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PubMedDate not supplied

[Physical and psychogenic effects of impact acceleration on the operator's functioning in the tracking system].

It has been shown experimentally that simulated impact acceleration of 10 to 16 G may have a distinct psychogenic effect, which aggravates the action of the physical factor per se and, consequently, deteriorates the quality of operator's functions in the tracking system. Conversely, this exposure has a training effect and accelerates the development of adaptive and protective mechanisms which increase acceleration resistance of subjects, depending on their psychophysiological characteristics.

Acceleration↗

PubMed1989

[Adaptation to low intensity positive radial acceleration during early ontogenesis].

In 5, 12, and 25 day old laboratory rats of our own breeding LD50 for positive radial acceleration of the intensity of 5 g, 7.5 g and 10 g was established. Resistance was found to decrease with age. All animals exhibited full adaptation on repeated exposure to acceleration of 5 g or 7.5 g, and even 10 g over a period corresponding to 20% duration of the lethal dose for the initial age applied 3 times a day in 3 hour intervals. The resistance of the animals to oxygen deficiency was significantly increased as demonstrated by the survival of all animals 3 hours after their exposure to 10 g acceleration in a dose lethal for the given age. Adaptation is presumed to occur at tissue level.

Acceleration↗

PubMed1988

A near-infrared spectrophotometric method for studying brain O2 sufficiency in man during +Gz acceleration.

A technique for the noninvasive monitoring of cerebral oxygen status was evaluated on volunteer subjects on the USAF School of Aerospace Medicine centrifuge. By using multiwavelength near-infrared spectrophotometry, the instrumentation measured changes in the quantities of reduced and oxygenated hemoglobin (and their sum, an indicator of cerebral blood volume), and the quantity of oxidized cytochrome c oxidase within the forebrain. Tests used acceleration of up to 9 G with onset rates from 0.1 to 5.0 G.s-1, anti-G suits and straining maneuvers, and hyperoxic and hypoxic breathing mixtures. In general, +Gz acceleration produced a fall in blood volume within the cerebral microcirculation with a relative increase in the content of reduced hemoglobin and a tendency towards reduction of cytochrome c oxidase. These findings are discussed in relation to accepted changes in arterial blood pressure, cerebral blood flow, and arterial oxygen saturation caused by acceleration exposure.

Acceleration↗

PubMedDate not supplied

[Management of electron accelerators for radiotherapy. Data as of 31 December 1984].

Several italian radiotherapeutic centers have supplied the data analysed, regarding problems connected with the management of electron accelerators in the years 1982-1983-1984. The data concern 27 out of the 35 accelerators settled in Italy. The average cost of purchase has proved to be of 940 M pounds with an expense of annual allowance of 94 M pounds. We have then analysed the incidences of the allowance of the purchase expenditure of the machine (23%), the allowance of the expenses for the construction of the bunker (22%), the expenses of maintenance of the machine (5%), the cost of the staff (48%) and the cost of the power supply (2%) on the management costs (about pounds 820.000 per each handled patient). The duration of the various phases of the machinery installment, from the purchase to the beginning of the treatment, the charge of work supported in the three considered years, the daily use of the machinery and the problems deriving from days of time out of services due to failures or to periodical maintenance have then been studied. The analysis of the average values of the parameters studied and of the range of their variability allows us to find out the sector in which it is possible, also at present, to intervene in order to ameliorate the employment of a linear accelerator, regarding the costs and the performance.

Cost-Benefit Analysis↗

PubMedDate not supplied

[Tolerance of +Gz acceleration in pilots with health problems].

Fighter pilots with health abnormalities were examined for their tolerance to +Gz acceleration. It was found that pilots with psychoneurological disorders and cardiac arrhythmias showed a lower acceleration tolerance. Pilots with arterial hypertension displayed a markedly higher tolerance as compared to the average pilot population. Other health disturbances produced no effect on +Gz acceleration tolerance.

Acceleration↗

PubMed1987

Induction and prevention of acceleration atelectasis.

Acceleration atelectasis is the absorptional collapse of alveoli in the dependent lung due to increased accelerative forces. It is exacerbated by breathing 100% oxygen and, during +Gz exposure, by the use of an anti-G suit. Experiments were conducted on 12 subjects using simulated aerial combat maneuvers (SACM) with G profiles having peak exposures of either 4.5 G or 9 G. Decreases in vital capacity (VC) measurements were used as quantification of atelectasis, two types of reduction being identified and described. Labile reductions in VC were readily restored by a deep breath or cough. Such reduction approximated 28% following the 4.5-G SACM and 25% following the 9-G SACM. More persistent (so called) stable reductions were of lesser degree, values of -20% being seen following both 9 G and 4.5 G maneuvers. Acceleration atelectasis causes symptoms of chest pain, coughing, and shortness of breath. Subjective ratings of the severity of these symptoms were obtained from the subjects, and these were much greater following the 4.5-G SACM exposures than after the 9-G runs. Acceleration atelectasis was reduced by dilution of the inspired oxygen concentration by argon and nitrogen (evaluated at 95, 82.5, 70, 50, and 20% oxygen); the addition of unassisted positive pressure at 30 mm Hg (4 kPa) to the breathing mask; or the performance of the anti-G straining maneuver (AGSM).

Acceleration↗

PubMed1987

Heart rate responses to moderate linear body accelerations: clinical implications in aeromedical evacuation.

Linear accelerations during take-off and landing were measured in both civilian and military aircraft usually involved in aeromedical evacuations in Denmark. Accelerations of similar durations and magnitudes were induced in six healthy subjects transported in an ambulance in different supine positions. Heart rate responses recorded depended significantly on the position of the subject. It was concluded that seriously ill patients must be positioned transversely to the axis of acceleration during aeromedical evacuation.

Acceleration↗

PubMedDate not supplied

[Adaptive and cumulative effects in the dog exposed to routine +GZ acceleration].

The development of adaptive and cumulative effects was investigated in 13 noninbred dogs regularly exposed to +GZ acceleration: Group I dogs were exposed 3 to 4 times a week for 2 months and Group 11 dogs were exposed 1 to 2 times a week for 5 months. The tolerance threshold was evaluated with respect to ECG abnormalities. The study of circulation reactions and acceleration tolerance threshold revealed the predominant development of adaptive changes that were more distinct in Group 11 dogs. Cumulative effects in the form of functional disorders of pulmonary vessels occurred in all experimental dogs but less frequently in Group II dogs. Morphological lesions of the lung tissue developed in Group I animals after 2 to 3 exposures and in Group II animals after 2 to 3 months, the incidence rate being lower in those latter. These findings suggest that adaptive and cumulative effects in response to regular exposures to threshold +GZ acceleration develop more or less in parallel.

Acceleration↗

PubMedDate not supplied

[Oxygen balance and regional blood flow in the gingival mucosa during exposure to head-pelvis (+Gz) acceleration].

The information content of a new contact rheopolarographic procedure used to determine the oxygen balance and regional circulation of the gingival mucosa was measured, bearing in mind the applicability of the procedure as an objective index of human tolerance to +Gz acceleration. It was found that the parameters of the oxygen balance and regional circulation of the gingival mucosa were well correlated with blood pressure in the floor of the auricle. In contrast to the traditional methods for assessing tolerance to acceleration, the new procedure provides information about the health condition of the centrifuged subjects on a continuous basis. Variations in the oxygen balance and regional circulation of the gingival mucosa helped to identify compensatory reactions of the cardiovascular system in response to +Gz acceleration.

Acceleration↗

PubMedDate not supplied

[Animal tolerance to exposure to repeated impact acceleration].

The harmful effect of repeated impact accelerations on the animal body was studied. The dogs were exposed to accelerations one, three, five or ten times. The experiments showed a cumulative effect of repeated exposures which included a consistent increase of changes in the physiological and morphological parameters. Tolerance to repeated accelerations increased due to better restraint of the animals.

Acceleration↗

PubMed1978

Method to quantify ride comfort and allowable accelerations.

When the motion of a vehicle includes "shocks" or impulsive velocity changes, R.M.S. acceleration has no relation to crew comfort or injury. Existing (R.M.S. G) methods of ride assessment can show lethal accelerations as being perfectly safe, and vice versa. It follows that R.M.S. acceleration is not meaningful for nonsinusoidal "random" vibration either. This paper presents a method of evading the difficulty, using fairly well established biodynamic modeling techniques, and an extension of Allen's "shock tolerance" concept. Among other advantages, the method "automates" the assessment of ride quality so that personal judgments are not involved and the relative ride quality of different vehicles can be placed on a quantitative basis. Since this work was inspired by the problem of Navy crew tolerance to the motions of high-speed ships, the discussion is in those terms. Also, the proposed criteria should probably be scaled down for more general populations.

Acceleration↗

PubMed1978

Mathematical model of the cardiovascular system under acceleration stress.

The pooling of blood in the lower part of the human body when it is subjected to longitudinal +Gz acceleration is one of the major reasons for cardiac insufficiency and the consequent impairment of certain important physiological functions. Headache, abdominal pain, change in heart rate, chest pain, impairment of vision, and hemorrhage are some of the manifestations of acceleration trauma. To predict the effects of time-dependent accelerations on the circulation, a mathematical model independent of assumptions extrapolated from normal G conditions must be considered. The model in the present study consists of a closed-loop hydrodynamic system comprising a heart pump, elastic tubes to represent the large arteries and veins, and a baroreceptor feedback mechanism to help to overcome cardiac insufficiency. The governing equations consist of the Navier-Stokes equations for fluid motion in the blood vessels, and equations of motion for time-dependent blood vessel deformation and ventricular contraction derived from nonlinear elasticity theory. In a numerical example, an experimentally measured deceleration profile is used and the calculated aortic flow is compared with the experimental values.

Acceleration↗

PubMed1983

[Dosimetric characteristics of the bremsstrahlung beam from the LUE-15M medical linear electron accelerator].

The paper presents methods and results of a study of radiation-physical characteristics of inhibitory radiation beam with the Grenz energy of 15MeV generated by an electron linear accelerator LUE-15M. Special emphasis is laid on primary dosimetric information used for the planning of radiotherapy: depth doses, beam profiles, dose functions of a collimated beam. It has been shown that in general the accelerator meets the requirements of the International Electrotechnical Commission. General error in the focal absorbed dose at the expense of variable parameters of the accelerator was evaluated. It does not exceed +/- 3.5%.

Particle Accelerators↗

PubMedDate not supplied

[Effect of water-salt dietary supplements on tolerance to head-pelvis acceleration after 7 days of "dry" immersion and during normal motor activity].

The effect of water-salt supplements as an agent increasing human tolerance to head-to-feet acceleration with a slow onset was examined. The test subjects were rotated in a 7.25 m arm centrifuge after 7-day dry immersion or normal motor activity. The water-salt supplements were given at a dose of 0.15 g NaCl and 18 ml water per kg body weight (with the total daily dose consumed in four fractions). During immersion fluid retention was significantly higher than during normal activity (818 +/- 139.7 ml versus 478 +/- 69 ml). Water-salt supplements consumed produced a positive effect on tolerance to head-to-feet acceleration. During centrifugation after water-salt supplementation the physiological responses were less strained. Water-salt supplements taken on the last immersion day increased the tolerance level as compared to the control. The amount of the fluid retained in the body was found to be inversely proportional to the tolerance level. It is concluded that water-salt supplements may be recommended to increase tolerance to head-to-feet acceleration in aerospace medicine.

Acceleration↗

PubMedDate not supplied

[The antigravity suit, chamberless type, as a means of increasing orthostatic tolerance after water immersion hypokinesis and acceleration].

Orthostatic tolerance after 7-day dry immersion and head-to-feet acceleration was investigated on test subjects with and without an antigravity suit of bladderless type. With the suit on, the 20 min tilt test at 70 degrees prior to immersion induced less marked changes than without the suit. When the suit was on, cardiovascular reactions to tilt tests after immersion and acceleration improved. The maximum heart rate decreased from 135 +/- 4 to 101 +/- 5 beats/min (p less than 0.01), minimum stroke volume increased from 29 +/- 2 to 41 +/- 3 ml (p less than 0.05), and pulse pressure grew. Thus, an antigravity suit may help increase initial orthostatic tolerance and maintain it after the combined effect of simulated hypogravity and acceleration.

Acceleration↗

PubMed1984

The effects of acceleration forces on night vision.

The effects of Gy and Gz acceleration forces on cone-type mesopic vision threshold values are examined. An experiment has been conducted on the Dynamic Environment Simulator, a three-axis human centrifuge, to reproduce an acceleration environment in a simulated night-flight combat situation. Acceleration environments studied were levels of +1 Gz, + 1Gy, +1.4 Gz, +2 Gz, +3 Gz, and +2 Gy in combination with +1 Gz. A visual task was performed which determined 20/50 visual acuity illumination threshold values. Physiological parameters recorded were arterial oxygen saturation (SaO2) by ear oximetry, heart rate, and visual acuity threshold values. There were 10 male subjects, all members of the United States Air Force. Their ages ranged from 25-39 years (mean +/- S.D., 29.1 +/- 4.3). Results were zero means obtained by self-pairing with +1 Gz controls. Analysis was done by self-pairing, two-tailed t test. Results showed no significant shift in luminance threshold values at +1 Gy or +1.4 Gz, and significant increases in luminance thresholds at the 0.01 level for +2 Gz, +3 Gz, and +2 Gy in combination with +1 Gz.

Acceleration↗

PubMedDate not supplied

[Statocyst regulation of the heart and statokinetic reflexes in the crab, Hemigrapsus sanguineus, during linear acceleration].

In experiments on the shore crab H. sanguineus studies have been made of the effect of variable longitudinal acceleration during swinging (for 15--30 min) upon cardiac activity and gravitational reflexes. High sensitivity of gravitational receptors of the canal statocyst to the effect of acceleration was demonstrated. Removal of the statocysts increases the frequency and amplitude of cardiac contractions as revealed by ECG recording. Changes in stato-kinetic coordinations cause both the disorder of overturning reactions and the disorder of reciprocal inhibition in antagonistic muscles of the dactylopodite. Statocyst regulation of skeletal muscles and heart is presumably realised via contralateral inhibitory canal which is sensitive to linear accelerations.

Acceleration↗

PubMedDate not supplied

[Changes in the electrocerebellogram and autonomic responses of mice to acceleration].

Nembutal narcotized white rats were exposed to + GZ accelerations of 10 g for 5 min. Changes in the frequency spectrum of the bioelectric spontaneous activity of the cerebellar cortex, respiration rate and heart rate were examined. A correlation between bioelectric reactions of the cerebellum and adaptive-compensatory responses of the cardiovascular and respiratory systems was established. The rats that showed no electrographic reactions of awakening at the onset of acceleration displayed a reduced resistance to acceleration.

Acceleration↗