An Overnight, 8-Hour Low Oxygen Exposure Increases Energy Expenditure with No Effect on Energy Intake: A Randomized,...

Area of Science:

• Physiology
• Altitude Medicine
• Metabolic Research

Background:

• High altitude exposure (hypobaric hypoxia) increases resting metabolic rate (RMR) and decreases energy intake, leading to negative energy balance.
• The effects of short-term, simulated normobaric hypoxia (NH) at sea level on energy balance mechanisms are not well understood.

Purpose of the Study:

• To investigate the impact of a single overnight exposure to NH on RMR, heart rate variability (HRV), appetite, and energy intake.
• To compare these effects against an overnight exposure to normobaric normoxia (NN) in healthy adults.

Main Methods:

• A randomized, single-blind, sham-controlled, crossover study involving 20 adults sleeping for 8 hours in a tent with either ~15% oxygen (NH) or ~20% oxygen (NN).
• Measurements included HRV, RMR, subjective appetite using visual analog scales, and ad-libitum energy intake from a breakfast buffet.

Main Results:

• Overnight NH exposure resulted in lower peripheral oxygen saturation compared to NN.
• Parasympathetic nervous system activity markers (RMSSD, HF activity) were reduced, while heart rate was elevated following NH.
• Resting metabolic rate (RMR) was significantly increased after NH exposure, but appetite and energy intake remained unchanged.

Conclusions:

• A single overnight exposure to normobaric hypoxia (NH) can decrease parasympathetic nervous system activity and increase heart rate and RMR.
• NH exposure does not appear to significantly alter appetite or energy intake in the short term.
• These findings provide insights into the acute physiological responses to simulated altitude at sea level.