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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Cardiovascular function following reduced aerobic activity

PURPOSE: The aim of this study was to test the hypothesis that a sustained reduction of physical activity (deconditioning) would alter the cardiovascular regulatory function. METHODS: Nineteen young, healthy volunteers participated in physical deconditioning for a period of 8 wk. Before (pre) and following (post) physical deconditioning, the responses of heart rate (HR), mean arterial pressure (MAP, measured by Finapres), central venous pressure (CVP), stroke volume (SV, Doppler), and forearm blood flow (FBF, plethysmography) were determined during lower body negative pressure (LBNP). The carotid baroreflex (CBR) function was assessed using a train of pulsatile neck pressure (NP) and suction, and the aortic baroreflex control of HR was assessed during steady-state phenylephrine (PE) infusion superimposed by LBNP and NP to counteract the PE increased CVP and carotid sinus pressure, respectively. RESULTS: Active physical deconditioning significantly decreased maximal oxygen uptake (-7%) and LBNP tolerance (-13%) without a change in baseline hemodynamics. Plasma volume (-3% at P = 0.135), determined by Evans Blue dilution, and blood volume (-4% at P = 0.107) were not significantly altered. During LBNP -20 to -50 torr, there was a significantly greater drop of SV per unit decrease in CVP in the post- (14.7 +/- 1.6%/mm Hg) than predeconditioning (11.2 +/- 0.7%/mm Hg) test accompanied by a greater tachycardia. Deconditioning increased the aortic baroreflex sensitivity (pre vs post: -0.61 +/- 0.12 vs -0.84 +/- 0.14 bpm.mm-1 Hg, P = 0.009) and the slope of forearm vascular resistance (calculated from [MAP-CVP]/FBF) to CVP (-2.75 +/- 0.26 vs -4.94 +/- 0.97 PRU/mm Hg, P = 0.086). However, neither the CBR-HR (-0.28 +/- 0.03 VS -0.39 +/- 0.10 bpm.mm-1 Hg) nor the CBR-MAP (-0.37 +/- 0.16 vs -0.25 +/- 0.07 mm Hg/mm Hg) gains were statistically different between pre- and postdeconditioning. CONCLUSIONS: We concluded that the functional modification of the cardiac pressure-volume relationship resulted in the reduced LBNP tolerance, despite the accentuated aortic and cardiopulmonary baroreflex function following deconditioning.

Non-NASA Center↗
NASA NTRS1998

Relative size perception at a distance is best at eye level

Relative size judgments were collected for two objects at 30.5 m and 23.8 from the observer in order to assess how performance depends on the relationship between the size of the objects and the eye level of the observer. In three experiments in an indoor hallway and in one experiment outdoors, accuracy was higher for objects in the neighborhood of eye level. We consider these results in the light of two hypotheses. One proposes that observers localize the horizon as a reference for judging relative size, and the other proposes that observers perceive the general neighborhood of the horizon and then employ a height-in-visual-field heuristic. The finding that relative size judgments are best around the horizon implies that information that is independent of distance perception is used in perceiving size.

NASA Center ARC↗
NASA NTRS1998

Cytoskeletal role in the transition from compensated to decompensated hypertrophy during adult canine left ventricular pressure overloading

Increased microtubule density causes cardiocyte contractile dysfunction in right ventricular (RV) pressure-overload hypertrophy, and these linked phenotypic and contractile abnormalities persist and progress during the transition to failure. Although more severe in cells from failing than hypertrophied RVs, the mechanical defects are normalized in each case by microtubule depolymerization. To define the role of increased microtubule density in left ventricular (LV) pressure-overload hypertrophy and failure, in a given LV we examined ventricular mechanics, sarcomere mechanics, and free tubulin and microtubule levels in control dogs and in dogs with aortic stenosis both with LV hypertrophy alone and with initially compensated hypertrophy that had progressed to LV muscle failure. In comparing initial values with those at study 8 weeks later, dogs with hypertrophy alone had a very substantial increase in LV mass but preservation of a normal ejection fraction and mean systolic wall stress. Dogs with hypertrophy and associated failure had a substantial but lesser increase in LV mass and a reduction in ejection fraction, as well as a marked increase in mean systolic wall stress. Cardiocyte contractile function was equivalent, and unaffected by microtubule depolymerization, in cells from control LVs and those with compensated hypertrophy. In contrast, cardiocyte contractile function in cells from failing LVs was quite depressed but was normalized by microtubule depolymerization. Microtubules were increased only in failing LVs. These contractile and cytoskeletal changes, when assayed longitudinally in a given dog by biopsy, appeared in failing ventricles only when wall stress began to increase and function began to decrease. Thus, the microtubule-based cardiocyte contractile dysfunction characteristic of pressure-hypertrophied myocardium, originally described in the RV, obtains equally in the LV but is shown here to have a specific association with increased wall stress.

Non-NASA Center↗
NASA NTRS1998

Working and strategic memory deficits in schizophrenia

Working memory and its contribution to performance on strategic memory tests in schizophrenia were studied. Patients (n = 18) and control participants (n = 15), all men, received tests of immediate memory (forward digit span), working memory (listening, computation, and backward digit span), and long-term strategic (free recall, temporal order, and self-ordered pointing) and nonstrategic (recognition) memory. Schizophrenia patients performed worse on all tests. Education, verbal intelligence, and immediate memory capacity did not account for deficits in working memory in schizophrenia patients. Reduced working memory capacity accounted for group differences in strategic memory but not in recognition memory. Working memory impairment may be central to the profile of impaired cognitive performance in schizophrenia and is consistent with hypothesized frontal lobe dysfunction associated with this disease. Additional medial-temporal dysfunction may account for the recognition memory deficit.

Memory Disorders/etiology/physiopathology↗
NASA NTRS1998

Autoregulation of cerebral blood flow in orthostatic hypotension

BACKGROUND AND PURPOSE: We sought to evaluate cerebral autoregulation in patients with orthostatic hypotension (OH). METHODS: We studied 21 patients (aged 52 to 78 years) with neurogenic OH during 80 degrees head-up tilt. Blood flow velocities (BFV) from the middle cerebral artery were continuously monitored with transcranial Doppler sonography, as were heart rate, blood pressure (BP), cardiac output, stroke volume, CO2, total peripheral resistance, and cerebrovascular resistance. RESULTS: All OH patients had lower BP (P<.0001), BFV_diastolic (P<.05), CVR (P<.007), and TPR (P<.02) during head-up tilt than control subjects. In control subjects, no correlations between BFV and BP were found during head-up tilt, suggesting normal autoregulation. OH patients could be separated into those with normal or expanded autoregulation (OH_NA; n=16) and those with autoregulatory failure (OH_AF; n=5). The OH_NA group showed either no correlation between BFV and BP (n=8) or had a positive BFV/BP correlation (R2>.75) but with a flat slope. An expansion of the "autoregulated" range was seen in some patients. The OH_AF group was characterized by a profound fall in BFV in response to a small reduction in BP (mean deltaBP <40 mm Hg; R2>.75). CONCLUSIONS: The most common patterns of cerebral response to OH are autoregulatory failure with a flat flow-pressure relationship or intact autoregulation with an expanded autoregulated range. The least common pattern is autoregulatory failure with a steep flow-pressure relationship. Patients with patterns 1 and 2 have an enhanced capacity to cope with OH, while those with pattern 3 have reduced capacity.

Non-NASA Center↗
NASA NTRS1997

Anterior segment sparing to reduce charged particle radiotherapy complications in uveal melanoma

PURPOSE: The purpose of this investigation is to delineate the risk factors in the development of neovascular glaucoma (NVG) after helium-ion irradiation of uveal melanoma patients and to propose treatment technique that may reduce this risk. METHODS AND MATERIALS: 347 uveal melanoma patients were treated with helium-ions using a single-port treatment technique. Using univariate and multivariate statistics, the NVG complication rate was analyzed according to the percent of anterior chamber in the radiation field, tumor size, tumor location, sex, age, dose, and other risk factors. Several University of California San Francisco-Lawrence Berkeley National Laboratory (LBNL) patients in each size category (medium, large, and extralarge) were retrospectively replanned using two ports instead of a single port. By using appropriate polar and azimuthal gaze angles or by treating patients with two ports, the maximum dose to the anterior segment of the eye can often be reduced. Although a larger volume of anterior chamber may receive a lower dose by using two ports than a single port treatment. We hypothesize that this could reduce the level of complications that result from the irradiation of the anterior chamber of the eye. Dose-volume histograms were calculated for the lens, and compared for the single and two-port techniques. RESULTS: NVG developed in 121 (35%) patients. The risk of NVG peaked between 1 and 2.5 years posttreatment. By univariate and multivariate analysis, the percent of lens in the field was strongly correlated with the development of NVG. Other contributing factors were tumor height, history of diabetes, and vitreous hemorrhage. Dose-volume histogram analysis of single-port vs. two-port techniques demonstrate that for some patients in the medium and large category tumor groups, a significant decrease in dose to the structures in the anterior segment of the eye could have been achieved with the use of two ports. CONCLUSION: The development of NVG after helium-ion irradiation is correlated to the amount of lens, anterior chamber in the treatment field, tumor height, proximity to the fovea, history of diabetes, and the development of vitreous hemorrhage. Although the influence of the higher LET deposition of helium-ions is unclear, this study suggests that by reducing the dose to the anterior segment of the eye may reduce the NVG complications. Based on this retrospective analysis of LBNL patients, we have implemented techniques to reduce the amount of the anterior segment receiving a high dose in our new series of patients treated with protons using the cyclotron at the UC Davis Crocker Nuclear Laboratory (CNL).

NASA Discipline Radiation Health↗
NASA NTRS1997

Insulin attenuates atrophy of unweighted soleus muscle by amplified inhibition of protein degradation

Unweighting atrophy of immature soleus muscle occurs rapidly over the first several days, followed by slower atrophy coinciding with increased sensitivity to insulin of in vitro protein metabolism. This study determined whether this increased sensitivity might account for the diminution of atrophy after 3 days of tall-cast hindlimb suspension. The physiological significance of the increased response to insulin in unweighted muscle was evaluated by analyzing in vivo protein metabolism for day 3 (48 to 72 hours) and day 4 (72 to 96 hours) of unweighting in diabetic animals either injected with insulin or not treated. Soleus from nontreated diabetic animals showed a similar loss of protein during day 3 (-16.2%) and day 4 (-14.5%) of unweighting, whereas muscle from insulin-treated animals showed rapid atrophy (-14.5%) during day 3 only, declining to just -3.1% the next day. Since fractional protein synthesis was similar for both day 3 (8.6%/d) and day 4 (7.0%/d) of unweighting in insulin-treated animals, the reduction in protein loss must be accounted for by a slowing of protein degradation due to circulating insulin. Intramuscular (IM) injection of insulin (600 nmol/L) stimulated in situ protein synthesis similarly in 4-day unweighted (+56%) and weight-bearing (+90%) soleus, even though unweighted muscle showed a greater in situ response of 2-deoxy-[3H]glucose uptake to IM injection of either insulin (133 nmol/L) or insulin-like growth factor-I (IGF-I) (200 nmol/L) than control muscle. These findings suggest that unweighted muscle is selectively more responsive in vivo to insulin, and that the slower atrophy after 3 days of unweighting was due to an increased effect of insulin on inhibiting protein degradation.

NASA Discipline Musculoskeletal↗
NASA NTRS1997

The effect of optokinetic stimulation on daytime sleepiness

This study examined the effect of optokinetic stimulation on objective sleepiness, as measured by the Multiple Sleep Latency Test (MSLT). The Nightcap, a portable sleep monitor, was used in a novel way to perform MSLTs, as well as record sleep in the home. Subjects wore the Nightcap for seven consecutive nights. On days 3 and 5 of the protocol, subjects came into the lab for an MSLT. On the experimental day, subjects underwent 10 minutes optokinetic stimulation (OKS), resulting in moderate motion sickness prior to each MSLT trial. Although subjects in the OKS condition reported significantly more drowsiness than controls, this did not result in significantly reduced sleep latencies.

NASA Discipline Neuroscience↗
NASA NTRS1997

Effects of static fingertip loading on carpal tunnel pressure

The purpose of this study was to explore the relationship between carpal tunnel pressure and fingertip force during a simple pressing task. Carpal tunnel pressure was measured in 15 healthy volunteers by means of a saline-filled catheter inserted percutaneously into the carpal tunnel of the nondominant hand. The subjects pressed on a load cell with the tip of the index finger and with 0, 6, 9, and 12 N of force. The task was repeated in 10 wrist postures: neutral; 10 and 20 degrees of ulnar deviation; 10 degrees of radial deviation; and 15, 30, and 45 degrees of both flexion and extension. Fingertip loading significantly increased carpal tunnel pressure for all wrist angles (p = 0.0001). Post hoc analyses identified significant increase (p < 0.05) in carpal tunnel pressure between unloaded (0 N) and all loaded conditions, as well as between the 6 and 12 N load conditions. This study demonstrates that the process whereby fingertip loading elevates carpal tunnel pressure is independent of wrist posture and that relatively small fingertip loads have a large effect on carpal tunnel pressure. It also reveals the response characteristics of carpal tunnel pressure to fingertip loading, which is one step in understanding the relationship between sustained grip and pinch activities and the aggravation or development of median neuropathy at the wrist.

NASA Center ARC↗
NASA NTRS1997

Neuromuscular activation patterns during treadmill walking after space flight

Astronauts adopt a variety of neuromuscular control strategies during space flight that are appropriate for locomoting in that unique environment, but are less than optimal upon return to Earth. We report here the first systematic investigation of potential adaptations in neuromuscular activity patterns associated with postflight locomotion. Astronaut-subjects were tasked with walking on a treadmill at 6.4 km/h while fixating a visual target 30 cm away from their eyes after space flights of 8-15 days. Surface electromyography was collected from selected lower limb muscles and normalized with regard to mean amplitude and temporal relation to heel strike. In general, high correlations (more than 0.80) were found between preflight and postflight activation waveforms for each muscle and each subject: however relative activation amplitude around heel strike and toe off was changed as a result of flight. The level of muscle cocontraction and activation variability, and the relationship between the phasic characteristics of the ankle musculature in preparation for toe off also were altered by space flight. Subjects also reported oscillopsia during treadmill walking after flight. These findings indicate that, after space flight, the sensory-motor system can generate neuromuscular-activation strategies that permit treadmill walking, but subtle changes in lower-limb neuromuscular activation are present that may contribute to increased lower limb kinematic variability and oscillopsia also present during postflight walking.

Flight Experiment↗
NASA NTRS1996

A mechanism of adaptation to hypergravity in the statocyst of Aplysia californica

The gravity-sensing organ of Aplysia californica consists of bilaterally paired statocysts containing statoconia, which are granules composed of calcium carbonate crystals in an organic matrix. In early embryonic development, Aplysia contain a single granule called a statolith, and as the animal matures, statoconia production takes place. The objective of this study was to determine the effect of hypergravity on statoconia production and homeostasis and explore a possible physiologic mechanism for regulating this process. Embryonic Aplysia were exposed to normogravity or 3 x g or 5.7 x g and each day samples were analyzed for changes in statocyst, statolith, and body dimensions until they hatched. In addition, early metamorphosed Aplysia (developmental stages 7-10) were exposed to hypergravity (2 x g) for 3 weeks, and statoconia number and statocyst and statoconia volumes were determined. We also determined the effects of hypergravity on statoconia production and homeostasis in statocysts isolated from developmental stage 10 Aplysia. Since prior studies demonstrated that urease was important in the regulation of statocyst pH and statoconia formation, we also evaluated the effect of hypergravity on urease activity. The results show that hypergravity decreased statolith and body diameter in embryonic Aplysia in a magnitude-dependent fashion. In early metamorphosed Aplysia, hypergravity decreased statoconia number and volume. Similarly, there was an inhibition of statoconia production and a decrease in statoconia volume in isolated statocysts exposed to hypergravity in culture. Urease activity in statocysts decreased after exposure to hypergravity and was correlated with the decrease in statoconia production observed. In short, there was a decrease in statoconia production with exposure to hypergravity both in vivo and in vitro and a decrease in urease activity. It is concluded that exposure to hypergravity downregulates urease activity, resulting in a significant decrease in the formation of statoconia.

NASA Program Space Biology↗
NASA NTRS1996

Submaximal exercise VO2 and Qc during 30-day 6 degrees head-down bed rest with isotonic and isokinetic exercise training

BACKGROUND: Maintaining intermediary metabolism is necessary for the health and well-being of astronauts on long-duration spaceflights. While peak oxygen uptake (VO2) is consistently decreased during prolonged bed rest, submaximal VO2 is either unchanged or decreased. METHODS: Submaximal exercise metabolism (61 +/- 3% peak VO2) was measured during ambulation (AMB day-2) and on bed rest days 4, 11, and 25 in 19 healthy men (32-42 yr) allocated into no exercise (NOE, N = 5) control, and isotonic exercise (ITE, N = 7) and isokinetic exercise (IKE, N = 7) training groups. Exercise training was conducted supine for two 30-min periods per day for 6 d per week: ITE training was intermittent at 60-90% peak VO2; IKE training was 10 sets of 5 repetitions of peak knee flexion-extension force at a velocity of 100 degrees s-1. Cardiac output was measured with the indirect Fick CO2 method, and plasma volume with Evans blue dye dilution. RESULTS: Supine submaximal exercise VO2 decreased significantly (*p < 0.05) by 10.3%* with ITE and by 7.3%* with IKE; similar to the submaximal cardiac output decrease of 14.5%* (ITE) and 20.3%* (IKE), but different from change in peak VO2 (+1.4% with ITE and -10.2%* with IKE) and decrease in plasma volume of -3.7% (ITE) and -18.0%* (IKE). Reduction of submaximal VO2 during bed rest correlated 0.79 (p < 0.01) with submaximal Qc, but was not related to change in peak VO2 or plasma volume. CONCLUSION: Reduction in submaximal oxygen uptake during prolonged bed rest is related to decrease in exercise but not resting cardiac output; perturbations in active skeletal muscle metabolism may be involved.

NASA Discipline Regulatory Physiology↗
NASA NTRS1996

Isokinetic and isometric strength-endurance after 6 hours of immersion and 6 degrees head-down tilt in men

PURPOSE: To determine weight (water) loss levels for onset of muscular strength and endurance changes during deconditioning. METHODS: Seven men (27-40 yr) performed maximal shoulder-, knee-, and ankle-joint isometric (0 degree.s(-1) load) and isokinetic (60 degrees, 120 degrees, 180 degrees.s(-1) velocity) exercise tests during ambulatory control (AC), after 6 h of 6 degrees head-down tilt (HDT; dry-bulb temp. = 23.2 +/- SD 0.6 degrees C, relative humidity = 31.1+/- 11.1%) and after 6 h of 80 degrees foot-down head-out water immersion (WI; water temp. = 35.0 +/- SD 0.1 degree C) treatments. RESULTS: Weight (water) loss after HDT (1.10 +/- SE 0.14 kg, 1.4 +/- 0.2% body wt) and WI (1.54+/- 0.19 kg, 2.0 +/- 0.2% body wt) were not different, but urinary excretion with WI (1,354 +/- 142 ml.6 h(-1)) was 28% greater (p < 0.05) than that of 975 +/- 139 ml.6 h(-1) with HDT. Muscular endurance (total work; maximal flexion-extension of the non-dominant knee at 180 degrees.s(-1) for 30 s) was not different between AC and the WI or HDT treatments. Shoulder-, knee-, and ankle-joint strength was unchanged except for three knee-joint peak torques: AC torque (120 degrees.s(-1), 285 +/- 20 Nm) decreased to 268 +/- 21 Nm (delta = -6%, p < 0.05) with WI; and AC torques (180 degrees.s(-1), 260 +/- 19 Nm) decreased to 236 +/- 15 Nm (delta = -9%, p < 0.01) with HDT, and to 235 +/- 19 Nm (delta = -10%, p < 0.01) with WI. CONCLUSION: Thus, the total body hypohydration threshold level for shoulder- and ankle-joint strength and endurance decrements is more than 2% body weight (water) loss, while significant reduction in knee-joint muscular strength-endurance occurred only at moderate (120 degrees.s(-1) and lighter (180 degrees.s(-1)) loads with body weight loss of 1.4-2.0% following WI or HDT, respectively. These weight (water) losses and knee-joint strength decrements are somewhat less than the mean weight loss of 2.6% and knee-joint strength decrements of 6-20% of American astronauts after Skylab flights to 84 d.

NASA Center ARC↗
NASA NTRS1996

The role of retinal versus perceived size in the effects of pitched displays on visually perceived eye level

Visually perceived eye level (VPEL) was measured while subjects viewed two vertical lines which were either upright or pitched about the horizontal axis. In separate conditions, the display consisted of a relatively large pair of lines viewed at a distance of 1 m, or a display scaled to one third the dimensions and viewed at a distance of either 1 m or 33.3 cm. The small display viewed at 33.3 cm produced a retinal image the same size as that of the large display at 1 m. Pitch of all three displays top-toward and top-away from the observer caused upward and downward VPEL shifts, respectively. These effects were highly similar for the large display and the small display viewed at 33.3 cm (ie equal retinal size), but were significantly smaller for the small display viewed at 1 m. In a second experiment, perceived size of the three displays was measured and found to be highly accurate. The results of the two experiments indicate that the effect of optical pitch on VPEL depends on the retinal image size of stimuli rather than on perceived size.

NASA Center ARC↗
NASA NTRS1996

Blood vessel adaptation to gravity in a semi-arboreal snake

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 vessel 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 that catecholamines, as well as other agonists, are important in mediating vascular responses to gravitational stresses in snakes.

NASA Discipline Number 14-10↗
NASA NTRS1996

Relation of systemic and local muscle exercise capacity to skeletal muscle characteristics in men with congestive heart failure

OBJECTIVES. The present study was undertaken to further characterize changes in skeletal muscle morphology and histochemistry in congestive heart failure and to determine the relation of these changes to abnormalities of systemic and local muscle exercise capacity. BACKGROUND. Abnormalities of skeletal muscle appear to play a role in the limitation of exercise capacity in congestive heart failure, but information on the changes in muscle morphology and biochemistry and their relation to alterations in muscle function is limited. METHODS. Eighteen men with predominantly mild to moderate congestive heart failure (mean +/- SEM New York Heart Association functional class 2.6 +/- 0.2, ejection fraction 24 +/- 2%) and eight age- and gender-matched sedentary control subjects underwent measurements of peak systemic oxygen consumption (VO2) during cycle ergometry, resistance to fatigue of the quadriceps femoris muscle group and biopsy of the vastus lateralis muscle. RESULTS. Peak VO2 and resistance to fatigue were lower in the patients with heart failure than in control subjects (15.7 +/- 1.2 vs. 25.1 +/- 1.5 ml/min-kg and 63 +/- 2% vs. 85 +/- 3%, respectively, both p < 0.001). Patients had a lower proportion of slow twitch, type I fibers than did control subjects (36 +/- 3% vs. 46 +/- 5%, p = 0.048) and a higher proportion of fast twitch, type IIab fibers (18 +/- 3% vs. 7 +/- 2%, p = 0.004). Fiber cross-sectional area was smaller, and single-fiber succinate dehydrogenase activity, a mitochondrial oxidative marker, was lower in patients (both p < or = 0.034). Likewise, the ratio of average fast twitch to slow twitch fiber cross-sectional area was lower in patients (0.780 +/- 0.06 vs. 1.05 +/- 0.08, p = 0.019). Peak VO2 was strongly related to integrated succinate dehydrogenase activity in patients (r = 0.896, p = 0.001). Peak VO2, resistance to fatigue and strength also correlated significantly with several measures of fiber size, especially of fast twitch fibers, in patients. None of the skeletal muscle characteristics examined correlated with exercise capacity in control subjects. CONCLUSIONS. These results indicate that congestive heart failure is associated with changes in the characteristics of skeletal muscle and local as well as systemic exercise performance. There are fewer slow twitch fibers, smaller fast twitch fibers and lower succinate dehydrogenase activity. The latter finding suggests that mitochondrial content of muscle is reduced in heart failure and that impaired aerobic-oxidative capacity may play a role in the limitation of systemic exercise capacity.

Non-NASA Center↗
NASA NTRS1995

Hindlimb suspension diminishes femoral cross-sectional growth in the rat

Growth, functional adaptation, and torsional strength were examined in the femora of 39-day-old male Sprague-Dawley rats subjected to hindlimb suspension for 0, 1, 2, 3, or 4 weeks and were compared with measurements for age-matched control animals. Our goal was to understand the effect of reduced loading on the normal age-related changes in femoral properties during growth. The control animals exhibited growth-related increases in all geometric and torsional properties of the femur. The mean body mass and femoral length of the hindlimb-suspended rats were similar to those of the controls throughout the experiment. Over 4 weeks, the femoral cross-sectional and torsional measurements from the hindlimb-suspended rats demonstrated increases in comparison with the basal values (+33% cross-sectional area, +64% polar moment of inertia, +67% ultimate torque, and +181% torsional rigidity), but the age-matched controls showed significantly greater growth-related increases (+71% cross-sectional area, +136% polar moment of inertia, +127% ultimate torque, and +367% torsional rigidity). The differences in femoral structural strength between the hindlimb-suspended animals and the age-matched controls were attributable to differences in altered cross-sectional geometry.

NASA Discipline Musculoskeletal↗