Fixed-Pressure or Automatic (a.k.a. CPAP or APAP)?
The difference between the two types of machines
There are two types of CPAP machines, fixed pressure ones or automatic ones. A fixed-pressure machine stays at one pressure level all the time. This pressure setting would be provided by your sleep clinic, or possibly your doctor. These are calculated for your requirements based on several factors. If you have been provided a fixed-pressure setting by your clinic or GP, then a regular CPAP machine should do nicely.
If you do not have a specific pressure setting (most do not), then you will need to opt for an automatic machine instead, often known as Auto-CPAP or APAP. Automatic machines have a range of sensors built-in that allow them to calculate how much pressure you require at any given time. It can detect when you are about to stop breathing, and raises the pressure accordingly, and once the danger has passed it will drop down again.
What this means is that on average you will get less pressure over the course of the night than you would with a fixed-pressure machine, which would be set at the highest setting required. Many find the therapy to be more comfortable and more effective as a result. We often find even those who have been provided a fixed-pressure setting opt for an automatic machine as a result. However, there is often an adjustment period as you get used to the different way an Automatic machine provides pressure compared to a fixed-pressure one. Some find the lower pressure alarming initially, like they are not getting enough air (you are, you just do not need high pressure all of the time - particularly when you're awake). Equally, the Auto may go higher than you're used to at times also, if it determines you need more pressure. So it can take a little to acclimbatize when switching to an Automatic initially, but in the long-term, therapy should be more comfortable and more effective.
One thing to note if you have the option of a fixed-pressure machine is that the pressure you have been prescribed will have been accurate at that time, but the pressure you require will change over time. For example; gaining or losing weight, or drinking alcohol before sleep can affect the severity of your OSA and therefore the pressure you require. Therefore it is important to regularly get assessed by your clinic to make sure your pressure setting is still at the optimum. Alternatively, you could choose an Auto-CPAP Machine which will always provide you with the exact pressure you need regardless of any changes.
So in short: If you have not been prescribed a fixed-pressure setting (for example, 12cmH2O), then you will need an Auto-CPAP Machine. If you have, you can either choose a regular CPAP Machine at that setting, or choose an Auto-CPAP Machine anyway for the additional benefits it offers.
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