The influence of short-term high-altitude acclimatization on cerebral and leg tissue oxygenation post-orthostasis.

PURPOSE: Orthostasis at sea level decreases brain tissue oxygenation and increases risk of syncope. High altitude reduces brain and peripheral muscle tissue oxygenation. This study determined the effect of short-term altitude acclimatization on cerebral and peripheral leg tissue oxygenation index (TOI) post-orthostasis. METHOD: Seven lowlanders completed a supine-to-stand maneuver at sea level (450 m) and for 3 consecutive days at high altitude (3776 m). Cardiorespiratory measurements and near-infrared spectroscopy-derived oxygenation of the frontal lobe (cerebral TOI) and vastus lateralis (leg TOI) were measured at supine and 5-min post-orthostasis. RESULTS: After orthostasis at sea level, cerebral TOI decreased [mean Δ% (95% confidential interval): - 4.5%, (- 7.5, - 1.5), P < 0.001], whilst leg TOI was unchanged [- 4.6%, (- 10.9, 1.7), P = 0.42]. High altitude had no effect on cerebral TOI following orthostasis [days 1-3: - 2.3%, (- 5.3, 0.7); - 2.4%, (- 5.4, 0.6); - 2.1%, (- 5.1, 0.9), respectively, all P > 0.05], whereas leg TOI decreased [days 1-3: - 12.0%, (- 18.3, - 5.7); - 12.1%, (- 18.4, - 5.8); - 10.2%, (- 16.5, - 3.9), respectively, all P < 0.001]. This response did not differ with days spent at high altitude, despite evidence of cardiorespiratory acclimatization [increased peripheral oxygen saturation (supine: P = 0.01; stand: P = 0.02) and decreased end-tidal carbon dioxide (supine: P = 0.003; stand: P = 0.01)]. CONCLUSION: Cerebral oxygenation is preferentially maintained over leg oxygenation post-orthostasis at high altitude, suggesting different vascular regulation between cerebral and peripheral circulations. Short-term acclimatization to high altitude did not alter cerebral and leg oxygenation responses to orthostasis.

Consecutive monitoring of sleep disturbance for four nights at the top of Mt Fuji (3776 m).

The purpose of the present study was to conduct consecutive monitoring of sleep from the second to the fifth night at altitude. Three healthy male subjects climbed the top of Mt Fuji (3776 m) and stayed there for 6 days. Polysomnographic recordings were performed during this period and control recordings were made at sea level 1 month after the mountaineering. Disturbed sleep characterized by an increased number of arousals and/or long wake time was observed to persist through the fifth night in all subjects. These results suggest that sleep disturbance might persist during initial days at altitude despite cumulating sleep pressure due to poor night's sleep.

Modulating effects of the menstrual cycle on cardiorespiratory responses to exercise under acute hypobaric hypoxia.

The purpose of this study was to examine the hypothesis that the menstrual cycle-induced modulation of the cardiorespiratory response to exercise might be altered by acute exposure to altitude. During both the luteal and follicular phases, 9 moderately trained female subjects with normal menstrual cycles performed incremental exercise to maximal effort on a cycle ergometer at sea level (SL) and under hypobaric hypoxia (HH) at the equivalent of 3,000 m altitude. Both at rest and during exercise, minute ventilation (.VE) and oxygen uptake (.VO(2)) did not differ between the luteal and follicular phases (either at SL or HH). However, the ratio of .VE to .VO(2) (.VE /.VO(2)), both at rest and during peak exercise, was greater in the luteal phase than in the follicular phase under HH conditions. Furthermore, the partial pressure of end-tidal carbon dioxide (PETCO(2)) during exercise was lower in the luteal phase than in the follicular phase in HH. These results suggest that the menstrual cycle-induced modulation of the ventilatory response to exercise may be altered under acute hypobaric-hypoxic conditions.