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Legal Concepts, Drowning, and Lifeguard Effectiveness
Published in John R. Fletemeyer, Ivonne Schmid, Principles and Practices of Aquatic Law, 2018
Drowning in cold water often dramatically changes survival outcomes, especially among children. In cold water, survival times are usually significantly increased when the mammalian diving reflex occurs. This reflex protects the body by putting it into an energy saving mode to maximize the time it can stay underwater. This reflex involves blood being shunted away from the extremities and being focused to the vital organs, thus delaying and prolonging life.
Breath-hold diving strategies to avoid loss of consciousness: speed is the key factor
Published in Sports Biomechanics, 2020
Clément Poiret, Marion Noulhiane, Eric Clua, Frédéric Lemaître
This study has limitations. As mentioned above, since we do not have data on ballasting, total lung capacity or the wet suit thickness, we cannot precisely determine the influence of these parameters on the speed differences observed in CNF and CWT and their respective roles in the LOC. Nor can we exclude that certain physiological parameters may have played a role in the occurrence of LOC. Several physiological hypotheses are conventionally put forward to explain the LOC during deep dives. The brain requires a constant supply in oxygen, but this supply is impaired by the underwater effort and while this is an inherent factor for the LOC, brain damages may also occur from repeated LOC (Billaut et al., 2018). Under normal circumstances, a diving response to BH protect vital organs (brain and heart) from extreme hypoxia. This diving reflex involves vagally mediated bradycardia, sympathetically mediated peripheral vasoconstriction with an increase in blood pressure, changes in cardiac output and spleen contraction (Dujic & Breskovic, 2012; Ferretti, 2001). The integration of both sympathetic and parasympathetic pathways underlies the ontogenetic origin of the dive responses (Lemaitre et al., 2015). In trained BHDs, dynamic cerebral autoregulation is acutely impaired during maximal BH (Cross et al., 2014), cerebral oxidative metabolism is decreased and a disruption of the blood-brain barrier has also been suggested (Bain et al., 2016, 2018). Thus, all these changes in brain circulation could contribute to increasing the risk of LOC. Pulmonary oedema during deep apnoea is very common (Schipke et al., 2019). It is also common to observe that in the case of LOC, oedema is also present. If pulmonary oedema occurs during deep apnoea, it can complicate gas exchanges and limit the supply of oxygen to the brain. Even if a rapid rate of descent may be a predisposing factor due to potential damages to capillary endothelium (Fitz-Clarke, 2006), the answer seems more complicated as there is a clear relationship between active descent speeds and the discipline (Table 3). This purely descriptive study does not yet allow us to know whether the BHDs who had LOC during these competitions had pulmonary oedema.