B. Neubauer et al., MATHEMATICAL-MODEL FOR THE CALCULATION OF OXYGEN CONCENTRATIONS IN A CLOSED-CIRCUIT OXYGEN REBREATHING APPARATUS, Aviation, space, and environmental medicine, 68(8), 1997, pp. 722-725
Background: Closed circuit oxygen rebreathing diving apparatus are use
d by armed forces in special tasks because of their advantages of long
endurance, low noise and minimal gas escape. There is little knowledg
e about the administered oxygen concentrations in these systems. Close
d circuit oxygen rebreathing apparatus are also used as a first aid de
vice for the treatment of severe disorders. Because of similar constru
ctive components, these rebreathing apparatus are comparable to the Dr
ager LAR V model. Hypothesis: This study was conducted to measure the
oxygen concentrations in the LAR V and estimate the correlation betwee
n oxygen concentration and pre-breathing purges. Method: Subjects were
12 males who performed the pre-breathing procedure. The oxygen concen
trations in the breathing loop were measured after each purge. Results
: The oxygen concentrations depended on the volume of the apparatus' d
ead space, the total capacity of the divers breathing system respectiv
e to the volume of the breathing purges and the number of pre-breathin
g purges. The maximum oxygen concentration was reached after eight pur
ges (O-2 = 85%). An equation to estimate the oxygen concentration insi
de the LAR V and first aid rebreather was derived. Conclusions: The re
sults indicated that the present purging procedure (three purges) befo
re diving is normally not sufficient to remove the nitrogen totally fr
om the deadspace of the LAR V, the divers airways and lungs. Only a sm
all modification (six purges) is necessary to improve the safety of th
e diver in case of a diving apparatus malfunction during the mission p
rofile.