Editorial: 50th Anniversary of the Silver Hut Expedition (p. 79)

This year is the 50th anniversary of the Silver Hut Expedition, the first major physiological study at very high altitude after World War II. This issue celebrates the anniversary and includes mini-reviews of four other extensive studies at extreme altitude.

Sightings

Edited by John W. Severinghaus (p. 83)

Clinician's Corner

Edited by Andrew Luks

Altitude Preexposure Recommendations for Inducing Acclimatization

Muza and colleagues (p. 87) review the topic of pre-exposing people to high altitude in the hope that this will improve their performance at their target altitude. This is a subject of great current interest.

Featured Topic: Physiology of Extreme Altitude

The Silver Hut Expedition 1960–1961

Milledge (p. 93) discusses this landmark expedition, which was the first to take place at very high altitude after World War II. Some eight physiologists spent up to five months at an altitude of 5800 m and a wealth of new data was obtained. Later some studies were made on Makalu, altitude 8481 m, including measurements of maximal oxygen consumption up to 7440 m. The expedition had a major influence on later studies at extreme altitude.

American Medical Research Expedition to Everest

West (p. 103) describes the first expedition to make physiological measurements at the highest point on earth. Necessarily, the data were limited, but it was shown that an absolute requirement for operating at these great altitudes is extreme hyperventilation. Even so, the maximal oxygen consumption on the summit is only about 1 l.min⁻¹.

Operation Everest II

Wagner (p. 111) reports on this extensive study using low pressure chambers to simulate an ascent of Mt. Everest. The advantage of a chamber study is that it allows much more invasive measurements than are possible in the field. For example, a great deal of new information was obtained on pulmonary gas exchange and the pulmonary circulation during extreme prolonged hypoxia.

Operation Everest III

Richalet (p. 121) gives an account of another chamber experiment, this time carried out in Marseilles, France, in 1997. It was similar to OEII in many respects, although an innovation was pre-acclimatizing the subjects to an altitude of 4350 m on Mont Blanc prior to their entering the chamber. A large series of metabolic studies were carried out, and several subjects had neurological symptoms that had not been seen on OEII.

Caudwell Extreme Everest Expedition

Grocott (p. 133) describes the recent British field expedition to Mt. Everest. A unique feature of the planning was two previous successful ascents of Cho Oyu, altitude 8153 m to ensure that the participants could tolerate extreme altitude. In the event eight people reached the summit and four arterial blood samples were taken at an altitude of 8400 m. Paradoxically however, much of the effort of the expedition was devoted to 200 trekkers to the Everest Base Camp in the expectation that their genomic patterns will clarify who is best able to tolerate high altitude.

Other Scientific Papers

The Impact of Moderate Altitude Staging on Pulmonary Arterial Hemodynamic after Ascent to High Altitude

Baggish and colleagues (p. 139) studied whether temporary residence at moderate altitude en route to high altitude reduces the incidence and severity of illness. Transthoracic echocardiography was used to measure pulmonary artery pressure in 10 subjects first at a simulated intermediate altitude, barometric pressure 548 Torr, and then at a much higher altitude, barometric pressure 460 Torr. It was found that in subjects who temporarily resided at the moderate altitude, the increase in pulmonary artery pressure was only 11 ± 6 mmHg whereas in subjects that moved to the high altitude chamber without temporary residence at the moderate altitude, the increase averaged 24 ± 10 mmHg.

Fatal Accidents among Elite Mountaineers: A Historical Perspective from the European Alps

Weinbruch and Nordby (p. 147) analyzed the lifetime risk of fatal mountaineering accidents in elite mountaineers using a published data base. They found a crude lifetime risk of fatal accidents of 0.23 with no significant difference between males and females. The highest risk was among people in the age bracket of 30–39 years.

PKC Regulates α1-Adrenoceptor-Mediated Contractions and Baseline Ca²⁺ Sensitivity in the Uterine Arteries of Nonpregnant and Pregnant Sheep Acclimatized to High Altitude Hypoxia

Xiao and co-workers (p. 153) studied how hypoxia affects uterine artery adaptation to pregnancy. They tested whether protein kinase C (PKC) is a factor regulating α1-adrenoceptor-mediated contractions and calcium ion sensitivity in pregnant sheep acclimatized to high altitude. Their conclusion was that the PKC-mediated thin filament regulatory pathway is up-regulated, during pregnancy at high altitude resulting in an increased baseline Ca²⁺ sensitivity.

Brief Report

Initial Orthostatic Hypotension at High Altitude

Thomas and colleagues (p. 163) note that there are reports of syncope following standing up at high altitude. They studied 10 subjects who stood up rapidly from the supine position at an altitude of 5050 m. A series of cardiovascular measurements including arterial blood pressure, middle cerebral artery blood pressure, velocity, and heart rate were studied at sea level and after 14 days at high altitude but no significant differences were observed. They concluded that partial acclimatization to high altitude did not affect the cardiovascular and cerebrovascular responses.

Special Article

English translation of the article The Nomenclature, Classification and Diagnostic Criteria of High Altitude Disease in China (p. 169)

Interesting guidelines on diagnostic criteria of high altitude diseases were published in China in 1996 and are generally not known outside that country. Some readers of High Altitude Medicine and Biology became aware of these as a result of the article by Ren et al. titled “Incidence of High Altitude Illnesses among Unacclimatized Persons who Acutely Ascended to Tibet” that was published in the December 2009 issue of the Journal. In a large study, the incidence of AMS that was reported was higher than expected. This can be explained by the fact that the criteria that the authors used were different from those of the Lake Louise score. In particular, headache was not an essential requirement for a diagnosis of AMS if a sufficient number and intensity of other symptoms occurred.