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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Effect of exercise training on cardiopulmonary baroreflex control of forearm vascular resistance in humans

We studied the stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR) in four groups of male volunteer subjects: i) unfit, ii) physically fit, iii) before and after 10 wk of endurance training (chronic blood volume expansion), and iv) before and after acute blood volume expansion. We assessed the relationship between reflex stimulus, i.e., changes in central venous pressure and response, i.e., FVR, during unloading of cardiopulmonary mechanoreceptors with lower body negative pressure (LBNP, 0 to -20 mm Hg). The slope of the linear relationship between FVR and CVP, the index of the responsiveness of this baroreflex, was significantly diminished (> 50%) in the fit subjects compared with the unfit. The slope of the FVR-CVP relationship was inversely correlated with the subject's total blood volume, suggesting that blood volume expansion was related to the attenuated CP baroreflex. In the exercise training study, maximal oxygen consumption and blood volume increased following 10 wk of endurance training (N = 14) but were unchanged in the time control group (N = 7). The slope of the FVR-CVP relationship was significantly reduced (32%) following 10 wk of training but was unchanged in the time control group. The reduction in slope of the FVR-CVP relationship was inversely related to the increase in blood volume associated with exercise training. Acute blood volume expansion 8 ml.kg-1 body weight with 5% human serum albumin solution) significantly reduced the slope of the FVR-CVP relationship. These data support the hypothesis that the attenuated forearm vascular reflex in physically fit individuals is related to a training-induced hypervolemia.(ABSTRACT TRUNCATED AT 250 WORDS).

Review↗
NASA NTRS1993

Polyamines in the lateral vestibular nuclei of the squirrel monkey and their potential role in vestibular compensation

Polyamine synthesis increases in response to injurious stimuli including axotomy and denervation. Reduced eye nystagmus and head-deviation have been observed in unilateral labyrinthectomized (UL) guinea pigs treated with an inhibitor of polyamine synthesis, alpha-difluoromethylornithine (DFMO). We quantified polyamines in the lateral vestibular nuclei (LVN) of control and UL squirrel monkeys during the phase of vestibular compensation (VC) and performed an experiment to determine if DFMO reduces nystagmus previously observed in the guinea pig. Polyamines were detected in the LVN of control and UL squirrel monkeys. Putrescine and spermidine increased in the ipsilateral LVN 3 days after UL with no change in the contralateral LVN. No left-right differences were noted in the 5-day post-UL monkey. DFMO reduced nystagmus in a UL squirrel monkey. These findings suggest that polyamines are important in vestibular function and may contribute to nystagmus observed in VC.

NASA Program Space Physiology and Countermeasures↗
NASA NTRS1993

Utricular otoconia of some amphibians have calcitic morphology

This report concerns the morphological features of otoconia removed from the inner ear of four amphibian species. Results from scanning electron microscopic examination are compared based on the site of origin. These results show that utricular otoconia have a mineral structure that mimics calcite, rather than the widely accepted idea that they are mineralized by calcium carbonate of the aragonite polymorph.

NASA Program Space Physiology and Countermeasures↗
NASA NTRS1993

Mechanical stimulation of skeletal muscle generates lipid-related second messengers by phospholipase activation

Repetitive mechanical stimulation of cultured avian skeletal muscle increases the synthesis of prostaglandins (PG) E2 and F2 alpha which regulate protein turnover rates and muscle cell growth. These stretch-induced PG increases are reduced in low extracellular calcium medium and by specific phospholipase inhibitors. Mechanical stimulation increases the breakdown rate of 3H-arachidonic acid labelled phospholipids, releasing free 3H-arachidonic acid, the rate-limiting precursor of PG synthesis. Mechanical stimulation also increases 3H-arachidonic acid labelled diacylglycerol formation and intracellular levels of inositol phosphates from myo-[2-3H]inositol labelled phospholipids. Phospholipase A2 (PLA2), phosphatidylinositol-specific phospholipase C (PLC), and phospholipase D (PLD) are all activated by stretch. The stretch-induced increases in PG production, 3H-arachidonic acid labelled phospholipid breakdown, and 3H-arachidonic acid labelled diacylglycerol formation occur independently of cellular electrical activity (tetrodotoxin insensitive) whereas the formation of inositol phosphates from myo-[2-3H]inositol labelled phospholipids is dependent on cellular electrical activity. These results indicate that mechanical stimulation increases the lipid-related second messengers arachidonic acid, diacylglycerol, and PG through activation of specific phospholipases such as PLA2 and PLD, but not by activation of phosphatidylinositol-specific PLC.

NASA Discipline Number 40-40↗
NASA NTRS1993

Human vertical eye movement responses to earth horizontal pitch

The vertical eye movements in humans produced in response to head-over-heels constant velocity pitch rotation about a horizontal axis resemble those from other species. At 60 degrees/s these are persistent and tend to have non-reversing slow components that are compensatory to the direction of rotation. In most, but not all subjects, the slow component velocity was well characterized by a rapid build-up followed by an exponential decay to a non-zero baseline. Super-imposed was a cyclic or modulation component whose frequency corresponded to the time for one revolution and whose maximum amplitude occurred during a specific head orientation. All response components (exponential decay, baseline and modulation) were larger during pitch backward compared to pitch forward runs. Decay time constants were shorter during the backward runs, thus, unlike left to right yaw axis rotation, pitch responses display significant asymmetries between paired forward and backward runs.

NASA Program Space Physiology and Countermeasures↗
NASA NTRS1993

Mathematical modelling of the human cardiovascular system in the presence of stenosis

This paper reports a theoretical study on the distribution of blood flow in the human cardiovascular system when one or more blood vessels are affected by stenosis. The analysis employs a mathematical model of the entire system based on the finite element method. The arterial-venous network is represented by a large number of interconnected segments in the model. Values for the model parameters are based upon the published data on the physiological and rheological properties of blood. Computational results show how blood flow through various parts of the cardiovascular system is affected by stenosis in different blood vessels. No significant changes in the flow parameters of the cardiovascular system were found to occur when the reduction in the lumen diameter of the stenosed vessels was less than 65%.

NASA Program Data Analysis↗
NASA NTRS1993

Contribution of irregular semicircular canal afferents to the horizontal vestibuloocular response during constant velocity rotation

1. The effects of constant anodal currents (100 microA) delivered bilaterally to both labyrinths on the horizontal vestibuloocular response (VOR) were studied in squirrel monkeys during steps of angular velocity in the dark. We report that bilateral anodal currents decreased eye velocity approximately 30-50% during the period of galvanic stimulation without a change in the time constant of VOR. The decrease in eye velocity, present during steps of angular velocity, was not observed during sinusoidal head rotation at 0.2, 0.5, and 1 Hz. The results suggest that responses from irregular vestibular afferents influence VOR amplitude during constant velocity rotation.

NASA Discipline Neuroscience↗
NASA NTRS1993

Orthostasis: exercise and exercise training

There are two major problems here that are not independent. One is the more practically oriented problem of determining the effect of various modes of exercise training on gravitational tolerances, i.e., the point of syncope (unconsciousness) usually estimated from the time of appearance of presyncopal signs and symptoms. The other is more theoretical and concerns the mechanism of blood pressure failure that results in syncope. In many experimental designs these two problems or purposes have been intermingled, with equivocal results.

Review, Tutorial↗
NASA NTRS1993

Calcium citrate without aluminum antacids does not cause aluminum retention in patients with functioning kidneys

It has been suggested that calcium citrate might enhance aluminum absorption from food, posing a threat of aluminum toxicity even in patients with normal renal function. We therefore measured serum and urinary aluminum before and following calcium citrate therapy in patients with moderate renal failure and in normal subjects maintained on constant metabolic diets with known aluminum content (967-1034 mumol/day, or 26.1-27.9 mg/day, in patients and either 834 or 1579 mumol/day, or 22.5 and 42.6 mg/day, in normal subjects). Seven patients with moderate renal failure (endogenous creatinine clearance of 43 ml/min) took 50 mmol (2 g) calcium/day as effervescent calcium citrate with meals for 17 days. Eight normal women received 25 mmol (1 g) calcium/day as tricalcium dicitrate tablets with meals for 7 days. In patients with moderate renal failure, serum and urinary aluminum were normal before treatment at 489 +/- 293 SD nmol/l (13.2 +/- 7.9 micrograms/l) and 767 +/- 497 nmol/day (20.7 +/- 13.4 micrograms/day), respectively. They remained within normal limits and did not change significantly during calcium citrate treatment (400 +/- 148 nmol/l and 600 +/- 441 nmol/day, respectively). Similarly, no significant change in serum and urinary aluminum was detected in normal women during calcium citrate administration (271 +/- 59 vs 293 +/- 85 nmol/l and 515 +/- 138 vs 615 +/- 170 nmol/day, respectively). In addition, skeletal bone aluminum content did not change significantly in 14 osteoporotic patients (endogenous creatinine clearance of 68.5 ml/min) treated for 24 months with calcium citrate, 10 mmol calcium twice/day separately from meals (29.3 +/- 13.9 ng/mg ash bone to 27.9 +/0- 10.4, P = 0.727). In them, histomorphometric examination did not show any evidence of mineralization defect. Thus, calcium citrate given alone without aluminum-containing drugs does not pose a risk of aluminum toxicity in subjects with normal or functioning kidneys, when it is administered on an empty stomach at a recommended dose of 20 mmol calcium/day.

Non-NASA Center↗
NASA NTRS1993

Effects of illumination on human nocturnal serum melatonin levels and performance

In humans, exposure to bright light at night suppresses the normal nocturnal elevation in circulating melatonin. Oral administration of pharmacological doses of melatonin during the day, when melatonin levels are normally minimal, induces fatigue. To examine the relationship between illumination, human pineal function, and behavior, we monitored the overnight serum melatonin profiles and behavioral performance of 24 healthy male subjects. On each of three separate occasions subjects participated in 13.5 h (1630-0800 h) testing sessions. Each subject was assigned to an individually illuminated workstation that was maintained throughout the night at an illumination level of approximately 300, 1500, or 3000 lux. Melatonin levels were significantly diminished by light treatment, F(2, 36) = 12.77, p < 0.001, in a dose-dependent manner. Performance on vigilance, reaction time, and other tasks deteriorated throughout the night, consistent with known circadian variations in these parameters, but independent of ambient light intensity and circulating melatonin levels.

NASA Program Space Physiology and Countermeasures↗
NASA NTRS1993

Cross-calibration of liquid and solid QCT calibration standards: corrections to the UCSF normative data

Quantitative computed tomography (QCT) has been shown to be a precise and sensitive method for evaluating spinal bone mineral density (BMD) and skeletal response to aging and therapy. Precise and accurate determination of BMD using QCT requires a calibration standard to compensate for and reduce the effects of beam-hardening artifacts and scanner drift. The first standards were based on dipotassium hydrogen phosphate (K2HPO4) solutions. Recently, several manufacturers have developed stable solid calibration standards based on calcium hydroxyapatite (CHA) in water-equivalent plastic. Due to differences in attenuating properties of the liquid and solid standards, the calibrated BMD values obtained with each system do not agree. In order to compare and interpret the results obtained on both systems, cross-calibration measurements were performed in phantoms and patients using the University of California San Francisco (UCSF) liquid standard and the Image Analysis (IA) solid standard on the UCSF GE 9800 CT scanner. From the phantom measurements, a highly linear relationship was found between the liquid- and solid-calibrated BMD values. No influence on the cross-calibration due to simulated variations in body size or vertebral fat content was seen, though a significant difference in the cross-calibration was observed between scans acquired at 80 and 140 kVp. From the patient measurements, a linear relationship between the liquid (UCSF) and solid (IA) calibrated values was derived for GE 9800 CT scanners at 80 kVp (IA = [1.15 x UCSF] - 7.32).(ABSTRACT TRUNCATED AT 250 WORDS).

NASA Program Space Physiology and Countermeasures↗
NASA NTRS1991

Elevated central venous pressure: a consequence of exercise training-induced hypervolemia?

Resting blood volumes and arterial and central venous pressures (CVP) were measured in 14 men before and after exercise training to determine whether training-induced hypervolemia is accompanied by a change in total vascular capacitance. In addition, resting levels of plasma arginine vasopressin (AVP), atrial natriuretic peptide (ANP), aldosterone (Ald), and norepinephrine (NE) were measured. The same measurements were conducted in seven subjects who did not undergo exercise and acted as controls. Exercise training consisted of 10 wk of controlled cycle exercise for 30 min/day, 4 days/wk at 75-80% of maximal O2 uptake (VO2max). A training effect was verified by a 20% increase in VO2max, a resting bradycardia, and a 9% increase in blood volume. Mean arterial blood pressure was unaltered by exercise training, but resting CVP increased by 16% (P less than 0.05). The percent change in blood volume from before to after training was linearly related to the percent change in CVP (r = 0.903, P less than 0.05). As a consequence of elevations in both blood volume and CVP, the volume-to-pressure ratio was unchanged after exercise training. Plasma AVP, ANP, Ald, and NE were unaltered. Our results indicate that elevated CVP is a consequence of training-induced hypervolemia without alteration in total effective venous capacitance.

NASA Program Space Physiology and Countermeasures↗
NASA NTRS2007

The NASA Space Environments and Effects Program (SEE): Over a Decade of Useful Products for Spacecraft Designers and Operators

SEE program management originated at LaRC in the early 1990's but was transferred to MSFC in FY 1995 and has remained at Marshall since that time, SEE uses 5 technical working groups and NRA's (three since 1994) to achieve its technical objectives. The SEE vision is to develop and maintain a preeminent program in SPACE ENVIRONMENTS AND EFFECTS which provides a coordinated national focus for innovative technology development to support design, development, and operation of spacecraft systems that will accommodate or mitigate effects due to the presence of the space environment. In working toward that goal, SEE has produced, through the years, over 30 major Space Environments and Effects Models and Databases, over 75 major Space Environments and Effects Publications, a website that has had over 112,000 hits since its inception (http://see.msfc.nasa.gov/), distribution of physical products that amounts to over a total of over 260 product deliveries, sponsorship of the last four international Spacecraft Charging Technology Conferences (the major subject matter conference in the world), and sponsorship of numerous technical standards and guidelines in the Space Environments area. Among the recent popular SEE products are the Electric Propulsion Interactions Code (EPIC), the NASA/Air Force Spacecraft Charging Analysis Program (NASCAP-2K), the Interactive Spacecraft Charging Handbook, the Cosmic Ray Effects on Microelectronics Code (CREME 96), the Spacecraft Contamination and Materials Outgassing Effects Knowledge base (SCMOEK), and the Lunar E-Library.

Ferguson, Dale C.↗
NASA NTRS1990

Programmatic status of NASA's CSTI high capacity power Stirling space power converter program

An overview is presented of the NASA Lewis Research Center Free-Piston Stirling Space Power Converter Technology Development Program. This work is being conducted under NASA's Civil Space Technology Initiative (CSTI). The goal of the CSTI High Capacity Power element is to develop the technology base needed to meet the long duration, high capacity power requirements for future NASA space initiatives. Efforts are focused upon increasing system thermal and electric energy conversion efficiency at least fivefold over current SP-100 technology, and on achieving systems that are compatible with space nuclear reactors. The status of test activities with the Space Power Research Engine (SPRE) is discussed. Design deficiencies are gradually being corrected and the power converter is now outputting 11.5 kWe at a temperature ratio of 2 (design output is 12.5 kWe). Detail designs were completed for the 1050 K Component Test Power Converter (CTPC). The success of these and future designs is dependent upon supporting research and technology efforts including heat pipes, gas bearings, superalloy joining technologies and high efficiency alternators. An update of progress in these technologies is provided.

Dudenhoefer, James E.↗