Influence of Repeated Exposures to Hypobaric Chamber on Acute Hypoxia Tolerance / 항공우주의학회지

BACKGROUND: Acute hypoxia tolerance has been evaluated by the time of useful consciousness, subjective symptoms, cardiovascular changes, visual deterioration, psychological performance, and so forth. But these methods are either subjective, lacking strict objectivity, or too demanding to collect sufficient data. Pulse oximeter monitoring has come to be used not only in hospitals but in the aviation environment. This noninvasive oxygen monitoring apparatus warrants a highly objective analysis to investigate acute hypoxia tolerance. METHODS: Eight healthy male volunteers (20-25 years old) were exposed three times to a simulated altitude of 25,000 ft (7,620 m) at intervals of 7 days. We monitored arterial oxygen saturation (SaO2) and pulse rate by a pulse oximeter. The duration from taking the mask off to the time of 60% SaO2 was regarded as acute hypoxia tolerance. The venous hemoglobin concentration was measured a day before exposure to hypoxia. A questionnaire on the 14 subjective hypoxic symptoms was obtained after hypobaric chamber training. RESULTS: There were neither differences of acute hypoxia tolerance, hemoglobin concentration, nor pulse rate according to the repeated exposure of hypoxia. Four symptoms of sleepiness, fatigue, flushing and thinking impairment were sustained regardless of repeated exposures to hypoxia. But the incidence of symptoms of ear pain, anxiety, abdominal pain were reduced according to the repeated hypoxia. CONCLUSION: With pulse oximeter monitoring there was no difference between the values of time of 60% SaO2 in repeated exposures to hypoxia. The incidence of some subjective symptoms was reduced according to the repeated exposures to hypoxia.

Difference of Hypoxia Tolerance with Reference to Sex

BACKGROUND: Time of useful consciousness is related with various factors including smoking, age, sex, drug, and temperature. It is still unclear whether acute hypoxia tolerance is different between male and female. METHOD: We included 32 healthy students (male, n=16; female, n=16) volunteered to participate in this study. The blood hemoglobin concentration was measured at a day before flight. With high altitude rapid decompression flight training chamber, flight to simulated altitude of 25,000 ft was performed after nitrogen extraction breath. At 25,000 ft, heart rate and arterial O2 saturation (SaO2) were measured by using pulse oximeter after taking off oxygen mask. We compared the duration from mask-off to the time at 60% SaO2 between male and female and correlated the time at 60% SaO2 with hemoglobin concentration. RESULTS: The duration from mask-off to SaO2 reaching 60% were significantly longer in the male group. There was a linear relationship between hemoglobin concentration and time at 60% SaO2. CONCLUSION: Acute hypoxia tolerance differs from the two sexes and the difference of hemoglobin concentration is one of possible causative factors of this difference.