To understand the health impact of long-duration spaceflight, one identical twin astronaut was monitored before, during, and after a 1-year mission onboard the International Space Station; his twin served as a genetically matched ground control. Longitudinal assessments identified spaceflight-specific changes, including decreased body mass, telomere elongation, genome instability, carotid artery distension and increased intima-media thickness, altered ocular structure, transcriptional and metabolic changes, DNA methylation changes in immune and oxidative stress–related pathways, gastrointestinal microbiota alterations, and some cognitive decline postflight. Although average telomere length, global gene expression, and microbiome changes returned to near preflight levels within 6 months after return to Earth, increased numbers of short telomeres were observed and expression of some genes was still disrupted. These multiomic, molecular, physiological, and behavioral datasets provide a valuable roadmap of the putative health risks for future human spaceflight.

One hundred fifty-nine patients were referred to the authors for evaluation of chronic exertional leg pain from 1978 to 1987. The records of 131 patients were complete and available for retrospective review. Forty-five patients were diagnosed as having a chronic compartment syndrome (CCS) and seventy-five patients had the syndrome ruled out by intramuscular pressure recordings. The only significant difference found between the two groups on history and physical examination was a 45.9% incidence of muscle herniae in the patients with CCS, compared to a 12.9% incidence in those without the syndrome. One-third of the patients with the syndrome and over one-half of those without it reported persistent, moderate to severe pain at 6 month to 9 year followup. Modified, objective criteria were developed for the diagnosis of CCS. The criteria were based upon the intramuscular pressures recorded with the slit catheter before and after exercise in 210 muscle compartments without CCS. In the presence of appropriate clinical findings, we consider one or more of the following intramuscular pressure criteria to be diagnostic of chronic compartment syndrome of the leg: 1) a preexercise pressure greater than or equal to 15 mm Hg, 2) a 1 minute postexercise pressure of greater than or equal to 30 mm Hg, or 3) a 5 minute postexercise pressure greater than or equal to 20 mm Hg.

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Intramuscular fluid pressures were recorded in the vastus medialis of seven healthy male volunteers. Pressures were measured simultaneously at three different sites in the muscle by a catheter-tip transducer with extremely low volume-displacement characteristics and by two extracorporeal transducers connected to slit catheters. All three recording systems gave qualitatively similar results provided the catheters had inner diameters exceeding 0.53 mm and allowed measurement of pressures lasting as short as 1 s. Wick catheters yielded slower responses than slit catheters. At any position intramuscular fluid pressure increased linearly with force up to maximal voluntary contraction (MVC). However, slopes of these curves varied greatly mainly because the pressure was also a linear function of the distance from the fascia. The highest recorded pressure was 570 Torr. At prolonged submaximal contractions intramuscular fluid pressure oscillated independent of contraction force. The linearity of both the pressure-force relationship and the pressure-depth relationship is compatible with a simple model based on the law of Laplace because the muscle fibers are curved during contraction in this muscle. It is hypothesized that blood flow is first compromised deep in the muscle where pressure is highest and in general at lower stress or tension in short bulging muscles with great curvature of the fibers compared with long slender ones.

This cohort study examines the internal jugular vein flow and morphology of crew members of the International Space Station and the use of lower body negative pressure as a countermeasure to the headward fluid shift experienced during space flight.