Am adding this to offer my perspective on why each cpap machine type was created and the basics of how it works (in this basic set of descriptions I won't go into c-flex, a-flex or EPR & any other exhale relief add-ons. They would introduce too many areas of confusion ) ...
1. Cpap - Mid 1980s
The original basic Cpap - delivered a single pressure to splint the airway open. Now, modern cpaps also monitor the pressure at the air exit port & when the sleeper breathes back into the hose, these machines will lower the pressure a little so as to maintain the pressure they are set for - if they didn't do this (as was the case in older cpaps) the pressure from the machine + the pressure from the sleeper breathing out, would combine to create a much larger pressure that contributed to mask leaks & user unhappiness & thus non-compliance.
The pressure a Basic Cpap is set to must 1) overcome the sleeper's worst OSA and 2) be set with just enough extra pressure to help significantly reduce hypopneas and flow limitations (the
simple difference between a hypopnea & a flow limitation is basically that a hypopnea is scored when the airflow from the sleeper drops by 50% for at least 10 secs - it the drop doesn't meet that test it is called a flow-limitation - i.e. if the 50% drop only lasted 9 secs it is not scored as a hypopnea)
2. Bilevel Cpap - Late 1980s
A Bilevel - delivers two pressures - a lower pressure when the sleeper breathes out (called Epap) & a higher pressure for when the sleeper breathes in (called Ipap). These machines sense the airflow to decide when to switch from epap to ipap & back. They also introduced 'risetime' which is a setting in the machine that adjusts how fast the machine goes from epap to ipap. Some people can't handle fast rises in pressure. But, setting the risetime too slow tends to reduce the amount of air pumped in a given breathing cycle.
Modern Bilevels have even more enhancements that help smooth the pumping action (wave shape) such that it better mimics natural breathing. The early bilevels were a bit rough in this regard.
The two pressures were needed for patients who could not tolerate single pressure therapy. This could be because of lung problems such as with COPD patients. Then by adding a timed mode to bilevels, they were used to treat people with central apneas as the timed mode could be used to switch pressure from epap to ipap at a timed interval which helped people with centrals to get their breathing going again. Originally all Bilevels were very very expensive but now not much dearer than a standard cpap and thus increasingly popular.
As happens with all new expensive advances these originally got designated for special case patients as medical funds do not want to pay more out than they have to to meet their basic obligations. Bilevels were originally classified as machines for such special cases. Today almost anyone put on cpap therapy can ask for one. To many users they are better than a single therapy pressure as delivered by a cpap or an auto cpap (see next para - even though autos can adjust that single delivered pressure slowly up & down).
3. Auto Cpap - Circa 2000
The auto machines are like a cpap that delivers a single breath-in breathe-out pressure but with an added ability to adjust the delivered pressure slowly up and later slowly back down. The pressure increase would be initiated when the machine detected changes in the sleeper's breathing during the night that indicated a looming obstruction. The pressure delivered was still the same for breathe-in as for breathe-out. This one pressure gets raised or lowered as circumstances alter during sleep. The intent was to help users start the night with a lower pressure than a cpap would be set to. Then as needed the machine would only raise pressure if it detected a reason to do so.
The pressure changes are
very slow and not rapid as we tended to believe in the early days of their arrival in the market. e.g. if the sleeper started out with a CMS of 8, and started to snore or show other patterns of breathing that indicated a looming obstruction, the machine would gently & slowly raise the pressure in short steps followed by a pause in the hope it could prevent a more serious apnea that would lower the sleepers blood oxygen saturation. The machine might say raise pressure over a few minutes to say 11 CMS. If the sleeper then appeared to be breathing normally the machine would usually then gently lower the one pressure to a lower number (eventually back 8 CMS in this example).
Auto Cpaps are not capable of treating central apneas and the reason they adjust so slowly is because they have to avoid mistaking a central apnea for an obstructive apnea plus many users can suddenly start having central apneas brought on by the pressure being applied by the machine (pressure induced centrals). These pressure induced centrals can be triggered by a cpap, an auto cpap or a bilevel.
What put Autos apart from both cpap and bilevel was that by aprox 2005 prices had come down but more importantly these machines included the ability for someone to extract the nights data from the machine onto a data card or by a serial link to a PC. This capability triggered a wave of consumer interest that made sales boom. At last people saw an opportunity to monitor their own therapy (and for very good reason). Standard cpaps and early bilevels (even up to 2006) could not fully provide the same level of data. But nowadays, almost all new machines (except the really el-cheapo bottom end cpaps), will gather nightly data and allow it to be download.
Auto cpaps had this nightly data because it was used by the the machine to carry out analysis so it could make its adjustments to the delivered pressure. The auto cpap machine created detailed data that the machine's internal computer used to make its decisions. Autos would have been the first general purpose cpap type machines to really exploit micro-processors.
Bilevels too soon incorporated micro-processors and they too eventually began to be able to deliver similar nightly data like Auto cpaps could.
4. Auto Bilevel Cpap - 2006
4) The next notable breakthrough for general cpap use was the introduction of Auto Bilevels. These offered the benefits of two pressures, the usual low breathe-out pressure (Epap) and the usual higher breath-in pressure (Ipap), and then to improve on that introduced the same sensing of pre-apnea obstruction events that the Auto cpaps did so could raise both the Epap pressure and Ipap pressure together in response to deteriorating breathing conditions brought on from OSA. Many people have benefited greatly from this advance. The Auto Bilevel is currently the most advanced type of cpap machine suitable for OSA patients. The standard Bilevel Auto still can't deal with centrals. These machines are targeted at the general OSA population.
5. Servo Ventilation (or Tri-Level Cpap) - approx 2007
In 2007 we started to see a new specialized machine that although it's predecessor had been around since 2001 and originally called the 'Autoset CS'. The CS stood for Cheynes-Stokes - a serious breathing disorder often associated with chronic heart failure (see
http://www.resprecare-medical.nl/autosetcs.html ), the Autoset CS was redesigned in the mid 2000s to expand beyond just Cheynes-Stokes breathing and then made more widely available in 2007. The new version was called the Vpap Adapt SV (in Australia, it was called the Vpap Autoset CS2). Another brand also appeared about this time and that was the Bipap Auto SV. It too was based on an earlier specialized machine.
The Auto used in the Bipap Auto SV name is not to be confused with the Auto as in 'Auto Cpap or Auto Bipap'. The Auto SV means automatically adjusting the peak-flow or the breathing rate or the instantaneous respiratory volume, rapidly - on a breath-by-breath basis. Auto as in Auto Cpap & Auto Bipap automatically adjusts the delivered pressure (slowly), in response to detecting looming OSA events by monitoring snoring, flow-limitations & hypopneas).
Both brands of SV machine were originally designed for very special case users uch as those people with periodic or irregular breathing as seen in Cheynes-Stokes breathing and later extended to include people with severe centrals or mixed apnea (OSA plus Centrals).
The current SV machines are not specifically designed to target OSA patients but by manually adjusting Epap can control enough aspects of standard OSA events. This is done for the patient by having the titration therapist set an Epap pressure high enough (during titration) such that this Epap pressure eliminates most OSA events, then an Ipap pressure (IpapMIN) gets set that further controls other OSA activity (hypopneas & flow limitations) and then a third higher pressure is set (IpapMAX) that the machine will apply if the sleeper's breathing volume of air or breathing rate (breaths per minute - BPM), drops below a tracked average value. So in normal situation with no irregular breathing or when the sleeper is maintaining a healthy flow of air, the SV machines operates like a normal bilevel but as soon as the sleeper slows their breathing rate too quickly or quickly drops how much air they are breathing, the machine on a breath-by-breath basis can rapidly increase Ipap above the IpapMIN setting up to a point where the machine determines the sleeper is back within a target range it has been tracking.
This approach has been very successful for people with irregular breathing who previously may have required a hospital ventilator or who were managing to get by with a timed mode Bilevel.
6. The Future ?
In time we may see a version of SV that adds similar auto adjustment to the Epap setting such that it looks for worsening OSA events and slowly raises Epap and Ipap up just like the Auto Bilevel does today, but any such machine is going to be a marvel of algorithmic sophistication as it will have so many variations of event to track and such a range of pressure to apply. Also, the mask needed for such sophistication may not have been created yet.
DSM
#2 revised & clarified.
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CPAPopedia Keywords Contained In This Post (Click For Definition):
cpap machine,
auto cpap,
bipap,
hose,
C-FLEX,
Titration,
CPAP,
Hypopnea,
auto
_________________
CPAPopedia Keywords Contained In This Post (Click For Definition):
cpap machine,
auto cpap,
bipap,
hose,
C-FLEX,
Titration,
CPAP,
Hypopnea,
auto
_________________
CPAPopedia Keywords Contained In This Post (Click For Definition):
cpap machine,
auto cpap,
bipap,
hose,
C-FLEX,
Titration,
CPAP,
Hypopnea,
auto
