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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Semicarbazide-sensitive amine oxidase and extracellular matrix deposition by smooth-muscle cells

We have recently reported in vivo disruption of collagen and elastin architecture within blood vessel walls resulting from the selective inhibition of the enzyme semicarbazide-sensitive amine oxidase (SSAO). This study further investigates the effects of SSAO inhibition on extracellular matrix deposition by smooth-muscle cells (SMCs) cultured from neonatal rat hearts. SMCs were characterized, SSAO activity was measured, and soluble and insoluble collagen and elastin in the extracellular matrix (ECM) were quantified. Cultured neonatal rat heart SMC exhibited a monotypic synthetic phenotype that likely represents a myofibroblast. Detectable levels of SSAO activity present throughout 30-d culture peaked at 7-14 d, coinciding with the production of ECM. The addition of enzyme inhibitors and alternate SSAO substrates (benzylamine) produced varied and, in some cases, marked changes in SSAO activity as well as in the composition of mature and soluble matrix components. Similar to our previous in vivo findings, in vitro SSAO inhibition produced aberrations in collagen and elastin deposition by heart SMC. Because changes in SSAO activity are associated with cardiovascular pathologic states, this enzyme may play a protective or modulating role by regulating ECM production during pathologic insult.

Allylamine/administration & dosage/analogs & deriv↗
NASA NTRS2001

STEM Analysis of Caenorhabditis elegans muscle thick filaments: evidence for microdifferentiated substructures

In the thick filaments of body muscle in Caenorhabditis elegans, myosin A and myosin B isoforms and a subpopulation of paramyosin, a homologue of myosin heavy chain rods, are organized about a tubular core. As determined by scanning transmission electron microscopy, the thick filaments show a continuous decrease in mass-per-length (MPL) from their central zones to their polar regions. This is consistent with previously reported morphological studies and suggests that both their content and structural organization are microdifferentiated as a function of position. The cores are composed of a second distinct subpopulation of paramyosin in association with the alpha, beta, and gamma-filagenins. MPL measurements suggest that cores are formed from seven subfilaments containing four strands of paramyosin molecules, rather than the two originally proposed. The periodic locations of the filagenins within different regions and the presence of a central zone where myosin A is located, implies that the cores are also microdifferentiated with respect to molecular content and structure. This differentiation may result from a novel "induced strain" assembly mechanism based upon the interaction of the filagenins, paramyosin and myosin A. The cores may then serve as "differentiated templates" for the assembly of myosin B and paramyosin in the tapering, microdifferentiated polar regions of the thick filaments.

NASA Discipline Musculoskeletal↗
NASA NTRS1998

Constitutive properties of adult mammalian cardiac muscle cells

BACKGROUND: The purpose of this study was to determine whether changes in the constitutive properties of the cardiac muscle cell play a causative role in the development of diastolic dysfunction. METHODS AND RESULTS: Cardiocytes from normal and pressure-hypertrophied cats were embedded in an agarose gel, placed on a stretching device, and subjected to a change in stress (sigma), and resultant changes in cell strain (epsilon) were measured. These measurements were used to examine the passive elastic spring, viscous damping, and myofilament activation. The passive elastic spring was assessed in protocol A by increasing the sigma on the agarose gel at a constant rate to define the cardiocyte sigma-versus-epsilon relationship. Viscous damping was assessed in protocol B from the loop area between the cardiocyte sigma-versus-epsilon relationship during an increase and then a decrease in sigma. In both protocols, myofilament activation was minimized by a reduction in [Ca2+]i. Myofilament activation effects were assessed in protocol C by defining cardiocyte sigma versus epsilon during an increase in sigma with physiological [Ca2+]i. In protocol A, the cardiocyte sigma-versus-epsilon relationship was similar in normal and hypertrophied cells. In protocol B, the loop area was greater in hypertrophied than normal cardiocytes. In protocol C, the sigma-versus-epsilon relation in hypertrophied cardiocytes was shifted to the left compared with normal cells. CONCLUSIONS: Changes in viscous damping and myofilament activation in combination may cause pressure-hypertrophied cardiocytes to resist changes in shape during diastole and contribute to diastolic dysfunction.

NASA Discipline Cardiopulmonary↗
NASA NTRS1998

Gel stretch method: a new method to measure constitutive properties of cardiac muscle cells

Diastolic dysfunction is an important cause of congestive heart failure; however, the basic mechanisms causing diastolic congestive heart failure are not fully understood, especially the role of the cardiac muscle cell, or cardiocyte, in this process. Before the role of the cardiocyte in this pathophysiology can be defined, methods for measuring cardiocyte constitutive properties must be developed and validated. Thus this study was designed to evaluate a new method to characterize cardiocyte constitutive properties, the gel stretch method. Cardiocytes were isolated enzymatically from normal feline hearts and embedded in a 2% agarose gel containing HEPES-Krebs buffer and laminin. This gel was cast in a shape that allowed it to be placed in a stretching device. The ends of the gel were held between a movable roller and fixed plates that acted as mandibles. Distance between the right and left mandibles was increased using a stepper motor system. The force applied to the gel was measured by a force transducer. The resultant cardiocyte strain was determined by imaging the cells with a microscope, capturing the images with a CCD camera, and measuring cardiocyte and sarcomere length changes. Cardiocyte stress was characterized with a finite-element method. These measurements of cardiocyte stress and strain were used to determine cardiocyte stiffness. Two variables affecting cardiocyte stiffness were measured, the passive elastic spring and viscous damping. The passive spring was assessed by increasing the force on the gel at 1 g/min, modeling the resultant stress vs. strain relationship as an exponential [sigma = A/k(ekepsilon - 1)]. In normal cardiocytes, A = 23.0 kN/m2 and k = 16. Viscous damping was assessed by examining the loop area between the stress vs. strain relationship during 1 g/min increases and decreases in force. Normal cardiocytes had a finite loop area = 1.39 kN/m2, indicating the presence of viscous damping. Thus the gel stretch method provided accurate measurements of cardiocyte constitutive properties. These measurements have allowed the first quantitative assessment of passive elastic spring properties and viscous damping in normal mammalian cardiocytes.

Non-NASA Center↗
NASA NTRS1996

Effects of pressure- or volume-overload hypertrophy on passive stiffness in isolated adult cardiac muscle cells

It has been hypothesized that the changes in myocardial stiffness induced by chronic hemodynamic overloading are dependent on changes in the passive stiffness of the cardiac muscle cell (cardiocyte). However, no previous studies have examined the passive constitutive properties of cardiocytes isolated from animals with myocardial hypertrophy. Accordingly, changes in relative passive stiffness of cardiocytes isolated from animals with chronic pressure- or volume-overload hypertrophy were determined by examining the effects of anisosmotic stress on cardiocyte size. Anisosmotic stress was produced by altering superfusate osmolarity. Hypertrophied cardiocytes were enzymatically isolated from 16 adult cats with right ventricular (RV) pressure-overload hypertrophy induced by pulmonary artery banding (PAB) and from 6 adult cats with RV volume-overload hypertrophy induced by creating an atrial septal defect (ASD). Left ventricular (LV) cardiocytes from each cat served as nonhypertrophied, normally loaded, same-animal controls. Superfusate osmolarity was decreased from 305 +/- 3 to 135 +/- 5 mosM and increased to 645 +/- 4 mosM. During anisosmotic stress, there were no significant differences between hypertrophied RV and normal LV cardiocytes in pressure overload PAB cats with respect to percent change in cardiocyte area (47 +/- 2% in RV vs. 48 +/- 2% in LV), diameter (46 +/- 3% in RV vs. 48 +/- 2% in LV), or length (2.4 +/- 0.2% in RV vs. 2.0 +/- 0.3% in LV), or sarcomere length (1.5 +/- 0.1% in RV vs. 1.3 +/- 0.3% in LV). Likewise, there were no significant differences in cardiocyte strain between hypertrophied RV and normal LV cardiocytes from ASD cats. In conclusion, chronic pressure-overload hypertrophy and chronic volume-overload hypertrophy did not alter the cardiocyte response to anisosmotic stress. Thus chronic overload hypertrophy did not alter relative passive cardiocyte stiffness.

Non-NASA Center↗
NASA NTRS1996

Effects of anisosmotic stress on cardiac muscle cell length, diameter, area, and sarcomere length

The purpose of this study was to examine the effects of anisosmotic stress on adult mammalian cardiac muscle cell (cardiocyte) size. Cardiocyte size and sarcomere length were measured in cardiocytes isolated from 10 normal rats and 10 normal cats. Superfusate osmolarity was decreased from 300 +/- 6 to 130 +/- 5 mosM and increased to 630 +/- 8 mosM. Cardiocyte size and sarcomere length increased progressively when osmolarity was decreased, and there were no significant differences between cat and rat cardiocytes with respect to percent change in cardiocyte area or diameter; however, there were significant differences in cardiocyte length (2.8 +/- 0.3% in cat vs. 6.1 +/- 0.3% in rat, P < 0.05) and sarcomere length (3.3 +/- 0.3% in cat vs. 6.1 +/- 0.3% in rat, P < 0.05). To determine whether these species-dependent differences in length were related to diastolic interaction of the contractile elements or differences in relative passive stiffness, cardiocytes were subjected to the osmolarity gradient 1) during treatment with 7 mM 2,3-butanedione monoxime (BDM), which inhibits cross-bridge interaction, or 2) after pretreatment with 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N, N,N',N'-tetraacetic acid (EGTA), a bivalent Ca2+ chelator. Treatment with EGTA or BDM abolished the differences between cat and rat cardiocytes. Species-dependent differences therefore appeared to be related to the degree of diastolic cross-bridge association and not differences in relative passive stiffness. In conclusion, the osmolarity vs. cell size relation is useful in assessing the cardiocyte response to anisosmotic stress and may in future studies be useful in assessing changes in relative passive cardiocyte stiffness produced by pathological processes.

Non-NASA Center↗
NASA NTRS1992

Effects of training on muscle O2 transport at VO2max

To quantify the relative contributions of convective and peripheral diffusive components of O2 transport to the increase in leg O2 uptake (VO2leg) at maximum O2 uptake (VO2max) after 9 wk of endurance training, 12 sedentary subjects (age 21.8 +/- 3.4 yr, VO2max 36.9 +/- 5.9 ml.min-1.kg-1) were studied. VO2max, leg blood flow (Qleg), and arterial and femoral venous PO2, and thus VO2leg, were measured while the subjects breathed room air, 15% O2, and 12% O2. The sequence of the three inspirates was balanced. After training, VO2max and VO2leg increased at each inspired O2 concentration [FIO2; mean over the 3 FIO2 values 25.2 +/- 17.8 and 36.5 +/- 33% (SD), respectively]. Before training, VO2leg and mean capillary PO2 were linearly related through the origin during hypoxia but not during room air breathing, suggesting that, at 21% O2, VO2max was not limited by O2 supply. After training, VO2leg and mean capillary PO2 at each FIO2 fell along a straight line with zero intercept, just as in athletes (Roca et al. J. Appl. Physiol. 67: 291-299, 1989). Calculated muscle O2 diffusing capacity (DO2) rose 34% while Qleg increased 19%. The relatively greater rise in DO2 increased the DO2/Qleg, which led to 9.9% greater O2 extraction. By numerical analysis, the increase in Qleg alone (constant DO2) would have raised VO2leg by 35 ml/min (mean), but that of DO2 (constant Qleg) would have increased VO2leg by 85 ml/min, more than twice as much. The sum of these individual effects (120 ml/min) was less (P = 0.013) than the observed rise of 164 ml/min (mean). This synergism (explained by the increase in DO2/Qleg) seems to be an important contribution to increases in VO2max with training.

NASA Discipline Musculoskeletal↗
NASA NTRS2005

Small Dog-Like Quadruped Robot Powered With McKibben Air Muscles

Planetary surface robotic exploration is typically done by wheeled robots, which are limited to traveling on relatively flat terrain. The goal of this project was to design a bio-inspired robot to mimic the movements and agility of animals to navigate in various types of natural terrain, such as found on Mars. My objective for the summer was to design and construct a quadruped robot with a locomotion gait similar to a small dog. The design includes four legs and an actuated flexible spine for added mobility and performance; each leg has three joints - hip, knee, and ankle. I created 3D CAD models and machined the pieces for the assemblies of each part. One of the key areas of concern is weight vs. power issues for the driving force of locomotion. To maximize the power-to-weight ratio, I used McKibben air muscles to drive the motion of the quadruped. The prototype went through several iterations to analyze performance, with adjustments made to each assembly. We expect the final working prototype will be capable of standing unassisted and pronking into the air without active control. It will serve as a research platform for future bio-inspired control algorithms.

Lacy, John M.↗
NASA NTRS1997

Low Mass Muscle Actuators (LoMMAs) Using Electroactive Polymers

NASA is using actuation devices for many space applications and there is an increasing need to cut their cost as well as reduce their size, mass, and power consumption. Existing transducing actuators, such as piezoceramics, are inducing limited displacement levels. Potentially, electroactive polymers (so called EAP) can be formed as inexpensive, low-mass, low-power, miniature muscle actuators that are superior to the widely used actuators.

actuators electroactive polymers active materials↗
NASA NTRS2001

Biologically inspired toys using artificial muscles

Recent developments in electroactive polymers, so-called artificial muscles, could one day be used to make bionics possible. Meanwhile, as this technology evolves novel mechanisms are expected to emerge that are biologically inspired.

bionics↗
NASA NTRS2006

Supine Treadmill Exercise in Lower Body Negative Pressure Combined with Resistive Exercise Counteracts Bone Loss, Reduced Aerobic Upright Exercise Capacity and Reduced Muscle Strength

Long-term exposure to weightlessness leads to cardiovascular and musculoskeletal deconditioning. In this report, the effectiveness of combined supine treadmill exercise in a lower body negative pressure chamber (LBNPex) and flywheel resistive exercise (Rex) countermeasures was determined to prevent bone loss, reduced aerobic upright exercise capacity and reduced muscle strength. We hypothesized that exercise subjects would show less decrease in bone mineral density (BMD), peak oxygen consumption (VO2pk) and knee extensor strength (KES) than control subjects. Sixteen healthy female subjects participated in a 60-d 6(sup 0) head-down tilt bed rest (BR) study after providing written informed consent. Subjects were assigned to one of two groups: a non-exercising control group CON or an exercise group EX performing LBNPex 2-4 d/wk and Rex every 3rd-d. VO2pk was measured with a maximal, graded, upright treadmill test performed pre-BR and on 3-d after BR. BMD was assessed before and 3-d after BR. Isokinetic KES was measured before and 5-d after BR. Two-way repeated measures ANOVA were performed. Statistical significance was set at p less than 0.05. CON experienced a significant decrease in BMD in the trochanter (PRE: 0.670 plus or minus 0.045; POST: 0.646 plus or minus 0.352 g (raised dot) per square centimeter) and in the whole hip (PRE=0.894 plus or minus 0.059; POST: 0.858 plus or minus 0.057 g (raised dot) per square centimeter). BMD also decreased significantly in EX in the trochanter (PRE: 0.753 plus or minus 0.0617; POST: 0.741 plus or minus 0.061 g (raised dot) per square centimeter) and whole hip (PRE: 0.954 plus or minus 0.067; POST: 0.935 plus or minus 0.069 g (raised dot) per square centimeter). BMD losses were significantly less in EX than in CON subjects. VO2pk was significantly decreased in the CON after BR (PRE: 38.0 plus or minus 4.8; POST: 29.9 plus or minus 4.2 ml (raised dot) per kilogram per minute), but not in the EX (PRE: 39.0 plus or minus 2.0; POST: 37.8 plus or minus 1.9 ml (raised dot) per kilogram per minute). KES was significantly reduced by 30% in Con (PRE: 113 plus or minus 12; POST: 78 plus or minus 8 N-m), but was not different in EX (PRE: 126 plus or minus 25; POST: 115 plus or minus 25 N-m). The combination LBNPex and Rex during 60-d BR protects against cardiovascular and musculoskeletal deconditioning and may be efficacious countermeasure for prolonged space flight.

Meuche, Sabine↗
NASA NTRS1980

Automated quantitative muscle biopsy analysis system

An automated system to aid the diagnosis of neuromuscular diseases by producing fiber size histograms utilizing histochemically stained muscle biopsy tissue. Televised images of the microscopic fibers are processed electronically by a multi-microprocessor computer, which isolates, measures, and classifies the fibers and displays the fiber size distribution. The architecture of the multi-microprocessor computer, which is iterated to any required degree of complexity, features a series of individual microprocessors P.sub.n each receiving data from a shared memory M.sub.n-1 and outputing processed data to a separate shared memory M.sub.n+1 under control of a program stored in dedicated memory M.sub.n.

Castleman, Kenneth R.↗
NASA NTRS2009

Biosensors for EVA: Muscle Oxygen and pH During Walking, Running and Simulated Reduced Gravity

During lunar excursions in the EVA suit, real-time measurement of metabolic rate is required to manage consumables and guide activities to ensure safe return to the base. Metabolic rate, or oxygen consumption (VO2), is normally measured from pulmonary parameters but cannot be determined with standard techniques in the oxygen-rich environment of a spacesuit. Our group developed novel near infrared spectroscopic (NIRS) methods to calculate muscle oxygen saturation (SmO2), hematocrit, and pH, and we recently demonstrated that we can use our NIRS sensor to measure VO2 on the leg during cycling. Our NSBRI-funded project is looking to extend this methodology to examine activities which more appropriately represent EVA activities, such as walking and running and to better understand factors that determine the metabolic cost of exercise in both normal and lunar gravity. Our 4 year project specifically addresses risk: ExMC 4.18: Lack of adequate biomedical monitoring capability for Constellation EVA Suits and EPSP risk: Risk of compromised EVA performance and crew health due to inadequate EVA suit systems.

Lee, S. M. C.↗
NASA NTRS2010

A Ground-Based Comparison of the Muscle Atrophy Research and Exercise System (MARES) and a Standard Isokinetic Dynamometer

PURPOSE: 1) To compare the test-to-test reliability of Muscle Atrophy Research and Exercise System (MARES) with a standard laboratory isokinetic dynamometer (ISOK DYN) and; 2) to determine if measures of peak torque and total work differ between devices. METHODS: Ten subjects (6M, 4F) completed two trials on both MARES and an ISOK DYN in a counterbalanced order. Peak torque values at 60 deg & 180 deg / s were obtained from five maximal repetitions of knee extension (KE) and knee flexion (KF). Total work at 180 deg / s was determined from the area under the torque vs. displacement curve during twenty maximal repetitions of KE and KF. Reliability of measures within devices was interpreted from the intraclass correlation coefficient (ICC) and compared between devices using the ratio of the within-device standard deviations. Indicators of agreement for the two devices were evaluated from: 1) a calculation of concordance (rho) and; 2) the correlation between the mean of measures versus the delta difference between measures (m u vs delta). RESULTS: For all outcome measures ICCs were high for both the ISOK DYN (0.95-0.99) and MARES (0.90-0.99). However, ratios of the within-device standard deviation were 1.3 to 4.3 times higher on MARES. On average, a wide range (3.3 to 1054 Nm) of differences existed between the values obtained. Only KE peak torque measured at 60 deg & 180 deg / s showed similarities between devices (rho = 0.91 & 0.87; Pearson's r for m u vs delta = -0.22 & -0.37, respectively). CONCLUSION: Although MARES was designed for use in microgravity it was quite reliable during ground-based testing. However, MARES was consistently more variable than an ISOK DYN. Future longitudinal studies evaluating a change in isokinetic peak torque or total work should be limited within one device.

Hackney, K. J.↗
NASA NTRS2002

Prediction of Muscle Performance During Dynamic Repetitive Exercise

A method for predicting human muscle performance was developed. Eight test subjects performed a repetitive dynamic exercise to failure using a Lordex spinal machine. Electromyography (EMG) data was collected from the erector spinae. Evaluation of the EMG data using a 5th order Autoregressive (AR) model and statistical regression analysis revealed that an AR parameter, the mean average magnitude of AR poles, can predict performance to failure as early as the second repetition of the exercise. Potential applications to the space program include evaluating on-orbit countermeasure effectiveness, maximizing post-flight recovery, and future real-time monitoring capability during Extravehicular Activity.

Byerly, D. L.↗
NASA NTRS2013

A Simple GPU-Accelerated Two-Dimensional MUSCL-Hancock Solver for Ideal Magnetohydrodynamics

We describe our experience using NVIDIA's CUDA (Compute Unified Device Architecture) C programming environment to implement a two-dimensional second-order MUSCL-Hancock ideal magnetohydrodynamics (MHD) solver on a GTX 480 Graphics Processing Unit (GPU). Taking a simple approach in which the MHD variables are stored exclusively in the global memory of the GTX 480 and accessed in a cache-friendly manner (without further optimizing memory access by, for example, staging data in the GPU's faster shared memory), we achieved a maximum speed-up of approx. = 126 for a sq 1024 grid relative to the sequential C code running on a single Intel Nehalem (2.8 GHz) core. This speedup is consistent with simple estimates based on the known floating point performance, memory throughput and parallel processing capacity of the GTX 480.

graphics processing units↗
NASA NTRS2015

Load Bearing Equipment for Bone and Muscle Project

Axial skeletal loads coupled with muscle torque forces around joints maintain bone. Astronauts working in pairs to exercise can provide high eccentric loads for each other that are most effective. A prototype of load bearing equipment that will allow astronauts to perform exercises using each other for counter force generation in a controlled fashion and provide eccentric overload is proposed. A frame and attachments that can be rapidly assembled for use and easily stored will demonstrate feasibility of a design that can be adapted for ISS testing and Orion use.

Terrier, Douglas↗
NASA NTRS2015

Load Bearing Equipment for Bone and Muscle

Resistance exercise on ISS has proven effective in maintaining bone mineral density and muscle mass. Exploration missions require exercise with similar high loads using equipment with less mass and volume and greater safety and reliability than resistance exercise equipment used on ISS (iRED, ARED, FWED). Load Bearing Equipment (LBE) uses each exercising person to create and control the load to the partner.

Shackelford, Linda↗