Cerebral Hypoxia During Intermittent Hypoxic-Hyperoxic Training (IHHT): A Case Study Using Cerebral Oximetry Based on Time-Domain Near-Infrared Spectroscopy.

Background: In intermittent hypoxia-hyperoxia training (IHHT), air is inhaled through a mask, with the O content of the air varying at intervals. IHHT is used in sports training (e.g. to improve exercise tolerance), but also in medical-therapeutic applications (e.g. to improve cognitive performance and functional exercise capacity in geriatric patients).

Aim: We aimed to evaluate the ability of a novel time-domain near-infrared spectroscopy (TD-NIRS) device to measure the effects of IHHT on cerebrovascular oxygenation and haemodynamics.

Subject And Methods: One subject (41 years old, male, athlete, colleague of the authors) performed an IHHT session as part of his regular training. In parallel, systemic physiological activity (arterial oxygenation (SpO) and pulse rate (PR)) as well as cerebrovascular oxygenation (StO) and haemodynamics (total haemoglobin concentration, [tHb]) were measured. For the measurement of StO and [tHb], a TD-NIRS device (NIRSBOX, PIONIRS, Italy) was employed. The TD-NIRS device uses two diode lasers (685 nm and 830 nm) as light sources and a solid-state light detector. The optode of the TD-NIRS device was placed over the left prefrontal cortex of the subject. The IHHT session had a total duration of 32 minutes and consisted of four cycles of hypoxia (5 min, O: 10%) followed by hyperoxia (3 min, O: 34%).

Results: The IHHT session caused significant changes in SpO, HR, StO and [tHb]. The hypoxia/hyperoxia challenges resulted in a decrease in SpO from 97% to ~70% and decrease in StO from ~70 to ~60%. During the hypoxia intervals, HR increased from ~50 to ~60, while [tHb] increased only moderately (from ~64 to ~66 μM).

Conclusions: The case study presented here demonstrates the feasibility of the novel TD-NIRS device to measure changes in cerebrovascular haemodynamics and oxygenation during an IHHT session. It was observed that an intense IHHT session causes significant cerebral hypoxia (decrease of StO by 10 percentage points). In contrast, cerebral haemodynamics (as indicated by changes in [tHb]) were only weakly influenced. Our study shows that IHHT can have a significant effect on the oxygen supply in the head, which should be taken into account in future applications of IHHT to prevent possible pathophysiological reactions that could be triggered by it.