Heart rate nonlinear dynamics during sudden hypoxia at 8230 m simulated altitude.
OBJECTIVE
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.


METHODS
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 (alphas) and the Sample Entropy index (SampEn).


RESULTS
Hypoxia was related to a decrease in linear HRV indexes at all frequency levels. A non-significant decrease in alphas (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.


CONCLUSIONS
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.
Vigo
Daniel E
DE
Departamento de Docencia e Investigación, Facultad de Ciencias Médicas, Pontificia Universidad Católica Argentina, Buenos Aires, Argentina.
Pérez Lloret
Santiago
S
Videla
Alejandro J
AJ
Pérez Chada
Daniel
D
Hünicken
Horacio M
HM
Mercuri
Jorge
J
Romero
Ramón
R
Nicola Siri
Leonardo C
LC
Cardinali
Daniel P
DP
D000328:Adult; D000531:Altitude; D001273:Atmosphere Exposure Chambers; D001274:Atmospheric Pressure; D001341:Autonomic Nervous System / Q000503:physiopathology; D001359:Aviation; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D008889:Military Personnel; D010101:Oxygen Consumption