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West, John B. Paralysis and blindness during a balloon ascent to high altitude. High Alt. Med. Biol. 5:453–456, 2004.—An account of the classic balloon ascent to over 29,000 ft (8840 m) by J. Glaisher and H. T. Coxwell on September 5, 1862, appeared in The Lancet and is reproduced here. Glaisher reported paralysis of his arms and legs and sudden loss of sight. Coxwell also lost the use of his hands and could only open the valve of the balloon to initiate its descent by seizing the cord with his teeth. These symptoms are unusual for acute hypoxia, and in a recent article Michael J. Doherty suggested that they may have been caused by decompression sickness. However, this seems unlikely based on many reported cases of subatmospheric decompression sickness.

When lowlanders go to high altitude, the resulting oxygen deprivation impairs mental and physical performance, quality of sleep, and general well-being. This paper compares the effects of ventilatory acclimatization and oxygen enrichment of room air on the improvement of oxygenation as judged by the increase in the alveolar PO2 and the reduction in equivalent altitude. The results show that, on the average, complete ventilatory acclimatization at an altitude of 5000 m increases the alveolar PO2 by nearly 8 torr, which corresponds to a reduction in equivalent altitude of about 1000 m, although there is considerable individual variability. By comparison, oxygen enrichment to 27% at 5000 m can easily reduce the equivalent altitude to 3200 m, which is generally well tolerated. Because full ventilatory acclimatization at altitudes up to about 3600 m reduces the equivalent altitude to about 3000 m, oxygen enrichment is not justified for well-acclimatized persons. At an altitude of 4200 m, where several telescopes are located on the summit of Mauna Kea, full acclimatization reduces the equivalent altitude to about 3400 m, but the pattern of commuting probably would not allow this. Therefore, at this altitude, oxygen enrichment would be beneficial but is not essential. At higher altitudes such as 5050 m, where other telescopes are located or planned, the gain in oxygenation from acclimatization is insufficient to produce an adequate mental or physical performance for most work, and oxygen enrichment is highly desirable. Full ventilatory acclimatization requires at least a week of continuous exposure, although much of the improvement is seen in the first 2 days.

The Swiss expedition to Everest (altitude 8848 m) in the spring of 1952 very nearly attained the summit with two of the climbers reaching 8595 m. This would have been the first ascent of Everest. One main reason for failure was the inadequate oxygen equipment which was modified from sets designed for mine rescue using potassium peroxide generators. Oxygen could not be inhaled while the mountaineers were climbing because of the rigid mouthpiece assembly and the high breathing resistance of the equipment. It was argued that breathing oxygen during rest periods would suffice, but this was a fallacy as had been demonstrated by Kellas 30 years before.

The aim of this analysis was to determine the altitude of the highest permanent human habitation in the hope that this will throw some light on what determines the highest altitude that a community can tolerate indefinitely. A number of places where people have lived at very high altitudes for long periods of time are reviewed. Individuals have lived for as long as 2 yr at an altitude of 5950 m, and there was a miner's camp at 5300 m for several years. The highest permanently inhabited town in the world at the present time appears to be La Rinconada, a mining village of over 7000 people in southern Peru at an altitude of up to 5100 m, which has been in existence for over 40 yr. The altitude of the highest permanent human habitation is determined partly by economic factors, rather than solely by human tolerance to hypoxia.

Increasingly, lowlanders are commuting to high altitude for commercial, scientific, or defense reasons. Oxygen enrichment of room air at high altitude is a simple but highly effective way of improving sleep quality, mental performance, work efficiency, and general well-being. This review summarizes some of the practical aspects of providing oxygen enrichment including room construction, oxygen concentrators, ventilation levels, costs, use of liquid oxygen, fire hazard, and safe upper limits for oxygen enrichment. The physiological and medical effects of oxygen enrichment are discussed under the headings of sleep, neuropsychological function, and general well-being, productivity, and fatigue. Oxygen enrichment of room air can play a major role in improving living and working conditions for commuters to high altitude.

Oxygen enrichment of room air has proved to be valuable for people who need to work at altitudes of 4000 m and above. In the present study the feasibility of using the same technique in ski and other mountain resorts at the lower altitudes of 2500 to 4000 m is considered. Although many people find these altitudes invigorating, some are distressed by the hypoxia, especially at night. The analysis shows that all resorts up to an altitude of 3250 m (10,600 ft) can have the equivalent altitude reduced to 1000 m (3280 ft) by oxygen enrichment without incurring a fire hazard. (The equivalent altitude is that which provides the same inspired PO2 during air breathing.) Even resorts or laboratories as high as 4250 m can have the equivalent altitude safely reduced to 1500 m, that is, lower than the altitude of Denver, Colorado. This application of oxygen enrichment is likely to be most valuable for improving sleep and assisting in the initial acclimatization process.

Sleep is known to be impaired at high altitude, and this may be a factor contributing to reduced work efficiency, general malaise, and the development of acute mountain sickness (AMS). Nocturnal room oxygen enrichment at 3800 m has been shown to reduce the time spent in periodic breathing and the number of apneas, to improve subjective quality of sleep, and to reduce the AMS score. The present study was designed to evaluate the effect of oxygen enrichment to 24% at 3800 m (lowering the equivalent altitude to 2800 m) on sleep architecture. Full polysomnography and actigraphy were performed on 12 subjects who ascended in 1 day to 3800 m and slept in a specially constructed room that allowed oxygen enrichment or ambient air conditions in a randomized, crossover, double-blind study. The results showed that subjects spent a significantly greater percentage of time in deep sleep (stages III and IV combined, or slow wave sleep) with oxygen enrichment versus ambient air (17.2 ± 10.0% and 13.9 ± 6.7%, respectively; p < 0.05 in paired analysis). No differences between treatments were seen with subjective assessments of sleep quality or with subject's assessment of the extent to which they suffered from AMS. This study provides further objective evidence of improved sleep as a result of oxygen enrichment at 3800 m and suggests that alleviating hypoxia may improve sleep quality.

Oxygen enrichment of room air at high altitude has been shown to improve mental performance, sleep quality, and work capacity. Until now, the usual strategy has been to use an oxygen concentration that reduces the equivalent altitude to about 3000 m, where the equivalent altitude is that which gives the same inspired PO2 during air breathing. However, standards adopted by the National Fire Protection Association allow considerably higher oxygen concentrations without introducing a fire hazard. For example, by raising the oxygen concentration to 31.5% at an altitude of 5000 m, the equivalent altitude can be safely reduced to less than 2000 m. At the extreme altitude of 8000 m, the equivalent altitude can be reduced to less than 4000 m without increasing the fire hazard. These increased levels of oxygen enrichment are feasible in practice using oxygen concentrators. They may be useful if lowlanders need to ascend rapidly and stay at high altitude, or for treating people with high altitude illnesses.

In a randomized, double-blind study, 24 sea-level residents drove to 3800-m altitude in 1 day, and then slept the first night in either ambient air or 24% oxygen, and the second night in the treatment that they did not receive on the first night. Oxygen enrichment, compared with ambient air, resulted in significantly fewer apneas, and significantly less time spent in periodic breathing during the night. The increase in SaO2 between evening and morning was significantly higher after sleeping in the oxygen-enriched atmosphere, compared with ambient air. However, this significant improvement in SaO2 did not persist into mid-day. The overnight treatment did not alter the ventilatory response to hypoxia or to carbon dioxide as measured the following morning. The results suggest that the elevation in SaO2 following overnight oxygen enrichment is probably not due to a change in the control of ventilation, but possibly to differences in subclinical lung pathology.

Cognitive and motor function are known to deteriorate with the hypoxia accompanying high altitude, posing a substantial challenge to the efficient operation of high altitude industrial and scientific projects. To evaluate the effectiveness of enriching room air oxygen by 6% at 5000 m altitude in ameliorating such deficits, 24 unacclimatized subjects (16 males, 8 females; mean age 37.8, range 20 to 47) underwent neuropsychological testing in a specially designed facility at 3800 m that can simulate an ambient 5000 m atmosphere and 6% enrichment at 5000 m. Each subject was tested in both conditions in a randomized, double-blinded fashion. The 2-h test battery of 16 tasks assessed various aspects of motor and cognitive performance. Compared with simulated breathing air at 5000 m, oxygen enrichment resulted in higher arterial oxygen saturations (93.0 vs. 81.6%), quicker reaction times, improved hand-eye coordination, and more positive sense of well-being (on 6 of 16 scales), each significant at the p < 0.05 level. Other aspects of neuropsychological function were not significantly improved by 6% additional oxygen.