Unformatted text preview: As snorkel size increases, VD increases and it becomes more difficult to
maintain V A- B. Breath Hold Diving
As the skin diver descends, the air in the lungs is compressed 9 lung squeeze. When lung volume is compressed below residual volume 9 lung damage
occurs as blood is sucked from the pulmonary capillaries into the alveoli "Normal" maximal breath holding time after a maximal inspiration of ambient
air is approximately 50 - 60 seconds. The arterial P02 then drops to about 60 mm Hg and the arterial PC02 rises to 50 mm Hg. Hyperventilation prior to breath-hold diving can significantly extend the
breath-hold time. This is very dangerous due to the risk of blackout — loss of
consciousness in the water. Hyperventilate forcefully for one minute - can decrease PaC02 from normal value of 40 mm Hg to 15-20 mm Hg.
Normal PaOz = 100 mm Hg. Unconsciousness will occur when Pa02 decreases to approximately 30 mm Hg. Paradoxical drowning - Diver hyperventilates, holds breath, and dives down
to a certain depth 9 gases in lung are compressed and partial pressures are
increased 9 diver holds breath as long as possible and then starts to ascend 9
partial pressure of gases in lung decrease on ascent 9 Pa02 decreases below critical point 9 diver loses consciousness and drowns. ...
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- Fall '09