Modifications of Bone and Connective Tissue after Orthostatic Bedrest

Uebelhart, Daniel; Bernard, J.; Hartmann, Daniel; Moro, Luigi; Roth, Marc; Uebelhart, Brigitte; Rehaïlia, M.; Mauco, Gérard; Schmitt, Didier; Alexandre, Christian; Vico, Laurence

doi:10.1007/s001980050007

Cited by 48 publications

(36 citation statements)

References 40 publications

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“…Thus, two independent measurements of BMD showed almost identical results. The results observed for DXA in spaceflight are supported by results from bed rest studies, (6,7) in which BMD loss is observed in a model of mechanical unloading that does not involve weightlessness. Furthermore, the total body BMD changes were shown to be significantly correlated with Ca balance, a technique that does not require assumptions regarding body composition.…”

supporting

confidence: 61%

Spaceflight, Weightlessness, and Bone Loss—What Are We Measuring?

Lang

LeBlanc

2005

Journal of Bone and Mineral Research

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contends that changes in the composition of the nonosseous components of the bone tissue and changes in body composition may have a significant impact on BMD changes measured in our study of astronauts undergoing spaceflight. With DXA, apparent changes in BMD may be introduced artifactually through severe weight loss or severe changes in body composition that might alter the regional spatial distribution of fat around the body circumference.(1)In QCT, artifactual changes might be produced, for example, if the fraction of adipose tissue in the bone marrow (2,3) increased as a function of spaceflight. This would result in an artifactual increase in the measured amount of bone loss. However, there is no evidence to support the existence of such changes in spaceflight. Subjects undergoing longduration spaceflight undergo weight loss but not of the magnitude known to introduce significant measurement errors into DXA. Whole body composition studies during 4-to 6-month flights on the MIR (N ‫ס‬ 14) have shown slight gains in body fat mass (0.5 kg) with losses in lean mass of 2.1 kg for a total body loss of 1.7 kg or 2.2%.(4) Furthermore, a study of crew members during a 17-day spaceflight showed no significant change in the cellular fraction of spinal marrow.(5) This has also been confirmed for longer-duration MIR missions.Even if Dr Bolotin's contention was correct, QCT and DXA BMD measurements, which have greatly different sources of error, ought to show different results in our spaceflight cohort. In fact, our measured changes in DXA and in integral QCT BMD are very similar. In the spine, average rates of loss for QCT and DXA were identical at 0.9% per month. In the total femur region of the hip, the results for integral QCT and DXA BMD were 1.4%/month and 1.5%/month, respectively. Thus, two independent measurements of BMD showed almost identical results. The results observed for DXA in spaceflight are supported by results from bed rest studies, (6,7) in which BMD loss is observed in a model of mechanical unloading that does not involve weightlessness. Furthermore, the total body BMD changes were shown to be significantly correlated with Ca balance, a technique that does not require assumptions regarding body composition.(6) Ca balance measurements were also conducted during Skylab, showing significant bone loss consistent with the single-photon absorptiometry (SPA) technique used at that time. (8) Finally, the bone changes observed with densitometry are in keeping with bone structural changes observed in rodent hindlimb unloading models. In these cases, microstructural changes observed in the unloaded hindlimb with CT and histology (9) show loss of cortical area and degradation of trabecular structure in the unloaded hindlimbs that are consistent with the patterns observed in our own findings, with a higher rate of trabecular compared with cortical bone loss. (10) In conclusion, we disagree with Dr Bolotin's contention that measurement artifacts are responsible for our results. The contention is not supported by st...

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supporting

confidence: 61%

Spaceflight, Weightlessness, and Bone Loss—What Are We Measuring?

Lang

LeBlanc

2005

Journal of Bone and Mineral Research

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“…These precision measures for DEXA scanning are also similar to those published. 27,28 The prevalence of osteoporosis was investigated from T-scores for BMD at di erent sites. The World Health Organisation (WHO) criteria were used to classify T-scores as normal (41 SD below young adult mean), osteopenic (1 ± 2.5 SD below young adult mean), or osteoporotic (42.5 SD below young adult mean).…”

Section: Methodsmentioning

confidence: 99%

Intensive exercise may preserve bone mass of the upper limbs in spinal cord injured males but does not retard demineralisation of the lower body

2002

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Study design: Cross-sectional study comparing a group of active spinal cord injured (SCI) males carefully matched for age, height, and weight with active able-bodied male controls. Objectives: To compare bone mass of the total body, upper and lower limbs, hip, and spine regions in active SCI and able-bodied individuals. Setting: Outpatient study undertaken in two centres in New Zealand. Methods: Dual energy X-ray absorptiometry (DEXA) scanning was used to determine bone mass. Questionnaires were used to ascertain total time spent in weekly physical activity for each individual. The criterion for entry into the study was regular participation in physical activity of more than 60 min per week, over and above that required for rehabilitation. Results: Seventeen SCI and their able-bodied controls met our required activity criterion. Bone mineral density (BMD) values of the total body and hip regions were signi®cantly lower in the SCI group than in their controls (P=0.0001). Leg BMD and bone mineral content (BMC) were also signi®cantly lower in the SCI group (P=0.0001). By contrast, lumbar spine BMD and arm BMD and BMC did not di er between the SCI and control groups. Arm BMD and BMC were greater (not signi®cant) than the reference norms (LUNAR database) for both groups.

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“…Similar results were obtained in another 17-week horizontal bed rest study (Shackelford et al 2004). However, in shorter studies, DXA analysis did not show changes in aBMD (Suzuki et al 1996;Uebelhart et al 2000;LeBlanc et al 1987). In a 90-day HDBR study Rittweger et al used pQCT to measure BMC in a resistive exercise group and the corresponding control group (Rittweger et al 2005).…”

Section: Physiological Adaptationmentioning

confidence: 96%

“…Using these techniques bone turnover markers reflecting the changes in bone formation and bone resorption processes in immobilization become obvious (Baecker et al 2003;Inoue et al 2000;Kim et al 2003;Zerwekh et al 1998;Vico et al 1987;Vico et al 1993;Vico et al 1998;Uebelhart et al 2000;Zerwekh et al 1998).…”

Section: Physiological Adaptationmentioning

confidence: 98%

From space to Earth: advances in human physiology from 20 years of bed rest studies (1986–2006)

Traon¹,

et al. 2007

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Bed rest studies of the past 20 years are reviewed. Head-down bed rest (HDBR) has proved its usefulness as a reliable simulation model for the most physiological effects of spaceflight. As well as continuing to search for better understanding of the physiological changes induced, these studies focused mostly on identifying effective countermeasures with encouraging but limited success. HDBR is characterised by immobilization, inactivity, confinement and elimination of Gz gravitational stimuli, such as posture change and direction, which affect body sensors and responses. These induce upward fluid shift, unloading the body's upright weight, absence of work against gravity, reduced energy requirements and reduction in overall sensory stimulation. The upward fluid shift by acting on central volume receptors induces a 10-15% reduction in plasma volume which leads to a now well-documented set of cardiovascular changes including changes in cardiac performance and baroreflex sensitivity that are identical to those in space. Calcium excretion is increased from the beginning of bed rest leading to a sustained negative calcium balance. Calcium absorption is reduced. Body weight, muscle mass, muscle strength is reduced, as is the resistance of muscle to insulin. Bone density, stiffness of bones of the lower limbs and spinal cord and bone architecture are altered. Circadian rhythms may shift and are dampened. Ways to improve the process of evaluating countermeasures--exercise (aerobic, resistive, vibration), nutritional and pharmacological--are proposed. Artificial gravity requires systematic evaluation. This review points to clinical applications of BR research revealing the crucial role of gravity to health.

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Modifications of Bone and Connective Tissue after Orthostatic Bedrest

Cited by 48 publications

References 40 publications

Spaceflight, Weightlessness, and Bone Loss—What Are We Measuring?

Spaceflight, Weightlessness, and Bone Loss—What Are We Measuring?

Intensive exercise may preserve bone mass of the upper limbs in spinal cord injured males but does not retard demineralisation of the lower body

From space to Earth: advances in human physiology from 20 years of bed rest studies (1986–2006)

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