Intensive exercise training during bed rest attenuates deconditioning.

A 30-d 6 degrees head-down bed rest project was conducted to evaluate variable high-intensity, short-duration, isotonic cycle ergometer exercise (ITE) training and high-intensity intermittent resistive isokinetic exercise (IKE) training regimens designed to maintain peak VO2 and muscle mass, strength, and endurance at ambulatory control levels throughout prolonged bed rest. Other elements of the deconditioning (adaptive) syndrome, such as proprioception, psychological performance, hypovolemia, water balance, body composition, and orthostatic tolerance, were also measured. Major findings are summarized in this paper.

An overview of the issues: physiological effects of bed rest and restricted physical activity.

Reduction of exercise capacity with confinement to bed rest is well recognized. Underlying physiological mechanisms include dramatic reductions in maximal stroke volume, cardiac output, and oxygen uptake. However, bed rest by itself does not appear to contribute to cardiac dysfunction.

Reduction of breast biopsies with a modified self-organizing map.

A modified self-organizing map with nonlinear weight adjustments has been applied to reduce the number of breast biopsies necessary for breast cancer diagnosis. Tissue features representing texture information from digital sonographic breast images were extracted from sonograms of benign and malignant breast tumors. The resulting hyperspace of data points was then used in a modified self-organizing map that objectively segments population distributions of lesions and accurately establishes benign and malignant regions.

Pre-exercise hypervolemia and cycle ergometer endurance in men.

Time to exhaustion at 87-91% of peak VO2 was measured in 5 untrained men (age: 31 +/- 8 years, body mass: 74.20 +/- 16.50 kg, body surface area: 1.

American College of Sports Medicine position stand. Heat and cold illnesses during distance running.

Many recreational and elite runners participate in distance races each year. When these events are conducted in hot or cold conditions, the risk of environmental illness increases. However, exertional hyperthermia, hypothermia, dehydration, and other related problems may be minimized with pre-event education and preparation.

Exposure to low-intensity ultrasound increases aggrecan gene expression in a rat femur fracture model.

The effects of ultrasound stimulation on various parameters of bone repair after diaphyseal injury were assessed in a standard rat femur fracture model. Bilateral closed femoral fractures were made in 79 skeletally mature male Long-Evans rats. An ultrasound signal consisting of a 200 microsecond burst sine wave of 0.

Neuroendocrine and immune system responses with spaceflights.

Despite the fact that the first human was in space during 1961 and individuals have existed in a microgravity environment for more than a year, there are limited spaceflight data available on the responses of the neuroendocrine and immune systems. Because of mutual interactions between these respective integrative systems, it is inappropriate to assume that the responses of one have no impact on functions of the other. Blood and plasma volume consistently decrease with spaceflight; hence, blood endocrine and immune constituents will be modified by both gravitational and measurement influences.

Magnetic resonance imaging of transverse acoustic strain waves.

We describe a phase contrast based MRI technique with high sensitivity to cyclic displacement that is capable of quantitatively imaging acoustic strain waves in tissue-like materials. A formalism for considering gradient waveforms as basis functions to measure arbitrary cyclic motion waveforms is introduced. Experiments with tissue-like agarose gel phantoms show that it is possible to measure small cyclic displacements at a submicron level by an appropriate choice of the applied gradient basis function and to use this capability to observe the spatial and temporal pattern of displacements caused by acoustic strain waves.

Acoustic radiation pressure in a three-dimensional lossy medium.

Acoustic radiation pressure exerted by an arbitrary acoustic wave in a three-dimensional lossy medium is calculated by extending an indirect approach developed by Chu and Apfel [B-T. Chu and R.E.

Ultrasound-mediated transfection of mammalian cells.

Mammalian cells were successfully transfected with plasmid DNA in vitro using ultrasound transmitted through the walls of cell culture flasks or plates. Primary rat fibroblasts or chondrocytes were exposed to ultrasound in the presence of plasmids containing lacZ or neo genes. The transfection efficiency was evaluated by counting the number of beta-galactosidase (beta-Gal) positive cells or neomycin-resistant colonies.

Drinking-induced plasma vasopressin and norepinephrine changes in dehydrated humans.

After 24-h water deprivation, five men (23-41 yr; 78 +/- 3.6 kg) consumed, within 4.0-6.

Statistics of the log-compressed echo envelope.

Log compression of A lines to produce B-scan images in clinical ultrasound imaging systems is a standard procedure to control the dynamic range of the images. The statistics of such compressed images in terms of underlying scatterer statistics have not been derived. The statistics are analyzed for partially formed speckle using a general K distribution model of envelope statistics to derive the density function for the log-compressed envelope.

The nonlinear interaction of two plane waves in a viscous medium.

Earlier studies [P.J. Westervelt, J.

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.

Stimulation of secretion from bovine adrenal chromaffin cells by microsecond bursts of therapeutic levels of ultrasound.

1. In this study the secretory response of individual bovine adrenal chromaffin cells was monitored using amperometric carbon-fibre microelectrodes. Cells were stimulated to secrete by exposure to 20-100 microseconds long tonebursts of ultrasound (2-4 x 10(5) Pa; peak pressure at 1 MHz).

The effect of concave and convex weight adjustments on self-organizing maps.

Two nonlinear models of weight adjustments of self-organizing maps are derived to obtain desirable densities of output units, one that approaches the probability distribution p(xi) of the inputs and one that approaches a uniform distribution. If a convex model is used to adjust weights, the density of output units can be made to approach p(xi) instead of the p(xi)(2/3) which results from the linear weight adjustment of Kohonen's self-organizing maps. If a concave model of weight adjustments is used, the density approaches a uniform distribution and the winner frequency distribution of output units is proportional to p(xi).

Adaptive speckle reduction filter for log-compressed B-scan images.

A good statistical model of speckle formation is useful for designing a good adaptive filter for speckle reduction In ultrasound B-scan images. Previously, statistical models have been used, but they failed to account for the log compression of the echo envelope employed by clinical ultrasound systems. Log-compression helps in reducing the dynamic range of the B-scan Images for display on a monitor as well as enhancing weak backscatters.

Real-time assessment of the parameter of nonlinearity in tissue using "nonlinear shadowing".

A real-time pulse-echo method for assessing tissue nonlinearity is presented. Here, tissue nonlinearity refers to the parameter of nonlinearity, B/A, and not the frequency dependence of the attenuation. Our nonlinearity assessment method is based on two pulse transmissions per beam position.

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.

Exercise thermoregulation after 6 h of chair rest, 6 degrees head-down bed-rest, and water immersion deconditioning in men.

The purpose was to investigate the mechanism for the excessive exercise hyperthermia following deconditioning (reduction of physical fitness). Rectal (Tre) and mean skin (Tsk) temperatures and thermoregulatory responses were measured in six men [mean (SD) age, 32 (6) years; mass, 78.26 (5.

Glucose infusion into exercising dogs after confinement: rectal and active muscle temperatures.

Background: Intravenous glucose infusion into ambulatory dogs results in attenuation of exercise-induced increase of both rectal and thigh muscle temperatures.

Hypothesis: That glucose (Glu) infusion attenuates excessive increase in body temperature from restricted activity during confinement deconditioning.

Methods: Rectal (Tre) and quadriceps femoris muscle (Tmu) temperatures, metabolic rate, and blood samples were taken before and after 90 min of moderate treadmill exercise (mean = 3.