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T Hedrick

Publications and source records attributed to T Hedrick.

4 recordsLinked to original sources
PubMed2000

Muscle volume, MRI relaxation times (T2), and body composition after spaceflight.

Postflight changes in muscle volume, calf muscle transverse relaxation time, and total body composition were measured in 4 crewmembers after a 17-day mission and in 14-16 crewmembers in multiple shuttle/Mir missions of 16- to 28-wk duration. During the 17-day mission, all muscle regions except the hamstrings significantly decreased 3-10% compared with baseline. During the shuttle/Mir missions, there were significant decreases in muscle volume (5-17%) in all muscle groups except the neck. These changes, which reached a new steady state by 4 mo of flight or less, were reversed within 30-60 days after landing. Postflight swelling and elevation of calf muscle transverse relaxation time persisted for several weeks after flight, which suggests possible muscle damage. In contrast to the 17-day flight, in which loss in fat, but not lean body mass, was found (25), losses in bone mineral content and lean body mass, but not fat, were seen after the longer shuttle/Mir missions. The percent losses in total body lean body mass and bone mineral content were similar at approximately 3.4-3.5%, whereas the pelvis demonstrated the largest regional bone loss at 13%.

Adult↗
PubMed1999

T2 vertebral bone marrow changes after space flight.

Bone biopsies indicate that during immobilization bone marrow adipose tissue increases while the functional cellular fraction decreases. One objective of our Spacelab flight experiment was to determine, using in vivo volume-localized magnetic resonance spectroscopy (VLMRS), whether bone marrow composition was altered by space flight. Four crew members of a 17 day Spacelab mission participated in the experiment. The apparent cellular fraction and transverse relaxation time (T2) were determined twice before launch and at several times after flight. Immediately after flight, no significant change in the cellular fraction was found. However, the T2 of the cellular, but not the fat component increased following flight, although to a variable extent, in all crew members with a time course for return to baseline lasting several months. The T2 of seven control subjects showed no significant change. Although these observations may have several explanations, it is speculated that the observed T2 changes might reflect increased marrow osteoblastic activity during recovery from space flight.

Adult↗
PubMed1995

Regional muscle loss after short duration spaceflight.

BACKGROUND: Muscle strength and limb girth measurements during Skylab and Apollo missions suggested that loss of muscle mass may occur as a result of spaceflight. Extended duration spaceflight is important for the economical and practical use of space. The loss of muscle mass during spaceflight is a medical concern for long duration flights to the planets or extended stays aboard space stations. Understanding the extent and temporal relationships of muscle loss is important for the development of effective spaceflight countermeasures. HYPOTHESIS: We hypothesized that significant and measurable changes in muscle volume would occur in Shuttle crewmembers following 8 d of weightlessness. METHODS: MRI was used to obtain the muscle volumes of the calf, thigh and lower back before and after the STS-47 Shuttle mission. RESULTS: Statistical analyses demonstrated that the soleus-gastrocnemius (-6.3%), anterior calf (-3.9%), hamstrings (-8.3%), quadriceps (-6.0%) and intrinsic back (-10.3%) muscles were decreased, p < 0.05, compared to baseline, 24 h after landing. At 2 weeks post recovery, the hamstrings and intrinsic lower back muscles were still below baseline, p < 0.05. CONCLUSIONS: These results demonstrate that even short duration spaceflight can result in significant muscle atrophy.

Adult↗