Recently at the AIDA 2004 World Championship, scientific talks were held and one of the speakers, Andrew P. Blaber, Ph.D., addressed something related to this.
In their studies they found that oxygen delivery to the brain was maintained at the same level from the beginning of the static to the end of the static. The longest static they witnessed under their control conditions, was a 6:30, and still with the same results.
This suggests, that statics, in practice, do not have a hypoxic effect on the brain directly. Other stresses of performing statics may indirectly damage the body and the brain, especially if a diet does not compliment the activity and considerable resting is not performed.
Now, this is in considerate of constant max attempts that take one into LMC and blackout conditions. There was no information regarding this presented, and I have not seen anything specific to the conditions of statics to suggest anything conclusive, other than the age-old, "after blackout, brain damage can occur in less than 4 min".