What are the effects of consistent high altitude then low altitude exposure?

I work at 13,500 feet at least three times a week. My shifts are from 6pm to 6am and pretty gruesome. I'll sleep at around 9,000 feet and head back up, doing this for two to three nights. I'm curious if anyone has written a medical paper or come to an educated conclusion about the physical and/or mental affects this can have on a person?