^^^ basically you are introducing a different gas (other then oxygen) into your blood stream/brain. So the physical effects you seek to find info on relate to this.
I have found the source I mentioned in my earlier post
link
Generally, what is available from a bulb hit when administered by a cracker/bulb machine etc is not really enough to do you serious damage on the spot. Most fatal incidents during administration have been due to carelessness. e.g. Someone nanging alone, takes a hit, goes semi-conscious, slips over and cracks their skull.
Tampa outlawed rave clubs after the well-publicized death of Kelly Hendershot a 19-year-old who died several days after falling and hitting her head at StudioRave Club in Tampa. Her friends told authorities that she had inhaled nitrous oxide inside the club.
Other long term effects are generally from serious over abuse (refer my story above) Some sources site long-term use of nitrous oxide leading to bone marrow suppression, blood cell problems and poisoning of the central nervous system.
Splatt has already mentioned possible Folic Acid and Vitamin B deficiancies. Physiologically what is happening from inhaling nitrous is big dirty word in the name of hyperhomocysteinemia, where homocysteine (an amino acid) accumulates in your blood. This then promotes cardio-vascular diseases, although I am struggling to find reliable sources to confirm exactly what vascular diseases. It has been suggested that accumulation of homocysteine in the blood stream of a pregnant woman coupled with B12 and folic acid deficiency can lead to the unborn featus developing spina bifida and anencephaly (childeren with no brains or open spinal cord).
Also studies on health care professionals (e.g. dentists) working in confined spaces, have shown women in these professions have displayed fertility issues.
Then you have this source...
Link
...which connects long term Nitrous abuse with Myeloneuropathy with symptoms such as loss of balance, leg weakness, gait ataxia, impotence, and sphincter disturbances (hhmmmm...). Once again this study sites the depletion of B12 from use of Nitrous.
Then there are other effects, which I think have been touched on already
, such as Frostbite to the lips, nose, gums and tounge. I have seen the damage it did to a friends lower lip and it was a very uncomfortable and damaging experience for him.