(12-30-2015, 09:32 PM)Ghost1958 Wrote: Once an obstructive event has happened no cpap or apap machine has enough pressure to "force" the blocked airway open.
As mentioned by surferdude2, most commonly the pressure will start increasing even before any apneas or hypopneas occur, because the machine will sense Flow Limitation or snoring.
Except for uncommon CPAP machines which have a "backup" respiration rate, standard CPAP or APAP or bilevel or bilevel Auto machines do not attempt to react when breathing stops, to end apneas or hypopneas while they are still in progress. Instead, most self-adjusting algorithms wait for the apnea to end (by an arousal).
However, I think a CPAP machine with a backup rate such as an ASV (Adaptive Servo Ventilator) can overcome at least mild blockages. Having a backup rate means that if a breath is not started then the machine will automatically start cycling between IPAP (the pressure for inhalation) and EPAP (the pressure for exhalation) at the backup rate. This will happen regardless of whether the apnea is central or obstructive in type.
Yes, I think some obstructions *can* be too strong to be counteracted by a machine with a backup rate, especially if the machine is using "ST" therapy mode which uses manually-adjusted Pressure Support of 10 cm H2O or less. (Pressure Support is the boost in pressure to aid or cause inhalation.)
But I think some blockages can be overcome by an ASV (Adaptive Servo Ventilator) machine which automatically increases Pressure Support breath-to-breath, especially when the "Max Pressure Support" setting is very high, like in the range 10 to 15 cm H2O. That large increase in pressure will kick in to help or cause inhalation, regardless whether the apnea is central or obstructive.
In my Flow waveforms, which show the rate of airflow being inhaled and exhaled, I sometimes see the pressure cycling between 14 and 25 cm H2O while the Flow is flat lined at zero. These are strong obstructive apneas. And sometimes I see inhalation Flow during the high inhalation pressure but stop-and-go Flow during the lower exhalation pressure, because the air is having some trouble coming out at the lower exhalation pressure. I think this is when the machine is helping me to overcome weak obstructive apneas.
Quote: Once the event is over the machine will raise pressure a bit to prevent another from happening.
Right. For example, the standard ResMed AutoSet algorithm notes how long the apnea lasted and this is one of the things the algorithm takes into account when deciding how much to raise the pressure after an apnea.