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Biomedical subjects

A LeBlanc

Publications and source records attributed to A LeBlanc.

70 records · Page 4Linked to original sources
PubMed1990

The French national system for external quality assessment.

Building upon the experience of professional organizations, which began in the 1970s, the French National Health Laboratory organized a national interlaboratory programme 10 years ago. Four thousand eight hundred laboratories are enrolled in this external quality control programme, which is compulsory for all clinical laboratories and is financed by a fee covering all expenses. Results are strictly anonymous and the programme is basically informative and educational. More than 20 surveys are conducted each year with four in haematology. During the last 10 years, the national programme has documented improved laboratory performances. The evaluations have had an impact on the instrument and reagents marketplace. Finally, it has helped the Ministry of Health to more efficiently manage the problems of laboratory medicine in France.

Blood Cell Count↗
PubMed1987

Changes in nuclear magnetic resonance (T2) relaxation of limb tissue with bed rest.

Bed rest is used to simulate the effects of weightlessness on human physiology. A spin-echo procedure was used to image the lower leg of 15 normal male volunteers before and after 5 weeks of horizontal bedrest. In addition to noninvasively measuring muscle size changes, accurate T2 images were produced to investigate possible relaxation time changes immediately (2-4 h) and 1-2 days after bed rest. Subcutaneous fat showed no change in T2, bone marrow showed a decrease, and muscle showed no change immediately after bed rest but increased 1-2 days following reambulation.

Adipose Tissue↗
PubMed1987

Spinal bone mineral after 5 weeks of bed rest.

Patients put at bedrest for medical reasons lose 1-2% of spinal bone mineral per week. Losses of this magnitude during even short-term space flights of a few months would pose a serious limitation and require countermeasures. The spinal bone mineral (L2-L4) was determined in 6 healthy males (precision = 2%) before and after 5 weeks of complete bed rest. Only one individual had a significant loss (3%) and the -0.9% mean change for the 6, was not significant (P = 0.06). The average negative calcium balance during the 5 weeks was 4 g or 0.36% of total body calcium, similar to that reported in other bed-rest studies. Spinal bone loss, however, in healthy bed-rested males is significantly less than reported for bed-rested patients, suggesting that a large loss of spinal bone mineral does not occur during space flight missions lasting 5 weeks or less.

Adult↗
PubMed1985

Bone and muscle atrophy with suspension of the rat.

A modification of the Morey tail suspension model was used to determine atrophic responses of rat bone and muscle with 14-90 days unloading of the hindlimbs. Bone uptake of methylene diphosphonate followed a phasic pattern similar to changes in bone formation rate in immobilized dogs and rats. Increased uptake at 60 days (P = 0.01, femur) indicated an increased bone metabolism. Regional densitometry demonstrated a preferential loss of bone mineral in the trabecular mass (P = 0.02) at 30 days and in the cortical shaft by 90 days (P = 0.03). Maximal muscle atrophy occurred within 14-30 days. The gastrocnemius was less severely affected by suspension than by immobilization techniques, whereas the soleus atrophied (by weight) similarly, suggesting that muscle atrophy in the suspension model is distinctly different from immobilization atrophy. One significant response of skeletal muscle to suspension was an altered blood distribution. Muscle blood distribution changes reflect the hypodynamic state of muscle that continues to contract but probably at an altered rate in response to altered functional demands.

Animals↗
PubMed1984

Clomiphene protects against osteoporosis in the mature ovariectomized rat.

Clomiphene citrate, a mixed estrogen agonist-antagonist, protects mature ovariectomized breeder rats from changes in total body calcium and from deterioration of femur structure. Over 6 months, mature ovariectomized rats took up calcium at the rate of 0.7 +/- 0.5 mg/day, while normal controls gained 2.5 +/- 0.7 mg/day (mean +/- SEM) as measured by whole body neutron activation analysis. Injections of clomiphene (20 mg/kg/week) kept ovariectomized rats in positive calcium balance at 2.0 +/- 0.5 mg/day. Reductions in total femur calcium content, cortical thickness, and visible trabeculae of femurs in ovariectomized animals were prevented by chronic clomiphene administration. These results in animals suggest a possible new line of investigation of the use of antiestrogenic drugs as therapeutic agents for hormone-dependent osteoporosis in animals and humans.

Animals↗
PubMed1984

High resolution bone mineral densitometry with a gamma camera.

A technique is described by which the regional distribution of bone mineral can be determined in bone samples from small animals. The technique employs an Anger camera interfaced to a medical computer. High resolution (less than 1 mm) imaging is possible by producing magnified images of the bone samples. Regional densitometry of femurs from oophorectomised and bone grafted rats demonstrated significant heterogenity of bone mineral loss.

Animals↗
PubMed1975

Response of local vascular volumes to lower body negative pressure stress.

The present study involved an intravenous injection of radio-active iodinated serum albumin, equilibration of this isotope within the vascular space, and the continuous measurement of isotope activity over selected anatomical areas before, during and following multiple human LBNP tests. Both rate and magnitude of vascular pooling were distinctly different within each of five selected lower body anatomical areas. In the upper body, all areas except the abdomen showed depletions from their resting vascular volumes during LBNP. The presence of uniquely different pooling patterns in the lower body, the apparent stability of abdominal vascular volumes, and a possible decrease in cerebral blood volume during LBNP represent the major findings of this study.

Abdomen↗
PubMedDate not supplied

Prediction of brain blood flow using pulsed Doppler ultrasonography in newborn lambs.

The purpose of this study was to evaluate the ability of pulsed Doppler ultrasonography to predict brain blood flow by comparing measurements made in basal cerebral arteries using a pulsed Doppler system with measurements of brain blood flow using radioactive microspheres in lambs. We measured the instantaneous maximum velocity during peak systole and end diastole and the mean velocity over the pulse cycle in basal cerebral arteries, calculated Pourcelot's index of resistance and Gosling's pulsatility index, and used regression analysis to compare the pulsed Doppler measurements with brain blood flow measured with radioactive microspheres. Pulsed Doppler measurements of the peak systolic, end diastolic, and mean flow velocity in basal cerebral arteries were directly related to brain blood flow. In contrast, no linear relationship was detected between the resistance or pulsatility indices and brain blood flow measured by microspheres (p greater than 0.14). Prediction of brain blood flow for individual subjects lacks the quantitative precision necessary for use as a clinical tool. However, the direct relationship between brain blood flow and the peak systolic, end diastolic, and mean flow velocities in basal cerebral arteries supports the use of these measurements in clinical research for the qualitative assessment of change in brain blood flow.

Animals↗
PubMedDate not supplied

Bone and body mass changes during space flight.

Body mass, calcium and skeletal changes occur in humans who have worked in microgravity. Physiologic changes are seen as early as one week and are still occurring 312 days into space flight. The physiologic changes in bone and mineral metabolism may be among those which limits long duration space flight if an adequate countermeasure is not developed. The purpose of this paper is to summarize what is known about calcium dynamics and bone mineral changes as well as associated changes of body mass induced by space flight. The data reported is from a variety of studies conducted in both actual and simulated space flight.

Aerospace Medicine↗
PubMedDate not supplied

Rapid, sensitive, and noninvasive sampling technique for determination of chloroform in alveolar breath.

A sampling technique for the determination of chloroform in alveolar breath is presented. Subjects exhale in a homemade device for collection of the alveolar fraction. The collected sample is transferred to a partially evacuated headspace vial and subsequently analyzed by capillary gas chromatography using electron-capture detection. Concentrations greater than 50 micrograms/m3 can readily be detected. Good correlation observed between chloroform levels in alveolar breath and plasma validates the sampling technique.

Breath Tests↗
PubMedDate not supplied

Relaxation times of normal and atrophied muscle.

Magnetic resonance imaging is being used to investigate physiological changes induced by microgravity. Using human (bed rest) and animal (tail suspension) models simulating zero gravity, muscle atrophy was studied. Despite significant physiological changes in muscle mass, distribution of blood flow, and muscle water, no changes in muscle proton relaxation times were found at several different resonant frequencies (6, 10, 20, and 200 MHz). These results suggest that observed changes in relaxation times as reported in pathologic studies are likely due to the pathological changes and not the accompanying muscle atrophy.

Animals↗
PubMedDate not supplied

Calf muscle area and strength changes after five weeks of horizontal bed rest.

Nine male volunteers participated in a 10 week metabolic study in which subjects underwent 5 weeks of ambulatory control and 5 weeks of complete horizontal bed rest. Bed rest is a model commonly used to simulate space flight. The changes in muscle area and strength of the calf dorsiflexors and plantar flexors were measured before and after bed rest using magnetic resonance imaging (MRI) and a Cybex II dynamometer. The muscle area of the plantar flexors (gastrocnemius and soleus) decreased 12%, whereas the muscle area of the dorsiflexors was not significantly decreased. The maximal muscle strength of the plantar flexors decreased 26%; the muscle strength of the dorsiflexors was not significantly decreased. These results, which demonstrate differential muscle atrophy and a larger loss in strength relative to muscle area, have important implications in the development of exercise counter-measures to be implemented during space flight. The results also have implications for patients who have severe orthopaedic disorders and must be bed rested for long periods of time, and for persons who are voluntarily inactive (a large number of the elderly).

Adult↗
PubMedDate not supplied

[Reactions of the human bone system in space flight: phenomenology].

Results of multi-year bone observations in crewmembers of long-term (6 to 14 mos.) Salyut and Mir missions have been summarized. The theoretical expectation of bone losses (mineral bone density, MBD) was consistent only in the trabecular of the lower skeleton (lumbar spine, femur proximal epiphysis, pelvis). The upper skeleton bones (skull, cervical spine) demonstrated a clears-defined trend toward an increase in mineral content. There is a direct dependence of MBD losses on a skeleton bone position relative to the gravity vector and bone structure. Post-flight MBD did not, as a rule, deviate from the WHO-defined limits (T-criterion); in several instances MBD loss was qualified as local osteopenia. Shifts in MBD, same as MBD recovery rate, vary with subjects and, therefore, deny their dependence on flight duration. By and large, MBD shifts are interpreted as a functional adaptation of bone tissue to changing mechanic demands.

Absorptiometry, Photon↗