Keith,
Let me start by saying that I am in no way any kind of expert on OSA/CA - I have though put a lot of effort into looking at the various machine types & how they work in the distant hope that understanding exactly what a machine does, may give me some insights into what they are trying to cure - very much a round a bout way of learning.
We have regulars here with considerable expertise in the medical aspects of OSA & CA. The best I can ever offer is my interpretation of what I think happens in particular circumstances. It is important that you understand that I am willing to offer my understandings & interpretations but that these are not always right when it comes to medical interpretations. But, I am not frightened to explore aspects of the therapy.
Very briefly, what led me to ASV type machines was my having a lack of progress when I started with cpap & apap. After ony 5 months on 1st cpap then auto, I got pretty desperate & tried several brands of bilevel then started to see light at the end of the tunnel. I had looked into how ASV machines worked & concluded (rightly or wrongly) the the principle of their operation looked such a natural progression from cpap itself. I had been using bilevels with timed mode & was getting by comfortably but my wife repeatedly would say to me - "you seem to be fighting the machine". She said I would just slowly stop breathing & the machine would whine & then air would leak & she would push me to breathe again. There was rarely any snoring involed. After 9 months or so on bilevels I was starting to feel that cloudiness in thinking plus feel the tiredness during the day.
Then I was able to buy a Bipap Auto SV at a good price. From the day I started using it I loved it - the sleep I was getting was so sound I called the box my 'dream machine'. I then managed to get a Vpap Adapt SV at a good price. The way I would describe my experience with the Vpap Adapt SV machine is of the two SV machines, that it forced me to change the way I breathe at night. For 2 months on & off I would use it then get very frustrated with it & revert to the Bipap Auto SV which was always very easy to use. after 3 or so months I got a better mask & then found I could work with the Vpap Auto SV. I have been on these two SV machines for just under 2 years and am fitter & healthier & have lost a lot of weight (am around 88KG at the moment) and am able to sustain it. My confidence has returned & so has my belief that ASV was the best therapy for me. I can't really explain why in therapy terms, I can only point to my state of health & fitness.
One other thing I did from the start, was to buy lots of cheap machines (before Yahoo Auctions dropped out) & along with the newer ones I pulled them all apart & being an engineer with an in-depth electronics background, felt I was able to see how the machines were designed and had evolved from the early 1990s models through to the very sophisticated machines of today. Again I was working on the belief that if I looked at what they did it may help me understand what they were trying to cure.
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I am game to offer some thoughts on the different uses a Bipap Auto SV can be put to but there are others here who can provide more authoritative info on this that I can. Again I am in no way any kind of expert here & on this topic.
The different types of Periodic Breathing appear to be between PB related to heart problems and PB related to blood CO2 issues where respiratory control failures other than heart problems, are responsible. The blood CO2 complications appear to divide into several sub- complications.
The basics elements as I see them (rather simplistically) include ...
- chemoreceptors in the brain that monitor the blood CO2 levels in the blood (
http://en.wikipedia.org/wiki/Chemosensor )
- gas exchange in the lungs where the lungs take in oxygen, transfer it into the blood, & expel CO2
- the heart pumping the oxygenated blood around the body
Considerations
- excess CO2 can lead to disorientation, panic, hyperventilation, convulsions, unconsciousness, and eventually death (hypercapnia-
http://en.wikipedia.org/wiki/Hypercapnia )
- too little CO2 in the blood can lead to transient dizziness, visual disturbances, and anxiety plus, A low partial pressure of carbon dioxide in the blood also causes alkalosis (because CO2 is acidic in solution), leading to lowered plasma calcium ions and nerve and muscle excitability. This explains the other common symptoms of hyperventilation —pins and needles, muscle cramps and tetany in the extremities, especially hands and feet. (hypocapnia,
http://en.wikipedia.org/wiki/Hypocapnia)
Actions ...
- The rate we breathe at is normally in balance where the blood oxygen is at a healthy level & the CO2 in the blood is also at a
healthy level. The chemoreceptors in the brain will react if the CO2 level goes out side normal ranges.
> If too much CO2 begins to show up the chemoreceptors with initiate faster/deeper breathing in an attempt to 'blow off' the excess CO2
> if too little CO2 is showing the chemoreceptors will signal slower breathing, often ceasing breathing, until the CO2 builds up (often seen a s a central apnea)
Observations on PB (based on the info posted earlier)
If a heart disorder causes slow flow of the blood & there is a lag in the CO2 level being detected at the chemoreceptors, the patient can exhibit the classic form of PB called Cheynes-Stokes Respiration which is characterized by fluctuating cycles of deep/fast breathing followed by slowing & cessation of breathing all in a repeating cycle. The typical time for such a cycle is around 2 minutes. This is triggered by the lag in the chemoreceptors getting the accurate CO2 level in the brain. The Vpap Adapt SV and the Bipap Adapt SV both look for the cyclic fluctuations & attempt typically to adjust pressure, often very quickly, breath-to-breath such that the machines compensate for the weak heart that is the cause of the cyclic breathing.
The above pattern called CSR is due to a lag in the brain getting the correct CO2 blood levels. It can also be caused by "Abnormally elevated chemoreflex sensitivity associated with increased sympathetic activity". This too can trigger CSR.
Another form of PB is "damage to the respiratory control center in the brain that impairs the feedback mechanism for controlling inspiration and respiration" which is explained as causing regular centrals followed by bursts of hyperventilation. Not necessarily in the cyclic pattern seen with typical CSR.
Some of the symptoms described above (see hypercapnia & hypocapnia) are as much side effects from the CO2 imbalance as they are direct effects of an imbalance.
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This is as much as I can figure out for now. As said though, I am offering my amateur interpretation of medical matters way outside my expertise. Am hoping I may have succeeded in lifting some of the haze that typically surrounds this topic. I apologize in advance if I have got any bits wrong.
DSM