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Introduction: Recreational freedivers typically perform repeated dives to moderate depths with short recovery intervals. According to freediving standards, these recovery intervals should be twice the dive duration; however, this has yet to be supported by scientific evidence. Methods: Six recreational freedivers performed three freedives to 11 metres of freshwater (mfw), separated by 2 min 30 s recovery intervals, while an underwater pulse oximeter measured peripheral oxygen saturation (SpO2 ) and heart rate (HR). Results: Median dive durations were 54.0 s, 103.0 s and 75.5 s (all dives median 81.5 s). Median baseline HR was 76.0 beats per minute (bpm), which decreased during dives to 48.0 bpm in dive one, 40.5 bpm in dive two and 48.5 bpm in dive three (all P < 0.05 from baseline). Median pre-dive baseline SpO2 was 99.5%. SpO2 remained similar to baseline for the first half of the dives, after which the rate of desaturation increased during the second half of the dives with each subsequent dive. Lowest median SpO2 after dive one was 97.0%, after dive two 83.5% (P < 0.05 from baseline) and after dive three 82.5% (P < 0.01 from baseline). SpO2 had returned to baseline within 20 s after all dives. Conclusions: We speculate that the enhanced rate of arterial oxygen desaturation across the serial dives may be attributed to a remaining ‘oxygen debt’, leading to progressively increased oxygen extraction by desaturated muscles. Despite being twice the dive duration, the recovery period may be too short to allow full recovery and to sustain prolonged serial diving, thus does not guarantee safe diving. [ABSTRACT FROM AUTHOR]

Introduction: This study compared the thermal balance of spinal cord injured (SCI) divers and able-bodied (AB) divers during recreational cold-water dives. Methods: Ten divers (5 AB, 5 SCI) in matched pairs dived in a shallow lake (temperature 6°C) for 30 to 36 min wearing 5 mm ‘Long John’ neoprene wetsuits. A gastrointestinal temperature radio pill recorded gastro-intestinal temperature (Tgi) prior to, immediately after and at 5, 10, 15, 30, 60, 120 min post-dive. Subjective ratings of temperature perception were recorded concomitantly using a visual analogue scale (VAS). Results: No difference between SCI and AB divers in Tgi before the dive was observed (P = 0.85). After the dive, SCI divers cooled significantly more than AB at all measured time intervals (P < 0.001). Post dive, the mean maximum fall in Tgi during the recovery phase in SCI divers was 0.85°C (SD 0.20) and in the AB group was 0.48°C (0.48). In addition, there was greater individual variation in SCI divers compared to AB divers. There were no statistically significant differences in temperature perception between the groups either before or at any time after the dives. Conclusions: In contrast to AB divers, divers with SCI were unable to maintain Tgi during short shallow dives in 6°C water and their temperatures fell further post-dive. The reduction in Tgi was not reflected in the subjective ratings of temperature perception by the SCI divers. The study was too small to assess how the level of spinal injury influenced thermal balance. [ABSTRACT FROM AUTHOR]

Introduction: Divers can make adjustments to diving computers when they may need or want to dive more conservatively (e.g., diving with a persistent (patent) foramen ovale). Information describing the effects of these alterations or how they compare to other methods, such as using enriched air nitrox (EANx) with air dive planning tools, is lacking. Methods: Seven models of dive computer from four manufacturers (Mares, Suunto, Oceanic and UWATEC) were subjected to single square-wave compression profiles (maximum depth: 20 or 40 metres' sea water, msw), single multi-level profiles (maximum depth: 30 msw; stops at 15 and 6 msw), and multi-dive series (two dives to 30 msw followed by one to 20 msw). Adjustable settings were employed for each dive profile; some modified profiles were compared against stand-alone use of EANx. Results: Dives were shorter or indicated longer decompression obligations when conservative settings were applied. However, some computers in default settings produced more conservative dives than others that had been modified. Some computer-generated penalties were greater than when using EANx alone, particularly at partial pressures of oxygen (PO2) below 1.40 bar. Some computers 'locked out' during the multi-dive series; others would continue to support decompression with, in some cases, automatically-reduced levels of conservatism. Changing reduced gradient bubble model values on Suunto computers produced few differences. Discussion: The range of possible adjustments and the non-standard computer response to them complicates the ability to provide accurate guidance to divers wanting to dive more conservatively. The use of EANx alone may not always generate satisfactory levels of conservatism. [ABSTRACT FROM AUTHOR]

Introduction: Dive computers are used in some occupational diving sectors to manage decompression but there is little independent assessment of their performance. A significant proportion of occupational diving operations employ single square-wave pressure exposures in support of their work. Methods: Single examples of 43 models of dive computer were compressed to five simulated depths between 15 and 50 metres' sea water (msw) and maintained at those depths until they had registered over 30 minutes of decompression. At each depth, and for each model, downloaded data were used to collate the times at which the unit was still registering "no decompression" and the times at which various levels of decompression were indicated or exceeded. Each depth profile was replicated three times for most models. Results: Decompression isopleths for no-stop dives indicated that computers tended to be more conservative than standard decompression tables at depths shallower than 30 msw but less conservative between 30-50 msw. For dives requiring decompression, computers were predominantly more conservative than tables across the whole depth range tested. There was considerable variation between models in the times permitted at all of the depth/decompression combinations. Conclusions: The present study would support the use of some dive computers for controlling single, square-wave diving by some occupational sectors. The choice of which makes and models to use would have to consider their specific dive management characteristics which may additionally be affected by the intended operational depth and whether staged decompression was permitted. [ABSTRACT FROM AUTHOR]

Rebreather divers use LED-based head-up displays (HUD) as a primary display and warning device for the partial pressure of 02 in the breathing loop. Such devices are usually mounted on the mouthpiece of the rebreather in the field of vision of the diver. LED-based HUDs are simple devices and can be designed so that they are easy to understand but have limited information content. Few alphanumeric or graphical screen-based HUDs have been developed in the past. Connecting such a device to a rebreather requires cable links, which divers dislike, and increases the risk of entanglement. State-of-the-art wireless data transmission uses ultrasonic waves or lowfrequency electromagnetic waves; the former is not silent, and the latter achieves only very low data transmission rates of a few bytes per second and does not meet the antimagnetic standards required by military divers. The present paper describes a novel HUD system that incorporates a simple LED-based primary HUD along with an advanced secondary head-up diving computer with a micro organic LED screen. An optical infrared data transmission system is used to transmit all rebreather relevant data from the primary to the secondary device. One prototype of the system was manufactured and successfully tested in the laboratory according to relevant European standards as well as during several dives in fresh and sea water. [ABSTRACT FROM AUTHOR]

Recreational rebreathers are increasingly popular, and recreational divertraining organizations now routinely offer training for rebreather diving. Few rebreathers on the market, however, fulfill the criteria of a dedicated recreational rebreather. These remain based on traditional sensor technology, which may be linked to rebreather use having an estimated 10 times the risk of mortality while diving compared with open circuit breathing systems. In the present work, a new recreational rebreather based on two innovative approaches is described. Firstly, the rebreather uses a novel sensor system including voltammetric and spectroscopic validation of galvanic p02 sensor cells, a redundant optical p02 sensor, and a two-wavelength infrared pC02 sensor. Secondly, a new breathing loop design is introduced, which reduces failure points, improves work of breathing, and can be mass fabricated at a comparatively low cost. Two prototypes were assembled and tested in the laboratory at a notified body for personal protective equipment before both pool and sea water diving trials. Work of breathing was well below the maximum allowed by the European Normative. These trials also demonstrated that optical p02 sensors can be successfully employed in rebreathers. The pC0M2 sensor detected pC02 from 0.0004 to 0.0024 bar. These new approaches, which include a new concept for simplified mechanical design as well as improved electronic control, may prove useful in future recreational diving apparatus [ABSTRACT FROM AUTHOR]

The article presents a preliminary study on solid-state electrolyte sensors for rebreather applications. Prototypes of zirconium dioxide and micro solid-state electrolyte oxygen and carbon dioxide sensors were examined for their suitability in rebreathers. The response times to a step variation of pressure were estimated. The study concluded that a major drawback is the high power consumption required to heat the sensors to high temperatures.

The article presents the results of a study on the development of an apnea dive computer which can be worn by divers. According to the authors, the computer can measure and display transcutaneous oxygen saturation, heart rate, plethysmographic pulse waveform, depth, time, and temperature during breath-hold dives. They add that the device is equipped with Microsoft Excel or Open Office software to process all measured data into a comma-separated-values. Other features of the device are mentioned.

The article presents a report by Arne Sieber, Antonio L'Abbate and Remo Bedini that features a rebreather controller that can be used for the safety of the rebreather diver. It notes that this rebreather controller offers true sensor-signal validation which allows efficient and reliable detection of sensor failure. It notes that an elecrtronic closed-circuit rebreather diving system contains components that may fail which are three oxygen sensors, a microcontroller and a solenoid valve, and this validation system contains additional two solenoids.

The article focuses on an oscillometric, automatic digital blood pressure (BP) measurement device designed to measure underwater arterial blood pressure. The device is composed of analogue and digital electronics in a lexan housing, a cuff and a solenoid for inflation of the cuff. Measurements of blood pressure (BP) were taken using the device and were compared from those obtained using manual and automated methods. The article also discusses the principle design of the BP module, signal acquisition board and measurement techniques.