The problem with a delay via signal processing is valid but the Marquette (now GE) Tram modules have a analogue output right at the front end of the input module itself (I'm talking electronically not just physically). The delay is slight (don't remember the numbers involved) but was sufficiently small to allow balloon pumps to be synchronised without any issues. Perhaps this may be worth looking at. Even the really old ones (Tram AR) would suffice and should be available for "bugger all" these days (team it up with an old 7010 series monitor to further reduce cost if you need to and you get the bonus of remembering what monitoring was like in days gone by
).
Given that you want to trigger for respiration this may be fast enough. Just a thought.
