Oxygen-enriched Air Decreases Ventilation during High-intensity Fin-swimming Underwater

Oxygen-enriched air is commonly used in the sport of SCUBAdiving and might affect ventilation and heart rate, but little work exists for applied diving settings. We hypothesized that ventilation is decreased especially during strenuous underwater fin-swimming when using oxygen-enriched air as breathing gas. Ten physically-fit divers (age: 25 +/- 4; 5 females; 67 +/- 113 open-water dives) performed incremental underwater finswimming until exhaustion at 4 m water depth with either normal air or oxygen-enriched air (40 % O2) in a double-blind, randomized within-subject design. Heart rate and ventilation were measured throughout the dive and maximum whole blood lactate samples were determined post-exercise. ANOVAs showed a significant effect for the factor breathing gas (F(1, 9) = 7.52; P = 0.023;.2 p = 0.455), with a lower ventilation for oxygen-enriched air during fin-swimming velocities of 0.6 m . s-1 (P = 0.032) and 0.8 m . s-1 (P = 0.037). Heart rate, lactate, and time to exhaustion showed no significant differences. These findings indicate decreased ventilation by an elevated oxygen fraction in the breathing gas when fin-swimming in shallow-water submersion with high velocity ( > 0.5 m . s- 1). Applications are within involuntary underwater exercise or rescue scenarios for all dives with limited gas supply.