Mike,
I sounds like you aunt has the typical domiciliary set-up where nearly pure oxygen is supplied to her via a mask and diluted by entrained air, when she breaths in, to get between 24% and 28% Oxygen. This is supplied either from a large cylinder, from liquid Oxygen in a Dewar or from the atmosphere by means of a concentrator. All very wastful.
Cylinders are the most expensive option.
When you breath by means of a DV no air (or water!) gets into the respiratory system so you breath what's in the tank.
What your aunt may be asking about is a portable oxygen device she can take with her when she leaves the house for a few puffs now and again when she becomes breathless. Of course, I do not know what the market is like in the 'States, but I do know of two devices available in England that may be adaptable to carry Oxygen.
The British firm Apex do a stage set-up M18 that combines cylinder valve and first stage combined with a normal second stage, is O2 compatible and can be fitted to a 0.4 l cylinder but is really only uselful in a car. I know this system works because I use one on a 3 litre bottle for one of my stage cylinders.
http://www.apeks.co.uk/apekshome.htm
Of course there is also Spareair, which is designed as a secondary air source for diving. Personally, I do not think the latter is much good for diving because it's capacity is so small but if it can be made O2 compatible it could be just what your aunt needs.
www.spareair.com
You will, of course understand these are not registered medical devices and may only be used for their intended purpose.
Hope this helps.
By the way, I need a new DV for my medical kit (DV and free flow to 25 l/min) and I am having considerable difficulty in finding a decent ditributor in the UK.
Can anyone help?
