Military Applications of Hypoxic Training for High-Altitude Operations

Abstract

Rapid deployment of unacclimatized soldiers to high mountainous environments causes debilitating effects on operational capabilities (physical work performance), and force health (altitude sickness). Most of these altitude-induced debilitations can be prevented or ameliorated by a wide range of physiological responses collectively referred to as altitude acclimatization. Acclimatization to a target altitude can be induced by slow progressive ascents or continuous sojourns at intermediate altitudes. However, this "altitude residency" requirement reduces their utilization in rapid response military missions that exploit the air mobility capability of modern military forces to quickly deploy to an area of operations on short notice. A more recent approach to induce altitude acclimatization is the use of daily intermittent hypoxic exposures (IHE) in lieu of continuous residence at high altitudes. IHE treatments consist of three elements: 1) IHE simulated altitude (inspired oxygen partial pressure: PIO2), 2) IHE session duration, and 3) total number of IHE sessions over the treatment period. This paper reviews and summarizes the results of 25 published IHE studies. This review finds that an IHE altitude>or=4000 m, and daily exposure duration of at least 1.5 h repeated over a week or more are required to have a high probability of developing altitude acclimatization. The efficacy of shorter duration (<1.5 h) hypoxic exposures at >or=4000 m simulated altitudes, and longer exposures (>4 h) at moderate altitudes (2500-3500 m) is not well documented. The predominate IHE-induced altitude acclimatization response appears to be increased arterial oxygen content through ventilatory acclimatization. Thus, IHE is a promising approach to provide the benefits of altitude acclimatization to low-altitude-based soldiers before their deployment to high mountainous regions.

Effect of repeated normobaric hypoxia exposures during sleep on acute mountain sickness, exercise performance, and sleep during exposure to terrestrial altitude

“…Under HH conditions, the higher sleep Sa O 2 may have contributed to a lessening of AMS upon awakening but had no impact on AMS or exercise performance for the remainder of each day. ventilatory acclimatization; physical performance; hypobaric hypoxia; arterial oxygen saturation ALTITUDE ACCLIMATIZATION RESULTS from numerous interrelated physiological adjustments that compensate for hypoxemia, with augmented ventilation being one of the most important and consistently reported (17,18,22,28). Ventilatory acclimatization (VEacc) can be characterized by the progressive decrease in the end-tidal PCO 2 (PET CO 2 ) that leads to an increase in arterial O 2 saturation (Sa O 2 ) during the first several days of moderate-to high-altitude residence [hypobaric hypoxia (HH), reduced barometric pressure (P B ) and 20.9% O 2 ] (7, 28).…”

“…A comparable degree of VEacc can similarly be induced as a result of repeated daily normobaric hypoxia (NH) exposures (maintained P B and Ͻ20.9% O 2 ) using many different combinations of hypoxia duration, severity, and frequency (22). What has not been established, however, is whether NH exposure is any more effective than no treatment for mitigating undesirable outcomes such as AMS or the initial large impairment in exercise performance during subsequent HH residence (22).…”

“…What has not been established, however, is whether NH exposure is any more effective than no treatment for mitigating undesirable outcomes such as AMS or the initial large impairment in exercise performance during subsequent HH residence (22). The only controlled, experimental studies reporting that AMS, exercise performance, and other physiological outcomes were affected favorably relative to no treatment utilized HH treatment prior to HH residence (2)(3)(4)18) or NH treatment prior to NH residence (17,22). Until two other studies were published recently (5,27), no data existed to determine directly whether NH treatment would be more beneficial than no treatment during subsequent HH residence.…”

Acute mountain sickness

“…The study in soldiers staying at 2000-3960 m a.s.l. revealed that symptoms of AMS occurred in 70% of them [26]. Another study in recruits staying in Chile at the altitude of 3550 m a.s.l.…”

Intermittent simulated hypoxia for pre-acclimatization

“…A proper acclimatization is of great importance for professional engagement at high altitude; however a step by step adaption process over several days seems to be more a hope than reality. In case of rescue and military [4] operations at high altitude, the exposition time and duration is often unknown and the subjects are not able to terminate the altitude stay by their own. Hypoxic chambers might be a solution to have staff prepared to leave for such missions.…”