Human tolerance and physiological responses to exercise while breathing oxygen at 2.0 ATA

Area of Science:

• Hyperbaric physiology
• Exercise physiology
• Neurophysiology

Background:

• Exposure to hyperbaric oxygen (HBO) can cause central nervous system (CNS) toxicity.
• Exercise during HBO exposure may alter CNS oxygen tolerance.
• Understanding physiological responses during combined HBO and exercise is crucial for safety.

Purpose of the Study:

• To investigate the physiological effects of moderate ergometer exercise during hyperbaric oxygen exposure.
• To determine if exercise exacerbates CNS oxygen toxicity symptoms under hyperbaric conditions.
• To assess the impact of exercise on arterial carbon dioxide partial pressure (PaCO2) during hyperbaric oxygen exposure.

Main Methods:

• Ten healthy men underwent two 30-min exercise bouts at 150 W during 120-min exposures to 100% oxygen at 2.0 atmospheres absolute (ATA).
• Physiological functions including visual fields, pulmonary mechanics, cognitive performance, and cardiovascular function were monitored.
• Arterial blood gases (PaCO2) were measured at rest and during graded exercise (50-200 W) in a separate cohort of six subjects breathing oxygen at 2.0 ATA.

Main Results:

• No CNS symptoms (convulsions, EEG changes) or significant alterations in monitored physiological functions were observed during or after exercise.
• Pre- and post-exposure assessments of visual acuity, accommodation, pupil diameter, and retinal/cortical activity showed no significant differences.
• Average PaCO2 increased by approximately 5 mm Hg during exercise at 150 W and rose linearly with workload, reaching 44.0 mm Hg at 200 W.

Conclusions:

• Moderate exercise during hyperbaric oxygen exposure at 2.0 ATA does not appear to induce CNS toxicity or impair key physiological functions in healthy men.
• The observed increase in PaCO2 during exercise may be a significant factor influencing CNS oxygen tolerance.
• Elevated PaCO2, leading to increased cerebral blood flow and partial pressure of oxygen in the brain, could contribute to the known detrimental effects of exercise on CNS oxygen tolerance.