Ausarbeitung - Stoffgebiet Ökologie

KURSUS DES ÖKOLOGISCHEN STOFFGEBIETES

Ausarbeitung „Umweltmedizinisches Thema“

Venous gas bubbles while flying in civil aircraft 3 hours after diving

Referring to recommendations of major diving associations (8-11), an interval of 24 hours between the last dive (with a maximum dive depth of 40 metres) and the next aircraft flight should be observed. This is to avoid side effects of diving like venous gas bubbles or the Caisson Sickness.

The National Defense Research Institute and Department of Environmental Medicine of Sweden undertook a study examining the amount of detected venous gas bubbles after no-stage compression dives to 15 or 39 meters and a simulated flight at altitudes of 1,000 to 3,000 m 3 hours after the dive (1). The results of the study also indicate the risk for ordinary SCUBA-divers enterering airliner aircraft, whose cabins are pressurized to a maximum altitude of 2,500 m (75kPa).Inflight cases of decompression sickness are reported after preceded SCUBA-diving (2, 3) – some studies recommend a minimum interval of 22 hours between no.stage decompression diving and flying in airliners (2, 4). The Manula of Civil Aviation Medicine forbids aviation duties for at least 24 hours after SCUBA diving (5).

10 healthy male SCUBA divers or military helicopter pilots were used for 31 experiments. Study regulations prescribed normal food intake, avoidance of heavy physical exercise and abstention from alcohol the day before the experiment. An interval of at least 1 week between the different experiments as well as a ban of flying or diving during the week before an experiment was to avoid recurrence of decompression sickness. A hyper – and hypobaric chamber served to simulate dives to 15 or 39 meters and flights to altitudes of 1,00 to 3,000 m (6). The venous gas bubbles entering the right side of the heart were detected by precordial Doppler ultrasound technique.

Each of the 10 subjects was exposed to simulated dives to 39m (490kPa) for 10 minutes and, with at least a week interval, to 15 m (250 kPa) for 100 minutes. The dives allowed no-stage compression – the compression time was 2-3 min to 39 meters and 1-2 min to 15 meters. The decompression rate was 18 m/min (equals the speed of expired air rushing in bubbles up to the surface). After a 3 hours-break the subjects returned for the hypobaric exposure corresponding to 3,000 meters altitude (70 kPa). The decompression to 3,000 meters took about 1 minute. The observation period lasted 2 hours. Subjects with bubbles at at least half of the cardiac periods were exposed to simulated flights to 2,000 meters (80 kPa) in similar experiments at least one week later. Finally, subjects who developped bubbles at this altitude at at least half of the cardiac periods were exposed to simulated flights to 1,000 meters (90 kPa) at least a week later. After the observation period and recompression to surface level pressure, the subject had hyperbaric oxygen treatment at 220 kPa for 30 minutes as an extra safety measure.

During the 20 flights for 2 hours at 3,000 m, intracardial gas bubbles could be detected in 60% with a mean début of 16 ± 13 minutes. Bubbles in less than half of the cardiac periods were registered in 35%, bubbles in all of the cardiac periods in only 10% with a mean onset of 53 ± 18 minutes. Subjects examined at 2,000 m flying altitude showed bubbles in 6 of the 7 experiments after 2 – 55 minutes; those tested at 1,000 meters showed a positive result in 2 of the 4 experients with a mean début after 29 ± 21 minutes. There was no case where the beginning of intracardial bubbles appeared after an observation period at altitude of more than 55 minutes.

When comparing the appearance of bubbles after shallow (15 m) and deep (39 m) dives, it was noted that bubbles appeared in the flights at 3,000 m in 90% after diving to 15 meters for 100 minutes and only in 30% after diving to 30 meters for 10 minutes. The onset of bubbles seemed to be faster after shallow dives than after deeper dives. Thus, an occasional bubble signal (with the great majority of cardiac periods free of bubbles) was registered with a mean onset of 12 ± 7 minutes after 15 meters/100 minutes dives and mean 28 ± 21 minutes after 39 metres/10 minutes dives. Whereas the débuts of bubble signals at at least half of the cardiac periods were detected after 7 - 44 minutes after shallow dives and after 21 minutes following the deeper dives.

Discussing the results of this study, it first of all is important to know that the has no decompression sickness been described while flying at such low altitudes as 3000 meters without preceding dives. Usually, a cabin altitude of 8000 – 9000 meters (gas supersaturation quotient about 3:1)is required for symptoms to appear without diving before the flight. On the other hand, described cases of decompression sickness in airline aircraft, preceded by SCUBA-diving, indicate that silent venous gas bubbles during similar conditions may not be uncommon (f. ex. during return charter flights or during general aviation with SCUBA activity before departure). This is confirmed by the great amount of bubbles at 1,000-3,000 meters in the present study - occuring at a pressure quotient of 2,8:1 (15 meters dive, 1,000 meters flight altitude) up to a qoutient of 7:1 (39 meters dive, 3,000 meters flight altitude).

Then, intracardial gas bubbles appearing at flight altitudes of 1,000 – 3,000 meters are most likely due to a release of preexisting bubbles already formed in the tissues in connection with the ascent from the prior dive. This agrees with bubble appearance during the first minutes of the flight. This phenomenon was also noted in a similar study with a 9,000 meter – cabin altitude and up to 24 hours between diving and flying.(7). During decompression to an altitude of 9,000 meters (31kPa), the already smaller bubbles must expand to a somewhat similar size as the previous bigger bubbles do, during decompression to only 1,000 – 3,000 meters (90 – 70 kPa). A longer interval than 3 hours should, therefore, have caused the bubbles in the present study to shrink to a size that gives rise to only a small risk of decompression sickness upon decompression to only 3,000 meters flight altitude.

Passive movements of the extremities have been shown to release decompression gas bubbles from the tissues to the circulation – this corresponds to a finding in an earlier study (6) as well as the results of the present study, where subjects moved their arms every minute, after which bubbles could often be detected. After some of the experiments, the subjects had also to do several knee-bendings after the compression to surface level pressure. In some cases without any bubbles during the 2 –hours observations period bubbles could be detected during knee-bending, whereupon bubbles sometimes appeared for several minutes. One could therefore be quite sure that, if no bubbles appear during knee-bending, no bubbles should exist during the hypobaric pressure either. Passive movements of extremeties have also been recommended as a technique for a better prediction of decompression sickness with the appearance of intracardial bubbles much earlier than without these movements (7).

Interestingly, the greater amount of bubbles appear after longer-lasting shallow dives than after short, deeper dives. This is because of the greater amount of dissolving gas, especially in the fat tissues during the longer-lasting dives.Therefore, there is a greater risk of flying after long-lasting shallow dives, even when using ordinary decompression tables.

Concluding, a great number of venous gas bubbles have been found during flying with cabin altitudes of airliners or general aviation aircraft 3 hours after ordinary no-stage decompression dives. Although there were only very vague and doubtful symptoms of decompression sickness in the present study, the probability of such symtoms must be considered high with the number of gas bubbles found. This might be especially valid in elderly and fat persons and possibly in women. Therefore, a safe interval between ordinary SCUBA-diving and such flying seems to be more than 3 hours.

REFERENCES:

1. Balldin, U. I.. Venous gas bubbbles while flying with cabin altitudes of airliners or general aviation aircraft 33 hours after diving. Aviat. Space Environ. Med. 51(7):649-652, 1980

2. Furry, D. E., E. Reeves, and E. Beckman. 1967. Relationship of SCUBA diving to the development of aviators´ decompression sickness. Aerospace Med. 338:8225-828.

3. Miner, A. D. 1961. SCUBA hazards to air crew. Business Pilots Safety Bulletin 61-204. Flight Safety Foundation, New York.

4. Edel, P. O. J. J. Carroll, R. W. Honaker, and E. L. Beckman. 1969. Interval at sea-level pressure required to prevent decompression sickness in humans who fly in commercial aircraft after diving. Aerospace Med. 40:1105-11110.

5. Manual of Civil Aviation Medicine. 1976. ICAO:Dooc 8984-AN/895 Addendum No. 2:III-3-10.

6. Balldin, U. I., and P. Borgström. 1976. Intracardial bubbles during decompression sickness to altitude in realtion to decompression sickness in man. Aviat. Space Environ. Med. 2:113-116.

7. Balldin, U. I. 1978. Intracardial gas bubbles and decompression sickness while flying at 9,000 m within 12-24 hours of diving. Aviat. Space Environ. Med. 49:1314-1318.

8. PADI: Professional Association of Diving Instructors, Hettlingen/Switzerland

9. Barakuda – International Aquanautic Club, Essen/Germany

10. CMAS: Confédération Mondiale des Activités Subaquatiques, Rome/Italy

11. VDST: Association of German Sport Divers, Moerfelden/Germany