Studies, no. I wrote a book (ubersleepbook.com, if ya'll don't mind me dropping that link -- if it's verboten, I'll remove it and sorry) that compiles as much as I've been able to get ahold of as far as information after a decade of running a site and communicating with people on the subject, and it has chapters that address your other two (very good!) questions. The short answer is: AFTER adaptation, polyphasic sleep copes with events (including sickness, travel, and "just life") just like monophasic sleep does, only in a compressed / hyperefficient manner. DURING adaptation it's super strict and will get thrown off by these, but once it's well-ingrained, things work surprisingly similarly -- just shorter.