Schweizerische Zeitschrift fur Sportmedizin最新文献

For industrial saturation dives over 50 m, Heliox (He-O2) is now used routinely as respiratory gas mix. The decompression after such dives has been investigated thoroughly as well on the animal (minipig, monkeys) as on humans. Results show that for a given ascending speed, the number of bubbles detectable by the Doppler method in the bloodstream rises according to the maximal depth. The incidence of decompression accidents follows the same trend. This finding prompted us to adopt since 1979 slower decompression speeds. Moreover we modified the ascension profile, using henceforth a linear decompression in maintaining a constant speed for a given partial oxygen pressure. For our research program Hydra, we replaced in part Helium by Hydrogen in the respiratory gas mix. We were thus able to do the first hydrogen saturation decompression between 450 and 200 meters, during our Hydra V (1985) experiment. During our following diving research program Hydra VI (1986), 8 divers were decompressed under Hydreliox (H2-He-O2) mix from 500 to 300 m by eliminating hydrogen by chemical means. We used for this purpose a dehydrogenation apparatus developed by our engineering team. These decompressions took place without any difficulty and only a low number of bubbles detected. It is therefore possible to use decompression speeds for hydrogen and helium which are very similar. A confirmatory experiment on mice, where we exposed them to a 2000 m depth dive under Hydreliox (H2-He-O2), gave good results. This gives us the possibility, to perform gas exchange studies on small animals and to extrapolate the results to humans.

An estimation of the risk incurred through the use of digital decompression computers used by the diver must be based on comparisons with hyperbaric chamber tests. We compared the decompression indications displayed by different commercial devices to depth/bottom time profiles for which hyperbaric chamber experiments have given us the relevant information on types and frequency of decompression sickness.

Only recently have electronic instruments been introduced in sports diving. By using the capabilities of microcomputers, it became possible to develop diving computers, which replace the older mechanical devices in giving the necessary information for decompression routines. This article describes how the ALADIN diving computer has been developed and shows several mainly technical problems which arose during the development and production stages of this instrument.

We show that among the numerous complications which may arise during diving, two have to be considered very carefully, namely decompression sickness and arterial gas embolism, for if treatment is being done inadequately, these may lead to permanent disability. Diagnosis and treatment are described. In general, therapy is given in a hyperbaric chamber by pure oxygen, in a hospital with the relevant equipment. Nevertheless, it is of prime importance to give, already on the scene of the diving emergency, as soon as possible pure normobaric oxygen as respiratory gas.

Only ten years ago, divers from the Fédération française d'études et de sport sous-marins followed the GERS (French Navy) tables. Today this technique, designed for military purposes, mainly observation dives, has been discarded spontaneously by many sports divers. They prefer using professional divers' tables, as described in a french ordinance of 1974. These tables permit physical activities at the bottom. In cave diving, it now often happens that divers use respiratory gas mixtures based on helium. During surfacing, oxygen is added according to a modified U.S. Navy method. Consequently, the physician has sometimes difficulty in making out the true cause of a diving incident or accident. Moreover, certain divers do successive dives following two different table procedures. Others undertake rapid surfacing according to the now obsolete procedure of half-depth. Hence, time is now pressing that we think about this problem, in order to specify more clearly the safety standards.

We are confronted with a considerable failure rate in the treatment of neurological decompression accidents. Facing the relatively poor knowledge about the physiopathological mechanisms involved, we present results obtained with our own treatment procedures. It consists mainly of a maximized oxygen therapy. Our conclusive results can be explained in retrospect by the works of Leitch and Hallenbeck.

The relationship between tolerated high-pressure tissue nitrogen and ambient pressure is practically linear. The tolerated nitrogen high pressure decreases at altitude, as the ambient pressure is lower. Additionally, tissues with short nitrogen half-times have a higher tolerance than tissues which retain nitrogen for longer duration. For the purpose of determining safe decompression routines, the human body can be regarded as consisting of 16 compartments with half-times from 4 to 635 minutes for nitrogen. The coefficients for calculation of the tolerated nitrogen-high pressure in the tissues can be deduced directly from the half-times for nitrogen. We show as application the results of 573 simulated air dives in the pressure-chamber and 544 real dives in mountain lakes in Switzerland (1400-2600 m above sea level) and in Lake Titicaca (3800 m above sea level). They are in accordance with the computed limits of tolerance.

After a given time at bottom, different tissues become saturated to different extents with nitrogen. In diving back to the surface a hydrostatic decompression occurs first, followed by the desaturation process some time later. It is during this time interval that all important events are taking place, namely: either a monophasic desaturation, whereby inert nitrogen gas is given off at the alveolar capillary interface. or a biphasic desaturation takes place, giving rise to gas bubbles in the blood-stream as well as in the tissues. We may then encounter pathologies which are benign incidents or, worse, lead to decompression sickness grade II. Since Paul Bert dedicated his thoughts in 1878 to this problem, numerous authors tried to explain this time delay, for trying to suppress it would be entirely unrealistic. Unfortunately, mathematical reasoning has too often overshadowed physiological thinking in these matters. We also stuck to Haldane's concept of 1908, in incorporating Workman's improvements of 1965. This method is based on two main principles: 1. all calculations were done with several "tissues" in mind. Their anatomical boundaries are of no importance as, only their desaturation half-times are relevant. 2. a natural limit is given by the critical saturation-coefficient (CS). It expresses the ratio between the partial pressure of the dissolved gas and the reduction of hydrostatic pressure during ascent (given as pressure gradient). Through experience we were able to put up tables which were more and more safe, in examining foremost the CS ratio and the desaturation times of certain tissues. Several examples are given, the values of which are statistically highly significant, as they incorporate the results of more than 60,000 air dives.

The appearance of bubbles in the organism induces events which may lead to the symptom of decompression sickness. In order to detecting these bubbles and to attain a better understanding of their role, we investigated these problems in the mini-pork by using a measuring device based on the Doppler effect. The results show that any hyperbaric stress which oversteps a certain time or depth limit, gives rise to circulating bubbles in the venous system. We therefore developed a portable detector for humans, as well as a quotation method (KM code) for quantifying the different bubble loads. We thus could show that the appearance time for bubbles can be exceedingly long and that intra- and interindividual variability is very high. Bubbles detection is of predictive value and this factor has to be taken into account for possible neurologic injuries.