I was careful each time to turn off the power and lock the card but it still got corrupted. I suspect the cheap card reader I used may have done something.
There is no utility in the Respironics machine to reset or troubleshoot the SD card so I had to explore other options. I really did not want to go back to my provider to pay 10 times the price for a standard SD card.
Anyway, I noticed when I looked at the Windows explorer that the file structure in the SD card looked just like any other data storage device on a Windows machine so I figured I had nothing to lose by reformatting the SD card and trying to start over. Now all I had to do was figure out how to reformat an SD card and hope it worked
Before the corruption, there was a folder visible that looked exactly like this:
After corruption, the folder looked like this:
Clearly a problem.
In that folder is where the actual data is written in about a dozen separate files with numeric names. I had seen them before but they were no longer visible or accessible at all following the corruption even though the card still reported over 1 gigabyte of data on it
After some research I discovered the SD Formatter Download from the SD Association.
It's completely free and they have documentation and it's pretty easy to set up and run.
I downloaded it, ran it at the least comprehensive (basic) level and all the gobbledygook on the card was gone.
With my fingers crossed I recreated the directory 'P-Series\' and placed the card back in my CPAP machine.
It has been happily recording data ever since. All is well again in SD Card land.
If you are a little bit comfortable with computers, this is not hard to do. I hope you'll never need this procedure, but here it is if you do. Good luck and good sleep