[Analysis of expiratory pressure reduction (C-Flex method) during CPAP therapy]

When treating OSAS with CPAP using the C-Flex device the expiratory pressure is reduced similar to that during bilevel CPAP. In the C-Flex mode, the pressure decreases depending on the expiratory flow and increases in the last phase of expiration to prevent collapse of the upper airways. To the best of our knowledge up to now the degree of pressure reduction and the influence of fine tuning with 3 Flex steps has not been investigated.

In this model study we examined--in 10 normal persons--the pressure dependent reduction during 6, 8 and 10 mbar CPAP with the Flex steps "1", "2" and "3". The prescribed breathing frequency was 15/min and 20/min. In each study we calculated the minimal expiratory pressure.

Except during CPAP at 6 mbar and breathing frequency of 15/min, the difference between Flex steps 1 and 3 during the application of 3 different CPAP levels with a breathing frequency of 15/min and 20/min was significant (p < 0.05). The reduction with Flex step 1 during CPAP at 10 mbar and a breathing frequency of 15/min was 1.72 +/- 0.88 and with Flex step 3 it was 2.77 +/- 0.86 mbar (p < 0.05). The largest pressure reduction was registered during a breathing frequency of 20/min and a CPAP of 10 mbar and Flex step 3.

On the basis of our results the pressure relief with flexible CPAP depending on pressure values, breathing frequency and Flex steps 1 to 3 can be estimated.