Intermittent hypoxia interventions for inducing ventilatory acclimatization to high altitude?

Accumulation of ∼200 h of hypoxia exposure (pre-acclimatization) has been suggested to prevent the development of acute mountain sickness when a person is subsequently exposed to high altitude. These pre-exposures are typically undertaken intermittently at or near the place of residence, primarily during sleep in hypoxic tents, and are likely to induce effective ventilatory acclimatization. However, the physiological consequences of different modes of intermittent hypoxia (IH) exposure on ventilatory acclimatization remain largely obscure and are the subject of much controversy. The aim of this review is therefore to summarize and discuss the findings of relevant studies and draw on our long-term practical experience to address the effects of IH exposure on ventilatory acclimatization and to provide suggestions for effective pre-acclimatization. We provide a balanced overview of studies investigating the effects of different types of altitude/hypoxia exposure on the hypoxic ventilatory response and renal compensation to hyperventilation-induced respiratory alkalosis. Although it has been demonstrated convincingly that the hypoxic ventilatory response can increase by 50%-100% with only a few short IH sessions (1 h per day for 7 days), the available data on the effects of IH on renal compensation do not permit definitive conclusions to be drawn. Long-term exposure to IH over several weeks appears to induce renal compensation effectively, allowing for a full ventilatory response and favourable oxygenation at high altitude. To clarify definitively which strategies are most suitable, long-term systematic investigations of various IH strategies are urgently needed.