Oxygen saturation meters

Some time in the past few weeks I ran into an article that had reasons
for soaring pilots to use "Oxygen saturation meters". For the life of
me, I can't find where I saw that article. It mentioned things like not
breathing correctly, poor lungs to begin with, etc. Have looked in the
last Soaring Magazine, RAS, several of my folders on my computer, etc.
If any one knows a source, would appreciate the URL.

mg