Heart Rate Nonlinear Dynamics During Sudden Hypoxia at 8230 m Simulated Altitude

• Published in: Wilderness & environmental medicine Vol. 21; no. 1; pp. 4 - 10
• Main Authors: Vigo, Daniel E., Pérez Lloret, Santiago, Videla, Alejandro J., Pérez Chada, Daniel, Hünicken, Horacio M., Mercuri, Jorge, Romero, Ramón, Nicola Siri, Leonardo C., Cardinali, Daniel P.
• Format: Journal Article
• Language: English
• Published: Los Angeles, CA Elsevier Inc 01.03.2010; SAGE Publications; Elsevier Limited
• Subjects: Adult; Altitude; Atmosphere Exposure Chambers; Atmospheric Pressure; autonomic nervous system; Autonomic Nervous System - physiopathology; Aviation; Emergency; Heart Rate - physiology; heart rate variability; high altitude; Humans; hypoxia; Hypoxia - physiopathology; Male; Military Personnel; nonlinear; Oxygen Consumption; hypoxia; high altitude; autonomic nervous system; nonlinear; heart rate variability
• ISSN: 1080-6032; 1545-1534; 1545-1534
• DOI: 10.1016/j.wem.2009.12.022

Acute hypobaric hypoxia is associated with autonomic changes that bring a global reduction of linear heart rate variability (HRV). Although changes in nonlinear HRV can be associated with physiologic stress and are relevant predictors of fatal arrhythmias in ischemic heart disease, to what extent these components vary in sudden hypobaric hypoxia is not known. Twelve military pilots were supplemented with increasing concentrations of oxygen during decompression to 8230 m in a hypobaric chamber. Linear and nonlinear HRV was evaluated at 8230 m altitude before, during, and after oxygen flow deprivation. Linear HRV was assessed through traditional time-domain and frequency-domain analysis. Nonlinear HRV was quantified through the short-term fractal correlation exponent alpha (αs) and the Sample Entropy index (SampEn). Hypoxia was related to a decrease in linear HRV indexes at all frequency levels. A non-significant decrease in αs (basal, 1.39 ± 0.07; hypoxia, 1.11 ± 0.13; recovery, 1.41 ± 0.05; P = .054) and a significant increase in SampEn (basal, 1.07 ± 0.11; hypoxia, 1.45 ± 0.12; recovery, 1.43 ± 0.09; P = .018) were detected. The observed pattern of diminished linear HRV and increased nonlinear HRV is similar to that seen in subjects undergoing heavy exercise or in patients with ischemic heart disease at high risk for ventricular fibrillation.