Diving Physiology The of FREEDIVING Text by Bret Gilliam Photography by Andrey Nekrasov LEt’S CLEAR am Espinosa parked his given much serious consideration of using modern dive computers battered pickup truck to that possibility. As the local with their more conservative full of yellowfin grouper, spearfishermen were to prove with decompression models, we’d THE AIR snapper and a smattering uncanny regularity over the next almost certainly have incurred of big pelagic fish in front few years, we were naive in our penalties, requiring stops or of my office and, with preliminary skepticism. ‘ceilings’ as the day progressed. obvious difficulty, climbed the front Both of these men recovered So can you get bent breath hold Swalk. He presented himself with completely and they kindled my diving? Most divers would answer YOU CAN GET progressive symptoms including interest in freediving-induced ‘no’. But there is no requirement limb pain, patchy areas of numbness DCS, for professional and personal that you breathe compressed air and tingling, along with exceptional reasons. Most Virgin Islands’ health from a scuba tank to manifest DCS. BENT WHILE fatigue and severe headache. He professionals had dismissed any The malady is dependent on time told me that he and his brother physiological threat of DCS to and depth primarily, and therefore had been spearfishing from early breath hold divers as impossible and expert breath hold divers can, in BREATH HOLD morning until just before sundown in were more inclined to catalog such exceptional diving circumstances, depths up to 125 feet (38m). presentations as traditional muscle place themselves within a window of He noticed the pain symptoms strains or carbon dioxide related vulnerability. around mid-afternoon, but attributed brain phenomena. DIVING them to the rigors of his work During this same time in the early Unique Risks wrestling large fish to the surface, 1970s, I was involved with some of Competitive spearfishermen, South so he continued his dive activities. the best freedivers in the Caribbean. Pacific islander working freedivers Both men had clearly identifiable They competed in spearfishing and Japanese Ama divers are decompression sickness (DCS) contests where depths could range most at risk. Typically, these divers symptomatology and I started from 60 feet (18m) over typical reef can attain relatively deep depths, them on demand valve 100 percent bottoms to hunting along drop-off 80 to 130 feet (25-40m) for up to oxygen and aggressive fluids. walls where 150-foot (46m) dives three minutes bottom time. Their Arrangements were made to would occasionally be made. profiles reflect an average to rapid evacuate them from St. Croix to a Following my experience with descent followed by a ‘working’ recompression chamber off island. the Espinosa brothers, several of period at depth. Ascents are rapid, So, you’re likely thinking big deal, us experimented during prolonged sometimes assisted by buoyant deep repetitive dives with a heavy diving days wearing the old apparatus. Considerable exertion exertion component. Is there any Scubapro/SOS deco meter. We may be expended on the dive if surprise that these guys got bent? got some interesting results. Many the diver must struggle to land a Right on all counts, but these men of us were able to advance the large fish or to swim objects off were not SCUBA diving. They were unit’s analog needle almost into the bottom. The new generation of professional commercial fishermen the ‘red zone’, indicating required competitive free divers can go far who did all their hunting by free decompression. And our diving deeper especially when clinging diving - holding their breath. This routine was far less demanding to descent sleds. And although was 1973 and until then I’d never than the local ‘pros’ who typically their exertion levels are lower, the seen a case of freediving DCS. In dove more frequently per hour intake of inert gas due to depth and fact, like most divers and chamber and for longer bottom times at the subsequent rapid buoyant ascent staff of that era, we had never even deeper depth. If we’d had the luxury pose unique risks for DCS. 42 Magazine www.divermag.com 43 Diving Physiology techniques that precipitate what we call the mammalian diving reflex. However, this practice is a double- edged sword; as depth-increased CO2 is produced by the body’s metabolism, the original ‘O2 storage’ achieved by hyperventilation is depleted (in the absence of any other source). To a certain degree, the inherent risk is counterbalanced by a corresponding rise in the percentage of carbon dioxide (PCO2) in the system, since this gas is a metabolic waste product as oxygen is burned. The relationship is important because high carbon dioxide is a major stimulus to breathe while low oxygen is not. As the diver holds his or her breath, oxygen is consumed and carbon dioxide partial pressures are elevated. Eventually a little voice generated by the CO2 whispers in your ear, “Hey buddy, I’ll continue to hurt you unless you get back to the surface for a fresh breath.” Now comes the insidious danger. As the diver ascends, both partial pressures of the gases drop. The stimulus to breathe is reduced as the partial pressure of carbon dioxide drops… while the oxygen partial pressure could be dropping to dangerous levels simultaneously. It takes an exceptional diver At some point, the diver passes to get bent holding his or her out from this ‘latent hypoxia’ breath, but it does happen syndrome or what’s commonly known as ‘shallow water black out’. Typically the diver shows no Early on, little serious relate, “Oxygen deprivation much the anchor. Within minutes after dives below 60 feet (18m), could (ATA). This is considered the High carbon signs or distress and simply goes consideration was given the longer (than four minutes)… getting back on board, he was spell trouble for those capable of reference point for ‘normoxic’ dioxide is a limp, sometimes within 10 feet (3m) major stimulus to likelihood of a freediver suffering a can be damaging or fatal. In symptomatic of DCS. His previous performing at this level. Forewarned conditions. of the surface. Those successfully breathe whereas bends hit, but Bob Croft’s dramatic the Tuamotos, those who make diving schedule was within the limits is forearmed! It is important to be aware of low oxygen is not rescued and revived say there’s no dive to 240 feet (73m) in 1968 successive, lengthy dives to great of the Navy tables but with little While you can’t get in trouble certain ranges of tolerance in warning of the impending blackout prompted some discussion. Dives depths, risk a condition they call safety margin. He was treated in the with lung over-expansion injuries normal, healthy persons. Most or any major stimulus to breathe. But exceeding four minutes had already taravana, a sickness that includes St. Croix recompression chamber from breath hold diving (unless people can maintain proper blood several fatalities occurred before been recorded and anecdotal vertigo, nausea, partial or complete operated by the National Oceanic you were to take a breath from oxygenation down to .16 ATA (16 these problems were identified and accounts of longer breath hold paralysis, and unconsciousness.” and Atmospheric Administration’s a compressed air source while percent oxygen in the mix at surface the hazards of deep breath-hold dives were in circulation. A 1962 Don’t these symptoms have (NOAA’s) Hydrolab facility with already underwater from a diver’s pressure) but dropping much diving were well communicated. National Geographic article something of familiar ring to them? full recovery. regulator, Spare Air, etc.), there is below this will limit performance/ The recreational snorkeler recounts the diving style of a South A quick glance through any DCS another serious hazard to consider endurance and unconsciousness splashing about enjoying the sights Pacific diver: “A man from the symptom list should provide some that deals with the consequences will likely result approaching .1 ATA on a shallow reef can still sleep Tuamotos who at 59 years old went easy match-ups. There’s no requirement that you of excessive hyperventilation and (10 percent oxygen at the surface). soundly. But as the popularity of to 100 feet (30m) as many as 50 Admittedly, it takes an exceptional the relationships of oxygen and You may recall the old reference freediving and more advanced times a day summed up his attitude diver to get bent holding his or breathe compressed air from a carbon dioxide. to the ‘Ten and Ten Rule’ that applications such as spearfishing toward this skill. ‘It is nothing… I her breath, but it does happen. Most divers are familiar with the proposes blackout will occur if the or competition attracts more divers have big lungs and a strong body. Readers are cautioned about SCUBA tank to manifest DCS basic characteristics of oxygen as percentage of either oxygen or to this purest form of underwater It is my work’. Two minutes, three, deep breath hold diving following it occurs in our atmosphere. It is a carbon dioxide (CO2) reaches 10 exploration, an awareness of these four…a long time if you are holding aggressive SCUBA diving activities. colourless, odorless and tasteless percent in the gas mixture. This was potential hazards is necessary. your breath, but what if you are Dive instructor Scott Valerga of Serious Hazard gas found free in dry air at 23.15 particularly important to competitive Just when you thought it was safe trying to follow a fish?” Virgin Gorda had made repetitive Although it’s unlikely that average percent by weight and 20.98 free divers and spearfishers holding to go back in the water….