5
I Introduction
I
3 Calculation Model ZH-L8 ADT
3.1 Description
The Model ZH-L8 ADT (8 compartments with nomi-
nal half-time periods from 5 to 640 minutes) differs
considerably from other models by the consideration
of additional physiological processes:
1. Blood perfusion of the organs is not constant.
Skin and muscles in particular are subject to
considerable changes of blood perfusion
depending on temperature and workload. A
change in blood perfusion also causes a change
of the saturation tolerance. The model takes
these effects into account. Therefore, skin and
muscle compartments show variable half-time
periods and saturation tolerances.
The necessary decompression times are calculated
according to the workload and the decreasing
skin temperature. The decrease of skin
temperature is estimated based on the water
temperature and the dive time. At the surface,
the diver’s physical performance is lower than
during the dive. By considering the differences in
physical performance the no fly time becomes
considerably longer.
2. The model considers inert gas not only in the
dissolved state, but also in the gaseous phase
(microbubbles). Formation of microbubbles is
calculated with allowance for the different
influences in arterial and venous blood. With nor-
mal ascents gas bubbles mainly form in venous
blood, with fast ascents also in arterial blood and
on ignoring decompression stops in the tissues.
As the model calculates microbubbles, those
physiological processes are reconstructed which
actually occur.
The bubbles on the venous side of the circulation
are carried into the lungs where they change the
arterial nitrogen pressure. This influences mainly
repetitive dives, dives with very long
decompression times and the no fly time.