Exploration divers often use so-called “rebreather” underwater breathing apparatus to extend their depth range and duration. Rebreathers are more complicated than the simple scuba equipment that most divers are familiar with. With this complexity comes increased risks of user error and technical failure.
The cumulative goal of this work is real-time detection of impending 3-H events (hypoxia, hyperoxia, and hypercapnia) and narcotic impairment that may predispose to causative errors through either monitoring technologies or enhancement of diver recognition (or both). The work will afford a better understanding of the relationship between cerebral oxygenation and cognitive performance in human subjects, and may identify potential real-time hypoxia or hypercapnia monitoring strategies in the form of eye tracking, quantitative EEG analysis (qEEG) and functional near infrared spectroscopy (fNIRS). In the case of qEEG, this work will complete the accumulation of indicative human EEG data in exposures to gas narcosis, hyperoxia, hypoxia, and hypercapnia, facilitating the possibility of an integrative EEG-based monitoring package for all relevant gas effects / toxicities.
In addition, the results will identify (or refute) easily implemented training exposures to improve diver recognition of critical 3-H events. This will also be of great interest to the military and civilian aviation communities who already conduct hypoxia exposures for this purpose largely without evidence of efficacy.
The project was awarded $A70,000 through the ANZCA research grants program for 2022.
Our project “Preventing hypoxia, hypercapnia and gas narcosis in rebreather diving” included three studies: The first study examined whether a prior open-label hypoxia exposure enhances a diver’s ability to recognize hypoxia and to more expeditiously initiate self-rescue (‘bail-out’) in a subsequent blinded exposure. The second study examined whether a prior open-label hypercapnia exposure enhances a diver’s ability to recognize hypercapnia and to more expeditiously initiate self-rescue in a subsequent blinded exposure. We also aimed to leverage the opportunity afforded by these exposures to severe hypoxia and hypercapnia to gather data on neurophysiological responses (eye tracking, functional near-infrared spectroscopy (fNIRS), electroencephalography (EEG)) and physiological responses (heart rate, blood pressure, breathing frequency, minute ventilation, end-tidal gases) to both conditions. The neurophysiological responses represent possible opportunities for real time monitoring modalities for these adverse states in divers.
In the third study, we test the previously developed nitrogen narcosis algorithm on a larger cohort of participants to establish its sensitivity, specificity, and adaptability to a real-time diving monitoring device. For this purpose, we exposed additional participants to the hyperbaric air protocol at 8 ATA.
The research fellow that was supported by the research grant was also involved in research projects in the wider diving medicine field, and supported junior doctors and anaesthetists in training in related research projects.
For both the hypoxia and the hypercapnia study forty healthy participants were recruited. In each of the two studies half of the participants underwent a hypoxia or hypercapnia exposure or received an information leaflet detailing the most frequent reported symptoms. After approximately one month the participants underwent a testing exposure with respectively hypoxia (study 1) or hypercapnia (study 2). Both studies also generated a unique contemporary database of human neurophysiological (EEG, fNIRS and eye tracking) and physiological responses (pulse, blood pressure, ventilation) to severe hypoxia and hypercapnia, which is currently being analysed.
The third study exposed twelve participants to hyperbaric pressures of 8 ATA. A real-time EEG visualization software has been developed.
Somewhat contrary to expectations, the hypoxia study indicated a significant effect of prior open label hypoxia exposure in facilitating earlier recognition and self-rescue in the subsequent blinded exposure one month later. This is the first properly designed validation of the military aviation practice of hypobaric hypoxia ‘training’ for aircrews (and may justify equivalent training for military divers), but we are yet to establish the durability of the training effect (planned for a follow up study).
However, the hypercapnia study did not show the same effect of a prior open label hypercapnia exposure on recognition and self-rescue in a subsequent blinded exposure a month later. This would indicate that the practice currently undertaken by some divers in the home situation would have no benefit.
The developed real-time EEG visualization can be further tested to be used as a gas narcosis monitor (analogous to the 4 bispectral index in anaesthesia) that could be used in diving.
Scientific publications
- Brenner RJ, Balan, KA, Andersen MPL, Dugrenot E, Vrijdag XCE, van Waart H, Tilmans F. A review of nutritional recommendations for scuba divers. J Int Soc Sports Nutr. 2024 Dec;21(1):2402386.
- Vrijdag XCE, van Waart H, Sames C, Sleigh JW, Mitchell SJ. Comparing the EMMA capnograph with sidestream capnography and arterial carbon dioxide pressure at 284 kPa. Diving Hyperb Med. 2023; 53(4): 327-332.
- Grundemann J, Vrijdag XCE, Wong NYE, Gant N, Mitchell SJ, van Waart H. Full-face snorkel masks increase the incidence of hypoxaemia and hypercapnia during simulated snorkelling compared to conventional snorkels. Diving Hyperb Med. 2023; 53(4): 313-320.
- Wong NYE, van Waart H, Sleigh JW, Mitchell SJ, Vrijdag XCE. A systematic review of electroencephalography in acute cerebral hypoxia: clinical and diving implications. Diving Hyperb Med. 2023; 53(3): 268-280.
- Allocco A, van Waart H, Connell C, Wong N, Charukonda A, Gant N, Vrijdag X, Mitchell S. Controlled Exposure to Hypoxia Enhances Subsequent Hypoxia Awareness in Rebreather Divers. Manuscript in preparation.
- Babbage T, van Waart H, Connell C, Gant N, Mitchell S, Vrijdag X. Hypercapnia awareness study. Manuscript in preparation.
Conference presentations
- Vrijdag X, van Waart H, Allocco A, Connell C, Wong N, Charukonda A, Gant N, Mitchell S. Controlled exposure to hypoxia enhances subsequent hypoxia awareness in divers. European Underwater and Baromedical Society (EUBS) meeting, Brest, France, September 2024
- van Waart H, Grundemann J, Vrijdag XCE, Wong N, Gant N, Mitchell SJ. Full-face snorkel masks increase the incidence of hypoxaemia and hypercapnia during simulated snorkelling compared to conventional snorkels. South Pacific Underwater Medicine Society (SPUMS), Fiji, May 2024
- Vrijdag X, van Waart H, Allocco A, Connell C, Wong N, Charukonda A, Gant N, Mitchell S. Controlled exposure to hypoxia enhances subsequent hypoxia awareness in divers. South Pacific Underwater Medicine Society (SPUMS), Fiji, May 2024
- van Waart H, Vrijdag XCE, Kuiper YS. Mitchell SJ. Hypercapnia in normobaric and hyperbaric environments. European Underwater and Baromedical Society (EUBS) meeting, Porto, Portugal, September 2023
- Vrijdag XCE, van Waart H, Sames C, Sleigh JW, Mitchell SJ. Comparing the EMMA capnograph with sidestream capnography and arterial carbon dioxide pressure at 284 kPa. European Underwater and Baromedical Society (EUBS) meeting, Porto, Portugal, September 2023
- Vrijdag XCE, van Waart H, Gant N, Kernagis D, Allocco A, Sleigh JW, Mitchell SJ. Hypoxia, hypercapnia and nitrogen narcosis in rebreather diving. Office of Naval Research (ONR) program review meeting, Washington, USA, May 2023
- Vrijdag XCE, van Waart H, Sames C, Sleigh JW, Mitchell SJ. Does hyperbaric oxygen cause narcosis or hyperexcitability? A quantitative EEG analysis. South Pacific Underwater Medicine Society (SPUMS), Auckland virtual, May 2022
- Vrijdag XCE, van Waart H, Gant N, Kernagis D, Sleigh JW, Mitchell SJ. Hypoxia, hypercapnia and nitrogen narcosis in rebreather diving. Office of Naval Research (ONR) program review meeting, Washington, USA, May 2022
- Vrijdag XCE, van Waart H, Sleigh JW, Mitchell SJ. EEG functional connectivity is sensitive for nitrogen narcosis at 608 kPa. Underwater Hyperbaric Medicine Society (UHMS), Reno NV, USA, May 2022
- van Waart H, Grundemann J, Vrijdag XCE, Wong N, Gant N, Mitchell SJ. Full-face snorkel masks safety during rest and exercise. European Underwater and Baromedical Society (EUBS) meeting, Prague, 5 Czech Republic, September 2022
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