freediver physiology

Physiology and the bluewater hunter

This chapter , written in two sections , covers physiologic principles important to your success and well-being as a bluewater hunter . The first half deals with the specter of freediver blackout , its causes and prevention . In the second half , I discuss selected topics aimed at enhancing your performance in the bluewater environment .
Freediver blackout is also known as shallowwater blackout . You might think that shark attacks , line tangles and boat accidents are the freediver ’ s worst fears ; in reality those risks pale in comparison to the death and destruction wrought by freediver blackout .
BLACKOUT TYPES : Blackout is the sudden loss of consciousness caused by oxygen starvation . Divers can experience two types of blackout . Shallow-water blackout occurs when divers ascending vertically in the water column undergo pressure changes that influence the
body ’ s physiology and trigger a blackout . Staticapnea refers to blackout that doesn ’ t involve a deep dive . It is generally related to breath-hold attempts in a shallow pool .
Shallow-water blackout strikes most commonly within 15 feet ( five meters ) of the surface , where expanding , oxygen-hungry lungs literally suck oxygen from the diver ’ s blood . The blackout occurs quickly , insidiously and without warning . Due to their lack of adaptation , beginning breath-hold divers are not generally subject to this condition . It is the intermediate diver who is most at risk . He is in an accelerated phase of training , and his physical and mental adaptations allow him to dive deeper and longer with each new diving day — sometimes too deep or too long . Advanced divers are not immune .
Skip Hellen ’ s story is typical of many shallowwater blackout incidents . Skip and I were diving at Ship ’ s Rock , one-half mile off of Catalina Island , California . We were competing in the