(08-15-2013, 11:11 AM)RonWessels Wrote: An auto servo machine typically is set for a large range between inhale pressure and exhale pressure, say 10 cmH2O for exhale and 20 cmH2O for inhale. It also has a watchdog backup that instigates the higher inhale pressure if it does not detect an inhale after a certain timed period.
The above ASV example also applies closely to a bi-level ST machine. The S stands for Synchronous (and also applies to just about all machines which try to synchronize their EPR or Flex or bi-level inhale versus exhale pressure difference to match our natural breathing rate). The T stands for Timed and signifies that if we stop breathing the machine will on its own start alternating between the higher inhale pressure and the lower exhale pressure, thereby treating central apneas. The difference between inhale and exhale pressures might be only a manually-adjusted non-adapting difference, such as 10. Or it might be very slowly adaptive (not breath by breath).
But unlike bi-level ST machines, ASV machines can also vary that difference between inhale versus exhale (named Pressure Support in bi-level machines) very quickly, breath by breath. So a more complex example of how an ASV machine might operate is for the Pressure Support to typically be small (perhaps zero or 2 or 4) until any sudden pause or reduction in breathing is detected, and then the Pressure Support would automatically increase as much as needed (perhaps to 6 or 10 or 12) to maintain adequate "tidal" airflow into and out of the lungs.