Apnoeic diving safety--experimental approaches to oxygen augmentation

A study was undertaken to determine whether a volume of oxygen injected from a 100 ml syringe and inhaled during a 10 m ascent would be exhaled again fully or partially by two experienced male divers. Each performed one apnoeic dive with and another without O2 augmentation. Analyses of mouth gas showed that the injected O2 had disappeared when the divers reached the surface. Any movement of the injected O2 to the alveoli through an open glottis probably resulted from simple diffusion as well as from agitation and mixing of gases by simulated respiratory activity. High-frequency positive-pressure ventilation applied by several authors, whereby sufficient gas exchange is achieved by oscillating small tidal volumes at frequencies of up to 900 per minute, may substantiate this possibility. The injected O2 was found also to have disappeared from the alveolar gas, shown by a comparison of O2 fraction differences between augmented and non-augmented dives. Injection and inhalation of the additional O2 will raise the partial pressure of O2 in the alveoli and increase oxygen transfer across the alveolar membrane into the blood, with more molecules being taken up within seconds during the ascent time. O2 augmentation in larger volumes during apnoeic diving could lead to a burst lung and must be regarded with suspicion. There is evidence that O2 augmentation by means of a small syringe attached to a trained diver's snorkel will help prevent apnoeic blackout.