The supplement is actually arginine alpha-ketoglutarate which stimulates vasodilation via the stimulation of increased nitric oxide.
There's no evidence (other than anecdotal) that it will "improve contraction velocity" and "maintain a perpetual pump" although I hear it helps one sport a mighty fine chubby when a non prescription viagra substitute is desired.
Your Boyle's law reference would only be an issue for inhaled nitrogen gas and to increase concentration in the blood it would need to be done under pressure like in scuba diving. That's why you ascend from a dive slowly to blow off the excess nitrogen. Come up too fast and the nitrogen comes out of solution and it's time to "get the bends" and perhaps die.
Excess nitrogen that is ingested is excreted as urea in the urine, feces, and any other nasty secretions you may be enjoying at the time.
Bill