I heard that there might be a problem (in German: "isobare Gegendiffusion") when you switch breathing gases while scuba diving if the difference in the fraction of helium is quite high.

Does this affect me when switching from trimix (or heliox) to air or from air to trimix?

*Example 1:*
I use air (21% O₂, 79% N₂) to go down to 30 m (100 ft) and want to switch to trimix (e.g. 21% O₂, 35% He, 44% N₂) to avoid nitrogen narcosis when going to 40 m (130 ft).
Upon reaching 30 m again, I would switch back to air (or nitrox).
The time spent below 30 m could be very short (e.g. < 5 min).

*Example 2:*
I use air to go down to 45 m (145 ft), stay a few minutes, and switch to trimix in order to experience the influence of nitrogen narcosis.

*Note:* I know that you need special training if you want to dive with trimix, but they don't teach about air in these courses.