Breath-Hold Diving

  • Michael B. Strauss, MD, Lientra Q. Lu, BS
  • Volume 08 - Issue 4

Introduction and Uniqueness

Breath-hold diving is a generic term for diving activities that does not utilize self-contained (SCUBA) or surface-supplied breathing apparatuses. It is a generic term because it includes snorkel diving with or without shallow, brief depth excursions, recreational breath-hold diving in lieu of using SCUBA gear, commercial foodstuff collection diving, competitive game hunting diving, and deep diving, record-setting attempts (Figure 1). Apneic (i.e. without breathing) diving is a term associated with breath-hold diving. Skin diving is another term often associated with breath-hold diving but is not technically correct, since thermal protection may or may not be used with breath-hold diving as well as SCUBA diving. Snorkels are typically used by the recreational breath-hold divers but not usually in the other breath-hold diving types. Thus, snorkel diving is not an exact substitute terminology for breath-hold diving.

FIGURE 1. Breath-Hold Diver on the Surface

FIGURE-1

This diver is enjoying the underwater panorama while snorkeling on the surface with only occasional breath-hold depth excursions to explore items on the bottom in 3 to 6 FSW (1 TO 2 MSW).
A lycra suit is being worn, more to offer protection from the sun and stings than for thermal comfort in the warm tropical water.

 

Each of these five variations of breath-hold diving has typical diving depths, goals and special circumstances (Table 1).

Snorkels are an energy-conserving piece of equipment. They negate the extra energy needed to lift one’s head out of the water to breathe. In addition they allow the diver to view without interruption the underwater panorama which otherwise would be interrupted by lifting the head out of the water to breathe. Snorkels vary from simple “J-shaped” tubes to tubes with additional curves, bends, and valves.
More elaborate snorkels have no return valves so water does not enter the snorkel tube. The advantage of the valve is the diver need not clear the snorkel tube of water before inhaling. However, the system is not always reliable and exhaling through the snorkel to be sure it is clear of water before inhaling is always recommended. Another snorkel device is a ball-type valve at the top of the snorkel. The purpose of this device is also to prevent inhalation of water should the top end of the snorkel not be above the surface of the water.

Several deserve additional commentaries such as the AMA of Japan, the pearl divers of the South Pacific and the extreme apneic (i.e. nonbreathing, breath-hold) divers) which will be included in the text box below and in succeeding portions of the paper.

The Ama divers of Japan and Korea are female commercial divers that harvest foodstuffs off the bottom. There are two categories of divers the shallow water dives that dive to about 15 feet of seawater (FSW)/5 Meters of seawater (MSW) and the deep divers whose maximum depths are 60 FSW/ 20 MSW.
It appears that women in the process of “natural selection” better tolerated the cold Japanese and Korean waters than men. This is attributed to the fact that women have additional subcutaneous fat, which is an insulation-type protection for cold water. Now that neoprene wet suits have become available, men divers are taking over these commercial diving activities.
For the deep diver category, in order conserve air, the Ama use stone weights to help them submerge. Men tenders on small surface craft tend the lines. Once the foodstuffs have been collected and placed in a basket along with the weight used for descent, the tenders pull-up the basket and the diver so energy expenditures are almost entirely due to the collecting process on the bottom. The deep diving Amas typical bottom times are about one minute.

 

TABLE 1. Types of Breath-Hold (Apneic) Diving

Name

Typical Depths

(feet of seawater/meters of seawater)

Goals Comments
Snorkeling Surface and depths to 3-6/1-2 Surface swims, viewing a wide expanse of the underwater environment Ideal for the young diver, for those with fear of going underwater, and for near-surface photography where color rendition is optimized.
Recreational Breath-hold Diving Surface to 30/10 Exploring shallow depth flora, game collecting (abalone, lobster, scallop) Requires swimming and breath-holding skills. Ear clearing challenges with each descent.
Commercial Breath-hold Diving Dive depths: 15/5 to 60/20. Pearl divers to > 100/30 Collect game for livelihood; sale for jewelry Most publicized and studied are the women "Ama" divers of Japan and Korea and the pearl/coral divers of the South Pacific islands
Competitive Spear Fishing Depths to 120/40 and more Spearfishing contests; personal use of fish Great risks for breath-holding blackouts; hyperventilation breath-holding distractional and diffusional (Chapter 7)
Extreme Apneic Dives Depths to over 200/60 and static breath-hold times > 10 minutes Set world and personal records Hazardous; for record attempts, standby personnel required. There are certification associations for record setting dives.

 

TABLE 2. Six of 11 AIDA/CMAS Recognized Types of Apneic Dives and Their Records*

Name Description Women's Record Men's Record
Static Breath-holding with head submerged

Molchanova (Rus)

9 min 2 sec

Mifsud (Fra)

11 min 35 sec

Dynamic w/fins Underwater swim for distance

Molchanova (Rus)

237 m (777.6 ft)

Malina (Pol)

300 m (984.3 ft)

Constant weight Maximum depth swimming down & backup w/wo fins

Molchanova (Rus)

101 m (331.4 ft) w/fins

Molchanova (Rus)

128 m (419.9 ft) w/fins

Free immersion Line for descent & ascent; no fins

Molchanova (rus)

91 m (298.6 ft)

Trubridge (Nzl)

124 m (406.8 ft)

Variable weight constant Weighted sled descent; line or swimming ascent

Van den Broek (Nld)

130 m (426.5 ft)

Kastrinakis (Grc)

146 m (479 ft)

No limits Weighted sled descent; inflatable lift bag ascent

Steeter (USA)

160 m (524.9 ft)

Nistch (Aut)

214 m (702.1 ft)

Note: *As of July 31, 2014. (https://en.wikipedia.org/wiki/AIDA_International)

Abbreviations: Aut = Austria, Fra = France, Ft = Feet, Grc = Greece, M = Meters, Nzl = New Zealand, Pol = Poland, Rus = Russia, USA = United States, W/WO = With/without fins

Records setting apneic dives generate much attention, often making headlines in newspapers and news broadcasts. Two organizations provide direction for apneic divers. They are AIDA (International Association for Development of Apneic Diving) and CMAS (Confederation Mondiale des Acivities Subaquatiques). Eleven apneic diving disciplines are recognized by AIDA and CMAS and 12 more are practiced locally. Disciplines vary from “static” i.e. breath-holding on the surface to “no limits” i.e. weighted sleds to aid with descent and inflated bags to aid with ascent (Table 2).

An example of an unrecognized discipline is that of Alex Segura Vendrell. On a static breath-hold he was able to hold his breath face submerged in a pool 24 minutes and 3 seconds after breathing oxygen. This record was set on 7 March 2016.

Advantages and Hazards of Breath-Hold Diving

For those who enjoy freedom of movement and the ability to demonstrate their own water “adaptability,” few activities are more exhilarating than breath-hold diving (Figure 2). Without the need for SCUBA tanks, the breath-hold diver has much more mobility and swimming speed capability. This obviates the drag created by the tanks and other related equipment such as regulators and buoyancy compensators when swimming. Preparations and donning of gear is much less for breath-hold diving due to the minimum equipment requirements as compared to that needed for SCUBA diving.

FIGURE 2. Breath-Hold Divers "on the Bottom"

FIGURE-2

"Resting" on the bottom in 33 FSW/10 MSW "uncluttered" with gear. Note: Because of positive buoyancy—a safety precaution—divers needed to hold onto cement anchor in order to remain on the bottom. The anchor line was used to reach the bottom to conserve "air", otherwise it would be expended for a swimming descent.

 

Other advantages of breath-hold diving include the quietness of not cycling the SCUBA regulator or dealing with exhalation bubbles. These features are less likely to disturb the marine flora for observation and photographic purposes. In addition, diving is essentially “unlimited” with breath-hold diving. Except in extreme situations (to be described later in this chapter), there are no decompression requirements and repetitive dives and immersion times are essentially unlimited.

Finally, breath-hold diving is a good conditioning activity because of the activity associated with it. The mastery of energy conserving movements while swimming underwater and improved performances manifested by increased breath-hold times and depth excursions occur rapidly with breath-hold divers. In the first author’s experiences, breath- hold dive times typical increase from about 45 seconds to over one and one- half minutes and depth excursions from 25 feet to 50 feet from the beginning to the end of a week’s diving activities. In contrast, the “ideal” SCUBA dive is one that minimizes activity in order to conserve energy and minimizes air usage and is therefore not a beneficial activity for aerobic/cardiac conditioning.

Studies of dive instructors the from the US Navy Submarine Escape Training Tank at Groton, Connecticut demonstrated they rapidly improved their diving abilities after starting their assignments. Changes included increases in total lung capacity and decreased sensitivity (i.e. need to take a breath) from elevated blood carbon dioxide tensions and protection from blackout from lower blood oxygen tensions. These changes were observed after six weeks of training. The increased total lung capacity was thought to offer protection from thoracic squeeze.1,2

As in other diving activities, hazards are associated with breath-hold diving. The major one is blackout, which is comprehensively discussed in Chapter 7. The more challenging the diving activities are, such as competitive spear fishing and extreme apneic diving, the greater the risks for blackout are present. This is ironical since inexperience and lack of fitness are major considerations in recreational SCUBA diving accidents while the most experienced, best conditioned divers are the ones at the greatest risk for blackout. A possible exception to this observation is the diver who from lack of knowledge or otherwise excessively hyperventilates in order to extend his/ her underwater water breath-hold time (Chapter 7).

PARADOX Inexperienced SCUBA divers primarily experience nonblackout medical problem of diving; experienced breath-hold diver primarily experience blackouts.

 

Unfortunately, statistics for breath- hold diving blackout and deaths are meager. In absence of wearing SCUBA gear, causes of death in breath-hold divers are usually listed as drowning without describing antecedent events (Figure 3). When the loss of consciousness is transient, and the diver recovers without sequelae, there is no mechanism to tract such events. This contrasts to a SCUBA diving medical problem such as decompression sickness, which is treated with hyperbaric oxygen-recompression and there is better collection of data on such occurrences. The Divers Alert Network (DAN), however, has started collecting data on breath-hold diving accidents in addition to their SCUBA diving data repository.

FIGURE 3. Deaths in Breath-Hold Divers

FIGURE-3

Deaths in breath-hold divers are usually reported as drownings. Review of dive history and the examination of circumstances can usually discover underlying causes. These causes and their frequencies are "best guesses" from the first author's experiences, review of the literature, diving medicine conferences, and discussions with colleagues.

FIGURE 4. The Body's Responses to increased Ambient Pressure with Breath-holding

FIGURE-4

The body when descending with breath-hold dives has analogies to the above model. The water-filled balloon transmits pressures equally and undiminished (Pascal's principle) as is the situation with almost 99% of the body. Air-filled, flexible walled structures like the lungs and gut decrease in size (Boyle's law). In both situations no pressure differentials develop.
The rigid-walled, air filled structure build-up pressure differentials in response to increased pressures. Body structures, rather than collapse, leak fluid and bleed into these structures in response to pressure differentials. It appears the lung's alveoli respond in a similar fashion once they are compressed beyond their residual volume.

 

A second hazard of breath-hold diving is thoracic squeeze. However, it is debatable whether or not this problem is a realistic concern. Ordinarily the majority of the body structures tolerate changes in pressure with breath-hold diving without problems (Figure 4). In theory, thoracic squeeze occurs when the total lung capacity (about 5 liters) during the breath-hold dive descent is compressed to the residual lung volume (about 1 liter).

The single reported case with lung pathology to verify its existence occurred in combination with a blackout.³ In this case the breath-hold diver loss consciousness during ascent from a 80 FSW/24.3 MSW) bottom drop (i.e. a dilutional blackout— chapter 7), passively lost the tidal volume of air in his lungs and began to sink. It is postulated that once the alveoli were compressed beyond their tidal volume, the pathology as described above occurred.

 

Application of Boyle’s law computes this threshold to be 132 feet. Compression of the lung beyond its residual volume apparently exceeds the alveoli’s ability to collapse and because of this, gradients develop that move fluid and blood from the lung capillaries into the alveoli. The result is essentially the diver “drowns” in his/her own body fluids. Obviously, the theoretical thoracic squeeze threshold has been far exceeded with breath-hold dives greater than 132 FSW on repeated occasions without evidence of thoracic squeezes.

Aquatic mammals exhale before they descend on their deep dives. This supposedly minimizes energy expenditures during descent. Thoracic squeeze is avoided by their alveoli being able to collapse completely and then re-expand upon surfacing without injury to the alveoli. This also has other protective benefits for the aquatic mammals. With alveolar collapse, there is no exchange of air across the alveoli, so problems of nitrogen narcosis, oxygen toxicity and decompression sickness do not occur (Chapter 5).

 

In humans, six different explanations, both empirical and theoretical, explain why apneic divers avoid thoracic squeeze even though the depths of their dives far exceed the theoretical total lung capacity reduction to the residual volume.4 Proposed explanations include:

First, the elasticity of the lung tissue (alveolar wall) itself may add an increased margin of tolerance so that damage from collapse of the alveoli does occur until well beyond the theoretical threshold.

Second, as descent continues while breath-holding, the increased ambient pressure symmetrically compresses the chest wall (Figure 5). Thus, there are proportionate decreases in the volume of the chest cavity with the decreases in the lung capacities. The secondary effect of “pressurization” of the air in the alveoli as demonstrated by Boyle’s law helps the alveoli resist collapsing.

Third, Expert apneic divers claim to be able to hyperinflate their lungs by “buccal pumping.” Thus, they begin their dives not only with a maximal inhalation but with a pressure in their lungs greater than the surface ambient pressure.

FIGURE 5. Caricature to Emphasize Chest Compression with Descent while Breath-holding

FIGURE-5

Chest and abdomen compression with deep descents while breath-holding have been offered as possible explanations for protection from thoracic squeeze. Symmetrical compression of chest and abdominal contents translates to alveoli. While reducing the volume of the alveoli (Boyle's law), it increases the pressure within the alveoli to help prevent their collapse.

 

Fourth, through neuro mechanisms initiated by the diving reflex, blood shifts from the extremities to the chest cavity. This has been demonstrated in the Ama divers of Japan as well as in a record setting apneic diver. This effect couple with elevation of the diaphragm pressure and shifting of the abdominal contents into the chest capacity as the air-filled bowel is compressed compensate for the decreased volume of the compressed lung.

Fifth, congenital or developmental anomalies such as asthma may increase the diver’s lung capacities which have been observed to exceed those found in the general population. In addition, acclimatized breath-hold divers significantly increase their TLC’s with relative decreases in their RV’s with practice. These effects increase the TLC—>RV thresholds thereby lowering the depth where thoracic squeeze will occur. The acclimatizations are short- lived, disappearing within a couple of months after stopping diving activities.

Finally, females may be endowed with hereditary factors that increase their resistance to thoracic squeeze just as they are to cold-water exposure. At one time, a woman exceeded the “no limits” apneic dive depth record.

Middle ear and sinus barotrauma is another risk to breath-hold divers who descend below the surface (Chapter 4). While water is more than 700 times as dense as air, density does not change to any significant degree with descent. In contrast, changes in is a significant consideration in both SCUBA and breath-hold diving (Figure 6). Pressure effects of water with descents are significant for two reasons. First, SCUBA divers have the benefit of descending slowly and halting their descents to facilitate middle ear pressure equilibration. Breath-hold divers do not have this luxury; they must descend as rapidly as possible in order to optimize their bottom times. Second, whereas a SCUBA diver may only perform a few descents and ascents during a day’s diving activities, the breath-hold diver will do 20 more in the course of an hour’s deep recreational breath-hold dives. Consequently, the experienced breath-hold diver becomes very adept at ear clearing with descents.

FIGURE 6. Water Density and Pressure Changes with Descent

FIGURE-6

Water density, which is over 700 times greater than air density, influences movement through water and contributes to the physical stresses of diving such as dealing with waves and currents, but does not change markedly with increased depths.
Pressure has many ramifications for the diver whether SCUBA or breath-holding. For the breath-hold diver, pressure changes are associated with middle ear barotrauma, diffusional blackout and possibly thoracic squeeze.

 

Finally, the risk of decompression sickness as a hazard for breath-hold divers must be mentioned for the sake of completeness. In the past, it was believed that human breath-hold divers could not get decompressions sickness. A US Navy diving manual stated that it is virtually impossible for the skin diver, because he cannot take up a troublesome amount of nitrogen–unless he has access to a supply of air at depth.5 However, decompression sickness has been observed with repeated deep breath-hold dives and was confirmed by Paulev.7 In his study, four experienced, well-conditioned, highly- trained dives participated in a series of repetitive breath-hold dives. Their dive profiles involved rapid  descents to 65 FSW/20 MSW and bottom times approaching two minutes. Surface intervals varied from a few seconds to a maximum of two minutes so that the accumulated time spent underwater was greater than the accumulate time of the surface intervals. After five hours diving, which included about 60 divers, signs and symptoms of decompression sickness appeared while the divers were on the surface. The diagnosis was confirmed when the findings resolved with recompression in a hyperbaric chamber. When Paulev calculated the amount of nitrogen accumulation with the dive profiles, he found that the tissue nitrogen tensions exceed the maximum allowable (M-values) tissue saturations.8 This confirmed that decompression sickness can occur in breath-hold divers in extraordinary situations.

Polynesian pearl divers of Tuamotu became paralyzed after repetitive deep breath-hold dives.6 They called their syndrome “taravana,” which translates into the “falling syndrome.” Symptoms were observed after four to five hours of breath-hold diving to depths as great as 165 FSW/50 MSW with very short surface intervals. Unfortunately, many of the afflicted divers remained permanently paralyzed due to lack of a recompression chamber on their island. Had their symptoms resolved with recompression, the diagnosis of decompression sickness would have been absolutely confirmed in these cases.
It is noteworthy that this problem was not observed in divers on an adjacent island who descended to equivalent depths, but had surface intervals two to three times the durations of the Tuamotu divers.

FIGURE 7. Deep Breath-hold Dive with Fins, Mask, and Snorkel

FIGURE-7

Note the swimming descent (no descending line available). Blue-gray coloration attests to the depth of the dive with filtering out of red and yellow colors to a homogenous bluish-gray coloration. Dive equipment limited to fins, mask, and snorkel and no lycra protective garment. Observe that water pressure (yellow oblong) is beginning to compress abdomen. Dive is being monitored by buddy on surface. Computer depth gauge and dive watch (white circles) are used to time and record depth of dive.

 

Special Equipment Needs

Equipment needs and costs are substantially less since fins, masks and snorkels are the main expenditures (Figure 7). In warm water, only a swimsuit is needed, but a Lycra® dive skin is recommended for sun and marine animal sting protection.

In cooler water, neoprene wetsuit protection is needed, but because of energy expenditures with breath-hold diving, substantial less “rubber” is needed to keep comfortably warm as compared to using SCUBA gear when diving in waters of equal temperature. Also, less weight is needed to neutralize buoyancy if less neoprene is used to maintain thermal comfort in the water.

Specialized diving fins are preferred by the competitive spear fisherman. They typically are much longer and much more flexible than the swim fins used by the recreational SCUBA diver. Monofins, where both feet are put into a single fin thereby simulating the tail flukes of dolphins and whales, have been used by apneic divers who do swimming ascents in their personal or world-record-breaking attempts.

For improved mobility for breath-hold divers as well as surface swimmers, neoprene wetsuits are thinner and utilize more flexible, less densely packed bubbles. Dry suits are not a realistic option for the breath-hold diver due to their bulkiness and need to have a separate compressed gas supply to maintain proper inflation of the dry suit.

A dive knife, wristwatch/timer, and depth gauge are essential pieces of equipment for the breath-hold diver (Figure 7). The dive knife should be small, but have a serrated blade to facilitate cutting through nylon rope entanglements and kelp. Depth gauges and watches are necessary to monitor depths and times of the dive. Dive computers may become “frustrated” with the repetitive dives a breath-hold diver does. A simple wrist depth gauge, preferable one that records maximum depth is recommended.

Capillary depth gauges are OK for shallow depths where big changes in the bubble diameter are maximized as demonstrated by Boyle’s law. The friction of the gas bubble in the glass cylinder leads to inaccurate readings. At this time the capillary depth gauge is all but obsolete.

FIGURE 8. Speargun Choices

FIGURE-8

Speargun options vary from a few dollars for a homemade Hawaiian sling to over a thousand dollars for a high-end pneumatic speargun.

For the spearfisherman, spearguns of varying sophistication are used (Figure 8). The most simple is the Hawaiian sling. Sophistication increases with gunstock- like barrels, multiple surgical tubes, and more precise trigger mechanisms. The most sophisticated are those spearguns that use gas (pneumatic systems) to thrust the spear forward. Prices range from a few dollars for a homemade Hawaiian sling up to $1500.00 for the high-end, gas-charged models.

The Hawaiian sling consists of a cylinder of wood about six inches long with a hole drilled through its center, which holds the spear. A trigger device can be fashioned from a door hinge attached to wood cylinder that has a hole in it to allow the spear to pass through it and the wood cylinder. However, typically the diver uses finger pressure on the spear against the forward portion of the wood cylinder. Surgical tubing is attached to the cylinder. The spear has a barb attached to its pointed end.
The sling is cocked by stretching the surgical tubing over the blunt end of the spear and using the friction of the finger pressure or the obliquity of the door hinge hole to maintain the cocked, surgical tubing tension position of the spear. By releasing finger pressure or closing the hinge  (the hole becomes round), the surgical tubing tension causes the spear to shoot out analogous to a hair trigger release. To be effective, the spear point must be close to the target fish.

For the record apneic dives, sophisticated equipment and a team approach is necessary (Figure 9). Equipment needs include boat support to platforms at the dive site, descending lines, sleds, depth recording devices, timers, water- filled goggles that accommodate for the refractive index of the water, remote monitors, and communication systems. Personnel include AIDA or CMAS officials to authenticate the dive, standby divers (often with closed circuit SCUBA for great depths), paramedics/ physicians and reporters. Obviously, the world- class apneic diving record attempts are expensive undertakings with possibilities of injuries and deaths. They frequently have equipment sponsors or publication companies help underwrite the costs.

Safety Considerations

As stated previously, breath-hold diving imposes significant risks for the divers engaged in this type of diving activity. Consequently, safety considerations and practices are of paramount importance. As in all diving activities, the buddy system should be used. However, for recreational breath-hold diving, the buddy should be of comparable skill (i.e. depth capabilities and breath-hold times) should a rescue attempt be necessary if the victim is at depth.

FIGURE 9. Examples of Support for Record Apneic Dive Attempt

FIGURE-9

A large complement of officials, safety personnel, and standby divers are required in order to maximize the safety of the apneic divers in their attempt to set new records.

 

Exceptions to the buddy system occur with competitive spearfishing competition and record attempt apneic diving. These activities are done individually. However, these specialized breath-hold diving activities require preplanning, for example, expected duration and maximum depth of the activity so the support staff will know when the diver is expected to reach the surface. In addition, standby SCUBA divers, suited up and ready to or already in the water are immediately available to retrieve the diver in trouble.

While one buddy is on the surface recuperating, the other buddy does the dive and vice versa. The dive site should be chosen so that the water is clear enough that the surface buddy can see the buddy throughout the dive. It is desirable to descend with the aid of a descending line. This conserves energy and can markedly extend the bottom time since hand-over-hand pulling oneself downward uses much less oxygen stores than a swimming descent (Figure 2). The diver should be weighted to be slightly positive so that if unconsciousness occurs, the diver will float to the surface rather than sink. However, the buoyancy effect is mitigated by lung compression so a breath-hold diver on the surface who is neutrally buoyant on the surface will become negatively buoyant after descending 20 FSW/6 MSW to 30 FSW/9 MSW.

Experienced freedivers take advantage of this change in buoyancy with descent. Once they reach a depth where they become negatively buoyant, they can stop their active swimming activities, descend without effort, and thereby conserve their air supply.
The “price paid” is that once ascent is started, active swimming efforts are required until they ascend to a depth where they again become positively buoyant.

Submersion times should be planned so the diver starts the ascent at pre-determined times rather than waiting until “air hunger” dictates urgent surfacing to “catch” one’s breath. This is because diffusional blackout (Chapter 7) can give the diver a false sense of comfort/lack of “air hunger” while at depth while during ascent the shifts in oxygen from the blood to the tissues result in hypoxia and loss of consciousness.

While deep breathing is acceptable while resting between breath-hold dives, hyperventilation to the point of numbness and tingling of the hands and feet is condemned. This is because lowering of the blood carbon dioxide levels with hyperventilation alters the breath-hold breakpoint enough that it is not reached before consciousness can be lost (Chapter 7). Another thing to be condemned is to use a SCUBA diver’s octopus air supply at depth to extend the bottom time of a breath-hold dive. The reason for this is the possibility of forgetting to exhale while ascending which would not ordinarily be done with a pure breath-hold dive. The result of the expanding gas in the lungs during ascent that was inhaled at depth could result in an arterial gas embolism. Reports exist of probable arterial gas embolisms after breath-hold dives.9

Is it hazardous to do recreational breath-hold dives immediately after surfacing from a SCUBA dive? Silent intravascular bubbles are known to exist in the venous side of the blood stream, filtered out through the lungs, and exhaled while ascending from a SCUBA dive. The concern is raised that pressurization during descent with the breath-hold dive, the silent intravascular bubbles, reduced in size aka Boyle’s law, will be forced through the lungs into the arterial circulation and result in an arterial gas embolism. While this is a theoretical possibility we are unaware of any reported cases of such.

Special Challenges

The challenges of breath-hold diving have been presented earlier in this chapter. Special challenges can be associated with the physical challenges of diving (Chapter 4). These include surface currents, rip tides, crashing surf zones, and swells. Without the ability to “duck under” and escape the challenges as is possible with SCUBA diving, the breath-hold diver is vulnerable to panic from exhaustion and/or disorientation. In general, breath-hold diving at night is not recommended. This is because of the reduced orientation associated with darkness, the need to handle dive lights, and the difficulty of checking gauges all during the short process of the breath- hold dive.

Perhaps the greatest challenge for the breath-hold diver is distraction. It is easy to appreciate why a recreational breath-hold diver can become distracted. If near the breath-hold break point and blackout from hypoxia is only moments away, and something special occurs, such as almost ready to grasp a lobster in a crevice or pry loose an abalone or getting the “perfect” underwater photograph, the breath- hold diver may suppress the desire to breath long enough that consciousness is lost in the process. This is setting for distractional blackouts (Chapter 7).

The  degree  of  hypoxia before  blackout occurs probably varies greatly from individual to individual. Conditioning and practice improve breath-hold times, increase tolerance to high carbon dioxide tensions, and lower the blackout point from hypoxia. Other factors such as heart arrhythmias or hypoglycemia may be precipitated by the hypoxic stress as the breath-hold break point is approached. These may lead to unconsciousness before the blackout can be attributed to distraction. If the blackout occurs earlier than the expected duration of the breath-hold dive (another strong indication for timing dimes), causes other than blackout must be sought.
 

Aquatic Mammals Adaptations to Improve Breath-Hold Diving Abilities

In addition to the adaptations of aquatic mammals to diving that were described at the end of each chapter of Part II, additional adaptations make them ideal breath-hold divers. These are the adaptations in blood and muscle tissue that improve oxygen transport and storage. Aquatic mammals have twice the oxygen-carrying and storage capacity that terrestrial mammals of corresponding sizes have.10  This is attributed to larger relative blood volumes, higher percentages of oxygen-carrying red blood cells, better oxygen storage capabilities in muscles, ability to extract oxygen from venous blood, greater oxygen extraction from hemoglobin, and reduction in fluid losses (Table 3). Contraction of the spleen can release large amounts of blood to the core circulation with volume reductions as much as five-fold in the seal versus the two- fold reduction in the elite human apneic diver.11,12 In addition, like the conditioned human breath-hold diver, aquatic mammals are able to tolerate higher carbon dioxide accumulations before needing to breathe and lower oxygen in the blood before losing consciousness than non-conditioned humans—or even the conditioned human diver.

Splenic contraction has two postulated advantages to the breath-hold diver. First, it moves blood into the core circulation. This may help displace the void created by lung collapse with the descent as a direct effect and reduce the likelihood of thoracic squeeze as an indirect effect.
The second benefit is that the oxygen in the blood (added to the core circulation with the splenic contraction) can be utilized to extend the breath- hold time.

 

TABLE 3. Enhanced Oxygen Carrying and Storage Capacity Adaptations of Aquatic Mammals
Adaptations Findings Advantage Comment
Relative (liters/mass) blood volumes Increased (versus that of nondiving mammals) based on percentage of body weight Enhanced perfusion Incremental increase of blood to core with shunting promotes oxygen delievery to brain & displaces lung collapse occurrence with descent
Increased percentage of oxygen-carrying red blood cells (RBCs) Decreased size of RBCs; increased percentage of RBCs (20% greater than humans) Better ability to transit capillaries in low flow states; increased oxygen delivery Smaller size of RBCs may prevent sludging during low flow states to noncritical structures during diving reflex
Better oxygen storage capacities in muscles (myoglobin) Greater muscle myoglobin oxygen than nondiving mammals Reservoir for oxygen to be used by muscles during diving reflex before anaerobic metabolism required About 50% of total oxygen storage in aquatic mammals at the beginning of the dive is in myoglobin
Oxygen extraction from venous blood After arterial oxygen is utilized, aquatic mammals extract oxygen from venous blood Enhanced oxygen utilization; prolongation of dive This adaptation couples with increased ability to tolerate low blood oxygen & high carbon dioxide tensions
Greater oxygen extraction from hemoglobin Blood more acidotic with carbon dioxide elevation during breath-hold More offloading of oxygen from hemoglobin during dive Acidotic blood is able to offload more oxygen to tissues (Bohr effect)
Fluid conservation No losses of insensible body fluid from lungs with breath-hold & during filtration from kidneys Maintenance of blood volume This contrasts with increased fluid losses in SCUBA divers insensible through respiratory losses & increased urine production

 

Myths and Misconceptions about Breath-Hold Diving

Myth Counterparts in humans exist for all the adaptations to diving that exist in diving mammals.

Fact Although elements of the diving reflex occur in humans, other adaptations such as ability to collapse lungs with descent, increased myoglobin stores, smaller sizes of red blood cells, enhanced ability to extract oxygen from venous blood, and avoidance of decompression sickness with deep dives do not have counterparts in human divers. Improved tolerance to elevated carbon dioxide tensions and low oxygen tensions observed as well as increased lung capacity in conditioned human breath-hold divers are acclimatizations that occur with practice but disappear when the diving activities cease.

Myth Knowledge is the overriding consideration in record-setting apneic dives.

Fact While knowledge (and safety) is important, natural abilities, experience and conditioning are more important considerations.

Myth The breath-hold breakpoint to breathe cannot be suppressed

Fact Distractions associated with underwater activities such as game collecting can result in the diver suppressing the desire to breathe long enough for the diver to lose consciousness from hypoxia. With deep dives, this may be compounded by the diffusional blackout effect (Chapter 7).

Myth Strong signals (i.e. physiological warning signs) almost always exist as a diver is at risk of becoming unconscious from hypoxia.

Fact Physiological warning signs of hypoxia may not be recognized if carbon dioxide elevation, which is the indirect stimulus of impending hypoxia, is altered by hyperventilation, oxygen dilution (i.e. diffusional blackout) or carbon dioxide scrubbers.

Myth Competitive spearfishermen disregard safety practices such as the buddy system.

Fact Contests are carefully supervised so the topside officials are aware of the diver’s planned bottom time and the intended diving area. Another safety feature is to have suited- up standby divers on the scene during each event.

Myth Females are better suited for commercial breath-hold diving than men.

Fact Whereas, women have an improved ability to tolerate cold water, the use of the wetsuit has negated this advantage so men are now involved in these Japanese and Korean commercial diving activities. Although women have done incredible diving feats, records for all categories of apneic diving reside with men divers.

 

References

  1. Schaefer KE, Allison RD, Dougherty CR, et al. Pulmonary and circulatory adjustment determining the limits of depths in breath-hold diving. Submarine Medical Research Laboratory; report No.531.1968.
  2. Strauss MB. Physiological aspects of mammalian breath-hold diving: A review. Aerosp Med. 1970; 41(12):1362-1381.
  3. Strauss MB and Wright PW. Thoracic squeeze diving casualty. Aerosp Med. 1971;42(6):673-675.
  4. Strauss MB, Aksenov IV, Miller SS, et al. Thoracic Squeeze: Fact or Fiction (Poster Presentation& Abstract). UHMS Ann Sci Mtg Proceedings. Orlando, Florida, US. 2006; 33(5)(J14):pp375.
  5. NAVMED. Submarine medical practice. Washington, DC: US Government Printing Office. 1956; P-5054, pp259.
  6. Cross ER. Taravana: Diving syndrome in the Tuamotu diver. In Physiology of breath-hold diving and the Ama of Japan, ed Rahn H. Washington, DC: National Academy of Sciences. National Research Council Publication 1341. 1965; pp207-220.
  7. Pauley PE. Decompression sickness following repeated breath-hold dives. J Appl Physiol. 1965; 20:1028-1031.
  8. Pauley PE. Nitrogen tissue tensions following repeated breath-hold dives. J Appl Physiol. 1967; 22(4):714-718.
  9. Harmsen S, Schramm D, Karenfort M, et al. Presumed Arterial Gas Embolism After Breath-Hold Diving in Shallow Water. Pediatrics. 2015; 136(3):e688-e690.
  10. Irving L, Solandt DM, Solandt DY, Fisher KC. Respiratory characteristics of the blood of the seal. J Cell Comp Physiol. 1935; 7:393.
  11.  Hurford WE, Hong SK, Park YS, et al. Splenic contraction during breath-hold diving in the Korean ama. J Appl Physiol. 1990; 69(3):932-936.
  12. Laub M, Hyid-Jacobsen K, Hoyind P, Kanstrup IL, Christensen NJ, Nielsen SL. Spleen emptying and venous hematocrit in humans during exercise. J. Appl. Physiol. 1993; 74:1024-1026.

 

About the Authors

Michael-Strauss

MICHAEL STRAUSS, M.D., an orthopaedic surgeon, is the retired medical director of the Hyperbaric Medicine Program at Long Beach Memorial Medical Center in Long Beach, California. He continues to be clinically active in the program and focuses his orthopaedic surgical practice on evaluation, management and prevention of challenging wounds. Dr. Strauss is a clinical professor of orthopaedic surgery at the University of California, Irvine, and the orthopaedic consultant for the Prevention-Amputation Veterans Everywhere (PAVE) Problem Wound Clinic at the VA Medical Center in Long Beach. He is well known to readers of WCHM from his multiple articles related to wounds and diving medicine published in previous editions of the journal. In addition, he has authored two highly acclaimed texts, Diving Science and MasterMinding Wounds. Dr. Strauss is actively studying the reliability and validity of the innovative, user-friendly Long Beach Wound Score, for which he already has authored a number of publications.

 

Lientra-Lu

LIENTRA LU is a research coordinator at the VA Medical Center in Long Beach, California, under the guidance of Dr. Ian Gordon, a California Institute for Research and Education (SCIRE). She received a bachelor of science degree in chemical biology at the University of California, Berkeley, in 2015 and subsequently has taken medically related courses at the University of California, Los Angeles. Miss Lu is helping with diabetic foot and venous leg ulcer studies at the VA Medical Center while also serving as an assistant in patient care at the PAVE Clinic there. She also works with the American Red Cross in her other interest, disaster preparedness.

 

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