Extreme human breath-hold diving.

Department of Physiology, University Medical Centre, 1 Rue Michel Servet, 1211 Geneva 4, Switzerland.
Arbeitsphysiologie (Impact Factor: 2.66). 05/2001; 84(4):254-71. DOI: 10.1007/s004210000377
Source: PubMed

ABSTRACT In this paper, the respiratory, circulatory and metabolic adjustments to human extreme breath-hold diving are reviewed. A survey of the literature reveals that in extreme divers, adaptive mechanisms take place that allow prolongation of apnoea beyond the limits attained by non-diving subjects, and preservation of oxygen stores during the dives. The occurrence of a diving response, including peripheral vasoconstriction, increased arterial blood pressure, bradycardia and lowered cardiac output, is strongly implicated. Some peripheral regions may be excluded from perfusion, with consequent reliance on anaerobic metabolism. In addition, extreme breath-hold divers show a blunted ventilatory response to carbon dioxide breathing, possibly as a consequence of frequent exposure to high carbon dioxide partial pressures during the dives. These mechanisms allow the attainment of particularly low alveolar oxygen (< 30 mmHg) and high alveolar carbon dioxide (> 50 mmHg) partial pressures at the end of maximal dry breath-holds, and reduce oxygen consumption during the dive at the expense of increased anaerobic glycolysis (rate of blood lactate accumulation > 0.04 mM.s-1). The current absolute world record for depth in breath-hold diving is 150 m. Its further improvement depends upon how far the equilibrium between starting oxygen stores, the overall rate of energy expenditure, the fraction of energy provided by anaerobic metabolism and the diving speed can be pushed, with consciousness upon emersion. The ultimate limit to breath-hold diving records may indeed be imposed by an energetic constraint.

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    ABSTRACT: Hallmarks of the mammalian diving response are protective apnea and bradycardia. These cardiorespiratory adaptations can be mimicked by stimulation of the trigeminal ethmoidal nerve (EN5) and reflect oxygen-conserving mechanisms during breath-hold dives. Increasing drive from peripheral chemoreceptors during sustained dives was reported to enhance the diving bradycardia. The underlying neuronal mechanisms, however, are unknown. In the present study, expression and plasticity of EN5-bradycardias after paired stimulation of the EN5 and peripheral chemoreceptors was investigated in the in situ working heart-brain stem preparation. Paired stimulations enhanced significantly the bradycardic responses compared with EN5-evoked bradycardia using submaximal stimulation intensity. Alternating stimulations of the EN5 followed by paired stimulation of the EN5 and chemoreceptors (10 trials, 3-min interval) caused a progressive and significant potentiation of EN5-evoked diving bradycardia. In contrast, bradycardias during paired stimulation remained unchanged during repetitive stimulation. The progressive potentiation of EN5-bradycardias was significantly enhanced after microinjection of the 5-HT(3) receptor agonist (CPBG hydrochloride) into the nucleus tractus solitarii (NTS), while the 5-HT(3) receptor antagonist (zacopride hydrochloride) attenuated the progressive potentiation. These results suggest an integrative function of the NTS for the multimodal mediation of the diving response. The potentiation or training of a submaximal diving bradycardia requires peripheral chemoreceptor drive and involves neurotransmission via 5-HT(3) receptor within the NTS.
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    ABSTRACT: Introduction. Human stay under water with breath hold is limited by production and accumulation in organism of carbon dioxide with simultaneous increase in oxygen shortage, high hydrostatic pressure in internal przyspace, especially on chest and ears. Physical and mental predispositions as well as the age belong to basic factors determining human adaptive prospects in breath hold diving. Technical skills and experience are bound to these factors. Advances in freediving testify systematic development of human adaptive mechanisms in water. Aim of the study. Evaluation and prediction of world records in freediving in individual competition, for men and women. Material and methods. The research material consists of 220 world records obtained between 1993 and 2009 in men and women categories, regarding 8 freediving competitions. Results analyses were conducted in 5-years-long periods, computing the predictions for 2014. Results. Conducted analyses show that world records in all freediving competitions from between 1993 and 2009 were beaten multiple times. Men more often than women have beaten world records, they also obtained better results. The largest progress was noted in Dynamic Apnea (DYN) and Dynamic Apnea Without Fins (DNF) as well as in Constant Weight Apnea Without Fins (CNF). The smallest increase in world records in freediving occurred in VWT (Variable Weight Apnea) and FIM (Free Immersion Apnea) in which success is determined not only by physical effort but also by increasing with depth water pressure. Conclusions. By the year 2014 freediving world records should have been improved in all competitions, for women mostly there where the main role plays time of immersion and high hydrostatic pressure, and for men additionally physical effort.
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