dsm wrote:-SWS wrote:So SWS, does the SV protocol consider those HI's seen on Bev's report as "obstructive" events? ...meaning do they want EPAP to also completely eliminate those? and IPAP then only targets peak flows and tidal volume? I could believe that, but I don't think its the case.
Right. The SV machines don't differentiate obstructive from central in any way. By design they are all about targeting an averaged flow peak or minute volume. A detected hypopnea is always undifferentiated, as is any detected apnea.
So both "Big R" manufacturers want the obstructive component manually addressed with the machine's fixed pressure component.
Steve,
Seeking some clarification - are you saying 'right' to the poster in that the HIs are regarded as 'obstructive' (I take that to mean AI the way the poster wrote it ("...meaning do they want EPAP to also completely eliminate those? and IPAP then only targets peak flows and tidal volume?")).
Doug, I specifically meant to say that any residual hypopnea is undifferentiated. That residual hypopnea might be obstructive or that residual hypopnea might be central.
Respironics wants the obstructive component manually addressed by the clinician with the machine's fixed pressure component. With the Respironics AutoSV that means one of two cases: 1) obstructive apneas, obstructive hypopneas, and FL all addressed by CPAP (with fluctuating IPAP peak to address central issues), or 2) obstructive apneas addressed by EPAP, and obstructive hypopneas + FL addressed by IPAP min (again with fluctuating IPAP peak to address central issues). As with any fixed BiLevel titration some lesser obstructive events are likely to get addressed by that lower EPAP pressure.
So in those view graphs, here's how Respironics summarizes the above:
1) THE OBSTRUCTIVE COMPONENT:
"BiPAP autoSV treats the obstructive component of SDB with a clinician adjustable CPAP or BiPAP pressure" (here the obstructive component gets manually adressed by either CPAP or EPAP/IPAP min)
2) THE CENTRAL COMPONENT OF SDB:
"BiPAP autoSV treats the central component of SDB with a timed backup rate (automatic or fixed)" (here a central apnea will trigger a timed EPAP-to-IPAP pressure delivery transition---that's standard BiLevel backup occurring to responsively treat a missing breath)
3) THE PERIODIC BREATHING:
"BiPAP autoSV treats the Periodic Breathing by: Normalizing ventilation by AUTOmatically adjusting Servo Ventilation (pressure support)" (here periodic breathing is countered with IPAP peak's per-breath pressure fluctuation between the set boundaries of IPAP min and IPAP max---that pressure response will actually prevent some central apneas and hypopneas that are associated with respiratory controller overshoot/undershoot)
So both "Big R" SV manufacturers ask that clinicians manually titrate away just as much of the obstructive component as possible so that fluctuating IPAP can address respiratory controller problems. Regardless, when a residual obstructive apnea or obstructive hypopnea does occur, the SV machines cannot differentiate that residual sleep event. The SV machines then treat that undifferentiated apnea or hypopnea identically---regardless of being obstructive or central.
Specifically the fluctuating IPAP peak pressures (between the values of IPAP min and IPAP max) are supposed to be reserved for highly dynamic treatment of respiratory controller oscillations. So let's assume that a patient needs to have their respiratory controller oscillations counteracted with varying IPAP peak pressures. The calculated IPAP peak values to counter that central dysregulation are going to be
entirely different pressure values in physics/biophysics than the IPAP peak values required to physically stent obstructions of identical under-target flow values. Oooops! If we have too many obstructive events not manually addressed by the machine's CPAP or EPAP/IPAP-min values, we've got a big problem calculating the necessray IPAP peak values per breath. Don't we? We have the concurrence of two sets of SDB event types, each requiring different pressure values to offset identical under-target flow values.
The algorithm can calculate flow targets efficiently when you're throwing almost exclusively all apples (central events) at the target pressure/flow calculations. And the algorithm can probably even calculate flow targets efficiently when you're throwing almost exclusively all oranges (obstructive events) at the target pressure/flow calculations. But, by God, throw a 25/75 or 33/66 mix of apples and oranges at that algorithm, and how is it going to know the required work in physics to offset a heavier obstructive event compared to a somewhat lighter central event----both dissimilar events having the same exact under-target flow measurement?
Do you see why the manufacturers want as many of the obstructive events manually addressed and out of the way so that low-flow targets are purely central and thus homogeneous as far as those pressure/flow target calculations are based?
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Snoredog, you have a handful of assumptions in your recommendations to Bev that I disagree with. I'll try to post my thoughts later, my good friend.
