New sleep study new questions (fixed pressure vs. APAP)

[Mosquitobait]

An important question to ask the pulmonologist is whether your elevation is a major factor in your son's problems. I know of two people who had to leave Denver and find work at lower elevations because their medical condition was problematic due to high elevation. All or most symptoms disappeared.

[Sleeprider]

There has been a bit of misinformation in this thread regarding pressure and oxygenation. In all non-invasive ventilation, including CPAP, PEEP (Positive End Expiratory Pressure) is how oxygenation is controlled. In CPAP, that is pressure, and in bilevel that is EPAP (expiratory Positive Air Pressure). Simply put, higher pressure during exhale results in higher oxygen saturation, and that is consistent with the advise you related from the technician in your first post. Pressure Support (PS) which is the difference between inspiratory pressure and expiratory pressure, specifically targets ventilation and reduces CO2.

With auto CPAP, it is the minimum pressure that improves oxygenation...not flex or EPR. We know that your son's obstructive events are mostly resolved at at CPAP pressure of 6.0, however, your sleep tech properly noted oxygenation was better at 9.0. This is very important information to have in your hip-pocket as you move forward in discussing matters with your doctor. Please be aware that Flex simply reduces expiratory pressure or PEEP. In other words, you should minimize the Flex setting to 1, and seriously consider a higher minimum pressure. In auto mode, I would not use any less than 6.0 minimum and allow the maximum pressure to be 9.0. If you monitor SpO2 using a recording oximeter, you can easily justify higher minimum pressure between 6.0 and 9.0 if oxygen is not consistently above 92.

[Ron AKA]

Here are some thoughts on the issue of the effect the elevation of Colorado may have on a CPAP treatment and blood oxygen levels. For sure the higher elevation the harder it is for the body to keep oxygen levels high enough. Mountain climbers that are not acclimatized to high elevation like the Sherpas need supplemental oxygen at about the 20,000 feet level. On a commercial airplane I believe they start to pressurize the cabin at about 10,000 feet, and hold the pressure at the equivalent of the 10,000 foot level as the plane goes up to the normal 35,000 feet or so. Denver is at about the 5,000 foot level so well below the level needed for oxygen for a fully healthy individual. And someone that has lived there for a long time is also going to get acclimatized to the lower absolute pressure of the atmosphere there. But, someone with health conditions may have more trouble at 5,000 feet.

So what does that mean for the CPAP therapy. I noted that the Dreamstation manual says it "compensates" for atmospheric pressure up to 7,500 feet. That is a little suspicious, as the machine does not produce an absolute pressure, but only a differential pressure above the actual ambient atmospheric pressure. I think what they are really saying is that even with the thin air at 7,500 feet, the fan/turbine can still enough volume to produce the rated 20 cm of water pressure. 

At the very basic level our airway is like a long skinny balloon laying on the table. If the balloon is thick and stiff enough it will not go flat. But we know it can with the conditions that cause apnea. A CPAP basically works by increasing the pressure inside the balloon against the pressure on the outside (atmospheric). It is the differential between what the CPAP produces and the atmospheric pressure that is important in creating the so called air splint that opens up the air passage. There are some more complexities than that, but at the basic level this is pretty much it. So if at sea level you need say 9 cm of water pressure to open up your airway, and if you travel to Denver, you will still need the same 9 cm of water pressure to do the job. No difference, so perhaps that is what Dreamstation is meaning by self compensating. 

But now for oxygen, it is a different matter. In the units that CPAP's use for pressure, the absolute pressure at sea level is about 1033 cm. In Denver it will be about 845 cm of water. That is quite a difference, and a CPAP producing 20 cm is not going to get you oxygen like being at sea level. Still 20 cm is better than nothing. So compared to not using a CPAP it is certainly going to increase O2 levels in the blood. The higher the pressure on inhale the more O2 should go up. And in my view if you lower the pressure on exhale that also will increase O2 levels. The reason is that you will exchange more air volume on each breath. That in my view again is why Flex and EPR will also increase O2 levels. The problem with Flex on a Dreamstation is that it does not fully reduce pressure for the whole exhale cycle and does not drop the pressure by a full 1 cm for each step on the Flex setting. It is a partial reduction. On the ResMed it appears to be a full reduction on exhale pretty much in line with 1 cm per step in EPR. You can see it in SleepyHead if you expand out the Mask Pressure graph to see the individual inhale/exhale cycles. 

The issue in all this though is that when you increase O2, you reduce CO2 in the blood. When you sleep the body uses the CO2 level to control the frequency and depth of breathing. As CO2 goes down you breath shallower and shallower and may stop breathing for periods of time. And that is essentially a central apnea, or open airway apnea. 

The reader's digest version is that increasing the treatment pressure (IPAP) and reducing the exhale pressure (EPAP) should increase O2 levels, but at some point may start to increase the frequency of central apneas.... Just my thoughts based on a fair amount of research into the issue.

[Sleepster]

I noted that the Dreamstation manual says it "compensates" for atmospheric pressure up to 7,500 feet. That is a little suspicious, as the machine does not produce an absolute pressure, but only a differential pressure above the actual ambient atmospheric pressure. I think what they are really saying is that even with the thin air at 7,500 feet, the fan/turbine can still enough volume to produce the rated 20 cm of water pressure.

But it does indeed have to spin faster when the air is thinner to produce the same gauge pressure of 20 cm. That is what is meant by compensation. Before CPAP machines had this automatic compensation they had to be manually adjusted. 

But now for oxygen, it is a different matter.

Some people require supplemental oxygen and it's introduced into the CPAP air stream by means of a tank of compressed oxygen. There indeed may be people who don't need supplemental oxygen at sea level but do need it at higher elevations. Some of those people use CPAP machines and some don't. You don't need a CPAP machine to provide supplemental oxygen.

[ColoradoMom]

Thank you once again to everyone for the great information and suggestions. Altitude does seem to to be a factor in my son's problems, both while awake and sleeping. My son has lived in Colorado his entire life, the elevation never seemed to be an issue until about a year ago. Two summers ago my son was climbing 14ers with no problem. Last summer we had to turn around after hiking only about a mile on a backpacking trip because my son was having blackouts, on that trip we were at about 11,000 feet. About a month before the backpacking trip we went on a week long 50 mile canoe trip at low elevation and my son did fine. I mentioned before that my son was recently diagnosed with asthma, I'm hoping that treating the asthma will alleviate the daytime issues. His sleep apnea is also worse at higher elevations. His AHI while using CPAP at home seems to top out around 6. A family member of mine owns a mountain home that is about 2300 feet higher than the elevation we live, at that higher elevation my son's AHI is always over 9. I have have also tested my son's O2 sats at the higher elevation, as expected his numbers dropped across the board by about 3. I have attached a Sleepyhead report from a night at higher elevation (9300 feet). I have discussed all of this with my son's doctors. The current strategy is treat the identified issues, then reevaluate and determine if further action (such as supplemental O2) is needed.

It's hard to be patient because the medical system often moves so slowly, but I have decided to wait on making any changes to my son's treatment until I talk to my son's doctor. As soon as his titration study report comes in I'll give his doctor a call and ask about raising the pressure, APAP, and flex. My son did not end up with an APAP machine by accident, his doctor wrote a very specific prescription that only allowed him to be given one of two specific machines. His doctor may have reasons for using CPAP mode that I am unaware of, so I will refrain from making any changes until consulting with her. Thank you again for all the information, it has been very helpful!

[ColoradoMom]

I don't believe your sons CA events are currently an issue, but definitely keep an eye on them.
The charts from the nights with the AHI near and over 6 are showing clusters of events.  If this happens regularly then it may be some position induced apnea typically from tucking the chin down.  I bring this up as a talking point with your Doctor.  Many users here have found that a soft loose fitting cervical collar (we are not trying to immobilize the neck) keeps the chin from tucking.  Note that this is not a medically recognized treatment.  You can try some pillow adjustments if these clusters persist.

Fred

Thank you for the suggestion of the cervical collar, I think your suspicion of position induced apnea may be correct. We took a trip out of town this weekend and my son and I shared a hotel room so I was able to make some observations about his apneas. Before CPAP when I observed apneas I noticed a cessation of breathing followed by a deep inhalation. While sharing the hotel room what I observed while my son was using CPAP was different, but I my guess is that it signaled apnea events. I would hear series of a long, loud exhalations through my son's mouth. I could not hear normal respiration between these long exhalations so my assumption is that they were apneas. The timing seemed to coincide with the clusters that I saw on Sleepyhead the next morning. I noticed that my son was on his back during the events. I discussed trying out a cervical collar with my son and he is opposed to the idea. My son alternates between sleeping on his back and his sides. He currently uses a CPAP  pillow that has cutouts on the sides. Before the CPAP pillow he had major leaks every time he rolled onto his side. He uses a wisp mask. He has tried nasal pillows, they leak less but he finds the wisp mask to be much more comfortable. 

So my question is to reduce chin tucking what kind of pillows would you use and how would you place them?

[Ron AKA]

That latest chart sure indicates he would benefit from putting it in Auto CPAP, and setting a higher max pressure. 6 cm might be OK for minimum C, but is too low for a max. CA's are certainly not high at the 6 cm fixed, but he is suffering from a large number of OA, and H events that should be addressed by higher pressure. As one goes up in elevation a higher pressure will be required to get the same oxygen effect as the air is thinner. Be sure to remind the doctor of the range in elevations that he will be sleeping at.

[Sleeprider]

I actually would like to see him promote to a BiPAP which would give him separate inhale and exhale pressures. With the large number of hypopnea and relatively low tidal volume, a bilevel machine could resolve all of those issues, while improving his oxygen saturation. He has an auto CPAP set to fixed pressure at very low levels. I tend to agree that changing the mode to Auto and allowing pressure to rise is a simple and logical first step. In addition, auto mode would at least allow therapy to adapt to changing elevations. I'm a little unsure why the system is being slow to deal with this. Many of us use our primary care doctors once the diagnosis is done. The sleep specialists are honestly a bit useless.