Mulder Eric, Schagatay Erika, Sieber Arne
Environmental Physiology Group, Department of Health Sciences, Mid Sweden University, Östersund, Sweden.
Swedish Winter Sports Research Centre, Mid Sweden University, Östersund, Sweden.
Front Physiol. 2021 Apr 1;12:651128. doi: 10.3389/fphys.2021.651128. eCollection 2021.
Deep freediving exposes humans to hypoxia and dramatic changes in pressure. The effect of depth on gas exchange may enhance risk of hypoxic blackout (BO) during the last part of the ascent. Our aim was to investigate arterial oxygen saturation (SpO) and heart rate (HR) in shallow and deep freedives, central variables, which have rarely been studied underwater in deep freediving. Four male elite competitive freedivers volunteered to wear a newly developed underwater pulse oximeter for continuous monitoring of SpO and HR during self-initiated training in the sea. Two probes were placed on the temples, connected to a recording unit on the back of the freediver. Divers performed one "shallow" and one "deep" constant weight dive with fins. Plethysmograms were recorded at 30 Hz, and SpO and HR were extracted. Mean ± SD depth of shallow dives was 19 ± 3 m, and 73 ± 12 m for deep dives. Duration was 82 ± 36 s in shallow and 150 ± 27 s in deep dives. All divers desaturated more during deeper dives (nadir 55 ± 10%) compared to shallow dives (nadir 80 ± 22%) with a lowest SpO of 44% in one deep dive. 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. HR increased before dives, followed by a decline, and upon resurfacing a peak after which HR normalized. 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. The underwater pulse oximeter allowed successful SpO and HR monitoring in freedives to 82 m depth - deeper than ever recorded before. 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. Recordings also indicated that the diving response is not powerful enough to fully override the exercise-induced tachycardia during active swimming. Pulse oximetry monitoring of essential variables underwater may be an important step to increase freediving safety.
深度自由潜水会使人体暴露于低氧环境和压力的剧烈变化之中。深度对气体交换的影响可能会增加上升阶段最后部分出现低氧性昏厥（BO）的风险。我们的目的是研究浅度和深度自由潜水中的动脉血氧饱和度（SpO）和心率（HR），这两个核心变量在深度自由潜水的水下研究中很少涉及。四名男性精英竞技自由潜水员自愿佩戴一种新开发的水下脉搏血氧仪，以便在自主进行的海上训练期间持续监测SpO和HR。两个探头放置在太阳穴上，与自由潜水员背部的记录单元相连。潜水员穿着脚蹼进行一次“浅度”和一次“深度”恒重潜水。以30赫兹的频率记录容积描记图，并提取SpO和HR数据。浅度潜水的平均±标准差深度为19±3米，深度潜水为73±12米。浅度潜水的时长为82±36秒，深度潜水为150±27秒。与浅度潜水（最低点为80±22%）相比，所有潜水员在深度潜水中的血氧饱和度下降得更多（最低点为55±10%），一次深度潜水中的最低SpO为44%。HR呈现出“潜水反应”，浅度和深度潜水的最低心率相似，均为42次/分钟；在一次浅度潜水中观察到最低值（28次/分钟）。潜水前HR升高，随后下降，浮出水面时出现峰值，之后HR恢复正常。在深度潜水中，HR受到不同潜水阶段运动强度的影响；在最初下降之后，在被动的“自由落体”阶段HR出现第二次下降。水下脉搏血氧仪成功监测到了深度达82米的自由潜水中的SpO和HR，这一深度比以往记录的更深。潜水员在深度潜水中血氧饱和度增加可能与运动强度增加和时长延长有关，但在接近水面时迅速降至50%以下的极端血氧饱和度下降可能是由于压力减小，这与低氧性BO风险在上升过程中可能增加的假设一致。记录还表明，潜水反应不足以完全克服主动游泳期间运动引起的心动过速。水下对关键变量进行脉搏血氧仪监测可能是提高自由潜水安全性的重要一步。
