Brownie Schoene is a physiologist with the Division of Pulmonary and Critical Care Medicine, Harborview Medical Center, at the University of Washington in Seattle.
NOVA: Is the Death Zone on the summit of Everest—is that the limit? Do you
think we could go any higher?
Schoene: Well, for years it was debated whether humans could even go to the
summit of Everest, but serendipitously the summit of Everest, which is the
terrestrial limit of the Earth, is probably very, very close to the physiologic
limit, and that we can put numbers on, and we've done that for years, at least
the past 15 years. The amount of oxygen that's available at 29,000 feet is so
low that the body's capability to adapt to that, to breathe enough, to get
enough of a cardiac output, a heart's output of blood and so forth is—there
are limits. And I think that if, for instance, we had bad weather one day and
the barometric pressure was 15 or 22 millimeters of mercury and lower, Everest
could not be climbed without supplemental oxygen. The fact that it's
right there at the limit is—I don't know if it's the Death Zone or it's
something above which, maybe 10 or 20 or 50 feet more people could go, but not
NOVA: Let's talk about adaptation. How does the adaptation we've seen in
humans at a high altitude apply to what you see in the Intensive Care Unit?
Schoene: Adaptation is really critical because whether it's in the Intensive
Care Unit where I spend most of my time here, where the body is stressed with
diseases—heart disease, lung disease and so forth—where the oxygen level
is low, or whether it's above 20,000 feet or above 25,000 feet, certain
adaptations have to take place. The breathing response has to be intact. The
blood response, particularly at high altitude, has to be intact so that the
blood can carry more oxygen and then the tissues have to be able to utilize the
low oxygen better. The mitochondria, the small capillaries in the muscle beds,
have to be augmented and all those capabilities have to adapt. And that's sort
of a strand in the fabric of what I've done for 20 years in the intensive care
unit that I can relate. It's all physiology. It's all the same questions. The
adaptations are a little bit different. The capability to adapt is different
in each of those situations, but it's the same theme.
NOVA: To what extent is this adaptability actually killing us at altitude?
When does it go too far?
Schoene: The question that's been asked for a long time is, is there an
altitude above which the human cannot adapt? And if you look at populations or
civilizations in the world who live at altitude, there seems to be a ceiling.
It may be 16, 17,000 feet at the most where people can live, thrive, reproduce,
and so forth in terms of population. The high-altitude climber doesn't stay at
those altitudes for more than days, weeks—so that he or she doesn't fully
adapt to those altitudes of 20, 24, 29,000 feet. The body is trying to get
there and never really gets there, and with enough time will deteriorate.
NOVA: What more do you want to learn in the near or far term about altitude and
Schoene: I think that we've gotten a lot of answers over the last 50 years,
certainly over the last 15 or 20 years, which have helped us to understand the
adaptations. But there is still, as in most areas of science, exciting areas
that we want to pursue. I think, one, we want to understand the cell a little
bit better, the muscle cell, the small capillaries and blood vessels that
deliver oxygen to the tissue. Those adaptations are not very well understood.
Is there a limit? The other thing that is really intriguing, since the heart
and lung have been studied quite extensively, is the brain. And I think that
we still don't know what really stops someone from exercising more vigorously
at extreme altitude. Yes, the oxygen level is low, but oxygen does get to
tissues—but is there an effective oxygen [level] in the brain that then tells
the body, "Listen just don't go any more?" And I think that's a critical
question that is wide open to be answered.