[PSUBS-MAILIST] Liquid Ventilation

[CWall@swri.edu]

One of the benefits of working at an interdisciplinary not-for-profit contract
research outfit is that you get to participate in all sorts of strange and
wonderful projects...

One I *didn't* work on (but shared facilities with) was a neonatal baboon study
 to develop liquid ventilation technology for premature infants. The project
involved delivering baboons early by Caesarean section before the lungs had
developed, and then placing them on liquid ventilation using the fluorine-based
 perfusion liquid.

The strange part is that the infant wasn't "breathing"- the fluid filled the
lungs and the gases were passed across the fluid outside the lungs, with a
pulsation that stirred the fluid slightly to agitate the boundary layer- the
damned thing was chugging away like a washing machine- but the lungs weren't
expanding and contracting. Apparently the fluid has very high gas diffusion
rates. 

 The project was a real success- but it was hard on the staff to pull the
premies and then watch them for a month or more in their little cribs with
tubes down their throats, and they got very attached to them....(these were
mostly military nurses, neonatal intensive care (NICU) specialists)...and then
watch them be sacrificed at the end so the lungs and other tissues could be
examined histologically.   Some of them just couldn't take it and bailed.   

 Every one of them was proud, however.  That project gave invaluable
information that contributes to the survival of premature infants every day,
and while liquid ventilation is not common yet (and may never be), it is one
more tool that works when nothing else will.  If you don't have working lungs,
liquid ventilation may be your only hope. 

  The upshot for submariners, though, is that it is a technology that is a LONG
 way from practical deployment.  You can drop a mouse into a beaker full of the
 stuff and keep him alive for an hour and recover him without damage- you can
keep a premie bab alive and doing well for 2 months....but you aren't going to
find this equipment at the dive shop any time soon.  In fact, the limitations
of the "pulsation" technique confers an upper size limit on the order of the
lungs of a 5 lb infant; trying to scale it up to a 200 lb person means you'd
have to redesign the lungs themselves to accomodate a couple more bronchi. 
Going in and coming out the same hole just isn't enough turnover to adequately
perfuse something that large, at least at 1 atm.

  Under pressure, things get better.   It may be possible for deep divers to
use something like this....but the transition on and off seem likely to be,
well....problematic.

  Who knows? It bears watching, but IMHO- don't get your hopes up. 

Craig Wall