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  • 1
    Electronic Resource
    Electronic Resource
    Blood vessel adaptation to gravity in a semi-arboreal snake (1996)
    Springer
    Journal of comparative physiology 165 (1996), S. 518-526 
    Details
    ISSN: 1432-136X
    Keywords: Blood vessels ; Gravity ; Catecholamines ; Vasoactive agents ; Snake ; Elaphe obsoleta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The effects of vasoactive agonists on systemic blood vessels were examined with respect to anatomical location and gravity acclimation in the semi-arboreal snake, Elaphe Obsoleta. Major blood vessels were reactive to putative neurotransmitters, hormones or local factors in vessel specific patterns. Catecholamines, adenosine triphosphate, histamine and high potassium (80 mM) stimulated significantly greater tension per unit vessel mass in posterior than anterior arteries. Anterior vessels were significantly more sensitive to catecholamines than midbody and posterior vessels. Angiotensin II stimulated significantly greater tension in carotid artery than in midbody and posterior dorsal aorta. Arginine vasotocin strongly contracted the left and right aortic arches and anterior dorsal aorta. Veins were strongly contracted by catecholamines, high potassium and angiotensin II, but less so by adenosine triphosphate, arginine vasotocin and histamine. Precontracted vessels were relaxed by acetylcholine and sodium nitroprusside, but not by atrial natriuretic peptide or bradykinin. Chronic exposure of snakes to intermittent hypergravity stress (+1.5 Gz at tail) did not affect the majority of vessel responses. These data demonstrate that in vitro tension correlates with known patterns of sympathetic innervation and suggest that catecholamines, as well as other agonists, are important in mediating vascular responses to gravitational stresses in snakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387512
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  • 2
    Electronic Resource
    Electronic Resource
    Cardiovascular responses of semi-arboreal snakes to chronic, intermittent hypergravity (1996)
    Springer
    Journal of comparative physiology 166 (1996), S. 241-253 
    Details
    ISSN: 1432-136X
    Keywords: Hypergravity ; Carotid blood flow ; Acceleration tolerance ; Cardiovascular acclimation ; Snake,Elaphe obsoleta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Cardiovascular functions were studied in semi-arboreal rat snakes (Elaphe obsoleta) following long-term, intermittent exposure to +1.5G z (head-totail acceleration) on a centrifuge. Snakes were held in a nearly straight position within horizontal plastic tubes during periods of centrifugation. Centrifugal acceleration, therefore, subjected snakes to a linear force gradient with the maximal force being experienced at the tail. Compared to non-centrifuged controls,G z-acceimated snakes showed greater increases of heart rate during head-up tilt or acceleration, greater sensitivity of arterial pressure to circulating catecholamines, higher blood levels of corticosterone, and higher blood ratios of prostaglandin F2α/prostaglandin E2. Cardiovascular tolerance to increased gravity during gradedG z acceleration was measured as the maximum (caudal) acceleration force at which carotid arterial blood flow became null. When such tolerances were adjusted for effects of body size and other continuous variables incorporated into an analysis of covariance, the difference between the adjusted mean values of control and acelimated snakes (2.37 and 2.84G z, respectively) corresponded closely to the 0.5G difference between the acelimationG (1.5) and Earth gravity (1.0). As in other vertebrates, cardiovascular tolerance toG z stress tended to be increased by acclimation, short body length, high arterial pressure, and comparatively large blood volume. Voluntary body movements were important for promoting carotid blood flow at the higher levels ofG z stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00262868
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  • 3
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    Intramuscular pressure and torque during isometric, concentric and eccentric muscular activity (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Intramuscular pressures, electromyography (EMG) and torque generation during isometric, concentric and eccentric maximal isokinetic muscle activity were recorded in 10 healthy volunteers. Pressure and EMG activity were continuously and simultaneously measured side by side in the tibialis anterior and soleus muscles. Ankle joint torque and position were monitored continuously by an isokinetic dynamometer during plantar flexion and dorsiflexion of the foot. The increased force generation during eccentric muscular activity, compared with other muscular activity, was not accompanied by higher intramuscular pressure. Thus, this study demonstrated that eccentric muscular activity generated higher torque values for each increment of intramuscular pressure. Intramuscular pressures during antagonistic co-activation were significantly higher in the tibilis anterior muscle (42-46% of maximal agonistic activity) compared with the soleus muscle (12-29% of maximal agonistic activity) and was largely due to active recruitment of muscle fibers. In summary, eccentric muscular activity creates higher torque values with no additional increase of the intramuscular pressure compared with concentric and isometric muscular activity.
    Keywords: Aerospace Medicine
    Type: Scandinavian journal of medicine & science in sports (ISSN 0905-7188); Volume 5; 5; 291-6
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  • 4
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    Hoffmann-reflex is delayed during 6 degree head-down tilt with balanced traction (1999)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: BACKGROUND: Increased spinal height due to the lack of of axial compression on spinal structures in microgravity may stretch the spinal cord, cauda equina, nerve roots, and paraspinal tissues. HYPOTHESIS: Exposure to simulated microgravity causes dysfunction of nerve roots so that the synaptic portion of the Achilles tendon reflex is delayed. METHODS: Six healthy male subjects were randomly divided into two groups with three in each group. The subjects in the first group underwent horizontal bed rest (HBR) for three days. After a two week interval they underwent bed rest in a position of head-down tilt with balanced traction (HDT). So that each subject could serve as his own control, the second group was treated identically but in opposite order. Bilateral F waves and H-reflexes were measured daily (18:30-20:30) on all subjects placed in a prone position. RESULTS: By means of ANOVA, differences between HDT and HBR were observed only in M-latency and F-ratio, not in F-latency, central latency, and H-latency. Differences during the course of the bed rest were observed in M-latency and H-latency only. Tibial H latency was significantly lengthened in HDT group on day 2 and 3, although no significant difference between HDT and HBR was observed. CONCLUSION: The monosynaptic reflex assessed by H-reflex was delayed during 6 degree HDT with traction. The exact mechanism of this delay and whether the change was due to lengthening of the lower part of the vertebrae remain to be clarified.
    Keywords: Aerospace Medicine
    Type: Aviation, space, and environmental medicine (ISSN 0095-6562); Volume 70; 3 Pt 1; 220-4
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  • 5
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    Cardiovascular responses of semi-arboreal snakes to chronic, intermittent hypergravity (1996)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Cardiovascular functions were studied in semi-arboreal rat snakes (Elaphe obsoleta) following long-term, intermittent exposure to +1.5 Gz (head-to-tail acceleration) on a centrifuge. Snakes were held in a nearly straight position within horizontal plastic tubes during periods of centrifugation. Centrifugal acceleration, therefore, subjected snakes to a linear force gradient with the maximal force being experienced at the tail. Compared to non-centrifuged controls, Gz-acclimated snakes showed greater increases of heart rate during head-up tilt or acceleration, greater sensitivity of arterial pressure to circulating catecholamines, higher blood levels of corticosterone, and higher blood ratios of prostaglandin F 2 alpha/prostaglandin E2. Cardiovascular tolerance to increased gravity during graded Gz acceleration was measured as the maximum (caudal) acceleration force at which carotid arterial blood flow became null. When such tolerances were adjusted for effects of body size and other continuous variables incorporated into an analysis of covariance, the difference between the adjusted mean values of control and acclimated snakes (2.37 and 2.84 Gz, respectively) corresponded closely to the 0.5 G difference between the acclimation G (1.5) and Earth gravity (1.0). As in other vertebrates, cardiovascular tolerance to Gz stress tended to be increased by acclimation, short body length, high arterial pressure, and comparatively large blood volume. Voluntary body movements were important for promoting carotid blood flow at the higher levels of Gz stress.
    Keywords: Life Sciences (General)
    Type: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology (ISSN 0174-1578); Volume 166; 241-53
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  • 6
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    Critical discussion of research issues in body fluid metabolism and control of intravascular volume (1996)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: No abstract available
    Keywords: Aerospace Medicine
    Type: Medicine and science in sports and exercise (ISSN 0195-9131); Volume 28; 10 Suppl; S56; discussion S56-9
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  • 7
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    Cutaneous microvascular flow in the foot during simulated variable gravities (1996)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Our objective was to understand how weight bearing with varying gravitational fields affects blood perfusion in the sole of the foot. Human subjects underwent whole body tilting at four angles: upright [1 gravitational vector from head to foot (Gz)], 22 degrees (0.38 Gz), 10 degrees (0.17 Gz), and supine (0 Gz), simulating the gravitational fields of Earth, Mars, Moon, and microgravity, respectively. Cutaneous capillary blood flow was monitored on the plantar surface of the heel by laser Doppler flowmetry while weight-bearing load was measured. At each tilt angle, subjects increased weight bearing on one foot in graded load increments of 1 kg beginning with zero. The weight bearing at which null flow first occurred was determined as the closing load. Subsequently, the weight bearing was reduced in reverse steps until blood flow returned (opening load). Mean closing loads for simulated Earth gravity, Mars gravity, Moon gravity, and microgravity were 9.1, 4.6, 4.4, and 3.6 kg, respectively. Mean opening loads were 7.9, 4.1, 3.5, and 3.1 kg, respectively. Mean arterial pressures in the foot (MAP(foot)) calculated for each simulated gravitational field were 192, 127, 106, and 87 mmHg, respectively. Closing load and opening load were significantly correlated with MAP(foot) (r =0.70, 0.72, respectively) and were significantly different (P 〈 0.001) from each other. The data suggest that decreased local arterial pressure in the foot lowers tolerance to external compression. Consequently, the human foot sole may be more prone to cutaneous ischemia during load bearing in microgravity than on Earth.
    Keywords: Life Sciences (General)
    Type: The American journal of physiology (ISSN 0002-9513); Volume 271; 4 Pt 2; R961-6
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  • 8
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    Cardiovascular adaptation to spaceflight (1996)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This article reviews recent flight and ground-based studies of cardiovascular adaptation to spaceflight. Prominent features of microgravity exposure include loss of gravitational pressures, relatively low venous pressures, headward fluid shifts, plasma volume loss, and postflight orthostatic intolerance and reduced exercise capacity. Many of these short-term responses to microgravity extend themselves during long-duration microgravity exposure and may be explained by altered pressures (blood and tissue) and fluid balance in local tissues nourished by the cardiovascular system. In this regard, it is particularly noteworthy that tissues of the lower body (e.g., foot) are well adapted to local hypertension on Earth, whereas tissues of the upper body (e.g., head) are not as well adapted to increase in local blood pressure. For these and other reasons, countermeasures for long-duration flight should include reestablishment of higher, Earth-like blood pressures in the lower body.
    Keywords: Life Sciences (General)
    Type: Medicine and science in sports and exercise (ISSN 0195-9131); Volume 28; 8; 977-82
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  • 9
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    Height increase, neuromuscular function, and back pain during 6 degrees head-down tilt with traction (1997)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: BACKGROUND: Spinal lengthening and back pain are commonly experienced by astronauts exposed to microgravity. METHODS: To develop a ground-based simulation for spinal adaptation to microgravity, we investigated height increase, neuromuscular function and back pain in 6 subjects all of whom underwent two forms of bed rest for 3 d. One form consisted of 6 degrees of head-down tilt (HDT) with balanced traction, while the other was horizontal bed rest (HBR). Subjects had a 2-week recovery period in between the studies. RESULTS: Total body and spinal length increased significantly more and the subjects had significantly more back pain during HDT with balanced traction compared to HBR. The distance between the lower endplate of L4 and upper endplate of S1, as measured by ultrasonography, increased significantly in both treatments to the same degree. Intramuscular pressures in the erector spinae muscles and ankle torque measurements during plantarflexion and dorsiflexion did not change significantly during either treatment. CONCLUSION: Compared to HBR, HDT with balanced traction may be a better method to simulate changes of total body and spinal lengths, as well as back pain seen in microgravity.
    Keywords: Aerospace Medicine
    Type: Aviation, space, and environmental medicine (ISSN 0095-6562); Volume 68; 1; 24-9
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  • 10
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    Noninvasive measurement of pulsatile intracranial pressure using ultrasound (1998)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The present study was designed to validate our noninvasive ultrasonic technique (pulse phase locked loop: PPLL) for measuring intracranial pressure (ICP) waveforms. The technique is based upon detecting skull movements which are known to occur in conjunction with altered intracranial pressure. In bench model studies, PPLL output was highly correlated with changes in the distance between a transducer and a reflecting target (R2 = 0.977). In cadaver studies, transcranial distance was measured while pulsations of ICP (amplitudes of zero to 10 mmHg) were generated by rhythmic injections of saline. Frequency analyses (fast Fourier transformation) clearly demonstrate the correspondence between the PPLL output and ICP pulse cycles. Although theoretically there is a slight possibility that changes in the PPLL output are caused by changes in the ultrasonic velocity of brain tissue, the decreased amplitudes of the PPLL output as the external compression of the head was increased indicates that the PPLL output represents substantial skull movement associated with altered ICP. In conclusion, the ultrasound device has sufficient sensitivity to detect transcranial pulsations which occur in association with the cardiac cycle. Our technique makes it possible to analyze ICP waveforms noninvasively and will be helpful for understanding intracranial compliance and cerebrovascular circulation.
    Keywords: Life Sciences (General)
    Type: Acta neurochirurgica. Supplementum (ISSN 0065-1419); Volume 71; 66-9
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