diving-concepts is a diving research facility of the University Clinic Innsbruck and combines scientific and clinical research in the field of decompression physiology and diving medicine for the benefit of divers. The special feature of this research unit lies in the interdisciplinary embedding of science and medicine in diving practice. This will improve existing decompression strategies and integrate new insights into future exploration dives. The divers of Protec Sardinia contribute to this research by collecting data and conducting measurements during their dives.

Diving-concepts was founded by Dr. Frank Hartig and Dr. Andrea Köhler in 2006. Frank is a cardiologist and intensive care physician and head of the emergency department of the University Clinic Innsbruck. Besides, he is an experienced diving medicine physician and technical diver. Andrea is a molecular biochemist and the scientific leader of diving-concepts. She is a renowned scientist in the field of decompression research and is doing contract research in military and civil areas. She is also an experienced cold water technical diver. Both are forensic experts for diving accidents and diving related fatalities.

Exploration cave divers are exposed to several risks. Besides the technical and logistical challenges, medical issues become substantial although there is lack of knowledge about diving in such extreme environments. Due to the long and multilevel dive profiles decompression becomes very complex and experimental. In addition, the use of rebreathers and thus the high oxygen partial pressure enhances the risks of pulmonal and cns oxygen toxicity. Also hydration, nutrition, exhaustion and fatigue are problems which has to be faced during such long dives.

In July 2019, Toddy performed an exploration cave dive in the Utopia cave of the Supramonte Carst System in Sardinia. To our knowledge it was the longest single entry cave dive with 5 km penetration depth, a complex multilevel dive profile with a maximum depth of 125 m and duration of 11 hours. To prepare Toddy optimally for this extreme exposition, he was preconditioned and treated with several known and experimental methods before, during and after the dive by the team of diving-concepts. To enable this exploration with the maximum of safety, the planning, preparation and realization of this project was challenging. Since only the first part of the dive profile was known, the decompression plan had to consider many variants to get Toddy back safely. Moreover, profound pulmonary, circulatory and cardiac changes are induced by immersion in water. Toddy had to tolerate and compensate for changes in pressure, temperature, nutrition and fatigue for many hours and diving at night. Finally, Toddy’s lung and central nervous system had to cope with the constant high oxygen partial pressure for hours.

The Utopia cave dive was a multilevel dive with MOD 120 m, non linear decompression and a dive time of estimated 10-14 h. The penetration distance in the cave system was about 5 km.
To our knowledge, such a profile has not been dived yet and pushes the human organ systems to its limits. As we know, it is not the MOD but the long multilevel exploration time, which is the challenging part. Compared to bounced MOD 200 m dives with relatively short bottom times and a straight ascending profile without yoyo`s, this dive is much more complex and needs a totally different management. Based on the latest findings in decompression and diving physiology research, such a dive and decompression can be done with an acceptable calculated minimum risk.
The settings of gradient factors in the different depth segments, the adaption of M-values and ascend rates during the multilevel yoyo ascend is quite complex and may break new grounds. Also the adaption of the CCR setpoint remains crucial and is a compromise between rapid decompression and oxygen toxicity. Other strategies such as OPT (Oxygen precondition time) before the descend are performed to minimize the microbubble formation and to reduce AHS (active hydrophobic spots). In the habitat the decompression is measured with live echocardiography to evaluate the progress of decompression and to set the optimum gas breaks.

The lungs are presumably the crucial target organ of such a dive. The pulmonary oxygen toxicity is enormous. Due to the high and long oxygen exposition, atelectases (collapsing areas of lung tissues with impeded gas exchanges) will form, as well as shunting mechanism and bronchiologic spasms. Also, the gas diffusion capacity will decrease and change during the decompression. Very important is the elimination of water immersion in the habitat, which will improve significantly decompression. Other important factors are gasbreaks, medications and a special designed breathing mask (flow safe II) to minimize atelectases. The decompression in the habitat can be performed without a regulator in the mouth, which is very comfortable after hours of regulator diving with scooter.

Hypercapnia is a problem during the habitat decompression. Measurements confirmed the fast CO2 increase in the habitat that has to be prevented by special absorbing soda curtains from submarine technologies. Medicine, technique and equipment are working hand in hand to allow a non-regulator breathing in the habitat.
In such long range dives we found a significant change in tissue/cellular shifts of blodd ions (potassium, saline, magnesium and phosphate) that can trigger cardiac arrhythmias. A special substitution with supplementation on the fly, during decompression in the habitat and post surfacing is therefore prepared and we borrow the tremendous experience from our austrian elite long range ahtletes (Peeroton is the leader of high quality supplemental substitution of elite athletes).
The cardiac aerobic endurance has also to be stable and resilient against influence of immersion effects. Especially the right heart function is challenged by long range underwater activities. Therefore, this complex training needs quite a few months of professional training.

The commonly known CNS toxicity in such a dive is also a risk factor, that is controlled with special designed breathing gases and adaptations of the diveplan together with special medications (anticonvulsiva). Here we can refer to pharmacologic results of former studies and research projects of our team, where divers were exposed up to 10 bar pO2.

The cardiovascular system is challenged to its limit during this extremely long dive. In the spiroergometry an excellent performance grade and an optimal maximum oxygen consumption uptake rate must be guaranteed. Due to the hours of inwater immersion combined with physical stress we also expect blood pressure peaks that are a big burden to the cardiovascular system and the lungs. In our first stress testing at the institute for cardiovascular research for elite athletes the results were good but not good enough for a project like the Utopia exploration. Further special training was required to master this 10-15 h dive. Especially the coping of hypercapnia remains a critical point. Thus, a special breathing muscle training program was started, which has been tested by the US Navy Seals for several years now. The spiroergometric data allows also a relatively exact calculation of scrubber consumption of the rebreather systems.

Eating, drinking and calory balance is crucial to keep the metabolic system in balance. Several 24 h diving experiments showed that after 16 hours a critical point is reached, where metabolic decompensation can occur. This must be be prevented with special prepared food und substances that can regain also mental focus to the dive. New designed non-coffein contenting supplementals increase the psychological concentration and prevent severe tiredness. Their compatibility and ability to pass through the blood brain barrier has to be tested in the next dives. An additional antioxidative support will be started days before the dive, not too early to prevent biochemical counter compensations.

Decompression in such dives is influenced by a lot of other factors (besides gradient factors or tissue compartments) that are not represented in the physical decompression algorhythms. Intravasal blood lipid status as well as the coagulation system are important and are influencing decompression. Also the immune system and the antioxidative system can trigger microbubble formation and those systems can harm or protect the outcome of overall decompression of the tissues. Also the changes of blood cells and proteins that are induced by tiredness and sleep-deprivation have to be calculated, which trigger not only CNS toxicity with the risk of cerebral convulsions.

Thermic effects such as central hypothermia have to be minimized not only by the fact, that a decrease of just 0,5°C stimulates the coagulation system that in turn influences decompression. Special designed heating systems are used in this project. On the other side we have to take care of solar exposition before and after the dive. This can be tricky, because the start time of the dive is in the night and the planned surfacing is in the afternoon, where we have temperatures of about 40°C.

A rescue plan for emergency inwater recompression (IWR) in the mobile habitat had to be organized and trained as well as a rescue plan in case of even more severe emergencies like respiratory or cardiovascular failures. A helicopter transport to the next hyperbaric chamber in Cagliari had to be planned and we had our friends from DAN Italy on stand by to arrange such transports. The ascending time had to be in daylight, otherwise the helicopter could not fly to Cagliari. Another problem was the possible emergency situation of other divers than Toddy (the support divers). A special emergency plan for those support divers was independently prepared and guaranteed by other team members. Special designed breathing devices with PEEP and NIV ventilations had been tested in the Tyrolean mountain lakes under pressure in the run-up of the exploration.