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G-forces cause morphological and cytochemical changes characteristic of the stress reaction. The cytochemical changes in RNA content on lymphocytes, glycogen, and activity of oxidative enzymes in granulocytes are phasal in nature.
The bioelectric activity of the musculature of animals and man was studied during alternating g-forces and weightlessness. The appropriate conditions were reproduced in flight along a parabolic curve; in this case, weightlessness lasting 25-30 sec alternated with g-forces of about 2 g magnitude. Quite regular changes in the bioelectric activity of various groups of muscles were disclosed under g-forces and in weightlessness. Thus, muscle biopotential amplitudes of 130-180 microvolt in horizontal flight, increased to 190-330 microvolt under g-forces. In the subsequent weightlessness, an abrupt reduction in oscillation voltage was observed and, in a number of cases, phenomena, similar to the picture of bioelectric silence were noted.
The high cost and long times required to develop research packages for space flight can often be offset by using ground test techniques. This paper describes a space shuttle launch and reentry simulating using the NASA Ames Research Center's 20G centrifuge facility. The combined G-forces and acoustic environment during shuttle launch and landing were simulated to evaluate the effect on a payload of laboratory rates. The launch G force and acoustic profiles are matched to actual shuttle launch data to produce the required G-forces and acoustic spectrum in the centrifuge test cab where the rats were caged on a free-swinging platform. For reentry, only G force is simulated as the aero-acoustic noise is insignificant compared to that during launch. The shuttle G-force profiles of launch and landing are achieved by programming the centrifuge drive computer to continuously adjust centrifuge rotational speed to obtain the correct launch and landing G forces. The shuttle launch acoustic environment is simulated using a high-power, low-frequency audio system. Accelerometer data from STS-56 and microphone data from STS-1 through STS-5 are used as baselines for the simulations. This paper provides a description of the test setup and the results of the simulation with recommendations for follow-on simulations.
Longitudinally and transversely applied g-forces as intolerable levels cause damage to the interlobular veins of the liver, with maximum damage caused by dorso-ventral g-force application. The portal vein system is more resilient with respect to g-forces at the limit of tolerance.
Multiple exposure to g-forces evokes alarm reactions in animals which are reflected in increased secretion from the ACTH cells and adrenocorticocytes, with increased lymphocytolysis and suppressed mitotic activity.
Arteries in the brain are constricted by g-forces applied in the head-pelvis direction. Transversely applied g-forces have less effect. Appropriate conditioning can reduce the severity of all g-force applications.
A device to be used with an aircraft simulator to apply positive and negative g forces to the pilot's arm is described. An arm harness fits around the arm which the pilot uses to operate the throttle. The device allows the harness to track intentional arm movements without exerting any restraining forces, and at the same time, applies g forces to to the pilots arm which are recorded by the aircraft simulator computer.
Cats and rabbits were subjected to rotation in the centrifuge. Controls were maintained to determine the individual tolerance to g-forces. Thickening of the vascular wall was found to occur due to the g-forces' effect, as well as other vascular changes. Nervous changes included edema and chromatolysis of the nerve cells.
Exposure of rats to g-forces of high magnitude results in changes in the ultrastructure of the intercellular channels of the adenohypophysis. Evidence indicates that the chromophobic cells in the walls of the channels and pseudofollicles exert a secretory activity.
Morphological and functional changes occur in the nerve apparatus of the cardiovascular system during exposure to g-forces. They are reversible at lower magnitudes but not at higher ones.
A centrifuge was used to provide chronic acceleration in order to study the nutation of six-day old sunflower hypocotyls at 1 to 20 times normal gravity (g). At the upper end of the g-range nutational movement was impeded and at times erratic evidently because the weight of the cotyledons exceeded the supportive abilities of the hypocotyls. Over the range from 1 to 9 g the period of nutation was independent of the resultant g-force. That finding is interpreted as evidence that the geotropic response time -- i.e., the time needed for growth hormone transport from the region of g-sensing to the region of bending response --was not influenced significantly by substantial increments of the g-level, since geotropic response time is related to the period of nutation.
The vascular system of the retina, uterus, and kidneys is highly resistant to the effects of exposure to g-forces. The uterine vessels recover more rapidly than those in the retina and kidneys.
On the Earth it is patently impossible to measure any tropistic, physiologic, or morphogenic reactions to environmental stimuli without taking into account our planet's gravitational influence on the time course of the test subject's response. It follows that all published reports of quantitative measurements of such responses must have been contaminated by an additional gravity dependent component which probably was not trivial. Our research effort has as its principal scientific objective, the acquisition of experimental data from tests in a microgravity environment that will address a number of basic questions about plants' gravitropic responses to the perception of transversely applied g forces in the hypogravity range, from essentially zero to unit g. Comparable tests on Earth but in the same flight hardware, referred to as the Gravitational Plant Physiology Facility (GPPF), will provide 1 g data for various useful comparisons. Four specific scientific questions are addressed.
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Circumnutations of hypocotyls of sunflower (Helianthus annuus L. cv. Californicus) were studied under 1 g and 3 g conditions. Root mean square values of the hypocotyl deviation from the plumbline and period of the movements were determined from calculations of the autocorrelation functions of the movements. The amplitude and the period of the circumnutations increased under 3 g as compared to 1 g. A transition from 3 to 1 g or vice versa also caused changes in period and amplitude of the movements. The results are interpreted as a support for the idea that gravity influences the circumnutation parameters in this sunflower variety. A comparison is made with published results on the dwarf sunflower cv. Teddy Bear where the force influence is very small or negligible. Simulations of a model for circumnutations show movements which are in qualitative agreement with the experimental results, provided adaptation to g-levels is included in the model. Finally, the results are discussed with the recent Spacelab-experiment (SL1) as a background.
Gravitropic responses of oat seedlings (Avena sativa L.) were measured on Earth and in microgravity (IML-1). The seedlings were grown at 1 g either on Earth or on 1 g centrifuges. They were challenged by centripetal accelerations for which the intensity and duration of the stimulations were varied. All stimulation intensities were in the hypogravity region from 0.1 to 1.0 g. All responses occurred either in Spacelab microgravity or during clinorotation on Earth. The experiments were carried out with the same apparatus in Spacelab and on Earth. The experiments addressed a series of scientific questions and useful data were obtained to provide answers to some but not all of those questions.
Elucidation of dorsal/ventral polarity and primary embryonic axis development in amphibian embryos requires an understanding of cytoplasmic rearrangements in fertile eggs at the biophysical, physiological, and biochemical levels. Evidence is presented that amphibian egg cytoplasmic components are compartmentalized. The effects of altered orientation to the gravitational vector (i.e., egg inversion) and alterations in gravity force ranging from hypergravity (centrifugation) to simulated microgravity (i.e., horizontal clinostat rotation) on cytoplasmic compartment rearrangements are reviewed. The behavior of yolk compartments as well as a newly defined (with monoclonal antibody) nonyolk cytoplasmic compartment, in inverted eggs and in eggs rotated on horizontal clinostats at their buoyant density, is discussed.
Arabidopsis plants were grown in centrifuge tubes under well standardized culture conditions. Each plant was subjected to centrifugation (roots out) for 10 min at one of a series of centripetal forces between 7 and 390g. No deformation was observed in plants centrifuged at less than 35g. An 'average' degree of deformation was attained at about 60g. All plants exposed to more than 95g were maximally deformed but none was broken nor otherwise damaged irreversibly even at 390g. In every case new shoot growth continued normally after the centrifugation. A plant population grown on horizontal clinostats (0.5 rpm) under culture conditions exactly the same as for the upright plants responded to centrifugation stress in a way that was not substantially different from the response pattern of the plants cultured upright at 1g.