[And]

Hi

In the dissolved gas model, diffusion is assumed to be infinite and thus cannot limit tissue gas uptake or removal. Helium and Nitrogen are independent of each other, so whether nitrogen is present or not in the deco gas it does not influence the offgassing of Helium. The same can be said with nitrogen when removing nitrogen from the decompression gas, and has been confirmed with studies using heliox and O2 in hyberbaric medicine.

Deco can be longer on a He based dive when using Nitrogen in the deco mix, as nitogen is diffusing into the tissues as helium is diffusing out.

Gas movement from lung to tissue and back is dependent on a partial pressure gradient. The oxygen window has been called a partial pressure vacancy simply because a part of the o2 is consumed by the tissue. It always exists. What GI discusses is enlarging this window.

Enlarging the oxygen window can only occur when Partial pressure of arterial O2 is increased to a maximum tolerated value, either by increasing depth or increasing Fraction of inspired O2 of the gas mix, or both. Although enlarging the oxygen window may not directly affect tissue gas removal, it does directly affect the ongassing of a tissue during decompression, which affects the amount of time required to decompress the tissue. Decompressing as quickly as possible is a good thing due to other factors such as hypothermia, dynamic ocean environment etc etc.

Breathing 80%, will obviously effect the rate of diffusion from the tissue, and as the dissolved model is only concerned with inert gasses, then it does not recognise the oxygen window at all.

Andy