Acute Hypobaric Hypoxia Effects on Finger Temperature During and After Local Cold Exposure.

Mountain environments have combined stressors of lower ambient temperature and hypoxia. Cold alone can reduce finger temperature, resulting in discomfort, impaired dexterity, and increased risk of cold injury. Whether hypobaric hypoxia exacerbates these effects is unclear. To examine this, finger temperature responses to two cold water immersion tests were measured at sea level (SL, 99 kPa), 3000 m (70 kPa), and 4675 m (56 kPa) at the same air temperature (22°-23°C). Nine males sat quietly for 30 min, then completed the tests in balanced order. For the cold-induced vasodilation (CIVD) test, middle finger pad temperature was measured during immersion in 4°C water for 30 min. For the Rewarming test, finger temperature was measured for 30 min following a 5 min hand immersion in 16°C water. Average oxygen saturation was 98.6% during SL, 90.7% at 3000 m, and 75.8% at 4657 m. Mean finger temperature during the CIVD test (7.1°C) was similar among trials. There was no difference in CIVD parameters of nadir, apex, or mean finger temperatures; however both onset and apex times were earlier at 3000 m, compared to SL (0.6 min and 1.6 min, respectively). These differences did not persist at 4657 m. Rewarming after hand immersion was similar among trials, reaching 22.7°C after 30 min, compared to an initial finger temperature of 29.3°C. The results of this study provide no evidence that hypobaric hypoxia increases risk of cold injury. Previous findings of blunted finger temperatures at altitude are likely due to the lower ambient temperature that typically occurs at higher elevations.