Breath-Hold Diving: Expanding Our Aquatic Range
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Breath-Hold Diving: Expanding Our Aquatic Range Freedivers, relying only on the air they can hold in their lungs, operate in a wide range of environments and pursue an assort- ment of goals. In recent years, freediving has evolved into an increasingly popular extreme competitive sport. Numerous disciplines are now recognized by the International Association for the Devel- opment of Apnea (AIDA; http://www. aida-international.org/). These are listed below with their respective record performances. The current no limits depth record of 702 feet (214 meters) for a freediver is mind-boggling. The ambient pressure at that depth is 22.3 atmospheres absolute. Breath-hold basics Physiological alterations begin with water immersion. The blood volume in the chest is increased while vital capacity (the total volume of gas in the lung that can be expired or inspired in a single breath) is decreased. Facial immersion, particularly in cool water, initiates the classic diving reflex observed during breath-hold — heart rate and cardiac output are decreased, periph- eral vasoconstriction and blood pressure are increased, and the spleen contracts to release more oxygen-carrying red blood cells into the bloodstream. COURTNEY PLATT PHOTO PLATT COURTNEY Mandy-Rae Cruickshank sets 88m constant ballast world record in 2007. In normal respiration, a period of apnea Breath-hold or apnea diving, also known as freediving, has a (an absence of breathing) follows every long history. It has been used in hunting, gathering, competition inspiration. It is the duration of the apnea and even warfare. Regardless of the reason for breath-hold that sets apart the unconscious breath-hold from the longer, voluntary breath-hold diving, doing it safely requires an appreciation of the risks and that occurs during freediving. The rising strategies for protection. This article is based on a brief review concentration of carbon dioxide in the of the topic.5 Additional technical details and references are blood is primarily responsible for the available in the published paper. drive to end breath-hold. The breaking point can be postponed by altering the By Neal Pollock, Ph.D. physiological conditions in the blood or 52 SEPTEMBER / OCTOBER 2008 Alert Diver www.DiversAlertNetwork.org FEATURE by increasing the individual tolerance to such conditions. Extreme breath-hold efforts are not without risk. Injury and death do occur, the latter most commonly with unsupervised divers. Techniques for improving breath-hold performance are best practiced in a con- trolled setting with responsible oversight. This can be done through professional training programs, which are increasing in numbers. Manipulative practices MARNIE LAING PHOTO Mandy-Rae Cruickshank’s sets 2002 static apnea world record, Kirk Krack safety. Reduce metabolic demand AIDA-recognized competitive freediving disciplines and records One of the simplest ways to extend breath- (as of June 13, 2008)5 hold time is to reduce physical effort and Discipline Description Record Performance thus the metabolic demand. Comparing Male Female the record performance between no-fin Static Apnea (min:s) resting, immersed 10:12 8:00 and fin subdisciplines of dynamic apnea breath-hold in and constant weight illustrates the energetic controlled water advantage of using fins. The static apnea (usually a shallow swimming pool) and no-limits disciplines demonstrate the Dynamic Apnea — horizontal swim1 in 801 (244)1 673 (205)1 extremes of what can be accomplished on a with fins (ft [m]) controlled water single breath of air if the diver uses minimal Dynamic Apnea — horizontal swim1 in 610 (186)1 489 (149)1 physical effort. Persons swimming while no fins (ft [m]) controlled water breath-holding are well served by using the No Limits (ft [m]) vertical descent to 702 (214) 525 (160) most efficient technique possible. a maximum depth on a weighted sled; ascent with a lift bag Distraction deployed by the diver A variety of manipulative practices can be Variable Weight vertical descent to 459 (140) 400 (122) employed to prolong breath-hold time. A (ft [m]) a maximum depth simple strategy involves the use of distrac- on weighted sled; tion. For example, a relatively inexperienced ascent by pulling up a line with kicking apnea diver nearing the voluntary break- Constant Weight — vertical self-propelled 367 (108) 295 (90) point may experience a brief but significant with fins (ft [m]) swimming to a reprieve if he or she tries to swallow a couple maximum depth of times before ending the breath-hold and back to surface; no line assistance dive. It will be difficult to swallow and the allowed distraction involved can temporarily reduce Constant Weight — vertical self-propelled 282 (86) 197 (60) the sense of urgency to breathe. no fins (ft [m]) swimming to a maximum depth and back to surface; Hyperventilation no line assistance The most well-known manipulative prac- allowed tice used to increase breath-hold time is Free Immersion vertical excursion 354 (108) 269 (82) hyperventilation. The basis for its effec- (ft [m]) propelled by pulling tiveness is the difference between the on the rope during descent and ascent; high concentration of carbon dioxide in no fins. the body and the low concentration in 1 horizontal swim Alert Diver DAN: a 501 (c)(3) nonprofit association SEPTEMBER / OCTOBER 2008 53 Glossopharyngeal breathing Glossopharyngeal insufflation (also known as ‘lung packing’ or ‘buccal pumping’) increases available gas above normal vital capacity. This involves gulping air in a series of small volumes after the point of normal full inspiration has been reached. This technique does allow additional gas to be stored, but aggressive efforts may also disrupt circulation and cause dizziness, tunnel vision, loss of consciousness and possibly pulmonary barotrauma. Glossopharyngeal exsufflation (also known as ‘reverse packing’) involves using the muscles of the mouth and throat to draw air out of the lungs when the lung volume is near or below residual volume. This technique can be used to enable middle ear equalization at depths deeper than would otherwise be possible. Dietary factors Increased competition means that small advantages can make a critical difference in a freediver’s final ranking. Studies of dietary intake and breath-hold perfor- mance have produced variable results. It CRAIG GENTRY PHOTO CRAIG GENTRY Mandy-Rae Cruickshank competing at the 2006 World Freediving Championships. is likely that further efforts will be directed normal air. Increasing ventilation beyond The risk of losing consciousness due to at developing optimal dietary patterns for that required to meet metabolic needs (in a hyperventilation is greatest during the competitors. word, hyperventilation) can rapidly reduce ascent phase of a breath-hold dive. In carbon dioxide levels in the blood. A breath- addition to the continued consumption of Breath-hold safety hold dive begun after hyperventilation can oxygen, the decreasing ambient pressure Training and supervision be prolonged since the drive to breathe will produces a rapid drop in the concentration Safety in breath-hold requires a respect not develop until the normal trigger point of oxygen in the blood — with the greatest for reasonable guidelines. The impressive of carbon dioxide is reached. drop in the shallowest water where the rela- safety record maintained in competitive tive pressure change is maximized. Loss of The primary risk of pre-breath-hold events can be replicated at other levels of consciousness will commonly occur just hyperventilation is hypoxia and loss of involvement only if suitable protections before the diver surfaces or shortly after consciousness. While hyperventilation are in place. As a primary rule, divers surfacing but before the oxygen in the first can greatly reduce carbon dioxide stores, it should not conduct breath-hold dives inspired breath can reach the brain. This does little to increase oxygen stores. Loss of alone. The finding that more than half condition is best referred to as hypoxia of consciousness due to hypoxia can develop of the recently reported fatal breath-hold ascent. The term ‘shallow-water blackout’ before the diver feels any urge to breathe. incidents were unwitnessed indicates a is ambiguous since it was first used to For the diver, the risk is increased with fundamental problem in practice.6 While describe the loss of consciousness associ- the magnitude of the hyperventilation. often impossible to confirm, it is likely that ated with the use of closed-circuit oxygen While the hazards of hyperventilation manipulative breath-hold practices were rebreathers. were well described almost 50 years ago, involved and that in many cases the ready imprudent use remains a factor in many presence of others could have provided fatal incidents.2,3,4,6 timely intervention. 54 SEPTEMBER / OCTOBER 2008 Alert Diver www.DiversAlertNetwork.org Effective direct supervision includes the also safe for most leisure circumstances. Conclusions pre-breath-hold, breath-hold and 30 sec- An alternative approach is to arbitrarily Breath-hold diving is experiencing a growth onds post-breath-hold periods. A simple restrict breath-hold time. in popularity that reflects an impressive two-person, one-up-one-down buddy A proposal in 2006 called for breath-hold evolution of record-setting performance. team with committed direct supervision by recreational freedivers to be voluntarily Safe participation in competitive events can provide effective protection for shallow limited to 60 seconds.1 This would allow for is fostered by a wide range of carefully diving situations. As dive depths increase, varying patterns of hyperventilation and developed regulations and protocols. a group of three (one-down, two-up) may physical activity with minimal risk of loss Appropriate safety protocols are required be preferable. Allowing a recovery period for all breath-hold divers. The elimination of twice the dive duration is a reasonable Learning from the mistakes of others of solo freediving and the incau- practice. That practice also ensures that tious use of hyperventilation would one of the divers available at the surface have the greatest positive impact on for backup is at least partially rested.