Interview with Tom Hornbein, MD
High Altitude Physiologist
NOVA: Take us back to the 70s before anyone summited Everest without oxygen.
What were the concerns scientists had, and why did they think it couldn't be
Hornbein: Before Messner climbed Everest without oxygen—he and Peter Habeler
in 1978—there seemed to be some people who questioned whether it was
possible to do that. Having been there in 1963, spending a bit of time on the
summit, I had figured out that physiologically it certainly was possible. The
question of whether it was functionally possible to spend the extra time it
would take and to do all the other things that needed to be done to translate
the physiology into a successful oxygenless climb had to wait for the proof of
the pudding, which in a sense took place in '78. But really the ultimate
resolution was a few years later when Messner soloed Everest from the north
side over the course of three or four days without oxygen, carrying a very
modest load on his back. And to me that's one of the great tour de forces of
Everest climbing and the history of the mountain.
NOVA: We're interested in this notion that there are milestones, and this was a
milestone—this question of whether you could summit without oxygen. And
they reached that milestone and came down. What did you, in this community,
think about it?
Hornbein: The question is why people were unsure that this could be done. I
guess I'm unsure why people felt this way, but I can remember when I was a kid
and reading the books before Everest was climbed for the first time, that there
was real uncertainty as to whether a human being could even survive at the
extreme altitude of the summit of Everest. So people had been within 1,000 feet
of the top a number of times. It was like there was a barrier above which a
human being couldn't go, so it seemed. And what we know now is that the summit
of Everest, physiologically for the human being, seems to be very close to the
limit as to how high an acclimatized or an adapted human being can go and
NOVA: What are the big changes taking place inside our bodies, in order of
Hornbein: The changes that go on in the body with acclimatization—it's
probably hard to define in order of importance—but taking it
chronologically, probably some of the earliest changes begin to
occur within hours of being exposed to a high altitude, or an increase in
breathing that occurs within minutes, or at least the process starts
immediately when you go to altitude. And some people are more vigorous
breathers in response to oxygen lack than others are, and interestingly, they
seem to do better in performing at extreme heights, such as at the top of
Everest. Associated with them are changes in blood flow to the brain that seem
to have the same time relationship, that is, resetting within a couple of days
to a new level related to the amount of altitude that you've gone up. There's
changes in the blood that have to do with the affinity of the hemoglobin for
oxygen, that occur again within 48 to 72 hours. Others, like the manufacture
of more red blood cells to carry more oxygen take place over several weeks.
And the question as to how important those are to performance at altitude is
still up for grabs.
NOVA: Describe the state of someone laboring along on Everest, with or without
Hornbein: Near the summit the rate at which you climb is probably your maximum
oxygen consumption, or very close to it. You're very breathless. This varies
from individual to individual and you're going very slowly. You often have to
stop and take a number of breaths for every step that you take. Probably to me
the more curious thing to wonder about is what happens to the brain when the
oxygen level is so low up there you're convinced that you're thinking
tremendously clearly. You could do all these simple-minded calculations about
how much oxygen is left in the tank. But at the same time if there were an
outside observer looking down on you, they might be struck by how stupid your
performance appears to be.
NOVA: It seems like the more you learn, the less you know. And you've been in
this game for a long time. Can you summarize what you've all learned in 34
years and what there still is to learn. Is it still just a big mystery?
Hornbein: The question as to whether, as you learn more, you ever think you
really answer any ultimate questions is the essence of what science seems to be
like. And in relation to man's ability to function at the limits of the height
above the sea, we do know a lot more; and, of course, everything prompts a whole
new set of questions. We know thanks to Messner and Habeler that humans can go
to the top of Everest without oxygen; one of the things that's most interesting
to me is to find that some people can do that with seemingly relative ease, Ed
[Viesturs] being one example, and for others there's no way that we can climb
to the top of Everest without the aid of oxygen. So there's tremendous
individual variability. And so one of the really interesting questions is what
is it that makes some people better able to function at those limits of near
survival than others. And that's, of course, where a lot of the current
exploration is going on.
NOVA: So is it an exciting and unique opportunity to have some well-trained
mountaineers who are capable of performing these tests doing this? Has it ever
been done before in a real live environment like this?
Hornbein: To me this trip in the spring of '97 is—there's some unique
aspects in relation to the observation that can be made, and one of them is it
takes a lot of energy to pull off this kind of analysis of how people function
at these incredible heights especially at the summit of the mountain. And the
people that are involved in the effort are people who have got a lot of mileage
under their belt in knowing that they have the energy and the capacities to do
some of the things that we would like to do. I mean the idea of being able
to do neuro-behavioral studies on the summit of Everest is—I mean that's a
little bit off the wall in a sense. But I think it can be done and it will be
fascinating to see if it can be pulled off. So having some old pros
involved or maybe not so old, as the case may be, is going to be a real asset
to getting some things done up there that otherwise are really hard to do.
NOVA: Have you ever ruminated on this kind of cosmic coincidence that this
mountain got us up to 29,048 feet and we can climb it without oxygen and it's
right at our limit?
Hornbein: It's an intriguing question to wonder about how Everest happened to
be about as high as we can go, and I spend a lot of time
ruminating on that. And I've decided with my scientific cold and calculating
brain that probably Everest isn't as high as we could go. And until somebody
builds something that we can walk on, we're not going to find out how much
higher it might be, at least on the surface of this earth.