(09-20-2014, 11:19 PM)vsheline Wrote:(09-20-2014, 09:09 PM)kfujioka Wrote: I have a an auto Bipap machine. What is an ASV machine?
My obstructive apneas are usually only 1 or 2 per hr and my mask leaks are 5.1 the data says. ... Last night the central apneas were 19, a bit lower than a few days ago.
Maybe the central apneas will reduce after I use the machine for awhile. I have only been using the machine every night, all night long, for about 3 weeks. The first week I was scared and uncomfortable and etc. etc. Now I put the mask on immediately and feel safe with the machine , like at least I know I will be having less events and more sleep. It is not uncomfortable at all. Except I wake for a drink 3 or 4 times a night.
I am curious about the ASV machine. Does it help with central apneas?
Like on Auto CPAP machines and like on your BiPAP Auto machine, recent ASV (Adaptive Servo Ventilator) machines can slowly adjust EPAP within a range, to reduce/avoid obstructive events like hypopneas, snore, apneas and Flow Limitation.
Flow Limitation (FL) is a partial restriction in our airway during inhalation which can disturb sleep, because FL can cause RERA (Respiratory Effort Related Arousal). RERA is an arousal caused by the effort of breathing, but the reduction in breathing was not as much as the 40% or 50% reduction needed to be called a hypopnea, so it is called RERA instead. Although RERA events disturb sleep, RERA events are not counted in the AHI. (Which is one possible reason why some patients who achieve a good AHI may still be suffering from fatigue and excessive daytime sleepiness.)
On most Auto bi-level machines, IPAP is higher than EPAP by a fixed amount, called Pressure Support (PS). IPAP always equals EPAP plus PS.
On your Auto bi-level machine, however, PS does not have to be one fixed number all night; PS can be given a range and periodically (every few minutes) PS will be slightly changed to see if a higher value for PS would further reduce/avoid Flow Limitation. Periodically it also tests whether it can reduce PS without allowing FL to return.
With Auto CPAP machines and with Auto bi-level machines, if an apnea begins the machine will make no adjustments to the pressure during the apnea event.
Unlike your machine, an ASV machine will react nearly immediately (in perhaps a couple seconds) when an apna or hypopnea begins; the ASV machine will increase PS as much as needed (perhaps to 10 or higher) in order to keep us breathing. During the time we are unable to breathe adequately on our own the ASV machine will be cycling between the exhale pressure EPAP and the inhale pressure (IPAP) at a "back-up respiration rate" (such as 10 or 12 breaths per minute), or it may automatically calculate the backup rate so that it matches our own recent natural respiration rate. The ASV machine reacts the same way (increases PS as much as needed) whether the apnea is obstructive or central.
Unless the apnea is a very strong obstructive apnea, the PS will be able to be increased enough to immediately counteract or compensate for the apnea and keep us breathing. For example, if EPAP was already at 10 and the ASV machine quickly increases PS to 10 (to prevent an apnea) the machine would start cycling itself back and forth between 10 (which in this example is EPAP) and 20 (which in this example is IPAP, which always equals EPAP plus PS) to keep us ventilated. Later, when we are able to breathe on our own again, PS will appropriately return to its normal value.
The problems with ASV machines is it can be hard for patients to adapt to the machine quickly raising PS to force us to continue breathing. It is not painful at all, but can be very annoying until we get used to it. And even after we get used to it, the high pressures needed for ASV therapy can cause a lot of air to get swallowed.
Thanks so much for this explanation ! You can't believe how much this has helped me understand the workings of my ResMed Adapt and how it reacts to my breathing.