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Recalling the Silver Hut...
Oct 23, 2007 13: 55 EST
Earlier this month at the World Congress of Mountain and Wilderness medicine, we were treated to a talk given by the 2007 World Congress award winner, Jim Milledge, who recounted his experience with the historic Silver Hut expedition. The photo to the left pictures (left to right) conference organizer Dr. Charley Clarke, Dr Brownie Schoene (co-awardee of the 2007 World Congress medal) and Dr. Jim Milledge. The following is the transcript of Jim's talk:
THE SILVER HUT EXPEDITION
James S. Milledge
The official name of the expedition was “The 1960-61 Himalayan Scientific and
Mountaineering Expedition” but soon after it was over, it became known popularly as
the Silver Hut Expedition after the unique high altitude station that was established at
5800 m on the Mingbo glacier just east of Ama Dablam or about 12 miles south of
Everest. This hut was prefabricated in England from boxed-up sections of marine
plywood with plastic foam insulation and painted with silver paint. It was almost
cylindrical in shape, looking like a London tube train, with snow porch, bunks, stove,
and laboratory space inside. It measured 22 ft long by 10 ft wide. It made a wonderful
home and workplace for us for the winter.
In Antarctica it was common to land a party of scientists on the ice one summer to
“winter over”, with all the necessary gear to survive and carry out its program. They
was left there for the long, dark winter and were relieved the next summer.
It was on the Transantarctic Expedition 1957 that Sir Edmund Hillary and Dr. Griffith
Pugh, who been together on both Cho Oyu and on the successful 1953 Everest
expeditions, dreamed up the idea of a Himalayan expedition that would combine the
Antarctic practice of "wintering over" with the Himalayan Expedition idea of
establishing a series of camps up a mountain. In this way the effect of prolonged
exposure to very high altitude could be studied. The actual plan, then, was to go out to
the Everest region of Nepal just after the monsoon, establish a base camp and a high
station at approximately 5800m with provisions and scientific gear to conduct
research, and then, in the next spring, to move over to Mt. Makalu (8425m), the 5th
highest mountain in the world, and continue physiologic studies as high as possible
during an attempt on the peak without oxygen.
Financing was provided from a single source - World Book Encyclopaedia of
Chicago, and members were recruited in about equal numbers from New Zealand, the
United States, and Great Britain. In the autumn, while a small party went straight out
to Solu Khumbu to establish the winter camps, the main body of the expedition went
east via the Rowling Valley to try and hunt the elusive Yeti. They failed to find it but
did bring back evidence to explain some of the “sightings” and tracks.
The expedition was carried through as planned, except that the Makalu summit was
not reached because of a combination of weather, accident, and the illness of a lead
climber. The physiologic program was carried out at base camp (4500m), the Silver
Hut (588m) and camps III and V on Makalu (6350m and 7400m). The beautiful,
difficult peak, Ama Dablam, (6828 m) was also climbed.
What were the scientific results of the expedition? It is impossible to do .justice to all
the studies, A bibliography of works emanating from the Expedition (below) numbers
2
thirty-six items of which 20 were papers in peer reviewed journals. The physiology
can be listed as studies on the effect of altitude acclimatization on the following:-
1. Submaximal exercise, ventilation, and VO2
2. Submaximal excrcise, heart rate, and cardiac output.
3. Maximal cxercisce, V02max and heart rate
4. Exercise and arterial O2 saturation
5. Difiusing capacity of the lungs for CO during exercise
6. Chemical control of breathing
7. Alveolar gas composition up to 7790m
8. ECG .changes
9. Blood volume and haemoglobin changes
10. Basal metabolic rate
11. Electroencephalography
12. Psychomotor function
The oxygen transport system of the body can be used as a sort of menu of many of the
studies. The barometric pressure at the Silver Hut was 380 mm Hg just half that at sea
level. The ambient PO2 is, of course, also half, about 80 mm Hg compared with 160 at
sea level, The drop in P02 due to water vapour at body temperature is similar at
altitude and results in a drop in P02 of 10 mm Hg P02 from mouth to trachea.
The next drop, from trachea to alveolus, is influenced by ventilation. An important
part of acclimatization is an increase in ventilation due to a change in its chemical
control, hence the importance of the study of this system. We confirmed the increase
in CO2 sensitivity previously reported and showed that after the first month there was
no further change. Our results for the hypoxic ventilatory response were that three of
the four subjects on whom we had most data showed an increase but the fourth a
decrease.
The study on alveolar gases up to greater heights than before or since, documented
this increase in resting ventilation with increasing altitude. The large study on
ventilation on exercise yielded data about this part of the system under stress.
The next stage in oxygen transport is from alveolus to pulmonary capillary. The
oxygen moves by diffusion, but of course the matching of ventilation and perfusion is
also important in this process. John West measured the diffusing capacity for CO as
an index of this process, and showed that there was no significant increase in DLCO
with acclimatization. This means that, especially on exercise, there is a diffusion
limitation to oxygen transport at altitude. He also showed, using ear oximetry, that on
severe exercise the arterial oxygen saturation dropped to as low as 45 percent,
indicating a wide alveolar-arterial gradient. This has been confirmed by numerous
later studies.
From arterial to mixed venous blood the PO2 drop is minimized by increasing the
haemoglobin concentration and increasing cardiac output. Again this area was
studied, both at rest and exercise. The heart rate and cardiac output were raised at rest
and during light work but seemed to be limited at higher work rates. The maximum
heart rate and cardiac output were limited to about 150 beats/min and 17 l/min,
compared with 200 beats/min and 24 I/min at sea level,
3
The increase in Hb concentration was shown to be achieved by a loss of plasma
volume at first, as well as a slow rise in red cell mass. After three months plasma
volume was restored and there was a further rise in red cell mass.
In the study of the electrocardiograph at altitude, we showed that the well-known shift
to the right of the main QRS vector continued up to 24,500 ft but was not reduced by
oxygen breathing. The T wave became inverted across the chest leads to V 4 or even
5, but this did not seem to indicate anything sinister, as judged by the performance of
climbers with this change. These changes are presumably due to the increasing
pulmonary artery pressure with increased altitude, increasing the work of the right
ventricle. We showed that after acclimatization oxygen breathing did not reverse these
changes.
Finally, it is interesting to note that 46 years after the Silver Hut Expedition, few of
the findings have been superseded and none of them have been disproved - and also
that members of the expedition are not only on speaking terms but are good friends
and have been on numerous expeditions together since then.
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