[Technical differences in various CPAP and BiLevel CPAP devices]

Since the first presentations of CPAP by Sullivan 1983 und BiPAP by Sanders 1990 as a successful treatment in obstructive sleep apnoea syndrome, many CPAP and BiLevel-CPAP devices have been developed by several companies around the world. Although all devices work on the same principle of continuous positive airway pressure delivered through nasal or facemasks, there are, however, significant technical differences between these devices, mainly due to different size and different maximum speed of the turbines. As far as we know, the only study concerning this technical difference in the devices was conducted by Raschke in 1995, who found significant differences in the pressure stability of the devices using a very complicated measurement model on volunteers who were breathing on the different devices. We intended to study the technical differences of the devices using a more simple technique in static conditions, but with very exact measurement.

We measured pressure stability on different inspiration flows and different pressure levels of 8 CPAP's and 4 BiLevel-CPAP's under static conditions using the "Höntzsch Exact ASD-G Messrohr ms 20201-18" flow-measurement device and the "Thommen HM 18.0020.A" pressure-measurement devixe. We measured the noise emission by these devices at different frequency levels using the "Brüel and Kjer Dual Channel Real Time Frequency Analyzer", and measured the speed to reach the adjusted pressure level with the "Multimeter Phillips PM 2518X" and "Oszillograph Phillips PM3350" using the voltage change due to different working of the electric engines at different turbine speeds. We also investigated the different construction of the devices by opening them and analysing the materials used in the devices.

The real pressure levels at an adjusted pressure of 10 mbar and at an inspiration flow of 1 Liter/sec range from 8.7 mbar to 15.6 mbar in CPAP's and from 9 mbar to 9.7 mbar in BiLevel devices. At higher inspiration flows the differences are larger, at lower flows smaller. The maximum noise emission in the 10 Hhz spectrum at a distance of 100 cm from the device at an adjusted pressure level of 10 mbar ranged from 29.6 dB to 39.9 dB in CPAP's and 30.4 dB to 42.2 dB in BiLevel-CPAP's. The time to reach an adjusted pressure level of 10 mbar after closing the airway of the device ranged from 0.26 to 0.66 sec in CPAP's and from 0.46 to 0.80 sec in BiLevel devices.

There are significant technical differences in the different CPAP and BiLevel devices due to different construction of the turbines and electrical engines of these devices. This should be considered when prescribing a device for a sleep apnoea patient. Not every device is suitable for every patient, and quality differences should be considered by all persons involved in the production and prescribing process.