of spaceflight. Moreover, a number of questions remain unanswered. In addition, facts needed to best appreciate any list of health-related risks of spaceflight (Tables 3–1, 3–2, 3–3, and 3–4) to plan for future space missions were not available. For instance, (1) how were the symptoms distributed among astronauts with different specialties (e.g., pilots versus payload specialists)? (2) did astronauts who flew more than one mission experience fewer symptoms on subsequent flights? and (3) what was the degree of severity of the reported symptoms?

It is therefore important to look at the totality of the data from space missions and what has been learned from other extreme isolated environments on Earth (e.g., Antarctica and extended underwater submarine missions). These data relate to the type and incidence of medical-surgical and behavioral health events that occur in these environments and are needed to best gauge and plan for future needs during extended space travel before commencement of exploration-class space missions with astronaut crews.

Evidence Base from Extended-Duration Submarine Missions

Medical events during submarine missions are instructive as they occur in a confined, remote environment where there is limited diagnostic and therapeutic support. They occur in an atmosphere where potentially life-threatening or other severe medical illnesses can end a mission, in the sense that the submarine is required to interrupt or even abort its mission.

The U.S. Navy described the incidence of illnesses and injuries on 136 submarine patrols from January 1, 1997, through December 31, 1998. The numbers of acute encounters were related to the total number of person-days under way, with 2,044 acute encounters in 1.3 million person-days at sea, or 157 acute encounters per 100,000 person-days (Table 3–5). Stratified by illness and injury, illness accounted for 112.9 episodes per 100,000 person-days, with 70 percent able to maintain full duty; and accidents accounted for 37.2 episodes/100,000 person-days, with 55 percent able to maintain full duty (Thomas et al., 2000).

A different perspective is obtained when the health disorders and medical-surgical procedures in Table 3–5 are compared with the reasons for medical evacuations from U.S. submarines (Table 3–6). A range of 1.9 to 2.3 medical evacuations per 1,000 person-months was reported for all submarines in the U.S. Atlantic Fleet from 1993 to 1996. A range of 1.8 to 2.6 evacuations per 1,000 person-months was reported for humane reasons (i.e., death or serious illness in the family) (Sack, 1998), suggesting that if these

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