Hello, recently i have visited an ent doctor and he told me the 40% of my nasal capacity occupied by deviation of the nasal septum. now i want to know can this problem effect on my brain and hit its cells beacuse lack of oxigen? thank you?

It doesn't. Your body gets the oxygen it needs by bypassing the obstruction. Your mouth is likely open awake & asleep or the blockage is not enough to trip the safety mechanisms your brain uses to protect itself. It is a non-issue.

A deviated nasal septum does not cause cerebral hypoxia, but can be uncomfortable, a source for infections, but readily repaired by a minor surgical procedure. Don't worry about oxygen, but get this fixed.