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Publication AbstractsAutonomic Response to Hypobaric Hypoxia Assessed by Time-Dependent Frequency Decomposition of Heart RateYair Barak, M.Sc., Daniel David, M.D., Laurence Keselbrener, Ph.D., and Solange Akselrod, Ph.D.Aviat Space Environ Med 2001; 72:992-1000 AbstractBackground: Acute hypoxia tolerance varies substantially among healthy individuals. We hypothesized that this variability results from a difference in autonomic (ANS) response to hypoxic stress. Methods: Peripheral oxygen saturation, respiration and ECG were recorded from 21 healthy subjects (age, 29 ± 7 yr) in an altitude chamber during normoxia, severe hypoxia (282 mm Hg), and mild hypoxia (360 mm Hg). Cardiovascular control was assessed by time-frequency decomposition of the heart rate signal applying the Selective Discrete Transform Algorithm (SDA). This procedure uses a variable time window, thus providing reliable physiological data even during transient states. Autonomic activity was quantified by power spectral density integrals over a 3-dimensional time-dependent spectral distribution of heart rate fluctuations. Results: Subjects who had slower peripheral oxygen desaturation during severe hypoxia onset (mean 92.9 vs. 58.4 s) were those who displayed higher ANS activity in all ambient states, namely normoxia and hypoxia. These same subjects withstood hypoxia for significantly longer time periods (mean 313 vs. 244 s). Conclusion: Improved hypoxia tolerance is linked to enhanced autonomic activity, involving a better management of peripheral blood flow.Keywords: acute hypobaric hypoxia, human hypoxia tolerance, autonomic activity. Information on subscribing, and on obtaining copies of an article or of an entire issue. Table of Contents for Volume 72, Number 11 of the ASME journal.
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