2007, Piran, Slovenia

Diving Physiology
HYPERVENTILATION PRIOR TO SUBMARINE ESCAPE: A METHOD
OF REDUCING DECOMPRESSION RISK?
Mikael Gennser
Department of Defence Medicine, Swedish Defence Research Agency,
Centre for Environmental Physiology, Karolinska Institutet, Stockholm, Sweden
Contact person: mikaelge@foi.se
INTRODUCTION
The rapid pressure changes during submarine escape (SubEsc) imposes a particular
breathing pattern on the escapers, which causes an expiratory hypoventilation during
compression and an expiratory hyperventilation during ascent. The concomitant
carbon dioxide changes cause the cerebral blood flow to change in such a manner that
nitrogen uptake in the brain is enhanced and wash-out is reduced, possibly increasing
the risk of decompression sickness in the central nervous system.
HYPOTHESIS
A short period of hyperventilation prior to the submarine escape would reduce the
peak cerebral blood flow during the deep part of the dive profile.
METHODS
To simulate the cardio-respiratory effects of SubEsc subjects (n = 8) were asked to
follow a breathing pattern that mimicked the gas exchange during real SubEsc, as the
subjects were immersed to the neck in water. End tidal gas pressures and expired and
inspired volumes were measured. Blood flow velocity in the median cerebral artery
was monitored via a Doppler probe placed over the right temple. Hyperventilation
was performed during lowering of the subjects into the water (30 s) and SubEsc
compression was simulated by breath hold (20 s) during simultaneous arm work.
During the ascent phase the respiratory pattern during SubEsc was simulated by
continuously increasing tidal volumes.
RESULTS
In the hyperventilation trials the average (SD) maximum blood flow velocity during
simulated SubEsc was reduced by 18.6 (11.0) % (p