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At least 289 records · Page 16Linked to original sources
PubMed2003

Electrophysiological properties of the utricular primary transducer are modified during development under hypergravity.

The electrophysiological development of hair cells between birth and the eight postnatal day (P8) was studied in the utricular macula of rats gestated in nest boxes mounted upon a centrifuge, subjecting the animals to a gravitational force of 2G. Whole-cell voltage-clamp recordings were made on cells in the acutely isolated epithelium. Cells were accessed through a tear in the epithelium, no enzymatic dissociation procedures were employed. Under artificially enhanced gravity, the whole cell conductance was dramatically altered in the two types of hair cells. Significant increases occurred from P3-4 in the type I cells while in the type II cells, the effect was delayed until P7-8. Fourfold and threefold increases of the mean slope conductance were observed at P7-8 in the type I and type II hair cells, respectively. These results indicate that the electrophysiological properties of a primary transducer such as utricle may be modified by variation of the primary stimulus during development.

Aging↗
PubMed1997

Effect of microgravity and hypergravity on deposition of 0.5- to 3-micron-diameter aerosol in the human lung.

We measured intrapulmonary deposition of 0. 5-, 1-, 2-, and 3-micron-diameter particles in four subjects on the ground (1 G) and during parabolic flights both in microgravity (microG) and at approximately 1.6 G. Subjects breathed aerosols at a constant flow rate (0.4 l/s) and tidal volume (0.75 liter). At 1 G and approximately 1.6 G, deposition increased with increasing particle size. In microG, differences in deposition as a function of particle size were almost abolished. Deposition was a nearly linear function of the G level for 2- and 3-micron-diameter particles, whereas for 0.5- and 1.0-micron-diameter particles, deposition increased less between microG and 1 G than between 1 G and approximately 1.6 G. Comparison with numerical predictions showed good agreement for 1-, 2-, and 3-micron-diameter particles at 1 and approximately 1.6 G, whereas the model consistently underestimated deposition in microG. The higher deposition observed in microG compared with model predictions might be explained by a larger deposition by diffusion because of a higher alveolar concentration of aerosol in microG and to the nonreversibility of the flow, causing additional mixing of the aerosols.

Adult↗
PubMed1998

Deposition and dispersion of 1-micrometer aerosol boluses in the human lung: effect of micro- and hypergravity.

We performed bolus inhalations of 1-micrometer particles in four subjects on the ground (1 G) and during parabolic flights both in microgravity (microG) and in approximately 1.6 G. Boluses of approximately 70 ml were inhaled at different points in an inspiration from residual volume to 1 liter above functional residual capacity. The volume of air inhaled after the bolus [the penetration volume (Vp)] ranged from 200 to 1,500 ml. Aerosol concentration and flow rate were continuously measured at the mouth. The deposition, dispersion, and position of the bolus in the expired gas were calculated from these data. For Vp >/=400 ml, both deposition and dispersion increased with Vp and were strongly gravity dependent, with the greatest deposition and dispersion occurring for the largest G level. At Vp = 800 ml, deposition and dispersion increased from 33.9% and 319 ml in microG to 56.9% and 573 ml at approximately 1.6 G, respectively (P < 0.05). At each G level, the bolus was expired at a smaller volume than Vp, and this volume became smaller with increasing Vp. Although dispersion was lower in microG than in 1 G and approximately 1.6 G, it still increased steadily with increasing Vp, showing that nongravitational ventilatory inhomogeneity is partly responsible for dispersion in the human lung.

Administration, Inhalation↗
PubMed2001

Effect of acute exposure to hypergravity (GX vs. GZ) on dynamic cerebral autoregulation.

We examined the effects of 30 min of exposure to either +3GX (front-to-back) or +GZ (head-to-foot) centrifugation on cerebrovascular responses to 80 degrees head-up tilt (HUT) in 14 healthy individuals. Both before and after +3 GX or +3 GZ centrifugation, eye-level blood pressure (BP(eye)), end tidal PCO2 (PET(CO2)), mean cerebral flow velocity (CFV) in the middle cerebral artery (transcranial Doppler ultrasound), cerebral vascular resistance (CVR), and dynamic cerebral autoregulatory gain (GAIN) were measured with subjects in the supine position and during subsequent 80 degrees HUT for 30 min. Mean BP(eye) decreased with HUT in both the GX (n = 7) and GZ (n = 7) groups (P < 0.001), with the decrease being greater after centrifugation only in the GZ group (P < 0.05). PET(CO2) also decreased with HUT in both groups (P < 0.01), but the absolute level of decrease was unaffected by centrifugation. CFV decreased during HUT more significantly after centrifugation than before centrifugation in both groups (P < 0.02). However, these greater decreases were not associated with greater increases in CVR. In the supine position after centrifugation compared with before centrifugation, GAIN increased in both groups (P < 0.05, suggesting an autoregulatory deficit), with the change being correlated to a measure of otolith function (the linear vestibulo-ocular reflex) in the GX group (r = 0.76, P < 0.05) but not in the GZ group (r = 0.24, P = 0.60). However, GAIN was subsequently restored to precentrifugation levels during postcentrifugation HUT (i.e., as BP(eye) decreased), suggesting that both types of centrifugation resulted in a leftward shift of the cerebral autoregulation curve. We speculate that this leftward shift may have been due to vestibular activation (especially during +GX) or potentially to an adaptation to reduced cerebral perfusion pressure during +GZ.

Adult↗
PubMed1998

Effects of 2 weeks hypergravity on the composition of the intervertebral disc.

BACKGROUND: The effects of loading on connective tissues similar to the intervertebral disk have primarily been studied using articular cartilage organ culture in vitro techniques. The effects of in vivo loading on the intervertebral disk are less well documented. METHODS: The lumbar annuli of rats centrifuged at 2G for 2 wk were compared with those of similar rats kept under analogous conditions at 1G. The studies involved the water, hydroxyproline (collagen), and uronic acid (proteoglycan, PG) content of the L4-5 and L5-6 annuli. Comparisons were also made between the 2G animals and the previous Cosmos 2044 spaceflight animals at 0G. RESULTS: The water content of annuli did not differ between the control and 2G annuli; however, the PG content of the tissue was decreased in the 2G animals and the collagen content slightly increased, resulting in an increased collagen-PG ratio in the 2G animals. When the annuli were immersed in water for 2 h, more PG leached from the annuli of the 2G animals than the control animals, suggesting an alteration in the nature of the PG population comprising the annuli. Interestingly, the direction of changes in the 2G annuli was identical to that of the previous Cosmos 2044 0G animals when they were compared with their respective controls. Therefore, directly opposite experimental conditions (2G and 0G) produced similar results. CONCLUSION: Previous studies regarding PG synthesis and content in cartilaginous tissues suggest alterations in intratissue pH and hydration to be among the factors involved in controlling the PG population. If the observed changes are permanent, they may affect the integrity of the intervertebral disk although it is likely they are totally reversible on return to 1G after an interim period, providing injuries are avoided.

Adaptation, Physiological↗
PubMed2000

[Inguinal lymph nodes of Rhesus macaque in hypokinesia and combined action of hypokinesia and hypergravity].

Peculiarities of microanatomy and cytoarchitecture of inguinal lymph nodes were studied under the effect of hypokinezia and combined effect of hypokinezia and hypergravitation experimentally in mature macaque rhesus monkeys for the first time. The data obtained indicate that on the background of intensive impairing effect of hypokinezia combined action was not only neutralized but the effect of hypokinezia also intensifies immunological action of lymph nodes of monkeys. This was supported by morphological signs and changes in correlation between lymphoid cells: number growth of lymphoid nodules with widened germinal centres and high fraction of mitotically dividing cells, the presence of dense thymus dependent (paracortical) zone and more dense medullar bands, filled basically with small lymphocytes and lowered level of destructive processes in all structural components of lymph nodes.

Animals↗
PubMed1997

Effects of hypergravic fields on serotonergic neuromodulation in the rat hippocampus.

The effects of 7 day exposure to 2G fields on serotonergic modulation at two synapses on a hippocampal pathway were examined by recording dentate gyrus and CA1 pyramidal cell layer electrical activity. Serotonin decreased the amplitude of the population spike (synchronous action potentials in hundreds of neurons) in both the dentate gyrus and CA1 regions of rats exposed to 2G fields for 7 days. The inhibition, averaging 26 +/- 4% (mean +/- SEM) in the dentate gyrus and 80 +/- 5% in the CA1 region, was not significantly different from inhibitory responses observed in 1G controls. The 5-HT1A agonist 8-OH-DPAT mimicked this inhibition in the dentate and CA1 regions of 1G rats. 8-OH-DPAT responses were not affected by exposure to 2G fields. We conclude that the hippocampus contains surplus 5-HT receptors so that decreases in receptor density reported in receptor binding studies do not result in a decrease in modulatory capability. A model to account for the physiological pathway that relates gravitational field strength to 5-HT receptor density without changing the effectiveness of 5-HT neuromodulation is discussed.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1999

Polychromatic percepts during hypergravity.

Future helmet mounted systems and cockpit displays will rely on color graphics and information that high performance aircraft pilots will need to discern and understand. Color in displays may help reduce pilot workload. The effect of high G and reduced eye level blood pressure on field-of-view has been study extensively. The effect of high sustained acceleration on color vision, however, is unknown. Research on visual contrast sensitivity, night vision, and visual acuity under acceleration in a human centrifuge has demonstrated changes in vision. We began by having normal color vision subjects view a magnified color aerial map and describe what they saw as we slowly ramped up the G profile from baseline (1.4 G) at 0.1G/sec until they experienced almost complete blackout. At that point subjects began straining and the centrifuge was rapidly decelerated. Several subjects described the river fading away before much else happened. Then the yellow and green features of the terrain faded together. Reds and dark blues appeared to change to black but remained legible until the entire image also faded to black. Computer types call the color of a river on a map cyan. So a display was created that resembled a device know as a "light bar" that is routinely used in centrifuge research. It consisted of a 45 degree wide square projection of green dots in the periphery and a red dot in the center on a white background. Due to our new curiosity about cyan we added dots halfway between the green and red that were cyan. We then ran several people through the same slow onset ramp until near blackout. Several reported that the cyan disappeared completely, significantly before the green. Then the green disappeared, and finally the central red dot. For those who experience it, it is a very useful and repeatable early end point where vision is affected but still available. Next we borrowed a color wheel from the hypobaric chamber and taped it to the wall of the cab. Several subjects reported discomforting angular optical vection due to torsional nystagmus. Thus, a vertical bar arrangement of colors was selected that minimized disruption from involuntary eye movements.

Aerospace Medicine↗
PubMed2001

[Effect of hypergravity on the oxidative-antioxidative status of rats].

The adaptogenic and antioxidant properties of new Ukrainian plant drug "Poliphytolum" was investigated on the model of stress, which was caused of hypergravitation 2 and 5 N.m2/kg2 action. It was established that hypergravitation makes typical stressory disturbances in oxidative homeostasis. The normalization action of "Polyphytolum" on lipid peroxidation is more strong in liver, spleen and blood, and less more--in brain. It may be caused of low level the drug in the brain tissue.

Animals↗
PubMed1975

Response and adaptation of beagle dogs to hypergravity.

Eight male Beagle dogs, five months old, were centrifuged for three months at progressively increasing loads ranging from 1.5 g to 2.5 g on a 7.9 m radius centrifuge. Dogs were maintained on the centrifuge, which was run almost continuously, by employing a special designed automated waste disposal and life support system. Heart rate and deep body temperature were monitored continuously by implant biotelemetry. Initially, centrifuged dogs showed transient decreases in heart rate and body temperature along with changes in their diurnal rhythm patterns. Compared with normal gravity controls, exposed dogs showed a slower growth rate and a reduced amount of body fat. Blood protein, total lipids, cholesterol, calcium, packed cell volume, red blood cell count, and hemoglobin were also decreased significantly. Absolute weights of the leg bones of centrifuged dogs were significantly greater than controls. Photon absorptiometry revealed significant density increases in selective regions of the femur and humerus of centrifuged dogs. In spite of the various changes noted, results from this and other studies affirm the view that dogs can tolerate and adapt to sustained loads as high as 2.5 g without serious impairment of their body structure and function.

Adaptation, Physiological↗
PubMed1977

Circulatory adaptive reactions under hypergravity in normal and cold environments.

Rats subjected to various levels of +Gz acceleration exhibited an increased blood concentration of noradrenalin and adrenalin, indicative of a sympatho-adrenergic reaction. Under the same conditions, from plasma determinations, and by histochemical examination of the supra-optic nucleus, an increased antidiuretic response was noted. This response was reduced in cold environment.

Animals↗