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PubMed1976

Human tolerance to acceleration after exposure to weightlessness.

The major role in the genesis of varying human tolerance to decelerations that follow weightlessness is evidently played by hypodynamic and hydrostatic factors. Long disuse of compensatory antigravity mechanisms in weightlessness may bring about their deconditioning and reduction of their functional capabilities, and may finally affect general tolerance of crewmembers to decelerations. Laboratory experiments demonstrated changes in the human tolerance to Gx accelerations of varying duration (from 3 to 100 days) and tested the efficacy of different countermeasures. A decrease in the human tolerance to +Gx is on the average -2.0g. It should be noted that an elongation of simulated weightlessness (from 7 to 100 days) caused no further decrease in the +Gx tolerance. Our investigations helped to assess the threshold of human tolerance to accelerations after an exposure to simulated weightlessness and to delineate the value of real risk. The tolerance limit to +Gx accelerations which followed simulated weightlessness of the above duration ranged from 9.5 to 13.0g, averaging 11.6 +/- 1.6g. The information on the tolerance of Soviet and American astronauts to decelerations shown during re-entry in real space flights give support to the laboratory results and predictions.

Acceleration↗

PubMedDate not supplied

[Human tolerance to +Gz acceleration during heating].

Eighty-six measurements of individual tolerance of 25 healthy test subjects to +Gz accelerations were carried out at two body temperatures. At moderate heating (body temperature 37.5+/-0.2degreesC) acceleration tolerance decreased by 1.4 g (maximally by 3 g) without an antigravity suit and by 0.5 g with an antigravit suit. In case of simulated poor fitting of the suit the tolerance decrease was 1.1 g. At high heating (body temperature 38.0+/-0.2degreesC) the decrease was great (2.1 g). In some cases centrifugation was terminated because of poor tolerance to hyperthermia. The regression analysis suggests that at body temperature of 37.3degreesC the acceleration tolerance decreases in some individuals only and at 37.6degreesC and over it declines in most subjects. The correlation between the level of water losses (0.8--2.4% of body weight) and decline in +Gz tolerance was low (r=0.33) and insignificant. The resulting data allow practical recommendations in relation to acrobatic flights in hot climate.

Acceleration↗

PubMed2002

Treatment of philadelphia chromosome-positive, accelerated-phase chronic myelogenous leukemia with imatinib mesylate.

PURPOSE: Imatinib mesylate, a specific Bcr-Abl tyrosine kinase inhibitor, has shown encouraging activity in chronic myelogenous leukemia (CML). EXPERIMENTAL DESIGN: We treated 237 patients (median age, 50 years; age range, 18-82 years) with Philadelphia chromosome (Ph)-positive accelerated-phase CML with oral imatinib mesylate at daily doses of 400 mg (26 patients) or 600 mg (211 patients) and evaluated response and survival characteristics in univariate and multivariate analyses. RESULTS: Among the 200 patients with accelerated-phase CML for whom follow-up was 3 months or more, rates of complete and partial hematological response were 80% and 10%. Cytogenetic responses were evident in 90 patients [45%; complete response in 47 patients (24%) and partial response (Ph 1-34%) in 21 patients (11%)]. The estimated 18-month survival rate was 73%. The estimated complete hematological response rate at 18 months was 68%; that for cytogenetic response was 82%. In multivariate analyses, a diagnosis-to-treatment interval of 3 years or more, splenomegaly, and peripheral blasts predicted poor major cytogenetic response; age >60 years, marrow basophilia, and clonal evolution predicted poor survival. The 600-mg drug dose was associated with better cytogenetic response and survival in univariate analysis (P < 0.01) but not in multivariate analysis. Landmark analysis showed that achieving a cytogenetic response at 3 months or a major cytogenetic response (Ph < 35%) at 6 months was associated with better long-term survival. Seven of 15 patients who were in a second chronic phase achieved major cytogenetic response. The incidence of severe nonhematological toxic effects was 23%; drug discontinuation for severe toxicity was needed in 3% of patients. CONCLUSIONS: Imatinib mesylate was active against Ph-positive, accelerated-phase CML, and the prognostic factors identified in this study could aid in tailoring treatment strategies to specific risk groups.

Adolescent↗

PubMedDate not supplied

[Tolerance of +Gz accelerations in chronic compensated cardiac muscle disease].

The functional potentialities of the cardiovascular system were investigated during an exposure of people with compensated chronic diseases of the cardiac muscle to acceleration (+Gz). The test subjects were exposed to acceleration of 3 and 5 g for 30 sec with an interval of 5 min. The parameters of hemodynamics, ECG and visual perception were recorded. The systolic blood volume, cardiac output and specific peripheral resistance were derived from the Bremser-Ranke formula. Seventy one subjects with heart diseases and 23 healthy subjects were examined. The subjects with myocardiodystrophy and myocarditic cardiosclerosis (12+/-16) showed a reduced tolerance to accelerations. During an exposure the subjects with atherosclerotic cardiosclerosis showed a higher pressure in vessels of ear conch than the healthy subjects. The myocardiodystrophic subjects frequently (20%) exhibited an inversion of electrocardiographic T2. The subjects with heart diseases (27-33%) showed extrasystolic disturbances. The results may be used in medical expertise of pilots.

Acceleration↗

PubMed2002

Relaxed acceleration tolerance in female pilot trainees.

BACKGROUND: Female pilots now fly many types of aircraft including military fighters capable of maneuvers that produce high, sustained acceleration in the +Gz axis. Although women have participated as subjects in various centrifuge studies, little is known about the acceleration tolerance of female pilots. METHODS: Between April 1995 and December 1997, 17 female pilot trainees were studied at the Institute of Aerospace Medicine, Bangalore, India. The subjects were 23.2 +/- 1.4 yr old and led physically active lives. Their relaxed +Gz tolerance limits (defined as peripheral light loss) were tested using the High G and Disorientation Demonstrator. The protocol included a series of rapid onset runs (RORs) to tolerance followed by a single gradual onset run (GOR) to tolerance. RESULTS: The mean ROR tolerance was 4.2 +/- 0.4 G. The mean GOR tolerance was 5.2 +/- 0.6 G. Three of the subjects were unable to complete the GOR due to severe nausea. Two women reported breast discomfort at levels of 3.5 G and beyond. No other problems were reported. CONCLUSIONS: The acceleration tolerances for the female pilot trainees were comparable to those for male pilots previously studied in our laboratory.

Acceleration↗

PubMed2002

Linear accelerator radiosurgery for meningiomas in and around the cavernous sinus.

OBJECTIVE: A retrospective study to evaluate the efficacy and side effects of linear accelerator radiosurgery in the treatment of cavernous sinus meningiomas. METHODS: Between 1993 and 2001, 42 patients with meningiomas involving the cavernous sinus underwent linear accelerator radiosurgery at our institution. A mean radiation dose of 14 Gy was delivered to the tumor margin. The median tumor volume was 8.2 cm3 (mean, 8.4 cm3). Median follow-up was 36 months (mean, 38 mo). RESULTS: Control of tumor growth was achieved in 97.5% of the patients. There was no mortality or permanent extraocular motor or pituitary dysfunction. Treatment-related complications included new trigeminal neuropathy in 4.7% and a new visual field defect in 2.8%. Two patients required shunt placement after developing hydrocephalus. One patient with symptomatic temporal lobe edema underwent partial excision of the tumor. Improvement of existing cranial neuropathies was noted in 29% of affected trigeminal nerves, in 22% of oculomotor nerves, and in 13% of Cranial Nerves IV and VI. CONCLUSION: This study indicates that linear accelerator radiosurgery can achieve a high control rate of meningiomas involving the cavernous sinus with no mortality and a low incidence of morbidity.

Adult↗

PubMedDate not supplied

[Effect of transversely directed accelerations on gastric motor function].

The motor function of the human stomach and starvation activity of dogs were investigated after their exposure to accelerations of various values and duration. Inhibition of the motor function of the stomach and alteration in the periodicity pattern were found. The alteration included suppression of hungry contractions, development of continuous motor activity and gradual recovery of periodic activity of the stomach. Motor changes were related to the acceleration value. The reaction of the motor apparatus of the stomach to accelerations was shown to be nonspecific. The changes in the motor function of the stomach seem to be secondary and to be associated with the changes in the functional state of regulatory centers of motor activity.

Acceleration↗

PubMed2003

Kinematics of synthetic flexible leaflet heart valves during accelerated testing.

BACKGROUND AND AIMS OF THE STUDY: The study aim was to examine the effect of variation of test frequencies on the duration and kinematics of valve leaflets during opening, and at the fully open position. METHODS: Trileaflet polyurethane heart valves were tested in a Rowan Ash fatigue accelerator at 5, 10 and 15 Hz. Images of the valves were acquired using a high-speed camera and assessed qualitatively during opening and in the fully open position. The bending strains along the leaflet free edge and leaflet belly were also calculated from these images. Results were compared with those found at 1 Hz in a pulsatile flow simulator. The time duration of each phase of the cycle and the strain time integral when opening were also determined. RESULTS: In the fully open position, the maximum bending strain found at the commissural regions of the valve was not dependent on the cycle rate. During opening, one leaflet always deformed more than either of the others, but this leaflet was not necessarily the same one each time. The opening characteristics of the valves were dependent on cycle rate: increasing bending was observed in the belly of the leaflet with increasing frequency. The ratio of time of opening of the leaflets to time whilst fully open increased with the cycle rate, and the period of time when the valve was fully open and fully closed reduced markedly with increased cycle rate. CONCLUSION: Leaflet kinematics, bending strains, the proportion of time the valve was fully closed or open, and the strain time integral were dependent on cycle rate in accelerated testing. This may influence the relative severity of accelerated testers.

Acceleration↗

PubMed2002

A neurophysiological approach to effects induced by accelerated particles on the central nervous system in mice.

This experiment was designed to study mechanisms of "phosphene vision". A beam of accelerated carbon particles (energy 100 and 300 MeV/n) was delivered into retina and sensorimotor cortex of anaesthetised mice bearing chronic electrodes. Cycles of light flashes were also administered. Following accelerated particles stimulation cycles to the retina, 500 to 5000 per stimulus, 30 stimuli per cycle, stimulus time-related brain waveforms in mice cortex were recorded. Their amplitude and latency appeared to be related to the energy delivered. The short waveforms latency (approximately 30 ms), and the lack of retinic potentials and oscillatory potentials following particles stimuli suggest that the impact of accelerated particles does not produce activation of retinic chemical structures.

Animals↗

PubMed2003

Production of isometric forces during sustained acceleration.

BACKGROUND: The operation of high-performance aircraft requires pilots to apply finely graded forces on controls. Since they are often exposed to high levels of acceleration in flight, we investigated to what extent this ability is degraded in such an environment. METHODS: Twelve healthy non-pilot volunteers were seated in the gondola of a centrifuge and their performance was tested at normal gravity (1 G) and while exposed to sustained forces of 1.5 G and 3 G oriented from head to foot (+Gz). Using an isometric joystick, they attempted to produce force vectors with specific lengths and directions commanded in random order by a visual display. RESULTS: Acceleration had substantial effects on the magnitude of produced force. Compared with 1 G, maximum produced force was about 2 N higher at 1.5 G and about 10 N higher at 3 G. The size of this effect was constant across the different magnitudes, but varied with the direction of the prescribed force. CONCLUSIONS: Acceleration degrades control of force production. This finding may indicate that the motor system misinterprets the unusual gravitoinertial environment and/or that proprioceptive feedback is degraded due to increased muscle tone. The production of excessive isometric force could affect the safe operation of high-performance aircraft.

Acceleration↗

PubMed2003

Acceleration effects on pupil size with control of mental and environmental factors.

BACKGROUND: Using still photography and cinematography, early studies reported that pupils dilate immediately on exposure to acceleration and the dilation persists during sustained +Gz. Due to the lack of control for mental and environmental factors and poor sampling rate in early techniques, we re-examined the effects of increased acceleration on pupil size in the human centrifuge. METHODS: Eight volunteers were dark adapted for 20 min by fixating on a 2.5 mm LED disk, 1 m away in otherwise complete darkness. Pupil diameters and horizontal and vertical eye movements were recorded binocularly in real time using an eye-tracking and pupillometry system. The recording sequence consisted of 1 min at +1 Gz, followed by transition to +3 Gz at 0.1 G x s(-1) 2 min at sustained +3 Gz, return to +1 Gz at 1 G x s(-1), and finally maintained at +1 Gz for another minute. During this sequence, the subject's heart rate was also monitored and the subject was instructed to subtract 2 from 1000 to maintain mental alertness. RESULTS: All subjects showed a significant decrease in pupil diameter (p < 0.05) and increase in heart rate (p = 0.02) during +3 Gz and regained the baseline level on sustained acceleration ranged from 0.6 to 3.3 mm. CONCLUSION: Our findings suggest that pupils constrict during hypergravity. It appears that the reflex regulation of pupil size is attributed to parasympathetic action through fibers originating in Edinger-Westphal's nucleus in the mesencephalon, which receives direct input from the otoliths.

Acceleration↗

PubMed2003

Proton and heavy ion acceleration facilities for space radiation research.

The particles and energies commonly used for medium energy nuclear physics and heavy charged particle radiobiology and radiotherapy at particle accelerators are in the charge and energy range of greatest interest for space radiation health. In this article we survey some of the particle accelerator facilities in the United States and around the world that are being used for space radiation health and related research, and illustrate some of their capabilities with discussions of selected accelerator experiments applicable to the human exploration of space.

Cosmic Radiation↗

PubMed1992

The dynamics of spatial orientation during complex and changing linear and angular acceleration.

The dynamics of spatial orientation perception were examined in a series of experiments in which a total of 43 subjects were passively exposed to various combinations of linear and angular acceleration during centrifuge runs. Perceptual effects during deceleration were much stronger than effects during acceleration. The dynamics of spatial orientation perception differed substantially from changes in the vestibulo-ocular reflex (VOR). VOR was fairly well predicted by a current model, but our experiments revealed perceived change in attitude (roll, pitch, yaw tilt position in space) and perceived angular velocity in space that was not reflected by parallel changes in the plane or magnitude of the VOR. This series of experiments establishes several facts concerning spatial orientation perception beyond the predictive domain of any current model. New concepts are needed and several are suggested to deal with changing reactions to complex combinations of linear and angular accelerations.

Acceleration↗

PubMed1992

Fos-defined activity in rat brainstem following centripetal acceleration.

To identify rat brainstem nuclei involved in the initial, short-term response to a change in gravito-inertial force, adult Long-Evans rats were rotated in the horizontal plane for 90 min in complete darkness after they were eccentrically positioned off the axis of rotation (off-axis) causing a centripetal acceleration of 2 g. Neural activation was defined by the brainstem distribution of the c-fos primary response gene protein, Fos, using immunohistochemistry. The Fos labeling in off-axis animals was compared with that of control animals who were rotated on the axis of rotation (on-axis) with no centripetal acceleration, or who were restrained but not rotated. In the off-axis animals there was a significant labeling of neurons: in the inferior, medial, and y-group subnuclei of the vestibular complex; in subnuclei of the inferior olive, especially the dorsomedial cell column; in midbrain nuclei, including the interstitial nucleus of Cajal, nucleus of Darkschewitsch, Edinger-Westphal nucleus, and dorsolateral periaqueductal gray; in autonomic centers including the solitary nucleus, area postrema, and locus coeruleus; and in reticular nuclei including the lateral reticular nucleus and the lateral parabrachial nucleus. Also, there was greater Fos expression in the dorsomedial cell column, the principal inferior olive subnuclei, inferior vestibular nucleus, the dorsolateral central gray, and the locus coeruleus in animals who had their heads restrained compared to animals whose heads were not restrained. As one control, the vestibular neuroepithelium was destroyed by injecting sodium arsanilate into the middle ear, bilaterally. This resulted in a complete lack of Fos labeling in the vestibular nuclei and the inferior olive, and a significant reduction in labeling in other nuclei in the off-axis condition, indicating that these nuclei have a significant labyrinth-sensitive component to their Fos labeling. The data indicate that several novel brainstem regions, including the dorsomedial cell column of the inferior olive and the periaqueductal gray, as well as more traditional brainstem nuclei including vestibular and oculomotor related nuclei, respond to otolith activation during a sustained centripetal acceleration.

Acceleration↗

PubMed2003

[Development of impact acceleration measurement facility in return-cabin of spacecraft].

OBJECTIVE: To provide the basis for medical evaluation of spacecraft, and to measure the impact acceleration of return-cabin of spacecraft. METHOD: A facility to measure the impact acceleration of "SZ-3" and "SZ-4" during landing was developed and the acquired test data were analyzed. RESULT: The data of impact acceleration of return-cabins of "SZ-3" and "SZ-4" were accurately recorded during landing. Most reliable and scientific data were gotten. CONCLUSION: This facility could validate and evaluate the specifications of relevant systems of spacecraft, and provided the scientific basis for the decision if "SZ-5", the manned spacecraft, could be launched.

Acceleration↗

PubMed2006

Roll-tilt perception during gondola centrifugation: influence of steady-state acceleration (G) level.

BACKGROUND: Spatial disorientation is an important problem in aviation. The significance of the C level for illusions elicited from the semicircular canals is not clear. The aim of the present investigation was to elucidate how a gravitoinertial force, acting in parallel with the subject's long (z) axis, may influence the magnitude and persistence of canal-induced tilts of the subjective visual horizontal (SVH) present after acceleration in a gondola centrifuge. METHODS: The SVH was measured by means of an adjustable luminous line in darkness. Two series of experiments were performed. In series 1, the SVH was measured in 13 subjects at 1.1 G, 1.7 G, and 2.5 G. In series 2, it was measured in 8 subjects at 2.5 G and 4.5 G. RESULTS: After acceleration of the centrifuge the SVH was tilted relative to the gravitoinertial horizontal. The direction of tilt was compensatory to the gondola inclination. In series 1 the initial SVH tilt was: 16.2 +/- 7.0 degrees (1.1 G), 24.2 +/- 10.2 degrees (1.7 G), and 27.1 +/- 13.9 degrees (2.5 G). In series 2 it was: 27.6 +/- 14.6 degrees (2.5 G), and 31.2 +/- 18.8 degrees (4.5 G). The gain for this response, defined as the ratio between the initial tilt and the inclination of the gondola, was: 0.65 +/- 0.28 (1.1 G), 0.45 +/- 0.19(1.7 G), 0.41 +/- 0.21 (2.5 G) (series 1); and 0.42 +/- 0.22 (2.5 G), and 0.40 +/- 0.24 (4.5 G) (series 2). Thus, an increase from 1.1 G to 1.7 G caused a reduction in the gain, but at G levels beyond 1.7 G there was no further decrease. The time constant for exponential decay tended to increase with the G level. It was: 61 +/- 31 s (1.1 G), 84 +/- 36 s (1.7 G), 89 +/- 42 s (2.5 G) (series 1); and 67 +/- 49 s (2.5 G), and 101 +/- 73 s (4.5 G) (series 2). CONCLUSION: It appears that otolithic stimulation via an increased gravitoinertial force vector, acting in parallel with the head and body long axis, does not substantially influence the magnitude of the canal-mediated sensation of roll-tilt after acceleration in a swing-out gondola centrifuge. Nor does it reduce the duration of this sensation.

Acceleration↗

PubMed1991

Diagnostic possibilities of closed head injuries of acceleration type using computed tomography.

A group of 42 patients with closed head injuries of acceleration type is reported. All of them were treated at various departments of the General Hospital in Maribor. The aim of investigation was to find out the diagnostic possibilities of head and brain damages in closed head injuries of acceleration type by the method of computed tomography (CT) and making comparison with the clinical picture of each individual patient. The patients were not investigated at random but were grouped in accordance with the direction of traumatic force action. The CT analyses were performed according to characteristic patterns of traumatic brain disease. The circumstances of head injury were reliable guidelines for devoting more attention to some brain areas. The density of each lesion was examined, too. The investigation has shown that lesions of "inner cerebral trauma" pattern (ICT-Grcević 1965) are visible on CT at least as often as coup-contrecoup lesions or even more. Only in cases with latero-lateral direction of traumatizing force (control group) coup-contrecoup lesions were found more frequently. Deep cerebral lesions of the latero-lateral type of acceleration head trauma were never or seldom encountered.

Acceleration↗

PubMed1991

Distribution of failures for increasing strain accelerated fatigue tests for elastomers can be approximated by a Gaussian distribution.

A step increasing strain accelerated fatigue test has been developed and validated for the evaluation of candidate elastomeric materials for the artificial heart program. Whereas standard fatigue tests can be approximated by a log-normal or Weibull distribution, the increasing strain accelerated fatigue test has the general appearance of being normally distributed (i.e., a Gaussian distribution). The hypothesis that the data is indeed normally distributed was examined using a variety of statistical tests. The mean and median were equivalent in all data sets compared, as they would be for normally distributed data. There was very little positive or negative skew found in data collected under a wide variety of conditions. The data was found to have a slightly stronger than expected central tendency (positive kurtosis), but most of this disappeared when the data were normalized. Chi-squared analysis found normally distributed data in most subset of the data except for those with small numbers of test specimens per test. Normalized test data was not found to differ significantly from a Gaussian distribution by the Kolmogorov-Smirnov test. It therefore appears that increasing strain accelerated fatigue test data can be approximated by a normal distribution. This allows for easy data interpretation and aids in the extrapolation of incomplete data sets.

Acceleration↗