Tube equipment use in high altitude?

This might seems like a strange question, but are tubes adversely affected by use in extremely high altitudes? The reason for my question is I will be moving to La Paz, Bolivia for two years which has an altitude of 12,000 ft. I do not currently own any tube equipment, but I was thinking about making the switch from solid-state. I know that because of the pressure differences, light bulbs don't last nearly as long. Do anybody have any personnal experience with this issue or a scientific explaination. Any help would be greatly appreciated. Thanks.