For freedivers, the ocean can be unforgiving

Story highlights

  • Natalia Molchanova, the world's best freediver, is feared dead after going missing during a recreational dive
  • Neal Pollock: Her case is a stark reminder of why freediving is an extreme sport that comes with serious risks

Dr. Neal Pollock is research director at Divers Alert Network (DAN) and a research associate at the Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center. He is also an associate editor at Wilderness and Environmental Medicine. The opinions expressed in this commentary are solely those of the author.

(CNN)Natalia Molchanova, perhaps the most highly decorated freediver, has been missing since Sunday. Her family and friends fear that she might be dead in the Mediterranean.

That something terrible may have happened to her during a recreational dive that wasn't intended to challenge her limits is a stark reminder of why freediving is an extreme sport. The ocean can be a very unforgiving place. Along with the thrills of freediving are serious risks of injury and sometimes even death.
Natalia Molchanova has gone missing
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Freediving is an evocative term, appropriate for the incredible human performance possible with virtually no equipment. While much of freediving is done for personal challenge, formal competition has become popular in recent years.
    Neal Pollock
    The Association Internationale pour le Développement de l'Apnée (AIDA) oversees competition and tracks record performance in eight immersion categories, from "static apnea" which involves resting breath-hold, to "no limits" -- which involves descending to great depths on weighted sleds and ascending by holding on to gas-filled lift bags.
    Breath-hold is an important component of freediving. Molchanova, who set 41 world records and 23 world champion titles, can hold her breath for more than 9 minutes.
    Breath-hold has long been used for underwater swimming, initially for harvesting seafood and precious materials, but increasingly for pleasure and personal challenge. The technique is a key part of synchronized swimming, underwater hockey, spearfishing, and competitive freediving.
    Freedivers use an array of methods to maximize breath-hold time: promoting mental and physical relaxation, increasing lung volume, maximizing economy and, to varying degrees, employing physiological manipulations such as hyperventilating.
    The volume of gas breathed is normally matched to metabolic need. Increasing the amount of work being done drives an increase in ventilation, which keeps levels of gas in the blood normal. Alternatively, a person could choose to increase lung ventilation beyond metabolic need. This is known as hyperventilation. This is important because of the effect on gases in the blood.
    Carbon dioxide levels in the blood are normally much higher than in air. Hyperventilation causes the blood levels to fall. Since carbon dioxide primarily drives the urge to breathe, lower blood levels means that the urge to breathe during a subsequent breath-hold is delayed, possibly long enough that the available oxygen is depleted to the point of loss of consciousness.
    Effectively, hyperventilation works by reducing the buffer between the point of normal drive to breathe and the loss of consciousness. Great caution is required.
    The art of freediving comes in optimizing performance while controlling risks. Smart freedivers train and practice in well-supported groups with good safety procedures in place, and then increase their performance in extremely small increments. The difference between success and failure can be small and the distance to the failure point stubbornly unclear. The discipline of small increments is absolutely critical to reducing the risk of a bad outcome.
    The best intentions to stay within safe personal limits can go awry in the dynamic world of water. Unexpected currents or entanglement with diving features are obvious complications, but subtle changes in the amount of ballast weight worn or hyperventilation can also alter the risk on a given dive.
    Additional weight, for example, will help the descent, but increases the work demands during ascent. This requires more oxygen for completion and reduces safe breath-hold time. Additional hyperventilation, whether it is called hyperventilation, "work up breathing" or any other euphemism, can make the freediver feel comfortable, but also makes it possible for loss of consciousness to develop before any urge to breathe arises.
    Shallow water blackout is a common problem associated with vertical freediving. The increasing ambient (surrounding) pressure during descent effectively concentrates the blood oxygen, reducing the physiological stress. The decreasing ambient pressure during ascent causes the blood oxygen concentration to fall much faster than it would from metabolic consumption alone. Ultimately, blackout is most likely to occur near the surface or immediately after surfacing if oxygen in the body is depleted too much. Close supervision during ascent and immediately after every dive is important to ensure that a diver's consciousness is maintained.
    The risk of loss of consciousness associated with freediving may seem crazy to accept, but human beings revel in challenges. For some, freediving is seen as a very pure sport that demands great focus to take a seemingly simple activity to almost unbelievable levels.
    The current world records for static apnea are 11 minutes 35 seconds and 9 minutes and 2 seconds for men and women, respectively. The current world records for no limits depth are 702 feet (214 meters) and 525 feet (160 meters) for men and women, respectively. These are truly awesome numbers, as are those in the other competitive categories.
    Those who are undaunted by the hazards of freediving should complete one of many good training programs to be fully informed of the risks and learn how to manage them. At the end of the day, it is a personal choice. But passion and enthusiasm must be tempered with the reality that there is very little room for error.