Fixed Pressure CPAP Machine and Automatic CPAP Machine Compared
If you have been diagnosed with obstructive sleep apnoea and have been recommended to undergo CPAP therapy by a qualified specialist, choosing which type of CPAP machine largely depends on the type of device recommended by the doctor.
Two Types of CPAP Machine
There are two main types of CPAP machine available: fixed pressure and automatic pressure. A fixed pressure machine is set and stays at one pressure level at all times. The pressure is as recommended by your doctor or sleep clinic and is arrived at based on your requirements. A point to consider is that your prescribed pressure is likely to change over time. Factors such as gaining or losing weight can affect the severity of your OSA thus the change in the required CPAP pressure.
An automatic CPAP or APAP machine has a built-in range of sensors that facilitate the calculation of pressure level you require at any given time. This machine has the capacity to detect when you are about to stop breathing thus it automatically raises the pressure to ensure that the airway is kept open. Once your breathing is back to ideal, the pressure will automatically decrease. Using APAP, you will get less pressure during night’s sleep than you would when using a fixed-pressure machine.
CPAP versus Auto-PAP
A standard CPAP machine is usually calibrated to generate a pressure from 4cm/H2O to 20cm/H20. Since it would be quite uncomfortable to take in a specified pressure in one go, most fixed-pressure CPAP machines have a ramp up feature that enables the CPAP machine to start at a very low level and gradually increase to the required level the entire course of the night. The “ramp up” period usually takes 20 minutes. In general, the ramp up time will give you time to adjust to your required setting.
An auto-CPAP machine also operates at a range of 4cm/H2O to 20cm/H2O and adjusts the pressure level during the course of night as you enter into different stages of sleep. Some stages are deeper and therefore relaxes your muscles more, especially the airway. Positions during sleep also make you more prone to apnoea events so in this effect, an auto-APAP machine seems to be more ideal. This machine can also be programmed to work as a fixed-pressure CPAP which is quite ideal as your attending physician can determine your treatment progress between two treatments.
Another positive feature of an auto-CPAP machine is that you can adjust the pressure to a minimum and maximum level. If you require a pressure range of 8cm/H2O to 12cm/H2O, the machine will not exceed the set range while you sleep. However, if the pressure is too low, you might be prone to experience apnoea before increasing to therapeutic level.
Both machines may leak during sleep, and this could affect the pressure produced by an auto-CPAP. Stuffy nose and dry mouth are added inconveniences.
Which is more Effective?
A study was conducted at the Respiratory Sleep Disorders Unit, St. Vincent’s University Hospital, Dublin, Ireland to determine the efficacy of automatic CPAP versus fixed-pressure CPAP in the treatment of mild to moderate OSA. Patients underwent eight weeks of APAP therapy and eight weeks of CPAP therapy in a randomized crossover design. The study concludes that APAP and CPAP therapies are equally effective in managing mild to moderate OSA patients with patients who require 8cm/H2O and higher-pressure preferring APAP and patients with lower than 8cm/H2O pressure preferring CPAP.
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