Thursday, July 28, 2011

A New Way to Control Pressure in CPAP for Obstructive Sleep Apnea

In the June edition of the Journal of Clinical Sleep Medicine is an article about Fisher & Paykel's SensAwake system. The authors describe how long-term compliance with CPAP varies from 29 to 83%. One of the factors that affects usage is perception of excessive pressure. Many of the new CPAPs have a comfort feature that allows the user to ramp the pressure up from the lowest setting to the prescribed pressure over a certain number of minutes. If a patient wakes in the middle of night, however, they would have to reach over and activate the CPAP ramp again. The SensAwake system allows the CPAP machine to evaluate the breathing patterns of a CPAP user while it is being worn. If the SensAwake CPAP detects a breathing pattern characteristic of being awake, then it automatically lowers the pressure. This will prevent the patient from having to lower the pressure with the ramp manually. The SensAwake will then automatically increase the pressure once it detects breathing patterns consistent with sleep. Thus, SensAwake might reduce the time a patient is awake at night with the CPAP on.

The hope is that the SensAwake will make the CPAP pressure more comfortable (and possibly lower) if and when the user wakes up in the middle of the night. In the study, 42 patients were randomly selected to wear either a regular CPAP or one with SensAwake for the first night in the lab. On the second night in the lab, the patient wore the other type of CPAP. The results showed that there was no difference in the amount of time patients spent awake at night, no difference in the stages of their sleep, and no difference in the patients' perception of therapy between the regular CPAP and the SensAwake one.

These results are not surprising. In my experience, when the overwhelming majority of patients wake in the middle of the night with their CPAP on, they do not complain of the pressure being too high - they report that they can't even tell if the CPAP is on because they have acclimated to the pressure while asleep. Also, a significant amount of patients don't like the ramp feature after they have worn a CPAP for several weeks. So I imagine the SensAwake feature might disturb those patients as well, since it automatically activates the ramp feature.

To be fair to the SensAwake system, this study only measured one night's effects. We need long-term studies to determine its effect on long-term compliance.

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