RTO MP-062 / HFM-050 - FTP Directory Listing - Nato

T-2
symptom debut, the rate of sequelae increased. Accordingly, stricken divers are rushed into
the recompression chamber, usually without sophisticated neurological examinations. Often,
the chamber attendant is not sufficiently trained to perform meticulous neurological
examinations or evaluate the results. Further, after pressurisation, light neurological
symptoms and signs may disappear, and avoid recognition during an examination at pressure.
Consequently, reports about the incidence of DCI II may be inaccurate.
The recent tragedy with the Russian submarine Kursk, illustrates the importance of paper 21.
Ideally, rescuees from a pressurised disabled submarine should be recompressed immediately
before slow decompression. However, sufficient pressure chamber capacity to take care of the
crew from a big submarine will most probably not be present at the scene. Accordingly, ample
amounts of oxygen breathing apparatuses should be available on board rescue vessels.
Intestinal application of inert gas-metabolising microbes, or intravenous injection of
perfluorocarbons, as presented in paper 22, is at present no operational issue, and will
probably not be so in the foreseeable future.
Deep blow-up of divers using self-contained heliox breathing apparatuses is rare, but caries a
high risk of fatality or serious permanent disability. Accordingly, adequate treatment
procedures are crucial. Continuous evaluation, and possibly improvement of treatment tables,
as discussed in papers 31-34, is thus an important operational issue for the alliance.
Hypobaric exposure
Eleven (24%) of the 46 presentations dealt with this issue, indicating the operational
importance of hypobaric DCI.
An air operation has analogies to an upward saturation diving excursion, since the crew in
both situations are saturated with inert gas. This may partly explain differences between DCI
in aviation and surface oriented bounce diving, where the diver avoids saturation.
The overview and conclusions given on this subject in the first Key Note speech are
important. Human physiology does not change fast, and safe cabin altitude is still thought to
be a maximum of 18,000 feet for extended flight. This is in accordance with Haldane’s
postulate that a pressure drop not exceeding one half of the original ambient pressure, should
be safe. However, altitude DCI has been observed below this altitude.
In paper 37 it is documented that venous gas emboli (VGE) formation occurs at cabin
altitudes that will be encountered by aircrew of future agile aircraft. However, one hour of
denitrogenation provided effective protection against DCI in resting subjects at 25,000 feet,
while extended exposure at that level without preoxygenation incurred a substantial risk of
developing DCI. Personnel at rest exposed to 30,000-35,000 feet were at risk even after prior
denitrogenation.
VGE has been observed as low as 15,000 feet, and exposure to 25,000 feet without
preoxygenation gave a DCI incidence of 88%, according to paper 40. Of operational
importance is also the observation that DCI risk is less with multiple short flights than with a
single continuous flight of equal duration. It is also interesting to note that the seriousness of
DCI symptoms is related to the prebreathing time, rather than to altitude. The alliance should
follow closely research regarding DCI risk in future combat aircraft while the crew perform
different workloads and breathe different gas mixtures.
Cabin pressurisation may effectively protect against altitude DCI. However, some Special
Operations Forces (SOF) missions, like high altitude airdrop, do not allow for the use of this
countermeasure. Further, restriction on post-flight physical activity, as practised after chamber
flights, is not applicable to SOF missions. The preliminary observation presented in paper 40,
that DCI was not observed in an exercise group after high altitude exposure, while one case of
DCI was observed in a resting group, is interesting. The final results of this investigation will
have operational implications for alliance operations, and should be followed closely.