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%.

Background-Detection of subclinical coronary artery disease (CAD) before the development of life-threatening cardiac complications has great potential clinical relevance. Electron beam computed tomography (EBCT) is currently the only noninvasive test that can detect CAD in all stages of its development and thus has the potential to be an excellent screening technique for identifying asymptomatic subjects with underlying myocardial ischemia. Methods and Results-Over 2.5 years, we prospectively studied 3895 generally asymptomatic subjects with EBCT, 411 of whom had stress myocardial perfusion tomography (SPECT) within a close (median, 17 days) time period. SPECT and exercise treadmill results were compared with the coronary artery calcium score (CACS) as assessed by EBCT. The total CACS identified a population at high risk for having myocardial ischemia by SPECT although only a minority of subjects (22%) with an abnormal EBCT had an abnormal SPECT. No subject with CACS Ͻ10 had an abnormal SPECT compared with 2.6% of those with scores from 11 to 100, 11.3% of those with scores from 101 to 399, and 46% of those with scores Ն400 (PϽ0.0001). CACS predicted an abnormal SPECT regardless of subject age or sex. Conclusions-CACS

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