Steve,

I'll second Linda's suggestion to get a 0-25 or 0-60 liter/minute oxygen regulator.  You can order a good 0-25 liter/minute regulator for $25 to $60 over the Internet. 

The 0-60 liter/minute regulator with DISS fitting for a demand valve will run $150 to $190 from Flotec.  Shoot me a PM and I can send you the ordering info as they build these regulators to order.

If you're having 3 or more attacks a day/24 hrs, you're going to need the larger 3,995 liter M-size oxygen cylinders.  I keep three of them on hand for a one month's supply at that rate.

The 25 foot oxygen extension tubing may look sexy, but the line loss at that length means you're actual flow rate at the mask will be much less than 15 liters/minute.  2 meters of oxygen tubing is usually sufficient.  Cut the straps off the disposable mask too... 

When you're ready, I'd also upgrade to one of the $27.50 O2PTIMASK™ kits here at the ch.com store.  A 3-liter reservoir bag and higher flow rates make a very big difference in abort times.

Here's a photo of my oxygen therapy kit.  As you can see I use both the O2PTIMASK and a demand valve.  They both work about the same in generating fast aborts, but each has its advantages.

The abort tally on that cylinder was at 30 and as I recall there was still over 500 psi left in the cylinder. 

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The M-size cylinders usually run around $30 a refill so that works out to $1.00 to $1.50/abort.  With a 20% insurance co-pay ($6.00) my actual cost per abort is usually 20 to 25 cents...  No side effects either...

Regarding how long to stay on oxygen...  There's really no need to worry as most of us will run out of oxygen before there's any real problems.

You would need to breathe 100% oxygen for 10 to 12 hours continuously without any breaks breathing room air before starting to feel the symptoms of pulmonary oxygen toxicity... 

If it takes 20 to 30 minutes to abort a CH attack at 15 liters/minute... no biggie (flow rates ≥ 25 liters/minute will get your average aborts down to 7 minutes).  If your mouth gets dry, take a sip of water.

I flew Navy fighters for 15 years logging over 3,000 hours flight time.  All of that flight time was spent breathing 100% oxygen from takeoff to landing aboard the carrier on missions lasting over two hours with several extended missions over 7 hours.  I've also used oxygen therapy at flow rates well above 25 liters/minute for five years...  I'm still here at 65...  with an excellent quality of life thanks to oxygen therapy at flow rates that support hyperventilation.

You may want to check out the Supplemental User's Guide for Oxygen Therapy at Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to or It will answer a lot of your questions.

Take care,

V/R, Batch