Autonomic control of the cardiovascular system during acute hypobaric hypoxia, assessed by time-frequency decomposition of the heart rate

Abstract

The time @om onset of severe hypoxia to loss of consciousness (TUC) varies among healthy individuals. We hypothesized that this variance is due to dference in autonomic modulation of the cardiovascular system. ECG and finger oxygen saturation patterns were recorded @om twenty-one consenting aircrew members, during controlled altitude chamber training at 25.000 feet. Autonomic activity was assessed by heart rate variability (HRV) using a selective Pequency-dependent-window algorithm (SDA) in the LF (0.04-0.15Hz) and HF (0.15-0.50 Hz) bands. Subjects who displayed the highest HR V integrals during baseline and experimental states, were able to remain conscious longer without supplemental oxygen (mean 364sec) "at altitude" compared to subjects with low HRV integrals (mean 231sec). Thus, hypoxia resistance may be related to autonomic activity and its ability to achieve selective blood shunting.

Dynamics of the heart rate variability and oxygen saturation response to acute normobaric hypoxia within the first 10 min of exposure

“…Dynamics of HRV after hypoxia onset was assessed using relatively unique spectral analysis (Barak et al ., ; Nesterov & Nesterov, ). However, Barak et al .…”

“…However, Barak et al . () did not specify the time resolution and Nesterov & Nesterov () provided outcomes of one subject only. Time domain indexes were calculated from the traditional HRV 5‐min recording duration (Buchheit et al ., ; Basualto‐Alarcón et al ., ; Wille et al ., ; Taralov et al ., ).…”

“…However, there is a paucity of studies reporting effects of hypoxia on ANS using ultra-short, for example 1 min, recordings. Such knowledge would be useful in specific circumstances, for example intermittent hypoxic training which consists of several bouts of hypoxia lasting a few minutes (Bobyleva & Glazachev, 2007) and aviation where a sudden loss of supplied oxygen can occur (Barak et al, 2001).…”

“…This obstacle can be overcome by using special spectral analysis that uses a shorter time resolution. Barak et al (2001) used selective window discrete transform and Nesterov & Nesterov (2007) used wavelet transform but these techniques do not enjoy widespread use in the medical literature and therefore we looked for another solution. Time domain HRV indexes can be calculated from short RR interval segments (Nussinovitch et al, 2011;Esco & Flatt, 2014).…”

Heart Rate Variability in Rats Acclimatized to High Altitude

“…fact, using HRV analysis, a combined role for parasympathetic withdrawal and sympathetic stimulation has been implicated in the tachycardia of these first days of acute hypoxia (Hughson et al, 1994;Perini et al, 1996;Barak et al, 2001;Bernardi et al, 2001;Kanai et al, 2001;Liu et al, 2001).…”