Technical diving

Abstract: Technical divers use gases other than air and advanced equipment configurations to conduct dives that are deeper and/or longer than typical recreational air dives. The use of oxygen-nitrogen (nitrox) mixes with oxygen fractions higher than air results in longer no-decompression limits for shallow diving, and faster decompression from deeper dives. For depths beyond the air-diving range, technical divers mix helium, a light non-narcotic gas, with nitrogen and oxygen to produce 'trimix'. These blends are tailored to the depth of intended use with a fraction of oxygen calculated to produce an inspired oxygen partial pressure unlikely to cause cerebral oxygen toxicity and a nitrogen fraction calculated to produce a tolerable degree of nitrogen narcosis. A typical deep technical dive will involve the use of trimix at the target depth with changes to gases containing more oxygen and less inert gas during the decompression. Open-circuit scuba may be used to carry and utilise such gases, but this is very wasteful of expensive helium. There is increasing use of closed-circuit 'rebreather' devices. These recycle expired gas and potentially limit gas consumption to a small amount of inert gas to maintain the volume of the breathing circuit during descent and the amount of oxygen metabolised by the diver. This paper reviews the basic approach to planning and execution of dives using these methods to better inform physicians of the physical demands and risks.

Abstract: BACKGROUND: The purpose of this study was to investigate the influence of diving experience and diving techniques on the lifetime incidence of decompression illness (DCI). METHODS: Attendants of three diving medical symposia voluntarily answered a questionnaire about their age, gender, medical history, diving experience, diving habits, diving certification levels, and diving associated incidents (cross-sectional survey). RESULTS: Out of 650 divers, 429 completed the questionnaire. The study population consisted of experienced divers with an average of 670 dives. The majority of the divers were certified diving instructors (43%). There were 37 participants (8.7%) who were classified as technical divers with an average of 1193 logged dives. There was an overall lifetime incidence of DCI of 1 per 5463 dives. The complete study group showed an increased lifetime incidence of DCI with decreased diving experience (1.97-fold to 8.17-fold higher). Of the divers, 27% reported severe DCI with neurological symptoms. The lifetime incidence for severe DCI was 1 in 20,291 dives. Again, lifetime incidence for severe DCI was increased with decreased diving certification level (1.1-fold to 13.7-fold higher). Technical divers showed a DCI lifetime incidence of 1 to 8591 dives compared to the non-technical divers with a lifetime incidence of 1 to 5077 dives (not significant). CONCLUSION: In our study population, the lifetime incidence of DCI was increased in divers with less diving experience. If further studies confirm this finding, diving federations should be encouraged to intensify their efforts of educating divers and should limit diving time and depth in inexperienced divers. Language: en

Abstract: Introduction Technical diving is very popular in Finland throughout the year despite diving conditions being challenging, especially due to arctic water and poor visibility. Cold water, immersion, submersion, hyperoxia, as well as psychological and physiological stress, all have an effect on the autonomic nervous system (ANS). Materials and methods To evaluate divers' ANS responses, short-term (5 min) heart rate variability (HRV) during dives in 2-4°C water was measured. HRV resting values were evaluated from separate measurements before and after the dives. Twenty-six experienced closed circuit rebreather (CCR) divers performed an identical 45-meter decompression dive with a non-physical task requiring concentration at the bottom depth. Results Activity of the ANS branches was evaluated with the parasympathetic (PNS) and sympathetic (SNS) indexes of the Kubios HRV Standard program. Compared to resting values, PNS activity decreased significantly on immersion with face out of water. From immersion, it increased significantly with facial immersion, just before decompression and just before surfacing. Compared to resting values, SNS activity increased significantly on immersion with face out of water. Face in water and submersion measures did not differ from the immersion measure. After these measurements, SNS activity decreased significantly over time. Conclusion Our study indicates that the trigeminocardiac part of the diving reflex causes the strong initial PNS activation at the beginning of the dive but the reaction seems to decrease quickly. After this initial activation, cold seemed to be the most prominent promoter of PNS activity - not pressure. Also, our study showed a concurrent increase in both SNS and PNS branches, which has been associated with an elevated risk for arrhythmia. Therefore, we recommend a short adaptation phase at the beginning of cold-water diving before physical activity.

Abstract: This article deals with conceptual development in an emerging activity, Technical diving. Tech divers are equipped with innovative, complex machines (the “rebreathers”) to perform deep dives. The developmental methodology of cross self-confrontation was used to investigate the psychological dimensions of safety in diving with a group of volunteers (divers and instructors). One sequence of these data helps us analyze carefully the development of one concept in use in this milieu, the “confidence in the machine.” Building on 30 years of French-speaking research in work analysis on conceptualization in the work activity, we highlight the conflicting nature of the professional concepts as well as their multifunctionality. In the sequence analyzed in this article, the conceptual development takes the form of the discursive discovery of this complexity, which may open new possibilities for action (here, through the transmission of renewed concepts to other practitioners). The argumentative logics of the dialogi...