Search

Projectional bone mineral density (PBMD) in the proximal region of both femoral bones, the distal part of the forearm bones on both sides and in the lumbar vertebrae was studied with the method of dual energy roentgen absorption (DEXA) in two male volunteers at the age of 40 and 60 years on a daily basis during one month. On the basis of the results of the estimation of each area of interest (AI) M(av), oscillation range (4(sigma)) and the greatest difference were calculated. In addition to it, a statistic mathematic modeling was conducted through smoothing out the dynamic rows of the results achieved for each AI. It was found out that the average oscillation range exceeded 9% of the average index value, which is thrice as much as the method reproducibility error. This kind of investigation in the process of treatment allows monitoring its efficiency taking into consideration both mechanisms (osteoblastic-osteoclastic remodeling and osteocytic remodeling) as well as estimating the toxic effects of medical agents on bone cells. As a result of statistic mathematic modeling, cercaseptane periodicity of PBMD changes with the average period of 5.5 days was found. The authors see the cause of these short-term changes in osteocytic remodeling and suggest to use a dynamic successive PBMD measurements during 7-10 days as a way of non-invasive monitoring of osteocyte resorption-synthetic activity in AI.

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.

Roentgenometric and roentgenodensitometric chronobiological characteristics of space and time remodeling of the bone tissue in tail vertebra XI and XII after osteotomy of the right femur are described. Examination of 179 white non-inbred male rats revealed circadian periodicity of vertebral bone tissue remodeling. Dynamics of asymmetry of this process also has a circadian periodicity.

By computer tomography, mineral density of lumbar vertebrae and their segments as well as back muscle (++ilio-costal, extensor and ++inter-spinal) density and mass were measured in four Salyut-7 crewmembers before and after extended flights (of 5 and 7 months in duration). These findings are in good agreement with the results of prolonged bed rest studies in which trabecular bone of vertebral bodies was investigated: mineral density diminished only in some (approximately 10%) of the test subjects. At the same time mineral density loss was seen in the vertebral elements where muscles were attached. Also, muscle mass was reduced. It is emphasized that the level of changes was not correlated with flight time. Further investigations in this area are discussed.