I found this on the internet.
An Introduction to HOTx
Trimix is a breathing mixture consisting of oyxgen, helium and nitrogen. Traditionally, Trimix has been used as a deep diving gas as it is less narcotic at depth than air or nitrox. Usually these mixes contained an oxygen percentage less than normoxic (less than 21% oxygen). The oxygen content was kept low due to the possibility of CNS oxygen toxicity problems when breathing partial pressures of oxygen greater than 1.6 atmosopheres.
The technical diving commumity has long recognized the risks associated with conducting deep dives while breathing narcotic mixes. More recently that recognition has been extended to include intermediate deep dives (100 to 170 feet seawater). To reduce the associated risks many divers are using Trimixes containing 21 percent and higher fractions of oxygen.
These intermediate deep diving gases are known by a variety of names. Call it "Normoxic Trimix," "Helitrox" or "High Oxygen Trimix" (HOTx), the principle is the same. By displacing some of the nitrogen content with helium the gas is less narcotic, thus reducing risk to the diver.
Technical diving courses providing training in the use of high oxygen trimix are gaining popularity. Via these programs it is now possible to climb the training ladder to the Trimix level without having to be exposed to deep air diving. Due to the special considerations involved in conducting these types of dives because of the addition of helium to the mix, divers should seek specialized training before attempting to execute HOTx dives.
Currently, HOTx is used almost exclusively for stage-decompression diving. As such it is considered a technical diving gas. Recently, however, a great deal of experimentation has been being done concerning using the gas for no-stop diving. In the not too distant future HOTx may become a mainstream recreational diving gas for no-stop dives in the 100 to 130 foot range.
http://www.sportdiverhq.com/hotx.htm
