complete educational system with respect to altitude. As is often said, the commanders know this, but the troops also need to know what to expect.
MURRAY HAMLET: Physiologically, the first change that occurs is physiological vasoconstriction, resulting from both cold and high altitude. Many studies define the impact of altitude on cold injury, and clearly physiological vasoconstriction has an impact. It is essentially a mediated constrictor response. We understand a little bit about how it works.
Decreased thirst also seems to be common to both cold and high altitude. But there is a concomitant increased water requirement for some reason. Therefore, not only are you not drinking as much as you need, you need more. These two things may be synergistic in cold and high altitude.
Regarding fatigue, clearly people become more tired in cold and altitude than they would under other conditions. There is also probably an increased caloric requirement in cold and high altitude.
Therefore peripheral constriction and its relation to the ability to perform certain tasks—to do things with one's hands, for example—affects a mission. Other examples of impaired tasks are preparing food and taking one's clothes on and off.
ROBERT NESHEIM: Is there any evidence that the fatigue you are talking about can be overcome if people take in an adequate amount of calories? Is that fatigue a result of inadequate caloric intake, or is there some other physiological activity going on?
RUSSELL SCHUMACHER: Anecdotally, I would say no. I think they are getting all the calories they need. I do not think anyone suffers in that regard below 12,000 ft (3,659 m). But fatigue over time drags you down. The physical nature of the cold in conjunction with the altitude is the cause.
ROBERT SCHOENE: Sleep is a problem. I think the problem of sleep needs to be addressed, particularly above 10,000 ft (3,049 m). Periodic breathing and all the things that take place that alter the sleep patterns might be very important factors.
A. J. DINMORE: The big problem at high altitude is the fatigue upon exertion. You perception of what can be done is actually much greater than what you are physically able to do. As soon as you try to do something, you immediately hit this fatigue barrier. I think over the long term, that is very worrying.
MURRAY HAMLET: It is both a physical and mental fatigue. It is a combination of ''I know I have got to do this," "I might be able to drive myself to do it," but psychologically "I do not think I want to bother."