Chervin et al have published a study in the February edition of the Journal Sleep about how sleep doctors determine obstructive sleep apnea (OSA) severity and response to CPAP therapy. On a sleep study, we grade the OSA severity by the number of times per hour a patient's airway collapses - abbreviated as the AHI. Often, airway collapse produces an arousal from sleep, seen in the brain wave changes measured on the EEG. Looking at the EEG with just our eyes, however, misses much smaller patterns that are visible only by computer analysis. These smaller patterns have been studied in patients with and without OSA, and researchers note some important differences. It's not known, however, if the brainwave patterns change with CPAP therapy.
The study authors did such an experiment, measuring brainwave changes during a diagnostic sleep study and then during the CPAP calibration study. The results showed that CPAP therapy tended to normalize the brainwaves. This might seem obvious, but remember, these are brainwaves that can only be seen by sophisticated computer software programs. Up until this study, sleep researchers had only suspected that CPAP therapy could change these brainwave patterns.
The implications have more to do with the way we diagnose OSA and how we determine the cause of someone's sleepiness. Currently, since we rely on human eyes to evaluate brainwaves, we miss the more subtle brainwave changes that could be clinically important. It's similar to looking at a tile mosaic from 20 feet versus 1 foot. At 1 foot away, you can see that the piece is made up of hundreds of different tiles, and you couldn't make that out at 20 feet. Anyway, this more detailed analysis of brainwaves could become a more accurate and standardized way that sleep patients are studied in the sleep lab.