Extreme human breath-hold diving

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.

Cardiovascular Regulation During Apnea in Elite Divers

“…In these unique individuals, arterial oxygen saturation may decrease to Ͻ50%, whereas alveolar carbon dioxide partial pressure increases substantially. 5 Typically, diving fish-catching competitions last for 5 hours with cumulative apnea duration of Ϸ1 hour.…”

The human diving response, its function, and its control

“…Some investigators suggest evidence of an oxygen (O 2 )-conserving effect of the diving response (Wolf et al, 1965;Andersson & Schagatay, 1998a;Lindholm et al, 1999;Ferretti, 2001;Andersson et al, 2002), whereas others do not (Craig & Medd, 1968;Hong et al, 1971). This section will provide support for an O 2 -conserving role of the diving response and is a preface to the subsequent section, which describes the diving response cardiorespiratory control mechanisms.…”

Relationships between the extent of apnea-induced bradycardia and the vascular response in the arm and leg during dynamic two-legged knee extension exercise

“…We conclude that individuals who show greater apnea-induced bradycardia during exercise also show greater vasoconstriction in both active and inactive muscle regions. mean arterial pressure; femoral blood flow; breath hold LARGE CARDIOVASCULAR RESPONSES occur during breath-hold diving in both animals and humans (10,12,14,19,28,36). The response is characterized by bradycardia and vasoconstriction related to the so-called "diving reflex" (1,8,10,20,24,36), and it has been proposed that the function of these changes is primarily to preserve an adequate O 2 supply to vital organs (1,4,15,18,19,24).…”