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At least 19 recordsLinked to original sources
PubMed2002

Animal flight dynamics II. Longitudinal stability in flapping flight.

Stability is essential to flying and is usually assumed to be especially problematic in flapping flight. If so, problems of stability may have presented a particular hurdle to the evolution of flapping flight. In spite of this, the stability of flapping flight has never been properly analysed. Here we use quasi-static and blade element approaches to analyse the stability provided by a flapping wing. By using reduced order approximations to the natural modes of motion, we show that wing beat frequencies are generally high enough compared to the natural frequencies of motion for a quasi-static approach to be valid as a first approximation. Contrary to expectations, we find that there is noting inherently destabilizing about flapping: beating the wings faster simply amplifies any existing stability or instability, and flapping can even enhance stability compared to gliding at the same air speed. This suggests that aerodynamic stability may not have been a particular hurdle in the evolution of flapping flight. Hovering animals, like hovering helicopters, are predicted to possess neutral static stability. Flapping animals, like fixed wing aircraft, are predicted to be stable in forward flight if the mean flight force acts above and/or behind the centre of gravity. In this case, the downstroke will always be stabilizing. The stabilizing contribution may be diminished by an active upstroke with a low advance ratio and more horizontal stroke plane; other forms of the upstroke may make a small positive contribution to stability. An active upstroke could, therefore, be used to lower stability and enhance manoeuvrability. Translatory mechanisms of unsteady lift production are predicted to amplify the stability predicted by a quasi-static analysis. Non-translatory mechanisms will make little or no contribution to stability. This may be one reason why flies, and other animals which rely upon non-translatory aerodynamic mechanisms, often appear inherently unstable.

Animals↗
PubMed1996

Animal flight mechanics in physically variable gas mixtures

Empirical studies of animal flight performance have generally been implemented within the contemporary atmosphere. Experimental alteration of the physical composition of gas mixtures, however, permits construction of novel flight media and the non-invasive manipulation of flight biomechanics. For example, replacement of atmospheric nitrogen with various noble gases results in a tenfold variation in air density at a constant oxygen concentration. Such variation in air density correspondingly elicits extraordinary biomechanical effort from flying animals; hummingbirds and euglossine orchid bees hovering in such low-density but normoxic mixtures have demonstrated exceptionally high values for the mechanical power output of aerobic flight muscle. As with mechanical power, lift coefficients during hovering increase at low air densities in spite of a concomitant decline in the Reynolds number of the wings. The physical effects of variable gas density may also be manifest in morphological and physiological adaptations of animals to flight across altitudinal gradients. Global variation in atmospheric composition during the late Paleozoic may also have influenced the initial evolution and subsequent diversification of ancestral pterygotes. For the present-day experimenter, the use of physically variable flight media represents a versatile opportunity to explore the range of kinematic and aerodynamic modulation available to flying animals.

Journal Article↗
PubMed1975

The effects of cosmic particle radiation on pocket mice aboard Apollo XVII: appendix I. Condition of flight animals on recovery; food intake; observations on hypothalamus, pituitary, and adrenal glands.

The rationale for studying certain hypothalamic nuclei and the pituitary and adrenal glands of the pocket mice that flew on Apollo XVII was the need to evaluate the effects of the potentially severe stress on these animals in the foreign environment of flight canister, weightlessness, increased G forces, and other unnatural conditions. Decrease in body weight and variability of food intake were significant among the four flight animals that were recovered alive. The mean nuclear diameter of neurons in the arcuate and ventromedial hypothalamic nuclei did not differ significantly from the values obtained in the control animals. On the other hand, the mean nuclear diameter of neurons in the supraoptic nucleus of the flight mice was significantly greater than in the control groups. Comparisons of the adeno- and neuropypophysis revealed no significant differences among the three groups. Insofar as they were studied, the adrenals were similar in all groups.

Adaptation, Physiological↗
PubMed2000

The evolutionary physiology of animal flight: paleobiological and present perspectives.

Recent geophysical analyses suggest the presence of a late Paleozoic oxygen pulse beginning in the late Devonian and continuing through to the late Carboniferous. During this period, plant terrestrialization and global carbon deposition resulted in a dramatic increase in atmospheric oxygen levels, ultimately yielding concentrations potentially as high as 35% relative to the contemporary value of 21%. Such hyperoxia of the late Paleozoic atmosphere may have physiologically facilitated the initial evolution of insect flight metabolism. Widespread gigantism in late Paleozoic insects and other arthropods is also consistent with enhanced oxygen flux within diffusion-limited tracheal systems. Because total atmospheric pressure increases with increased oxygen partial pressure, concurrently hyperdense conditions would have augmented aerodynamic force production in early forms of flying insects. By the late Permian, evolution of decompositional microbial and fungal communities, together with disequilibrium in rates of carbon deposition, gradually reduced oxygen concentrations to values possibly as low as 15%. The disappearance of giant insects by the end of the Permian is consistent with extinction of these taxa for reasons of asphyxiation on a geological time scale. As with winged insects, the multiple historical origins of vertebrate flight in the late Jurassic and Cretaceous correlate temporally with periods of elevated atmospheric oxygen. Much discussion of flight performance in Archaeopteryx assumes a contemporary atmospheric composition. Elevated oxygen levels in the mid- to late Mesozoic would, however, have facilitated aerodynamic force production and enhanced muscle power output for ancestral birds, as well as for precursors to bats and pterosaurs.

Animals↗
PubMed2001

Animal flight dynamics I. Stability in gliding flight.

Stability is as essential to flying as lift itself, but previous discussions of how flying animals maintain stability have been limited in both number and scope. By developing the pitching moment equations for gliding animals and by discussing potential sources of roll and yaw stability, we consider the various sources of static stability used by gliding animals. We find that gliding animals differ markedly from aircraft in how they maintain stability. In particular, the pendulum stability provided when the centre of gravity lies below the wings is a much more important source of stability in flying animals than in most conventional aircraft. Drag-based stability also appears to be important for many gliding animals, whereas in aircraft, drag is usually kept to a minimum. One unexpected consequence of these differences is that the golden measure of static pitching stability in aircraft--the static margin--can only strictly be applied to flying animals if the equilibrium angle of attack is specified. We also derive several rules of thumb by which stable fliers can be identified. Stable fliers are expected to exhibit one or more of the following features: (1) Wings that are swept forward in slow flight. (2) Wings that are twisted down at the tips when swept back (wash-out) and twisted up at the tips when swept forwards (wash-in). (3) Additional lifting surfaces (canard, hindwings or a tail) inclined nose-up to the main wing if they lie forward of it, and nose-down if they lie behind it (longitudinal dihedral). Each of these predictions is directional--the opposite is expected to apply in unstable animals. In addition, animals with reduced stability are expected to display direct flight patterns in turbulent conditions, in contrast to the erratic flight patterns predicted for stable animals, in which large restoring forces are generated. Using these predictions, we find that flying animals possess a far higher degree of inherent stability than has generally been recognized. This conclusion is reinforced by measurements of the relative positions of the centres of gravity and lift in birds, which suggest that the wings alone may be sufficient to provide longitudinal static stability. Birds may therefore resemble tailless aircraft more closely than conventional aircraft with a tailplane.

Animals↗
PubMedDate not supplied

[Intensity of DNA synthesis in animal organs after a flight on the Kosmos-782 biosatellite].

With respect to H3-thymidine incorporation the rate of DNA synthesis in the liver, spleen and thymus of rats was determined in flight and synchronous rats. Six hours post-flight the rate of H3-thymidine incorporation into the liver of flight rats did not differ from the normal (vivarium controls) and was 50% higher than in the synchronous rats. In the spleen and thymus of flight animals this parameter was 60 and 33% below the norm. Similar but less pronounced changes in the spleen were found in the synchronous rats. Twenty-five days postflight the rate of DNA synthesis in lymph organs recovered completely and tended to increase, whereas in the liver it remained significantly below the norm.

Animals↗
PubMed1991

Pineal physiology in microgravity: relation to rat gonadal function aboard Cosmos 1887.

For the first time pineal glands obtained from 5 male rats flown aboard an orbiting satellite (Soviet Biosatellite #1887) were analyzed for their melatonin, serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA), and calcium content. In addition, plasma 5-HT and 5-HIAA were measured. These parameters were compared to indicators of gonadal function: plasma testosterone concentration and spermatogonia development. Plasma melatonin was low at the time of euthanasia (lights on) and was not different among the experimental groups (flight animals, synchronous controls, and vivarium controls). Pineal calcium of flight animals was not different from ground controls. However, pineal 5-HT and 5-HIAA in the flight group were significantly higher than those in ground controls (p less than 0.05). These findings suggest a possible increase in pineal 5-HT turnover in flight animals which may result in increased melatonin secretion. Since melatonin is known to possess antigonadal properties, the alteration of pineal 5-HT turnover and its expected effects on melatonin secretion may, in part, explain the lower plasma testosterone levels (p less than 0.001) and 4-11% fewer spermatogonia cells (p less than 0.02) observed in flight animals.

Animals↗
PubMed1990

Histomorphometric and electron microscopic analyses of tibial epiphyseal plates from Cosmos 1887 rats.

Previous studies have shown that the changes seen in the bones of growing rats exposed to microgravity are due in part to changes that occur in the growth plate during spaceflight. In this study, growth plates of rats flown aboard Cosmos 1887 (12.5-day flight plus 53.5-h recovery at 1 g) were analyzed using light and electron microscopy and computerized planimetry. The proliferative zone of flight animals was found to be significantly (P less than or equal to 0.01) larger than that of controls, while the reserve and hypertrophic/calcification zones were significantly reduced. Flight animals also had more cells per column in the proliferative zone than did controls and less in the hypertrophic/calcification region. The total number of cells, however, was significantly greater in flight animals. No difference was found in perimeter or in shape factor, but area was significantly less in flight animals. Electron microscopy showed that collagen fibrils in flight animals were wider than in controls. Since the time required for a cell to cycle through the growth plate is 2-3 days at 1 g, the results reported here represent both the effects of exposure to microgravity and the initial stages of recovery from that exposure.

Animals↗
PubMedDate not supplied

[General characteristics of an experiment to study the ontogeny of rats on board the Kosmos-1514 biosatellite].

Ten female Wistar rats were exposed to zero-g during 5 days, i. e., from gestation day 13 to day 18. After recovery the flight animals showed a significant delay in weight gain, thymus involution, decreased liver weight, hemoglobin concentration. Nevertheless, their reproductive function did not differ from that of the controls: the rate of preimplantation and total fetal mortality as well as the number of live fetuses were very similar in the experimental and control animals. The flight group showed a slight decline of fetal weight and water content. The size of the litters produced by the flight and control rats was identical but the mortality rate of those former during the first 7 days after birth was significantly higher. This experiment has demonstrated that the mammalian fetus exposed to zero-g during the last term of pregnancy, i. e., at the stage of active organogenesis, can grow and develop in the normal way. A large body of biological material has been obtained for biochemical and histological examinations that will help evaluate the condition of dams, fetuses, and newborns.

Animals↗
PubMed1999

Effects of space flight and IGF-1 on immune function.

We tested the hypothesis that insulin-like growth factor-1 (IGF-1) would ameliorate space flight-induced effects on the immune system. Twelve male, Sprague-Dawley rats, surgically implanted with mini osmotic pumps, were subjected to space flight for 10 days on STS-77. Six rats received 10 mg/kg/day of IGF-1 and 6 rats received saline. Flight animals had a lymphocytopenia and granulocytosis which were reversed by IGF-1. Flight animals had significantly higher corticosterone levels than ground controls but IGF-1 did not impact this stress hormone. Therefore, the reversed granulocytosis did not correlate with serum corticosterone. Space flight and IGF-1 also combined to induce a monocytopenia that was not evident in ground control animals treated with IGF-1 or in animals subjected to space flight but given physiological saline. There was a significant increase in spleen weights in vivarium animals treated with IGF-1, however, this change did not occur in flight animals. We observed reduced agonist-induced lymph node cell proliferation by cells from flight animals compared to ground controls. The reduced proliferation was not augmented by IGF-1 treatment. There was enhanced secretion of TNF, IL-6 and NO by flight-animal peritoneal macrophages compared to vivarium controls, however, O2(-) secretion was not affected. These data suggest that IGF-1 can ameliorate some of the effects of space flight but that space flight can also impact the normal response to IGF-1. Grant Numbers: NAGW-1197, NAGW-2328.

Animals↗
PubMedDate not supplied

[Ultrastructure of the submandibular glands in rats kept in weightlessness].

Submandibular salivary glands of male rats weighing 330-350 g were examined after space flight and ground-based control study. Light microscopy was carried out using hematoxylin-eosin staining and PAS-reaction. Electron microscopy was performed using glutaraldehyde and osmium tetroxide fixation and contrasting according to Reynolds. Light microscopy revealed no destructive changes in the gland parenchyma; differences between flight and control rats remained within physiological limits. Electron microscopy of acinar cells of flight animals showed chromatin condensation, darkening of cells and nuclei, appearance of electron-dense vacuoles, fragmentation fo the granular endoplasmatic reticulum as well as enlargement of interstitial spaces, lumens of acini and intercellular canaliculi, loosening of basal membranes, and thinning of capillary walls. Electron microscopy of acinar cells of control rats demonstrated chromatin condensation in nuclei and fragmentation of the GER. Thus, both animal groups exhibited ultrastructural signs of inhibition of the synthesis and excretion of salivary protein. In addition, flight animals showed increased excretion and, probably, secretion of water and electrolytes. Examinations of granulocytes revealed enlargement of secretory granules in both animal groups, the largest granules being seen in flight animals. They also showed mitochondrial swelling which was most significant in control rats. After the ground-based study cells of the striated compartment also displayed a very distinct mitochondrial swelling which may reduce the reabsorption capacity and enhance salivation of the compartment. However the mechanism of these changes seems to be different from that underlying changes after real space flight.

Animals↗
PubMed1992

Effect of spaceflight on rat hepatocytes: a morphometric study.

Hepatic tissue from flight, synchronous, vivarium, and tail-suspended rats was examined by light microscopy and computer-assisted image analysis. Glycogen levels in flight rats were found to be significantly elevated over those in controls. Lipid was also higher but not significantly different. Hepatocytes appeared larger in flight animals because of area attributed to increased glycogen. Sinusoids were less prominent in flight animals than in controls. The total Kupffer cell population appeared to be reduced in flight animals and may represent changes in defensive capacity of the liver. Alterations in the storage of glycogen and number of Kupffer cells suggest an important effect of spaceflight on the function of the liver that may have important implications for long-term spaceflight.

Animals↗
PubMed2002

Calcium metabolism and cardiovascular function after spaceflight.

To determine the influence of dietary calcium on spaceflight-induced alterations in calcium metabolism and blood pressure (BP), 9-wk-old spontaneously hypertensive rats, fed either high- (2%) or low-calcium (0.02%) diets, were flown on an 18-day shuttle flight. On landing, flight animals had increased ionized calcium (P < 0.001), elevated parathyroid hormone levels (P < 0.001), reduced calcitonin levels (P < 0.05), unchanged 1,25(OH)(2)D(3) levels, and elevated skull (P < 0.01) and reduced femur bone mineral density. Basal and thrombin-stimulated platelet free calcium (intracellular calcium concentration) were also reduced (P < 0.05). There was a tendency for indirect systolic BP to be reduced in conscious flight animals (P = 0.057). However, mean arterial pressure was elevated (P < 0.001) after anesthesia. Dietary calcium altered all aspects of calcium metabolism (P < 0.001), as well as BP (P < 0.001), but the only interaction with flight was a relatively greater increase in ionized calcium in flight animals fed low- compared with high-calcium diets (P < 0.05). The results indicate that 1) flight-induced disruptions of calcium metabolism are relatively impervious to dietary calcium in the short term, 2) increased ionized calcium did not normalize low-calcium-induced elevations of BP, and 3) parathyroid hormone was paradoxically increased in the high-calcium-fed flight animals after landing.

Animals↗
PubMed1995

Blood volume and erythropoiesis in the rat during spaceflight.

A decreased red blood cell mass (RBCM) and plasma volume (PV) have been consistently found in humans after return from spaceflight. Rats flown on the Spacelab Life Sciences-1 mission were studied to assess changes in RBCM, PV, erythropoiesis, and iron economy. The RBCM and PV increased in both ground control and flight animals as expected for growing rats. However on landing day, both the RBCM and PV, when normalized for body mass, were significantly decreased in the spaceflight animals. During an 8-d postflight observation period, iron incorporation into circulating red blood cells was diminished in the flight animals. During the first 4 d postflight, increases in reticulocyte counts were significantly smaller in the flight than the control animals. Fewer erythropoietin-responsive progenitor cells were recovered from the bone marrow of flight animals after landing than control rats. Serum erythropoietin (EPO) levels were the same in both groups. Thus, rats subjected to a 9-d spaceflight had less increase in RBCM than controls and diminished erythropoiesis during an 8-d post-spaceflight observation period. The rat, like humans, appears to require a smaller blood volume in microgravity.

Animals↗
PubMed1994

Effects of spaceflight on the number of rat peripheral blood leukocytes and lymphocyte subsets.

Experiments were carried out on peripheral blood leukocytes and spleen lymphocytes from 29 male rats that were flown during the Spacelab Life Sciences 1 (SLS-1) nine-day mission on the shuttle Columbia in June 1991 and on appropriate ground controls. On the day of landing, there was a significant decrease in the total white blood cell counts (P < 0.0001) of flight animals in comparison to controls. There was also a significant decrease in the absolute number of lymphocytes (P < 0.0001) and monocytes (P < 0.0001) in the flight animals. A slight decrease in the absolute number of eosinophils and a slight increase in the number of neutrophils were observed at landing, compared with preflight values. Immunophenotyping of the peripheral blood and spleen lymphocytes of flight and control animals indicated that, on the day of landing, there was a decrease in the absolute number of CD4 and CD8 positive cells and B lymphocytes. However, relative percentages of peripheral blood CD4+, CD8+, and B cells were not found to be depressed. No differences were discerned in the percent reactivity of spleen lymphocytes of flight animals compared with controls. The observed decrease in the number of leukocytes and lymphocytes at the immediate postflight period was transient and all values returned to the control levels by nine days postflight.

Animals↗
PubMed1992

Thermoregulatory responses of rhesus monkeys during spaceflight.

This study examines the activity, axillary temperature (T(ax)), and ankle skin temperature (Tsk) of two male Rhesus monkeys exposed to microgravity in space. The animals were flown on a Soviet biosatellite mission (COSMOS 1514). Measurements on the flight animals, as well as synchronous flight controls, were performed in the Soviet Union. Additional control studies were performed in the United States to examine the possible role of metabolic heat production in the T(ax) response observed during the spaceflight. All monkeys were exposed to a 24-h light-dark cycle (LD 16:8) throughout these studies. During weightlessness, T(ax) in both flight animals was lower than on earth. The largest difference (0.75 degree C) occurred during the night. There was a reduction in mean heart rate and Tsk during flight. This suggests a reduction in both heat loss and metabolic rate during spaceflight. Although the circadian rhythms in all variables were present during flight, some differences were noted. For example, the amplitude of the rhythms in Tsk and activity were attenuated. Furthermore, the T(ax) and activity rhythms did not have precise 24.0 hour periods and may have been externally desynchronized from the 24-h LD cycle. These data suggest a weakening of the coupling between the internal circadian pacemaker and the external LD synchronizer.

Animals↗
PubMed1998

Reduction of pituitary AVP and OT contents in rats following spaceflight.

BACKGROUND: Responses of pituitary concentrations of vasopressin (AVP) and oxytocin (OT) during spaceflight have been variable, possibly due to differences in flight conditions or in age and strain of flight animals. METHODS: We reviewed findings of three space-flights of varying flight and recovery durations in which rats of different ages and strains were used. Male rats ranging in weight from 248-396 g were flown in space for 7-14 d. Flight animals were then compared with vivarium controls and synchronous controls. Parallel ground-based studies (hypergravity and simulated hypogravity) were conducted. RESULTS: Pituitary content of AVP was significantly (p < or = 0.05) decreased by spaceflight (6.3 +/- 0.3 micrograms.mg-1 protein in flight vs. 8.3 +/- 0.5 micrograms.mg-1 protein in vivarium). OT content was also reduced during spaceflight (4.3 +/- 0.2 micrograms.mg-1 protein in flight vs. 6.1 +/- 0.3 micrograms.mg-1 protein in vivarium). Vivarium and synchronous control rats showed no difference in pituitary contents. Flight duration or recovery times did not appear to influence pituitary hormone contents. Strain of rat had an effect on content but not on responses to spaceflight. Age of animals confounded the response to spaceflight: pituitary contents of AVP and OT were not altered in young animals (< or = 60 d old). Hindlimb suspended animals showed no difference in AVP but OT content was decreased. Ground-based exposure to hypergravity (2 G) did not alter content of AVP or OT in young animals. CONCLUSIONS: Decreases in pituitary content of AVP and OT with spaceflight may be due to a variety of factors unique to the microgravity environment. Differences between studies may be due in part to differences in size and age of rats used.

Age Factors↗
PubMed1998

Alteration of renal function of rats following spaceflight.

Following spaceflight, changes in renal function of humans have been suggested. To assess the effects of readaptation on renal function, urine was collected from male rats ( approximately 245 g) over a 2-wk period following a 14-day spaceflight. Rats were assigned to three groups: flight animals (n = 6), flight controls (n = 6) housed in the flight cages on the ground, and vivarium controls (n = 5) housed in standard shoe box cages. Animals were placed into individual metabolic cages for urine collection. Urine output was significantly increased for 3 days following flight. Excretion rates of Na+ and K+ were increased, resulting in an increased osmotic excretion rate. Creatinine excretion rate increased over the first two postflight days. Glomerular filtration rate increased immediately following spaceflight without changes in plasma creatinine, Na+, K+, or osmolality. Increased excretion of solute was thus the result of increased delivery and a decreased percent reabsorption of the filtered load. Osmolal clearance was increased immediately postflight while free water clearance was decreased. In growing rats, the diuresis after short-duration spaceflight is the result of an increase in solute excretion with an accompanying reduction in free water clearance.

Animals↗