Smart MICROBUBBLE MANAGEMENT SMART MICROBUBBLE MANAGEMENT 2 ADAPTIVE COMPUTERS UWATEC dive computers have long included the Bühlmann ZH-L8 ADT mathematical model that allows the computer to adapt to actual diver behaviors and environmental conditions. The name of the model was derived from ZH Zurich where the model was developed, L8 refers to the number of body tissue groups that the model considers and ADT is short for `adaptive'. With an adaptive model, if a diver exceeds the prescribed ascent rate, works too hard, or is exposed to really cold water, the dive computer may ask the diver to complete a compensation decompression stop. Another advantage of the adaptive model is that it allows UWATEC dive computers to more accurately predict the remaining gas requirements on deep dives and it provides more accurate monitoring of the CNS loading for Nitrox divers. UWATEC has now proven that divers who conduct repetitive dives even within the standard no decompression limits produce microbubbles. Microbubbles may be a precondition for the formation of larger bubbles that can lead to decompression illness. Microbubbles usually present no visible symptoms to the diver, but may cause permanent damage. Divers with a PFO (Patent Foramen Ovale - a hole between the two chambers of the heart) are particularly susceptible. With two additional letters, the Bühlmann adaptive model has been expanded to be called the ZH-L8 ADT MB. This stands for microbubble, because the UWATEC Smart can be programmed for microbubble suppression. Smart PRO Wrist Smart PRO Console Smart COM The Smart COM displays the cylinder pressure, calculates and displays the Remaining Bottom Time (RBT), and warns when RBT is less than 3 minutes. · · · · · · · Displays tank pressure - psi (bar) Remaining dive time at current depth (RBT) User adjustable tank reserve warning Low air warning Quantity of air used RBT is less than 3 alarm RBT less than 0 alarm GAS CONSUMPTION On deeper dives, divers need to carry sufficient gas reserves to ascend and complete any necessary decompression stops. The Smart COM displays a Remaining Bottom Time field, which is an estimate of the time remaining at the current depth until an ascent must be commenced. Once the ascent commences, the Smart COM has already included a prediction of the gas reserves necessary to ascend at the prescribed ascent rate and complete the necessary decompression stops. The baseline for the RBT is the "tank reserve value" which can be set via Smart TRAK in 50 PSI increments between 300 and 1750 PSI. An RBT of 0 means that if an ascent is commenced at that time and carried out at the correct ascent rate, respecting all decompression stops, the diver will be on the surface with approximately the tank reserve left in the tank. The calculation is based on the diver's current rate of gas consumption, temperature and the current tank pressure and starts 1.5 minutes after the start of a dive. It is updated every 4 seconds. The computer accurately modifies the Remaining Bottom Time according to variations in the diver's rate of breathing. If the diver is experiencing heavy exertion, then the RBT is reduced. If the diver is relaxed, then the RBT is extended. The accuracy of this calculation is due to the pressure sensor's ability to accurately measure a single breath of air. The accuracy is further enhanced because it considers the ambient temperature and air pressure is affected by ambient temperature variations. This is particularly useful for a diver who is diving through thermoclines. After a dive, the data from the Smart COM can be downloaded to Personal Computer with the Smart TRAK software that is included with the Smart COM. The actual rate of breathing is displayed in cft/min, as is the workload level. Also displayed is microbubble buildup and temperature. At the conclusion of a dive the Smart COM displays the "differential pressure". This value represents the gas that is consumed during the dive. Also displayed are any warnings that may have occurred throughout the dive, in this example both RBT and Workload warnings are displayed. SMART MICROBUBBLE MANAGEMENT 4 The Smart COM considers the effect that exertion has on the decompression schedule. When the lung symbol appears the diver should relax the breathing rate. · · High breathing rate alarm (High Air Consumption) Adaptive decompression model Bühlmann ZH-L8 ADT MB · CNS clock is adjusted by O2 uptake according to workload · · User adjustable air workload warning Workload is displayed in Smart TRAK WORKLOAD Some dive computer models assume an average workload throughout the dive. However, an unfit diver, for example, who is working hard at depth will breathe more heavily. Even fit divers sometimes find themselves working hard in situations such as swimming against a current or removing an anchor that is stuck under a rock. In such high workload circumstances the diver can absorb more nitrogen, particularly in the muscle tissue groups. This additional uptake of nitrogen, in turn, is exposing the diver to a greater risk of microbubble formation and the possibility of decompression sickness. The Smart COM understands that different divers have different levels of fitness and different levels of exertion on different dives. The Smart COM can actually influence a diver who is working hard, to reduce the level of exertion, by relaxing and breathing more slowly. The Smart COM can do this because it is accurately monitoring the diver's rate of air consumption and changes in the rate of air consumption. If a diver persists in working hard at depth the Smart COM may ask the diver to complete an additional decompression stop. With Smart TRAK the sensitivity of the breathing rate warning is adjustable according to the diver's level of fitness. With the Smart TRAK software that is supplied with the Smart COM, the sensitivity of the workload setting can be set by the diver according to their own level of fitness. Earlier mathematical models assumed a mean workload output of 50W. With the ZH-L8 ADT MB model, even at level 0, if workload is increased to 85W then on a 50ft (15m) dive the ascent time is increased from 30 to 60 mins. The Smart PRO and Smart COM include the effect of temperature on the decompression schedule and display both the ambient and water temperature. · · · · · Displays ambient temperature on the surface Measures and displays water temperature Includes temperature in decompression model Logs temperature (dive computer) Logs temperature (Smart TRAK) T E M P E R AT U R E The human body likes to maintain a core temperature of 98°F (37°C) and it has strategies such as shivering (involuntary muscle activity), to help maintain that temperature in cold situations. Diving in cold water causes vasoconstriction, i.e. a reduction of blood flow to arms and legs in favor of the main organs, in an attempt to conserve body heat. The skin is the tissue that is most affected by this. Vasoconstriction does not take place right away since the diver starts with a uniformly warm body. So, nitrogen absorption in the skin at first is normal. As the diver ascends and starts offgassing, vasoconstriction is now limiting the process. So, diving in cold water makes the diver more susceptible to microbubble build up in the skin tissues and the possibility of "skin bends". The Smart computer is constantly monitoring and displaying the ambient temperature and is considering the temperature in the calculation of the decompression schedule, with the objective of minimising skin bends. For example, in normal dives, the spinal tissue is usually considered as the first tissue to affect the decompression schedule. However, when it comes to diving in cold water the Smart considers that the skin is the most important tissue. As a consequence, for a diver in cold water, the Smart may suggest a shorter no-decompression schedule, or in the case of a decompression dive, longer decompression stops. A diver can view the whole temperature profile of a dive with the Smart TRAK software and a Personal Computer. On a cold water dive a fixed model advises a 28 minute ascent, whereas the ZH-L8 ADT MB advises a 48 minute ascent. On the second dive the skin tissues, which were the leading tissues at the end of dive 1, are already relatively cold at the beginning of the dive so they have a slower speed. Hence the smaller difference in total ascent time. SMART MICROBUBBLE MANAGEMENT 6 Smart can provide a visual warning to the diver to take an advisory level stop and reduce microbubble formation. SMART REDUCES MICROBUBBLES Divers who have long term exposure to microbubbles risk soft tissue damage. Examples of soft tissue include the brain, spinal tissues and the retina. Divers who are at risk include professional divers such as instructors and dive masters who typically do a lot of repetitive diving. Sport divers who conduct multiple repetitive dives over the duration of a dive holiday are also at risk from microbubble build up. Microbubbles don't produce visible symptoms and they can only be measured with the aid of a Doppler detecting device. This hand held device generates an ultrasonic signal that strikes a microbubble in a diver's body to reflect back a distinct chirping sound. This is recorded and the recordings are then analyzed. The more "chirps" that can be heard on a recording, the greater the incidence of microbubbles in a diver. As part of a major study DAN Europe "Doppler Scanned" divers from a substantial sample of 1058 dives within 30 minutes of each dive's conclusion. The participating divers were average open water divers, who conducted typical open water dives with a large range of depths and bottom times. DAN Europe discovered that in the case of repetitive dives 67% of all divers produced High Grade Microbubbles. This correlates with the DAN Diving Accident Reports of the last 15 years that show a relatively higher frequency of Decompression Illness after repetitive dives. Post dive Doppler monitoring of 1058 dives observed Doppler detectable microbubbles in 37% of all the monitored dives and 67% of the repetitive dives. Not only was there a higher incidence of microbubbles in repetitive dives, but there was a higher incidence of high bubble grade microbubbles - level 2 or higher on the Spencer Scale. · · · · · 6 microbubble suppression levels User adjustable microbubble suppression Integrates level stops and deco stops Total time to ascend includes level stop data Warns if level stop is ignored "Cascading" microbubble levels Surface warning of reduced microbubble suppression levels The above table demonstrates what sort of level stop profiles can occur for a diver on the second of two "repetitive" dives. The first dive is to 99 ft (30 m) for 16 minutes and the second dive follows a surface interval of 1 hour and 49 minutes and is also for 99 feet and 16 minutes. To demonstrate the likely level stops a diver could expect for the 2nd dive, at various levels of microbubble suppression, UWATEC Engineers "dived" 6 UWATEC Smart Dive Computers with no suppression for the first dive, while computers 2 to 6 were set at the 5 different levels of microbubble suppression on the second dive. At level 0 the 6 minute stop at 10 ft (3 m) is actually a decompression stop, which is mandatory. While this is actually displayed separately on the UWATEC Smart Dive Computer's screen, for convenience we have included this 6 minute stop in the final stops in the above table. · · · Cautions diver on high microbubble count Experiments with deeper stops at the conclusion of a repetitive dive were proven to reduce microbubbles by up to 61% and in some cases eliminated microbubble formation. So, for example, if a diver has done three dives in one day, if on all dives the diver considered doing a series of deeper stops prior to the conclusion of the dives, microbubbles were substantially reduced. A Smart Dive Computer can be programmed to suppress the formation of microbubbles according to the diver's actual diving circumstances. The diver selects the level of suppression required for the particular dive. The Smart Dive Computer then assesses the likely microbubble build up from the previous dives and recommends an advisory deeper stop or "level stop" to be completed prior to the conclusion of the last dive. A diver may manually select prior to the dive, 6 levels of suppression from level 0 where there is no suppression to level 5 where there is maximum suppression. Unlike decompression stops, which are compulsory, level stops are advisory. This is because the effects of microbubble formation are largely a long term condition, whereas decompression illness produces symptoms which require immediate treatment. If a diver ignores the recommended level stops by more than 5 ft (1.5 m), the Smart "cascades" down to the next microbubble level. UWATEC set up two series (one we ...