Breath Hold Diving As a Brain Survival Response
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Review Article • DOI: 10.2478/s13380-013-0130-5 • Translational Neuroscience • 4(3) • 2013 • 302-313 Translational Neuroscience Zeljko Dujic*, BREATHHOLD DIVING Toni Breskovic, Darija Bakovic AS A BRAIN SURVIVAL RESPONSE Department of Integrative Physiology, Abstract University of Split School of Medicine, Elite breath-hold divers are unique athletes challenged with compression induced by hydrostatic pressure and Split, Croatia extreme hypoxia/hypercapnia during maximal field dives. The current world records for men are 214 meters for depth (Herbert Nitsch, No-Limits Apnea discipline), 11:35 minutes for duration (Stephane Mifsud, Static Apnea discipline), and 281 meters for distance (Goran Čolak, Dynamic Apnea with Fins discipline). The major physi- ological adaptations that allow breath-hold divers to achieve such depths and duration are called the “diving response” that is comprised of peripheral vasoconstriction and increased blood pressure, bradycardia, decreased cardiac output, increased cerebral and myocardial blood flow, splenic contraction, and preserved 2O delivery to the brain and heart. This complex of physiological adaptations is not unique to humans, but can be found in all diving mammals. Despite these profound physiological adaptations, divers may frequently show hypoxic loss of consciousness. The breath-hold starts with an easy-going phase in which respiratory muscles are inactive, whereas during the second so-called “struggle” phase, involuntary breathing movements start. These contrac- tions increase cerebral blood flow by facilitating left stroke volume, cardiac output, and arterial pressure. The analysis of the compensatory mechanisms involved in maximal breath-holds can improve brain survival during conditions involving profound brain hypoperfusion and deoxygenation. Keywords • Apnea • Breath-hold diving • Brain perfusion • Brain oxygenation Received 13 July 2013 accepted 25 July 2013 © Versita Sp. z o.o. Past and the modern history of became known as the “father of free-diving”. spite of the variety of physiological adaptations free-diving (breath-hold diving) After World War II, breath-hold diving became during breath-hold diving, a large number an international sport where athletes test the of neurological events appear regularly with Men and women have been breath-hold diving limits of human diving in depth, time, and apnea training and competitions. The most for thousands of years to harvest a variety distance. The depth records set by elite divers frequent are loss of consciousness, restrictions of items (such as sponges, pearls, fish), to have increased several-fold during the second of cognitive efficiency, and loss of motor conduct rescue and military operations, and for half of the 20th century. control [1]. The loss of motor control is also exploration. The oldest group of breath-hold Exposure to excessive depths can be very called “samba” by the divers, because, despite divers (BHD) is the women Ama divers from dangerous and cause serious acute health full consciousness, tremor develops on both Japan and diving women of Korea (Cachido problems such a collapse of the lungs, sides of the body and the head undergoes Ama) who dive primarily to obtain food. They barotrauma during descent and ascent, tremor-like movements (“head bobbing”). More have continued their diving routines for the pulmonary edema and alveolar hemorrhage, detailed information regarding the effects of past 2000 years fairly unchanged, except for cardiac arrest, blackouts, nitrogen narcosis, breath-holding on cardiovascular, respiratory, the recent decades, when they started to use decompression sickness and even death. and cerebrovascular health can be found wetsuits for protection against cold. During Moreover, long-term health risks of frequent elsewhere [2]. their daily diving practice, Ama divers usually maximal apneas are not currently known, dive to a depth of up to 25 meters of seawater but should be addressed in future research. Apnea disciplines and current (msw), and the duration of dives is relatively Additionally, shallow but frequent apnea records short (up to 1 min). In 1911, one of the first dives are made not only by BHD, but also by free-diving competitions was held when a underwater hockey and rugby players and Breath-hold divers compete in different Greek fisherman, Yorgos Haggi Statti, was synchronized and spring swimmers. Such disciplines such as Static Apnea, Dynamic oered a few dollars to dive and to rescue the healthy athletes in fact practice voluntary Apnea, Constant Weight, and No-Limits Apnea. anchor of an Italian ship sunk at depth of 77 apnea on a regular basis. Thus, apnea divers are During static apnea, divers float motionless msw. The Italian ship was set free and Yorgos only an extreme example of voluntary apnea. In face down in a pool, while during dynamic * E-mail: [email protected] 302 Translational Neuroscience apnea, the goal is to attain maximal underwater to residual volume (RV) [7]. Due to hydrostatic maximal inspiratory apnea; however, there swimming distances. During constant weight, pressure-induced compression, injuries was no evidence of severe biventricular divers swim down as deeply as possible along or pathologies after deep dives include dysfunction as reported by Potkin et al. [10]. a vertically suspended rope using fins while in pulmonary edema, alveolar hemorrhage, and The extent of heart compression during TLC the no limit discipline the dive is performed hemoptysis. To prevent lung collapse and or functional residual capacity (FRC) apnea is by descending using a weight and ascending compression during descent, divers try to shown in Figure 1. During a maximal breath- with help of flotation device (balloon). While achieve lung volumes above TLC at the start hold in dry conditions, mean arterial pressure performing static and dynamic apnea, divers of breath-hold. Having large lung volumes (MAP) is substantially reduced at the start of are exposed to progressively increasing enables better equilibration of the inner ear the attempt, followed by renormalization and hypercapnic hypoxia. During constant weight by extra volume and increases oxygen stores, finally with significant hypertension [12,13]. diving, divers are exposed during descent which all improve apnea performance. One Thus during few minutes the cardiovascular and at the bottom to progressive hyperoxic technique used to achieve lung volume above system of the elite diver is stressed to the hypercapnia due to hydrostatic pressure- TLC is called glossopharhyngeal insufflation maximum, starting from extreme hypotension induced compression of the chest wall [3], (GI), by which, after maximal inspiration to and ending with marked hypertension. while the hypoxic hypercapnia is experienced TLC, the diver fills his or her mouth with air These previously described hemodynamic only at the end of the dive just below the and, after opening of the glottis, forces this consequences of the GI maneuver are surface (due to chest wall expansion). Current air into the lung. This respiratory technique attenuated in the immersed conditions due world records for men and women in dierent results in a significant increase of lung volume to redistribution of approximately 1 l of apnea disciplines are presented in Table 1. above TLC, up to almost 50% [8]. However, this blood from the periphery to the intrathoracic This review describes physiological maneuver performed in laboratory conditions vascular compartment, due to the increased adaptations (primarily cardiovascular and increases intrathoracic pressure, decreases surrounding hydrostatic pressure. cerebrovascular) to breath-holding, taking venous return, compromises cardiac pumping Divers are adapted to extreme hypoxia/ special consideration that the majority of the by changing the geometry of both ventricles, hypercapnia due to ventilatory, cardiovascular, experimental data in this field was collected and decreases arterial blood pressure, which and cerebrovascular adjustments, such as in dry laboratory conditions and some of them may lead to symptomatic hypotension or decreased ventilatory sensitivity to CO2, may not apply to real situations during field syncope called ‘packing blackout’ [9,10]. increased lung volume, enhanced peripheral diving (immersion, cold, hydrostatic pressure, Thus, apnea divers provide an excellent sympathetic and parasympathetic activation, psychological stress, etc). Further studies model for cardiac and hemodynamic studies and increased lactate production, among should be directed to monitoring physiological on lung hyperinflation. Lindholm and others [13-15]. Furthermore, they show data during underwater immersion at rest or Nyren [7] investigated the morphological reduced post-apnea as well as post-exercise during swimming, made possible by using cardiovascular consequences of GI with blood acidosis and oxidative stress, mimicking recently produced portable physiological magnetic resonance imaging (MRI) and the responses of diving animals [16]. monitors [4-6]. found extreme reduction in thoracic blood volume with a small heart and compressed Physiological diving response Challenging the traditional thoracic vessels. In addition, Potkin et al. [10] concepts employed transthoracic echocardiography The success of breath-hold diving depends on during GI and reported acute biventricular how well a diver tolerates the physiological Breath-hold diving to depths up to 200 msw systolic dysfunction (right consistent with and psychological stress related