Suunto Fused™ RGBM Copyright © 2012 by Suunto Oy

THE PATH TO FUSED™ RGBM

At the heart of every Suunto dive com- Over the next decade, the algo- With the launch of the Suunto HelO2 puter is an algorithm that calculates rithm was further improved to in- in 2009, Suunto introduced a new decompression for a dive, called the re- crease diver safety. These include, for decompression model, the Suunto duced gradient bubble model (RGBM). example, voluntary safety stops, asym- Technical RGBM, also developed with Relentlessly pursuing ever safer models metric on and off -gassing, as well as Dr. Wienke. This algorithm included all for divers of all types, Suunto continues modifi cations based on the work of previous implementations and added to push for RGBM perfection. A storied Dr. Merrill P. Spencer. new features for handling helium gas. history full of science, development, and underwater experience lies within During this time, the dive community Since the late 1980s, Dr. Wienke had every Suunto dive computer. was still seeing too many accidents. been working at the Los Alamos To address these problems, Suunto Nuclear Laboratory on the so-called This document explains detailes of our launched the Suunto Vyper in 1999 ‘full’ RGBM. This development was tar- algorithm, and how the new Suunto which featured the new Suunto Re- geting the needs of deep divers and FusedTM RGBM has been developed. duced Gradient Bubble Model (RGBM). military personnel carrying out diffi - cult dives. Suunto's work on decompression The Suunto RGBM was developed in models for dive computers spans over co-operation with Dr. Bruce Wienke. The new Suunto Fused™ RGBM com- three decades. A pioneer in the fi eld, The new algorithm could account for bines the benefi ts of Suunto’s Techni- Suunto’s modelling has adopted the diver behaviors which increase health cal RGBM and the ‘full’ RGBM, bringing latest scientifi c know-how and theo- risks. These behaviors include multiday the benefi ts of both to recreational ries from leading experts. diving, reverse dive profi les and short divers and technical divers. surface intervals. Suunto’s fi rst dive computer was the None of this development would have Suunto SME ML (1987). Given the When deep stops (Pyle stops) became been possible without the pioneering technology available at the time, it a proven benefi cial method for de- work of Dr. Wienke. Despite the range was essentially an electronic dive tab- compression, they were added to the of dive computers off ered by Suunto le. This was obviously not adequate, Suunto D9 and Vytec DS (2004) as a for most any type of diver, he has and soon Suunto’s Ari Nikkola im- voluntary notifi cation. played a vital role in the practical im- plemented the Buhlman model for plementation of his theories. Suunto dive computers.

1987 1999 2009 Suunto’s rst dive computer Suunto Vyper Suunto HelO2 Suunto SME ML Suunto Redudec Gradient Technical RGBM Bubble Model (RGBM) Implementation of Developed with Buhlman model Developed with Dr. Bruce Wienke Dr. Bruce Wienke

1990’s 2004 2012 Algorithm improvement: Voluntary Suunto D9 Suunto Fused™ RGBM safety stops, asymmetric on and Vytec DS o-gassing Developed with Dr. Bruce Wienke Dr. Merrill P. Spencer

Suunto has been working together with Dr. Bruce Wienke for well over a decade. Dr. Wienke is a Program Manager in the Nuclear Weapons Technology Simulation And Computing Offi ce at the Los Alamos National Laboratory (LANL), with interests in computational decompression and models, gas transport, and phase mechanics. He is the developer of the Reduced Gradient Bubble Model (RGBM), a dual phase approach to staging diver ascents over an extended range of diving applications (altitude, nonstop, decompression, multiday, repetitive, multilevel, mixed gas, and saturation).

"RGBM is the most realistic model in science. The parameters are correlated with real data of thousands of dives which makes it good physics, and the data is validated and correlated. I have been working with Suunto since the 90’s and Suunto’s progression from Suunto RGBM to Technical RGBM and now to Suunto Fused™ RGBM is a very natural one. The new algorithm is a supermodel that covers all types of diving." - Dr. Bruce Wienke

DIvING AND YOUR BODY Diving is a great activity with the The pressure change under water can potential for one-of-a-kind experi- aff ect sensitive areas such as your ears ences you can only get in an aquatic and sinuses. Discomfort in the ears environment. Our land-loving bo- when taking off in an airplane is also dies, however, can react negatively to felt just diving down to the bottom of diving if we are not careful. Whenever a pool that is three meters deep. you enter the water, be aware how your behavior before, during and But the most signifi cant impact is on after the dive can aff ect your health. your circulatory and respiratory systems. These need to be taken seri- Under water your body is being pus- ously as they can lead to major health hed in from all sides. This added pres- risks. To understand and avoid these sure changes how your body func- risks, we need to fi rst have a look at tions. Some of the changes you notice, the world of gases. like with breathing. Other changes 10 meters you may not immediately feel, but the eff ects can cause serious damage to your body, and even lead to death.

Ambient pressure Ambient pressure increases much faster underwater because water is denser than air. Ten meters down is already twice the 20 meters pressure at the surface.

A WORLD OF GASES

In the physical world, we are most gas. The oxygen dissolved in water, It is these gases that can cause so familiar with three phases of matter for example, is what allows fi sh and much trouble for divers. Even oxygen – gas, liquid and solid. Certain ele- other aquatic life to breathe. which our bodies thrive on at surface ments and compounds are naturally pressures can become toxic under in one state or the other at a given Our bodies are also full of dissolved certain conditions. temperature. gases. Some of them, like oxygen, our bodies actively use. Other so- Nitrogen and helium are the main Typically we think of water being called inert gases like nitrogen and culprits when we look at the number merely a liquid, but that is only true helium, are not used by our bodies, one risk divers are concerned about: for pure H2O (between 0-100 C). Both but are carried in blood and tissues decompression sickness (DCS). liquids and solids naturally contain nonetheless.

Gas exchange in alveoli When air enters the lungs, it goes through a maze of smaller and smaller tubes until it reaches tiny sacs called alveoli. Woven into the walls of these sacks are very fi ne, almost transparent, capillaries.

DECOMPRESSION SICKNESS The amount of gases dissolved in When we go down to sea-level and There are different stages and forms our bodies depends on the ambi- then under water, we increase the of DCS. Symptoms can range from ent pressure around us. Each gas has pressure on our bodies, allowing minor joint pain and skin irritation to a specific partial pressure, and the more gas to be carried by blood and severe nerve damage and death. For combined pressures of the gases in tissues. Again, to equalize the pres- a diver with DCS, the symptoms may our bodies stays in equilibrium with sures, our bodies take on more dis- commence while still underwater, or our environment. solved gas from the air we breathe. it may take several hours after sur- This is called on-gassing. facing. In some cases the symptoms Your body is fully saturated with may not show for several days. Most gases at the elevation where you If we come up from a dive too quickly cases are treatable with, for example, typically reside. If you hike up a (dropping ambient pressure), the recompression chamber treatment mountain, air pressure drops, so your natural off-gassing mechanisms are (hyperbaric oxygen treatment). body can hold less gas. Your tissues overloaded. Like the bubbles you see are at this point supersaturated rela- when you pop open that soda, the tive to the new ambient pressure. To dissolved gas in our bodies comes get back to equilibrium, our bodies out of solution too fast, forming bub- release gas through diffusion and bles which can ultimately cause DCS. breathing. This is called off-gassing.

DECOMPRESSION MODELLING

A century ago, our understanding of DCS was fairly rudimentary and there 100 were no good ways to ensure divers avoid it. In the early 20th century, 90 work by John Scott Haldane helped lay the foundations for future decom- 80 pression models which divers could 70 follow to minimize risks of DCS. Halftime 60 During a dive, tissues saturate at different rates. This is determined by the 50 blood flow to the tissue in question. 40 The brain, for example, has a very good blood supply, and is classified 30 as a “fast” tissue, whilst joints have 20 poor blood supply and are rated as “slow” tissue. There are several 10 others in between. % 0 The length of time that it takes for a 0 5 10 15 20 25 30 tissue to reach a 50% saturation level at a given depth is called the tissue Time halftime and is usually measured in minutes. However, the saturation Tissue half time rate does not remain linear. A tissue reaches 50% saturation relatively For all practical purposes, it takes 6 halftimes for a given tissue to reach full saturation. quickly. After that, the rate slows. This graph represents a 5 min tissue. It takes another five halftimes for a given tissue to, theoretically, reach saturation.

Tissue Compartment The Suunto Fused™ RGBM divides the human body into 15 theoretical tissue compartments according to the rate at which each tissue group on- or off-gasses. These halftimes range from 1 to 720 minutes (2.5 min) Blood (10 min) Spinal cord (40 min) Skin (120 min) Muscle (480 min) Joints

In decompression modelling, tissues Decompression models assign each compression model was incomplete are categorized into theoretical com- compartment a theoretical critical or because it assumed that off-gassing partments which share a common “maximum” pressure ratio (meaning only happens via diffusion. Today's halftime. Haldane used six compart- the difference between tissue and research has revealed that off-gas- ments. The Suunto Technical RGBM ambient pressures) above which sing also happens via perfusion. uses nine compartments, and the bubbles form. This ratio, called the latest model, the Fused™ RGBM, uses M-Value, changes at depth. Further advances in technology al- 15 compartments. lowed scientists to get a more accu- Haldane’s model proved to be effective rate view of how gases behave in the It is important to understand that a and showed that the tissue halftime body. What they discovered was that compartment is not a specific tissue theory was correct. His model assumed not all gas bubbles cause DCS. but a group of tissues with theoreti- that the mechanisms for on and off- cal properties. Real tissues are excep- gassing were equal. Off-gassing was tionally complex and varied, making it considered simply the reverse of on- nearly impossible to know their exact gassing and happened at the same properties. rate. Although correct, Haldane’s de-

NOT ALL BUBBLES ARE EQUAL

With the use of Doppler technology bubble either expanding or collap- Bubbles form much easier in human and later electron microscopes, sci- sing is determined by a range of fac- tissues than in pure liquids, 200 times entists discovered that the body can tors. These factors include the surface easier, in fact. Careless diving prac- have “silent” bubbles that are present tension of the bubble, the pressure tices are exceptionally risky because throughout blood and tissues. They within the bubble and the ambient of this. are called silent because they do not pressure relative to the bubble. cause DCS. Some of these are small A process called nucleation is the rea- microbubbles while others are full- A diver who completes multiple dives son behind the rapid bubble forma- blown, easily detected bubbles. And within a given day or even over a tion in tissues. The human body has yet neither kind necessarily causes number of days may have a build-up what are called micronuclei, micro- DCS symptoms. of silent bubbles. The accumulation scopic pockets caused, for example, of bubbles may lead to a higher risk by friction between tissue surfaces Although it is not yet clear the exact of DCS. It is also known that micro- or changes in tissue dimensions (like relationship between these and DCS- bubbles can cause longer-term prob- muscle contractions). These micro-nu- causing bubbles, studies have shown lems such as neurological damage. clei can fi ll with gas and act as seeds that higher microbubble counts for bubbles. increase the likelihood of DCS and This is particularly relevant to profes- other illnesses. sional divers such as instructors, who It is unknown how many micronuclei complete many of repetitive dives, are in the body at any given time, but it What has also been established is often with many ascents in one trai- appears heavy exercise creates more. that once formed, these bubbles ning session. Microbubbles can col- Studies have also shown that rapid in- are unstable. They have an ability to lect inside the alveoli, obstructing crease in pressure crushes micronuclei attract dissolved gas from surroun- and slowing off -gassing. and reduces the overall count. Regular ding tissues and the likelihood of a exercise also reduces overall count.

Microbubbles obstruct blood fl ow Microbubbles in the capillaries around the alveoli may obstruct the blood stream and inhibit off - gassing.

Microbubbles block nerves By shutting off the blood fl ow, microbubbles can also cause tissue death, for example in the sensitive retina of the eye. The synapse is the junction between a nerve terminal and the nextneurone in a long chain of neurones. Microbubbles can interpose themselves in these junctions causing long term neurological damage by preventing electrical transmissions.

SUUNTO Fused™ RGBM IN PRACTICE Earlier Haldanian dissolved gas mo- bubbles and prevent any pre-existing sentation of what is happening in rea- dels assumed that in order to decom- bubbles from growing by applying an lity in your body during (and after) a press, a diver should ascend as quickly appropriate ascent protocol. dive. It has the ability to adapt to a as possible to a shallow depth to maxi- wide variety of situations with little or mise off-gassing. However, by quickly The Suunto Fused™ RGBM is a state of no manual input from the diver. reaching that shallow depth, the diver the art algorithm for managing both may have already formed microbubb- dissolved gas and free-gas (micro- les. bubbles) in the tissues and blood of a diver. At the very least, these microbubles could potentially obstruct off-gas- It is a significant advancement over sing and at the worst, may have al- the classical Haldane models, which ready caused some tissue damage. do not predict microbubbles or micro- Therefore, there is a need to keep the nuclei. The advantage of the Suunto micronuclei from forming into micro- RGBM is a more accurate repre-

120 The Suunto RGBM uses exponential formula for calculating the uptake of 100 Exponential curve inert gases such as nitrogen Because of the added safety from proven 80 RGBM factors, Suunto now uses symmetric gas elimination. Additional safety is pro- vided by the RGBM model developed by Dr. 60 Bruce Wienke. This combination allows divers to maximize dive time without decompression obligations. If decompression is needed, (zero subscript) value (%) subscript) value (zero

0 40 the Suunto model calculates the most efficient decompression possible.

20 Percentage of M Percentage

0 0 10 20 30 40 50 60 70 80 90 100 110 120 140

Dive time (min)

The RGBMs address a number of robubble build up and adverse dive pression model, so it is not critical to diving circumstances that have not profiles in the current dive series. It will understand their theoretical back- been considered by previous de- further modify these calculations ac- ground. The key thing to remember compression models, adapting to: cording to the personal setting that a when diving is that microbubbles will diver can select. always form. • Continuous multiday diving • Repetitive dives with short Depending on the diver’s behaviour There are no actual supersaturation surface intervals during the dive and the personal set- limits above or below which bubbles • Dives deeper than the previous ting, the Suunto RGBM model adjusts would not form. The aim of decom- dive the M-values downwards in order to pression models is to prevent forma- • Rapid ascents which produce protect the diver from the effects of tion of bubbles. Starting already with high microbubble build up the generated free-gas. the Suunto Technical RGBM, Suunto’s modelling adds an additional layer of The algorithm automatically adapts its Note that M-values are only relevant protection by managing existing mic- predictions of both the effects of mic- to the calculations for the decom- robubbles and other silent bubbles.

1.2

0.8 F1 Repetitive dives F2 Reverse Pro le F3 Multiday 0.6

0.4

0.2 Per unit Reduction Per

0 0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 1020

Surface Interval Time (min)

Repetitive dives - F1 - Microbubbles mainly Reverse Profile - F2 - In any series of dives, Multi-day- F3 - Pre-existing micro-nuclei are occur in the venous circulation during the sur- the Suunto Fused™ RGBM calculates that excited into a higher energy state by diving face intervals between dives. They are washed diving deeper than the previous dive stimu- (compression and decompression). They are with the blood to the pulmonary filter (lungs), lated mic-ronuclei growth. During the surface thought to return to their normal energy level where they may reduce the surface area and interval following such an event, Fused™ RGBM over time scales of days. The Suunto Fused™ inhibit off-gassing. This effect will continue recalculates future decompression obligations RGBM multi-day factor calculates adjustments until the production of microbubbles ceases based upon the depth excess of the last dive for a surface interval period of 100 hours. The and the bubbles in the lungs dissipate. This compared to the one before it. combination of the correction factors is app- continues for about three hours after surfacing. lied to the Suunto M-values, which affects the The Suunto Fused™ RGBM algorithm calculates required decompression obligation. correction factors to cope with this issue.

Some diving patterns cumulatively add a higher risk of DCS, such as dives with short surface intervals, repetitive dives deeper than earlier ones, multiple ascents (and descents) and substantial multiday diving. Dive alarm Depending on the circumstances, If a Suunto RGBM model predicts an excess of micro- the automatic adjustments built bubble build up after the dive, a flashing warning sign into the Suunto RGBMs may: will prompt the diver to extend the surface interval. • Add Mandatory Safety stops • Reduce no-decompression stop times • Increase decompression stop times

Safety/stop (recommended)

Gradient Bubble Stop (mandatory)

Ascent rate violations Depth

Dive time

Automatic adjustments in Suunto's RGBM algorithms Recommended and mandatory safety stops are added depending on the actual profile of the real dive with possible ascent rate violations.

CONTINUOUS DECOMPRESSION Traditionally, since Haldane’s 1908 Off-gassing in the leading fast tissues the ceiling but above the floor, the tables, decompression stops have will be slow at or near the floor be- diver is still decompressing, although always been deployed in fixed steps cause the outward gradient is small. slower than optimal, and provides an such as 15m, 12m, 9m, 6m and 3m. Slower tissues may be still on-gassing additional buffer to minimise the risk This practical method was intro- and given enough time, the decom- that waves will lift the diver above the duced before the advent of dive pression obligation may increase, ceiling. Also, the continuous decom- computers. However, when ascen- in which case the ceiling may move pression curve used by Suunto pro- ding, a diver actually decompresses down and the floor may move up. vides a much smoother and a more in a series of more gradual mini- natural decompression profile than steps, effectively creating a smooth Suunto RGBMs optimise these two the traditional “step” decompression. decompression curve. contradictory issues through a combination of a slow ascent rate and Suunto dive computers have a unique The advent of microprocessors has continuous decompression curve. It feature of displaying not only the allowed Suunto to more accurately all comes down to proper control of decompression ceiling, but also the model the actual decompression the expanding gas during an ascent. decompression floor. As long as you behaviour. A continuous decompres- This is why all Suunto RGBMs use a are below the “floor”, i.e. still on-gas- sion curve is included in the Suunto maximum ascent rate at 10m/mi- sing, an upward arrow is displayed. Fused™ RGBM’s working assumption. nute, which has proven over the Once above the floor, the leading years to be an effective protective tissues start off-gassing, and the During any ascent involving decom- measure. upward arrow disappears. The op- pression-stops, Suunto dive compu- timal decompression occurs in the ters calculate the point at which the The decompression floor repre- ceiling zone, which is displayed by control compartment crosses the sents the point at which the RGBM is both upward and downward ar- ambient pressure line (that is the seeking to maximise bubble com- rows. If the ceiling depth is violated point at which the tissue’s pressure is pression, while the decompression a downward pointing arrow and an greater than the ambient pressure), “ceiling” is maximising off-gassing. audible alarm will prompt the diver and off-gassing starts. This is referred to descend back to the ceiling zone. to as the decompression floor. Above The added advantage of having a de- this floor depth and below the cei- compression ceiling and floor is that ling depth is the “decompression it recognises that in rough water, it zone”. The range of the decompres- might be difficult to maintain the sion zone is dependent on the dive exact depth to optimise decompres- profile. sion. By maintaining a depth below

0 Continuous decompression

3 The unique continuous decompression used Traditional Fixed Stops by Suunto computers provides a smooth Suunto Continuous and more natural decompression curve 6 Decompression Curve compared to traditional predetermined ceiling depths.

9 If preferred, the diver may still decompress at traditional fixed depths.

12 Depth (m)

Time

Microbubbles In this illustration we can see a cross-section of a capillary delivering blood to muscle tissue.

Friction between the muscle cells create micronuclei which attract dissolved gas from the surrounding tissue, forming microbubbles that disturb the blood flow and slow off-gassing. Microbubbles are present after almost any kind of dive.

YOUR PERSONAL DECOMPRESSION MODEL

Decompression models can be con- Aggressive models, on the other The Personal Modes refl ect the fact servative or aggressive. Generally hand, increase the potential health that personal health and behaviour speaking, conservative means safer. risks of a dive. For recreational divers, have an impact on your DCS sus- In practice it means that a dive at a an aggressive model allows more ceptibility. Any of the following can given depth is shorter due to the de- time at depth, but may signifi cantly potentially increase your risk for DCS: compression obligation (the no de- increase the risk of DCS. compression time is short). • BMI that is considered obese The Suunto Fused™ RGBM adapts Conservative also means that the its predictions of both the eff ect of • Poor physical fi tness time the diver needs to spend on de- microbubble build up and adverse compression is longer. So for recrea- dive behavior in the current series • Age, particularly for divers over tional divers, a conservative model of dives. The default setting for the the age of 50 means less time in the water in order Suunto Fused™ RGBM is to use a to avoid decompression require- compromise (P0 setting) between • Fatigue, for example from over ments. For technical divers, however, conservative and aggressive. With exercising, strenuous travel, or conservative means more time in the Personal Modes, you can select lack of sleep the water because of the longer de- gradually more conservative or more compression requirements imposed aggressive calculations. • Cold water exposure, which can during ascent. cause the blood vessels at the body’s extremities to close down and maintain the body’s core Personal temperature adjustment Condition Description value • Exercising after a dive increases the potential for bubble forma- Ideal conditions, excellent tion P-2 physical fi tness, highly experienced with a lot of dives in the near past Progressively less • Strenuous activity during a dive, conservative which can increase blood fl ow, Ideal conditions, good physical bringing additional gas to tis- P-1 fi tness, well experienced with sues dives in the near past • Tight fi tting equipment, which P0 Ideal conditions Default can slow off -gassing P1 Some risk factors or conditions exist Progressively more • Dehydration, which effects Several risk factors or conservative circulation and can slow down P2 conditions exist off -gassing

P-2 15 P-1 P0 P1 20 P2

30 Depth (metres) 35 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Dive time (min)

Example: Eﬀ ect of personal adjustment setting to bottom time on a 30 m dive

BEST OF BOTH WORLDS WITH SUUNTO Fused™ RGBM Over 30 years of development and To meet the needs of both recrea- to go further with your dive hobby. thousands upon thousands of test tional diving and more demanding You can use the same Suunto dive dives have resulted in what is today technical or deep diving, Suunto to- computer including Fused™ RGBM the Suunto Technical RGBM. The real gether with Dr. Bruce Wienke created in the more challenging dives. breakthrough in this model came the new Suunto Fused™ RGBM. when Suunto added the ability to the Advanced divers performing techni- behaviour of microbubbles. The Suunto Fused™ RGBM seamlessly cal or deep dives can be sure their combines the benefits of the Suunto Suunto dive computer using Suunto Divers who properly follow the Technical RGBM with Dr. Wienke’s Fused™ RGBM is going to give them instructions of a dive computer that latest full RGBM for deep dives. With- the most optimum dive profile pro- utilises the Suunto Technical RGBM out any input from the diver, the viding them a slow continuous ascent are certain to reduce the risks of Fused™ RGBM automatically switches from depth leading to shorter total diving incidents. This is accomplished between these two models to effec- decompression time. The Fused™ without requiring a more conserva- tively manage the risks of DCS. RGBM will guide advanced divers tive decompression model for most using the most sophisticated of dives. Under normal conditions, the transi- RGBMs available today, taking full tion is linear between depths of 30m advantage of the combined experi- The Suunto Technical RGBM, despite to 45m. If there is little to no helium ence and development of Suunto the name, is ideal for recreational in the breathing gas, the transition and Dr. Wienke. diving, maximizing bottom time range starts up to 10 meters deeper while minimizing ascent time. How- depending on the gas mixture. Suunto's testing team has been ever, beyond a certain depth, the thoroughly testing the Suunto complexity of DCS risks increase sig- For recreational divers, the new Fused™ algorithm with over 1000 nificantly, requiring a different mo- Fused™ RGBM not only maximizes actual dives making sure that delling approach. bottom time while minimizing ascent divers around the world can time, but it also means your Suunto enjoy the benefits of this new and dive computer is ready when you are advanced algorithm.

Suunto Technical RGBM Wienke's "full" RGBM 100 % Suunto Fused™ RGBM at work Linear transition between the two algorithms starts at 30 m and ends at 45 m when diving on gas mixes containing > 20% of Helium. On air/nitrox the transition begins at 40 m and gas ends at 55 m. 0 % 0 30 45 Depth (m)

20 RB: Suunto Fused™ RGBM 25 RB: Buhlmann; ZH-L16C; GF: 20/80 30 RB: Buhlmann; ZH-L16C; GF 10/100 35

75 Depth (meters) 80

00:00 00:05 00:10 00:15 00:20 00:25 00:30 00:35 00:40 00:45 00:50 00:55 01:00 01:05 01:10 01:15 01:20 01:25 01:30

Time

RGBMs an decompression In this example there are SuuntoTM Fused on red compared with Buhlman algorithm with different gradient factors. You can see that Suunto Fused TM algorithm provides a slow continuous ascent leading to shorter total decompression time.

Suunto Fused™ RGBM for rebreather diving

Whilst implementing and testing adjustment from Suunto Technical Set points are the constant PO2 limits Bruce Wienke’s Full RGBM for dive RGBM to ‘full’ RGBM allows for one set for the dive. It is usual that you computers, Suunto took on massive algorithm to be suitable for both. would have a low and a high set task of implementing and testing point. Typical values for the low set constant PO2 mode at the same There are several important dis- point are 0.7bar and 1.3bar for the time. Now using Fused™ RGBM and tinctions between diving open high set point but of course this is rebreather together is possible! Just circuit and closed circuit systems. dependent on the type of dive you define the PO2s and set points of When diving open circuit the gas are conducting. The low set point is your dive computer to match those you breathe always consists of the usually used at the beginning of the of your rebreather, and you will get same mixture regardless of depth dive until a predetermined depth is the benefits of the latest decompres- (air = 21% oxygen etc) and it is the reached where a switch to the high sion researchon your wrist and on partial pressure of gas that changes set point is made. The high set point your dive. with depth (Daltons Law). In open is normally used for the deeper phase circuit nitrox diving we are used to of the dive and for decompression The development of the FusedTM monitoring the PO2 (partial pressure to optimize your decompression re- RGBM algorithm has for the first of Oxygen) as it varies with depth. quirement. During a dive it is pos- time in Suunto’s history allowed the However, a significant advantage sible to swap between set points. implementation of a CCR constant of diving a rebreather is that you PO2 mode. This means that the al- can select a constant PO2 for vari- Suunto FusedTM RGBM allows the use gorithm is now suitable for shallow ous stages of your dive to ensure of constant PO2 mode in the CCR recreational dives through to 150m the most optimal decompression mode and together with the plan- CCR (Closed Circuit Rebreather) dives. obligation. The rebreather does this ning software will allow you to plan The decompression requirements for by having a fixed PO2 and as your and conduct dives using a Closed Cir- these two types of diving vary signifi- depth varies the gas composition cuit Rebreather. cantly and the introduction of Fused you are breathing is altered to main- RGBM with its transitional zone of tain the set PO2.

Variation of Oxygen Fraction in an OC (21%) dive against a CCR dive with set points of 0.7 and 1.3 bar with switch 80

% O2 CCR 30 OC 20

0 0 10 20 30 40 50 Depth / m

Oxygen % Variation of OC dive and CCR dive illustrating how gas changes in constant PO2

TERM LIST

Conservative (vs. aggressive): in M-value: a mathematical expression Supersaturation: a principle pro- decompression modelling, conserva- of the supersaturation limit of give perty of human tissues allowing tive is used to indicate a calculation tissue compartment used in decom- them to temporarily hold more dis- that aims to minimize the risks of pression algorithms solved gas than ambient pressure DCS; an aggressive calculation allows theoretically dictate; in other words, longer no-deco time and/or shorter On-gassing: the process by which this allows us to survive when our in- deco but increases risk of DCS. the human body accumulates dis- ternal body pressure is not equal to solved gases through the blood cir- ambient pressure Control compartment: the tissue culation and tissues compartment that dictates the as- Supersaturation limit: the theo- cent profile of a given dive because Off-gassing: the process by which retical pressure ratio between tissue of its on and off-gassing properties the human body releases dissolved pressure and ambient pressure above gases back into the surrounding en- which the off-gassing process is over- Decompression illness (DCI): a term vironment loaded and DCS bubbles (likely) form used to refer to illness cause by DCS or lung trauma (pulmonary baro- Partial pressure: the pressure a gas Tissue compartment: a theoretical trauma) would have if it alone filled a given group of tissues that share similar gas volume; the partial pressure of a gas saturation properties Decompression sickness (DCS): an determines its behavior in a mixture illness caused by gas bubbles in the with other gases or liquids human body, the symptoms of which range from minor aches and pains to Perfusion: the process of delivery of death blood to a capillary bed in the biolo- gical tissue. Tissues like the heart are Diffusion: the process by which dis- considered overperfused and receive solved gas is transferred from one lo- more blood than would be expected cation to the next through the effect to meet the metabolic needs of the of pressure differences tissue. In the case of skin, extra blood flow is used for thermoregulation. In Microbubble: microscopic bubbles addition to delivering oxygen and that are not visible with ultrasound or inert gases, the blood helps dissipate Doppler, yet can affect the likelihood heat by redirecting warm blood close DCS by slowing off-gassing; they can to the surface where it can cool the also have long-term health impacts, body through sweating and thermal for example, in the nervous system dissipation. Micronuclei: microscopic cavities Pressure gradient: the difference throughout the human body that between tissue pressure and ambi- act as bubble seeds by attracting dis- ent pressure solved gas

Suunto Fused™ RGBM www.suunto.com 14