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arterial oxygen saturation

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    The oxygen saturation values reported in the high altitude literature are usually taken during a few minutes of measurement either at rest or during exercise. We aimed to investigate the daily hypoxic profile by monitoring oxygen saturation for 24 h in 8 lowlanders (4 females, ages 26 to 59) during trekking from Lukla (2850 m) to the Pyramid Laboratory (5050 m). Oxygen saturation was measured (1) daily at each altitude (sm), (2) for 24-h during ascent to 3500 m, 4200 m, and on day 1 at 5050 m (lm), and (3) during a standardized exercise (em). Results: (1) the sm and lm values were 90.9% (+/-0.5) and 86.4% (+/-1.1) at 3500 m; 85.2%(+/-1.1), and 80% (+/-1.9) at 4200 m; 83.8%(+/-1) and 77% (+/-1.7) at 5050 m (p < or = 0.05); (2) the daily time spent with oxygen saturation < or =90% was 56.5% at 3500 m, 81% at 4200 m, and 95.5% at 5050 m; (3) during exercise, oxygen saturation decreased by 10.58%, 13.43%, and 11.24% at 3500, 4200, and 5050 m, respectively. In conclusion, our data show that the level of hypoxemia during trekking at altitude is more severe than expected on the basis of a short evaluation at rest and should be taken into account.

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    We tested the hypothesis that the individual ventilatory adaptation to high altitude (HA, 5050 m) may influence renal water excretion in response to water loading. In 8 healthy humans (33+/-4 S.D. years) we studied, at sea level (SL) and at HA, resting ventilation (VE), arterial oxygen saturation (SpO2), urinary output after water loading (WL, 20 mL/kg), and total body water (TBW). Ventilatory response to HA was defined as the difference in resting VE over SpO2 (DeltaVE/DeltaSpO2) from SL to HA. At HA, a significant increase in urinary volume after the first hour from WL (%WLt0-60) was observed. Significant correlations were found between DeltaVE/DeltaSpO2 versus %WLt0-60 at HA and versus changes in TBW, from SL to HA. In conclusion, in healthy subjects the ventilatory response to HA influences water balance and correlates with kidney response to WL. A higher ventilatory response at HA, allowing a more efficient water renal handling, is likely to be a protective mechanisms from altitude illness.