Snippets from the Research World
Exhaling the evidence: markers of oxygen toxicity in divers’ breath
When lungs are exposed for long periods to high levels of oxygen it can cause discomfort and acute respiratory distress. First discovered in 1899 by Lorrain Smith, pulmonary oxygen toxicity (POT) has been widely studied in divers. In recent years it has been possible to detect novel volatile organic compounds (VOCs) in the breath of subjects breathing high partial pressures of oxygen for a prolonged time, providing a new means of studying the pre-clinical progression of pulmonary oxygen toxicity. To date studies had only been undertaken in hyperbaric chambers and shallow diving environments, but in their December 2023 paper published in Diving and Hyperbaric Medicine, Feiko de Jong and co-workers from the Netherland took research a stage further and studied VOCs in the breath of heliox divers after dives to 81m seawater. The study showed that even in deep heliox dives with surface recompression on oxygen, the production of the VOCs is reversible and the results supported previous findings that pulmonary oxygen toxicity develops sub-clinically before there are any discernible symptoms. More research is certainly required but the ability to capture specific VOCs in exhaled breath in operational setting provides a tool to further explore the dose-response relationship. It also opens the door to studying factors such as the potential protective effects of breathing helium compared to nitrogen in both controlled and real-world situations.
de Jong FJM, Brinkman P, Wingelaar TT, van Ooij PJAM, van Hulst RA. Pulmonary oxygen toxicity breath markers after heliox diving to 81 metres. Diving and Hyperbaric Medicine. 2023 December 20;53(4):340−344. doi: 10.28920/dhm53.4.340-344. PMID: 38091594.
Don’t gamble at depth: nitrogen narcosis and decision making
Decision making in scuba diving is a critical skill that can mean the difference between a safe dive and a dangerous situation. As divers descend they must navigate a complex environment where multiple split-second judgments can have significant consequences. In challenging situations divers must remain calm and focused, using problem-solving skills to address unexpected obstacles. Decision making is critical. While gas narcosis is often experienced by divers beyond 30m the significance of its effects remain poorly understood. Dives to 30m or shallower are often considered safe from risks from nitrogen narcosis due the lack of noticeable effects, but both DAN and BSAC incident reports have previously cited nitrogen narcosis as a factor at depths from 20m+, often due to impaired capacity to respond to an issue underwater. In the December issue of Diving and Hyperbaric Medicine, Pauliina Ahti and Jan Wikren report an interesting study of divers at 30m on air using the widely used and validated Iowa Gambling Task (IGT) as a measure of impairments in decision making. The tool was originally developed and validated to predict real-life decision deficits. In their study the IGT measure was undertaken using an underwater tablet by a group at 30m with an equivalent group undertaking the same tasks at 5m as a control. Although the groups were small, the results suggested that nitrogen narcosis potentially affects decision making at 30m through altering higher cognitive functions in the brain. So nitrogen narcosis may be more than it seems, and higher brain functions may be affected long before the diver is aware of any deficit. Further research will show whether these deficits can be measured at less than 30m and at what depth the effects are first measurable.
Ahti PA, Wikgren J. Rapture of the deep: gas narcosis may impair decision-making in scuba divers. Diving and Hyperbaric Medicine. 2023 December 20;53(4):306−312. doi: 10.28920/dhm53.4.306-312. PMID: 38091589.
Scuba tank maintenance: it’s not all about pressure and strength!
Most divers know that scuba tanks should be periodically tested using visual checks (inside and out) and hydrostatic pressure tests. The potential of moisture inside a cylinder to damage the structure due to rusting are well known and understood. It may therefore be tempting to think that any diving cylinder reading 150-200 bar (or lower!) is relatively safe to use if nothing else is available. The paper recently published in Diving and Hyperbaric Medicine by Arnaud Druelle and colleagues dramatically demonstrates why that is absolutely not the case! They report two separate instances where divers have been rapidly rendered unconscious due to breathing gas mixes unable to sustain life, primarily due to internal cylinder corrosion.
The first instance involved a father and son testing a BCD in a pool using an old cylinder with 60 bar air. The son breathed from the regulator with his head above water and rapidly lost consciousness, fully recovering without resuscitation shortly after removing the regulator. Unperturbed, the father repeated the ‘experiment’ and also lost consciousness before also making a full recovery on removal of the regulator. On testing the oxygen content of the cylinder was measured at less than 1% (air is 21% oxygen).
The second instance involved a diver using a ‘safety scuba tank’ found on a dive boat after realising his own tank held insufficient air for him to complete his planned dive. He started his descent and was retrieved at 14m having been found unconscious without his regulator in his mouth. The diver was lifted to the surface, revived using mouth-to-mouth and made a full recovery. On analysis of the ‘air’ in the tank the oxygen level was measured at 8% despite the cylinder having been topped up to 180bar with air since the incident.
The main issue in both cases was hypoxia caused by the oxygen in the air being ‘used up’ in the chemical reaction (oxidation) that converts steel (iron) to rust (iron oxide). These incidents clearly show that the ability of a scuba cylinder to contain pressure is no indication of the quality of the gas inside. Divers should be acutely aware that untested cylinders harbour greater threats to life than simply exploding if the cylinders are not tested and in date!
Druelle A, Daubresse L, Mullot JU, Streit H, Louge P. Hypoxic loss of consciousness in air diving: two cases of mixtures made hypoxic by oxidation of the scuba diving cylinder. Diving and Hyperbaric Medicine. 2023 December 20;53(4):356−359. doi: 10.28920/dhm53.4.356-359. PMID: 38091597.