![]() ![]() Therefore, although all freedivers are exposed to risk of hypoxic syncope ( Craig, 1961 Lin et al., 1974), which is called “blackout” (BO) by the divers, its consequences may be more severe in deep diving. The most obvious limitation to deep freediving is the freediver’s maximal breath-holding capacity, as the diver cannot immediately return to the surface once depth has been reached. A typical deep freedive is characterized by four different phases, with different physiological demands, as buoyancy may help or counteract the swimming efforts ( Schagatay, 2011). In competition freediving “Apnea” there are four disciplines with the aim to reach the greatest possible depth on one breath, and to return back to the surface with one’s own muscular effort, and to date competitive freedivers have reached 130 m using a monofin and 102 m swimming without fins ( International Association for the Development of Apnea, 2021). These changes have several physiological effects, both by direct compression of air filled cavities (Boyles law) and on gas exchange, as partial pressure of oxygen changes proportionally with ambient pressure (Dalton’s law). While most freediving is done in the depth range down to 20 m, deep freediving is an increasingly popular extreme sport where elite divers reach far beyond that depth, exposing themselves not only to progressive hypoxia but also to dramatic changes in pressure. Pulse oximetry monitoring of essential variables underwater may be an important step to increase freediving safety.įreediving is increasing in popularity both as a recreational and competitive sport ( Divers Alert Network, 2017), where all activities are performed on one breath of air. Recordings also indicated that the diving response is not powerful enough to fully override the exercise-induced tachycardia during active swimming. Divers’ enhanced desaturation during deep dives was likely related to increased exertion and extended duration, but the rapid extreme desaturation to below 50% near surfacing could result from the diminishing pressure, in line with the hypothesis that risk of hypoxic BO may increase during ascent. The underwater pulse oximeter allowed successful SpO 2 and HR monitoring in freedives to 82 m depth – deeper than ever recorded before. During deep dives, HR was influenced by the level of exertion across different diving phases after an initial drop, a second HR decline occurred during the passive “free fall” phase. HR increased before dives, followed by a decline, and upon resurfacing a peak after which HR normalized. ![]() HR showed a “diving response,” with similar lowest HR of 42 bpm in shallow and deep dives the lowest value (28 bpm) was observed in one shallow dive. All divers desaturated more during deeper dives (nadir 55 ± 10%) compared to shallow dives (nadir 80 ± 22%) with a lowest SpO 2 of 44% in one deep dive. Duration was 82 ± 36 s in shallow and 150 ± 27 s in deep dives. Mean ± SD depth of shallow dives was 19 ± 3 m, and 73 ± 12 m for deep dives. Plethysmograms were recorded at 30 Hz, and SpO 2 and HR were extracted. ![]() Divers performed one “shallow” and one “deep” constant weight dive with fins. Two probes were placed on the temples, connected to a recording unit on the back of the freediver. Four male elite competitive freedivers volunteered to wear a newly developed underwater pulse oximeter for continuous monitoring of SpO 2 and HR during self-initiated training in the sea. Our aim was to investigate arterial oxygen saturation (SpO 2) and heart rate (HR) in shallow and deep freedives, central variables, which have rarely been studied underwater in deep freediving. ![]() The effect of depth on gas exchange may enhance risk of hypoxic blackout (BO) during the last part of the ascent. 2Swedish Winter Sports Research Centre, Mid Sweden University, Östersund, Swedenĭeep freediving exposes humans to hypoxia and dramatic changes in pressure.1Environmental Physiology Group, Department of Health Sciences, Mid Sweden University, Östersund, Sweden.Eric Mulder 1 *, Arne Sieber 1 and Erika Schagatay 1,2 ![]()
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