. As parameters of evaluation we used coherence and alteration of the visual acuity. RESULTS: When the frequency was increased while the eyes were closed, coherence increased and the number of people with vertical eye movements increased. Amplitude was observed to increase and a phase shift occurred. A significant value of coherence (> 0.8) was observed at a frequency above 2.5 Hz. During the test of visual acuity, coherence also increased but did not reach quantity we observed initially. A significant loss of visual acuity occurred at a frequency above 2.5 Hz. A phase shift was also observed. The reason for the loss of visual acuity was the increment of amplitude and the phase shift, which had a negative influence on fixation. CONCLUSIONS: In summary, reactions with closed eyes are best tested at frequencies of 2.5 and 2.7 Hz. We recommended frequencies of 1.5 and 2 Hz for testing visual acuity.

Acceleration↗

PubMed1976

The visual perception of accelerated motion.

The present research is an investigation of how changes in the rate of motion are percieved. Five separate experiments were performed with the use of filmed stimulus material and a variety of response measures, including both categorical judgments and reporduction techniques. It was found that (a) the smaller the ratio of terminal to initial velocity, the less frequent the judgments of acceleration or deceleration, (b) deceleration was significantly easier to perceive than acceleration, (c) the perception of acceleration was facilitated when the velocity of a lead-in segment was the same as the velocity at onset of motion, (d) a short tunnel centered in the motion path facilitated the perception of acceleration and deceleration, and (e) instantaneous changes in velocity were much more easily perceived than gradual changes. A one-event model for the perception of motion change in which there is a continuous interplay between earlier, later, and interpolated motion segments is favored over a two-event model in which earlier and later segments of velocity are compared.

Acceleration↗

PubMed2000

Use of accelerometers as an ergonomic assessment method for arm acceleration-a large-scale field trial.

Ergonomists need easy-to-use, quantitative job evaluation methods to assess risk factors for upper extremity work-related musculoskeletal disorders in field-based epidemiology studies. One device that may provide an objective measure of exposure to arm acceleration is a wrist-worn accelerometer or activity monitor. A field trial was conducted to evaluate the performance of a single-axis accelerometer using an industrial population (n=158) known to have diverse upper limb motion characteristics. The second phase of the field trial involved an examination of the relationship between more traditional observation-based ergonomic exposure measures and the monitor output among a group of assembly-line production employees (n=48) performing work tasks with highly stereotypic upper limb motion patterns. As expected, the linear acceleration data obtained from the activity monitor showed statistically significant differences between three occupational groups known observationally to have different upper limb motion requirements. Among the assembly-line production employees who performed different short-cycle assembly work tasks, statistically significant differences were also observed. Several observation-based ergonomic exposure measures were found to explain differences in the acceleration measure among the production employees who performed different jobs: hand and arm motion speed, use of the hand as a hammer, and, negatively, resisting forearm rotation from the torque of a power tool. The activity monitors were found to be easy to use and non-intrusive, and to be able to distinguish arm acceleration among groups with diverse upper limb motion characteristics as well as between different assembly job tasks where arm monitors were performed repeatedly at a fixed rate.

Acceleration↗