The Residual Nitrogen Time or RNT is a way to convert the saturated nitrogen in the body in time to be easier to use with tables.
Trimix is a mixture of three breathable gases. Oxygen, Nitrogen and Helium. It is used in technical diving to reduce the effects of nitrogen narcosis. Because helium has lower density, Trimix is also used to reduce the effort of breathing caused by surrounding pressure at greater depths.
Narcosis also called nitrogen narcosis or inert gas narcosis is the name of the impairment that affect divers when the nitrogen in what we breath becomes narcotic under pressure. It has been given the name of rapture from the deep by Jacques Cousteau when divers started pushing the depth limits of diving beyond the 30 meters mark.