Gary Gray

Effects of exercise on lung lymph flow in sheep and goats during normoxia and hypoxia.

Vigorous exercise causes a marked increase in cardiac output with only a minimal increase in measureable pulmonary vascular pressures. These changes in pulmonary hemodynamics should affect lung water and solute movement. On nine occasions, we measured the effect of normoxic exercise on lung lymph flow in four sheep and two goats with chronic lymph fistulas (wt = 15-25 kg). In addition, lymph flow was also measured on five occasions in sheep during exercise at reduced barometric pressures (430 and 380 mmHg). During normobaria, the animals ran at 3-5 km/h with 0-10% elevation of the treadmill for 15 to 85 min. Exercise on average caused a 100% increase in cardiac output, a 140% increase in lung lymph flow, and a slight but significant reduction in lymph to plasma concentration ratio (l/p) for total protein and albumin (mol wt = 70,000). There was a significant linear correlation between lymph flow and cardiac output (r = 0.87, P less than 0.01). There was no change in l/p for IgG (mol wt = 150,000) or IgM (mol wt = 900,000) and no significant change in mean pulmonary arterial (Ppa) or mean left atrial (Pla) pressures. Transition from normobaria to hypobaria caused an increase in Ppa but no change in Pla, cardiac output, or lymph flow. Exercise during hypobaria caused increases in lymph flow that were qualitatively similar to changes observed during normobaric exercise: there was a 60% increase in cardiac output, a 90% increase in lymph flow, and an 11% reduction in l/p for total protein. There was no change in l/p for albumin, IgG, or IgM, and no further change in Ppa. The increased lymph flow during normoxic and hypobaric exercise is best explained by an increase in pulmonary vascular surface area for fluid and protein exchange. Our results suggest that the normal ovine lung has the potential to nearly triple the amount of perfused microvascular surface area. This speculation is relevant to the interpretation of lymph flow data from other experiments.

Astronaut medical selection during the shuttle era: 1981-2011.

INTRODUCTION U.S. astronauts undergo extensive job-related screening and medical examinations prior to selection in order to identify candidates optimally suited for careers in spaceflight. Screening medical standards evolved over many years and after extensive spaceflight experience. These standards assess health-related risks for each astronaut candidate, minimizing the potential for medical impact on future mission success. This document discusses the evolution of the Shuttle-era medical selection standards and the most common reasons for medical dis-qualification of applicants. METHODS Data for astronaut candidate finalists were compiled from medical records and NASA archives from the period of 1978 to 2004 and were retrospectively reviewed for medically disqualifying conditions. RESULTS During Shuttle selection cycles, a total of 372 applicants were disqualified due to 425 medical concerns. The most common disqualifying conditions included visual, cardiovascular, psychiatric, and behavioral disorders. During this time period, three major expert panel reviews resulted in refinements and alterations to selection standards for future cycles. DISCUSSION Shuttle-era screening, testing, and specialist evaluations evolved through periodic expert reviews, evidence-based medicine, and astronaut medical care experience. The Shuttle medical program contributed to the development and implementation of NASA and international standards, longitudinal data collection, improved medical care, and occupational surveillance models. The lessons learned from the Shuttle program serve as the basis for medical selection for the ISS, exploration-class missions, and for those expected to participate in commercial spaceflight.

Clinical risk management approach for long-duration space missions.

INTRODUCTION In the process of crewmember evaluation and certification for long-duration orbital missions, the International Space Station (ISS) Multilateral Space Medicine Board (MSMB) encounters a surprisingly wide spectrum of clinical problems. Some of these conditions are identified within the ISS Medical Standards as requiring special consideration, or as falling outside the consensus Medical Standards promulgated for the ISS program. METHODS To assess the suitability for long-duration missions on ISS for individuals with medical problems that fall outside of standards or are otherwise of significant concern, the MSMB has developed a risk matrix approach to assess the risks to the individual, the mission, and the program. The goal of this risk assessment is to provide a more objective, evidence- and risk-based approach for aeromedical disposition. Using a 4 x 4 risk matrix, the probability of an event is plotted against the potential impact. Event probability is derived from a detailed review of clinical and aerospace literature, and based on the best available evidence. The event impact (consequences) is assessed and assigned within the matrix. RESULTS The result has been a refinement of MSMB case assessment based on evidence-based data incorporated into a risk stratification process. This has encouraged an objective assessment of risk and, in some cases, has resulted in recertification of crewmembers with medical conditions which hitherto would likely have been disqualifying. CONCLUSIONS This paper describes a risk matrix approach developed for MSMB disposition decisions. Such an approach promotes objective, evidence-based decision-making and is broadly applicable within the aerospace medicine community.