Breath-hold diving as a brain survival response

Abstract

Apnea disciplines and current records BREATH HOLD DIVING AS A BRAIN SURVIVAL RESPONSE AbstractElite breath-hold divers are unique athletes challenged with compression induced by hydrostatic pressure and 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 physiological 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 O 2 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 contractions 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.

Presumed Arterial Gas Embolism After Breath-Hold Diving in Shallow Water

“…6 Recent findings of cerebral watershed lesions in extreme breath-hold divers and areas of focal or diffuse cerebral hypoperfusion suggest that mechanisms other than embolism may play an important role. 19 Thus, even though the exact pathomechanism leading to the barotrauma in such a clinical situation is very difficult to be finally proved, AGE after a pulmonary barotrauma is the most plausible explanation for the reported symptoms in these patients.…”

“…Among others, this includes hypercapnia, reduction of cardiac output, peripheral vasoconstriction, increase of blood pressure, increase of cerebral blood flow, and involuntary diaphragmatic contractions. 19 In addition, it has been demonstrated recently that cerebral autoregulation is acutely impaired during maximal voluntary apnea. 20 All these changes will likely depend on additional factors, such as age, hydration, fitness, current illnesses, depth, and water temperature.…”

Sports-related lung injury during breath-hold diving

“…Additionally, GPI leads to increased intrathoracic pressure which impedes venous return [28] and consequently decreases cardiac output [4,27,29]. These profound haemodynamic changes may result in a prompt drop in systemic arterial blood pressure and syncope, which can easily lead to a fatal outcome if occurring underwater [15,28,30]. In contrast, glossopharyngeal exsufflation is used to further decrease RV and reduce lung recoil by constantly deforming the chest to ever-smaller volumes [25].…”

“…For other aspects of breath-hold diving physiology and pathophysiology, see other reports [11,[14][15][16]. A literature search using PubMed was conducted, using the keywords "breath-hold diving" or "apnoea diving" and "lung injury" or "pulmonary oedema" or "haemoptysis".…”

Apnea Training Specificity and its Implications for Performance in Aquatic Sports: Case Study Reports

“…Further, evidence suggests that apnea training improves respiratory muscle performance by delaying fatigue during continuous exercise at maximum effort [31]. Apparently, apnea training causes physiological adaptations allowing individuals not only to exert an improved breath control but also, to cope with conditions of hypoxia in an effective and efficient manner although contradictory evidence exists [32][33][34].…”