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by Dawn Kernagis, PhD
If you follow the current trends in health and fitness, the words; ‘ketone’, ‘ketogenic’, and ‘ketosis’ have recently become synonymous with weight loss, wellness, endurance, and (of course) controversy with respect to effectiveness and safety. Despite the popularity of these terms, there is still a bit of confusion surrounding each of them and, specific to the undersea community, what research has been conducted on ketones and diving.
In this post, I will provide a brief, high-level overview of what ketosis is, what we know about potential diving-related applications of ketones, and next steps in diving-related ketosis research.
Ketosis refers to the presence of elevated ketone bodies (also known as ketones) in the blood. Ketones (beta-hydroxybutyrate, acetoacetate, and acetone) are produced by the liver from stored fat when a person either strictly fasts (typically a minimum of 24-48 hours) or undertakes a ‘ketogenic diet’ (very low carbohydrate, low-moderate protein, high fat). During ketosis, the body shifts from using glucose as a fuel, as a result of carbohydrate restriction, to burning ketone bodies.
In addition to fasting and the ketogenic diet (endogenous approaches), ketosis is also achievable exogenously by consuming substances such as ketone salts or ketone esters. Exogenous ketones increase blood ketone levels to varying degrees, with the latter raising blood ketone levels greater than 4mmol/liter without depletion of carbohydrate stores, even in the presence of a carbohydrate-rich meal (Stubbs 2017). Induction of ketosis by eating or drinking ketones is rapid and acute; that is, the ketones will typically be metabolized within a maximum of four to eight hours. Given their short-lived effects, research is underway to understand if regular consumption of exogenous ketones has the same effect on our cells, tissues, and overall physiology as a sustained keto diet or fasting.
Ketosis can be monitored using a variety of commercially available options, including sampling blood from the fingertip (similar to blood glucose testing) to measuring blood ketones with a handheld meter, using urine test trips, and analyzing exhaled breath. The ketogenic diet is actually one of the few diets that has a biomarker that tells you whether or not you are actually ‘on’ the diet: if your ketone levels are above the threshold, you are in the physiological state of ketosis, and vice versa!
The number of studies assessing the benefits versus potential risks of sustained ketosis are increasing, and the medical and sports science communities are grasping an improved understanding about if, when, and how a ketogenic diet or exogenous ketone consumption could either benefit or negatively impact health and performance. While summarizing these studies would be the subject of an extensive series of blog posts, the study that piqued the diving community’s interest in ketones was focused on protecting rats from CNS oxygen toxicity seizures.
Bringing Ketones into Diving
The history of ketosis in the medical community is largely centered around epilepsy treatment. While there are historic records of the starvation ketosis being used as a treatment approach going back to 400 B.C., the first formal clinical trials using dietary ketosis to treat epilepsy were conducted in the 1920s. Dr. Russell Morse Wilder at the Mayo Clinic developed the ketogenic diet as a way to obtain the benefits of fasting through a nutritional approach that could be sustained long-term. In 1921, he conducted the first trial to assess the effect of a ketogenic diet on epilepsy patients.
Flash forward to just a decade ago, when Dr. Dominic D’Agostino at University of South Florida became interested in the effects of ketosis on seizure latency and its potential as a mitigation strategy for CNS oxygen toxicity in divers. With previous experience conducting research in undersea medicine, Dr. D’Agostino developed a study to assess the effects of exogenous ketosis (induced by consumption of a novel ketone ester, known as an acetoacetate diester) on oxygen toxicity seizure latency in small animals (D’Agostino 2013). Rats were monitored for oxygen toxicity symptoms and brain activity using EEG during a 5 ATA chamber dive on 100% oxygen, and they were either dosed with ketone diester (which exogenously increases all three ketone bodies), butanediol (which only increases the ketone body beta-hydroxybutyrate), or water (control) prior to their dive.
Compared to water, the ketone diester induced a rapid and sustained elevation of all three ketone bodies and increased latency by a factor of five compared with water. Butanediol did not increase seizure latency even though it did effectively elevate blood beta-hydroxybutyrate. Demonstration of the increased oxygen toxicity seizure latency in rats in response to the ketone bodies acetoacetate and acetone, but not beta-hydroxybutyrate, was a significant finding. The study results also point to the different effects of the three different ketone bodies and the fact that not all exogenous ketones are the same when it comes to their potential applications.
It is important to note that findings from animal studies can fail to translate effectively to humans due to differences in physiology and a variety of additional factors. A human study that assesses the effects of the ketone diester on CNS oxygen toxicity will be critical before potential translation to the diving community. However, controlled human studies of human oxygen toxicity are also rare and can be difficult to conduct.
Given the low incidence of oxygen toxicity in divers, along with the ethical considerations of conducting oxygen toxicity interventional research in a non-medical, field-based setting, these human studies need to be conducted in a laboratory environment with the appropriate safety considerations, statistically-driven study design, and outcome measurements. As a starting point, and at the time of this article, a double-blinded, lab-based study of oxygen toxicity in humans on a ketogenic diet compared to normal diet was underway at Duke University.
When it comes to ketosis, there is still a significant amount of research that needs to be conducted before we know whether it could be beneficial and, most importantly, reliably safe in divers in a variety of conditions and exposures. In addition to the Duke oxygen toxicity study in humans, there are laboratory studies currently underway to evaluate the effect of ketone esters on cold water performance (e.g., core temperature, hand temperature, dexterity, and diver performance), hypoxia mitigation, and a variety of physical performance parameters. Beyond diving-specific applications, long-range studies that assess the health effects of sustained ketosis are underway and will provide a better understanding as to how the ketogenic diet and repetitive dosing of exogenous ketones impact long-term health and performance.
Dr. Dawn Kernagis is a research scientist in the area of human performance optimization and risk mitigation for operators in extreme environments, such as those working undersea, at altitude, and in space. Her team’s current research efforts are funded through several DoD agencies and the NASA Translational Institute for Space Health.
Dawn came to IHMC from Duke University Medical Center, where she was an American Heart Association Postdoctoral Fellow and funded by the Office of Naval Research (ONR) to identify mechanisms and potential therapeutic targets for acute brain injury. She completed her PhD at Duke University as ONR Undersea Medicine’s first Predoctoral Award recipient.
Dawn is a technical diver and has managed numerous underwater exploration, research, and conservation projects around the world since 1993, including the deep underwater exploration of Wakulla Springs and surrounding caves. Dawn was inducted into the Women Divers Hall of Fame in 2016, and is a Fellow of The Explorers Club. In 2018, she received the Undersea and Hyperbaric Medical Society’s Young Scientist Award. She loves traveling, playing piano, and spending as much time outdoors and on the water as possible.
The Thought Process Behind GUE’s CCR Configuration
GUE is known for taking its own holistic approach to gear configuration. Here GUE board member and Instructor Trainer Richard Lundgren explains the reasoning behind its unique closed-circuit rebreather configuration. It’s all about the gas!
By Richard Lundgren
Header photo by Ortwin Khan
Numerous incidents over the years have resulted in tragic and fatal outcomes due to inefficient and insufficient bailout procedures and systems. At the present time, there are no community standards that detail:
- How much bailout gas volume should be reserved
- How to store and access the bailout gas
- How to chose bailout gas properties
Accordingly, Global Underwater Explorers (GUE) created a standardized bailout system consistent with GUE’s holistic gear configuration, Standard Operating Procedures(SOP), and diver training system. The system was designed holistically; consequently, the value and usefulness of the system are jeopardized if any of its components are removed.
Bailout Gas Reserve Volumes
The volume of gas needed to sustain a diver while bailing from a rebreather is difficult to assess, as many different factors impacts the result— including respiratory rate, depth and time, CO2 levels, and stress levels. These are but a few of the variables. All reserve gas calculations may be appropriate under ideal conditions and circumstances, but they should be regarded as estimates, or predictions at best.
The gas volume needed for two divers to safely ascend to the first gas switch is referred to as Minimum Gas (MG) for scuba divers. The gas volume needed for one rebreather diver to ascend on open-circuit during duress is referred to as Bailout Minimum Gas (BMG). The BMG is calculated using the following variables:
Consumption (C): GUE recommends using a surface consumption rate (SCR) of 20 liters per minute, or 0.75 f3 if imperial is used.
Average Pressure (AvP or average ATA): The average pressure between the target depth (max depth) to the first available gas source or the surface (min depth)
Time (T): The ascent rate should be according to the decompression profile (variable ascent rate). However, in order to simplify and increase conservatism, the ascent rate used in the BMG formula is set to 3 meters/10 ft per minute. Any decompression time required before the gas switch (first available gas source) must be added to the total time. One minute should be added for the adverse event (the bailout) and one minute additionally for performing the gas switch.
BMG = C x AvP x T
Note that Bailout Minimum Gas reserves are estimations and may not be sufficient! Even though catastrophic failures are unlikely, other factors like hypercapnia (CO2 poisoning) and stress warrants a cautious approach.
Decompression bailout gas volumes are calculated based on the diver’s actual need (based on their decompression table/algorithm), and no additional reserve is added.
It should be noted that GUE does not endorse the use of “team bailout,” i.e. when one diver carries bottom gas bailout and another diver carries decompression gas based on only one diver’s need. A separation or an equipment failure would quickly render a system like this useless.
Common Tech Community Rebreather Configuration
- Backmount rebreather (note side mount rebreathers are gaining in popularity)
- Typically, three-liter oxygen and a three-liter diluent cylinder on board (each hold 712 l/25 f3)
- Bailout gas in one or more stage bottles which could be connected to an integrated Bailout Valve (BOV).
Containment and Access
Rather than carry bailout minimum gas (BMG) in a stage bottle, which is typical in the rebreather diving community, GUE has designed its bailout system as a redundant open-circuit system consisting of two 7-liter, 232 bar cylinders (57 f3 each) that are integrated into the rebreather frame, and called the “D7” system, i.e. D for doubles, 7 for seven liter. Note that GUE has standardized the JJ-CCR closed-circuit rebreather for training and operations.
These cylinders, each with individual valves, are linked together using a flexible manifold. This system holds up to 3250 liters of gas (114 f3), of which only about 10% is used by the rebreather as diluent. Hence, close to 3000 liters (106 f3) is reserved for a bailout situation. This gives a tremendous capacity and flexibility in a relatively small form factor for dives requiring additional gas reserves (when direct ascent is not possible or desirable).
The following advantages were considered when designing the bailout system:
- The D7 system is consistent with existing open-circuit systems utilized by GUE divers. A bailout system that is familiar to the user will not increase stress levels, which is important. A GUE diver will rely on previous experience and procedures when most needed.
- The system contains the gas volumes needed according to the GUE BMG calculations as well as the diluent needed for a wide range of dive missions.
- The system is fully redundant and has the capacity to isolate failing components, like a set of open-circuit doubles and still allowing full access to the gas.
- The overall weight of the system is less, compared to a standard system with an AL11 liter (aluminum 80 f3) bailout cylinder. In addition, it contains 800-900 liters/20-32 f3 more gas available for a bailout situation compared to the AL11 liter system. Weight has been traded for gas.
- The system does not occupy the position of a stage bottle which allows for additional stages or decompression bottles to be added.
- If the ISO valves on each side were closed, the flex manifold can be removed and the cylinders transported individually while still full.
Bailout gas can be accessed quickly by a bailout valve (BOV), which is typically configured as a separate open-circuit regulator worn on a necklace, consistent with GUE’s open-circuit configuration. However, some GUE divers use an integrated BOV. After evaluation of the situation, while breathing open-circuit from the BOV, the user can transition to a high-performance regulator worn on a long hose if the situation calls for it.
The long hose is carried under the loop when diving the rebreather. The chances of having to donate to another GUE rebreather diver is low, as both carry redundant bailout. Still, GUE maintains that the capacity to donate gas must be present. The process is more likely to involve a handover of the long hose rather than a donation.
Still, if needed, such a donation is made possible by either removing the loop temporarily or by simply donating the long hose from under the loop.
Bailout decompression gasses are carried in decompression stage bottles. If more than three bottles are needed, the bottles that are to be used at the shallowest depths are carried on a stage leash (i.e. a short lease that clips to your side D-ring to carry multiple stage bottles). Maintaining bottle-rotation techniques and capacity through regular practice is important and challenging, as this skill is rarely used with the rebreather.
Bailout Gas Properties
The choice of bailout gas is extremely important, as survival may well depend on it. It is not only the volume that is important, the individual gas properties will decide if the bailout gas will be optimal or not. As the D7 system contains both the diluent and bailout gas, both gasses share the same characteristic. The following gas characteristics must be considered when choosing gas:
The equivalent (air) gas density depth should not exceed 30 meters/100 ft or 5.1 grams/liter. This is consistent with the latest research by Gavin Anthony and Simon Mitchell that recommends that divers maintain maximum gas density ideally below 5.2 g/l, equivalent to air at 31 m/102 ft, and a hard maximum of 6.2 g/l, the equivalent to air at 39 m/128 ft. You can find a simple gas density calculator here.
Ventilation is impaired when diving, due to several factors which increase the work of breathing (WOB); when diving rebreathers, the impairment is even more so. High gas density, for example, when diving gas containing no or low fractions of helium, significantly decreases a diver’s ventilation capacity and increases the risk of dynamic airway compression. CO2 washout from blood depends on ventilation capacity and can be hindered if a high-density gas is used. The impact of density is very important, and the risk of using dense gases is not to be neglected. Note that this effect is not limited to deep diving. Using a dense gas as shallow as 30 meters/100 ft reduces a diver’s ventilation capacity by a staggering 50%.
The (air) equivalent narcotic depth should also not exceed 30 m/100 ft, or PN2=3.16. Rebreathers and emergency situations are complex enough without further being aided by narcosis.
The PO2 should be limited to allow for long exposures. GUE operating standards call for a maximum PO2 for bottom gases of 1.2 atm, a PO2 of 1.4 for deep decompression gases, and a PO2 of 1.6 for shallow decompression gases. GUE recommends using the next deeper GUE standard bottom gas for diluent/bailout when diving a rebreather in combination with GUE standard decompression gases.
Bailout gasses are not chosen in order to give the shortest possible decompression obligation. They are chosen in order to give the best odds of surviving a potentially life-threatening situation.
GUE’s D7 bailout system is flexible and contains the rebreather’s diluent as well as bailout gas reserves needed for a range of different missions. The familiarity the system, along with the knowledge that they are carrying ample gas reserves, gives GUE divers peace of mind. Choosing gases with properties that will aid a diver in duress while dealing with an emergency completes the system.
GUE did not prioritize the ease of climbing boat ladders or reducing decompression by a few minutes. These are more appropriately addressed with sessions at the gym, combined with finding aquatic comfort. Nothing prevents a complete removal of the entire system at the surface if an easy exit is needed.
Founder of Scandinavia’s Baltic Sea Divers and Ocean Discovery diving groups, and a member of GUE’s Board of Directors and GUE’s Technical Administrator, Richard Lundgren has participated in numerous underwater expeditions worldwide and is one of Europe’s most experienced trimix divers. With more than 4000 dives to his credit, Richard Lundgren was a member of the GUE expeditions to dive the Britannic (sister ship of the ill-fated Titanic) in 1997 and 1999, and has been involved in numerous projects to explore mines and caves in Sweden, Norway, and Finland. In 1997, in arctic conditions, he performed the longest cave dive ever carried out in Scandinavia. Richard’s other exploration work has included the 1999 filming of the famous submarine, M1, for the BBC; the side scan sonar surveys of the Spanish gold galleons outside Florida’s Key West in 2000; and the search for the Admiral’s Fleet, an ongoing project that has already led to the discovery of more than 40 virgin wrecks perfectly preserved in the cold waters of the Swedish Baltic Sea.
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