Hey Robbie,
Joe summed it all up regarding published studies on oxygen flow rates of 25 liters/minute and higher for cluster headaches. We've one study underway at the Geisinger Center for Clinical Studies in Wilkes-Barre, PA with Dr. Todd Rozen as the Principal Investigator, but I don't expect any published results until this Fall at the soonest and more likely early next year. They're still accepting study participants if you're interested...
We conducted an informal study of oxygen therapy at these flow rates in 2008 with seven participants that gave us data on 366 aborts giving us proof that the efficacy of this method of oxygen therapy is high. Abort data also indicated cluster headache aborts at flow rates of 25 liters/minute and higher that support hyperventilation were on average three times faster than at a flow rate of 15 liters/minute. However, I doubt any editors of the headache periodicals would accept an article on an informal study for publishing written by a fighter pilot... So we wait...
That said, this method of oxygen therapy is nearly 100% effective with average abort times around 7 minutes for headaches between 3 and 9 on the 10-Point headache pain scale as long as there are no conflicting comorbid conditions.
The following chart from the National Guideline Clearing House lists the standards of care in the EFNS guidelines on the treatment of cluster headache and other trigeminal-autonomic cephalalgias. As you'll see, it calls for an oxygen flow rate of 15 liters/minute as the first abortive of choice in the acute treatment of cluster headache.
Multimedia File Viewing and Clickable Links are available for Registered Members only!! You need to

or

You can reach this recommended standard of care at the following link:
Multimedia File Viewing and Clickable Links are available for Registered Members only!! You need to

or

You may want to take or send this chart and link to your neurologist if you want to get a flow rate of at least 15 liters/minute. Check your PM inbox for additional info.
In the mean time, only a few neurologist will prescribe a flow rate of 25 liters/minute so you may as well plan on buying one for yourself.
You can usually find a 0-25 liter/minute regulator on the Internet for less than $60, but most are CGA-870 for the smaller E-size oxygen cylinders. The best regulator available, called the InGage™ is made by Flotec Inc. It's a 0 to 60 liter/minute CGA-540 regulator with barb fitting for your O2PTIMASK™ kit and also a DISS fitting should you decide to buy an oxygen demand valve at a later date.
Multimedia File Viewing and Clickable Links are available for Registered Members only!! You need to

or

This regulator is ruggedized with an internal cylinder pressure gauge and it has a knurled knob you use to hand tighten it to the CGA-540 fitting on the M-size and larger oxygen cylinders... No Crescent wrench needed...
The photo above shows my InGage™ attached to an aluminum M60 I used as a "roadie" for local travel.
The InGage™ regulator runs around $190 and is made to order in 10 days to two weeks after order confirmation... Let me know if you're interested as the ordering spec's are a bit complicated and they'll want you to confirm them before they start fabrication.
I know 60 liters/minute sounds like a high flow rate, but there are times you'll be glad you have it... like when the beast is jumping ugly and you want to kick start the oxygen therapy process.
Our study found that a flow rate of 40 liters/minute worked almost as fast as 60 liters/minute in aborting a CH and you could sustain that flow rate until the abort. You'll get pooped out and tire rapidly in less than a minute breathing at a flow rate 60 liters/minute, but it can shave as much as a minute off the abort times if you use it for a minute at the start of therapy.
You may want to give the anti-inflammatory regimen a try before you order an oxygen regulator. You'll find it at the following link:
Multimedia File Viewing and Clickable Links are available for Registered Members only!! You need to

or

The post is titled: "123 Days PF And I Think I know Why." I've been pain free since starting this regimen last October after six years as a CCH'er. I was knocking down 4 hits a night the day I started it.
At less than 20 cents a day for the ingredients if you buy them at Costco, the price is right.
Multimedia File Viewing and Clickable Links are available for Registered Members only!! You need to

or

I still take it and so does my wife... and she doesn't have CH... Lots of other health benefits... like it's good for the heart... it lowers BP, cholesterol and triglycerides. It's also good for the bones.
So far of the CH'ers who have tried this regimen and posted their results or sent me PMs or email, 80% have reported favorable results with a marked reduction in the frequency and severity of their CH or they've gone into a pain free remission... At best, verapamil is 50% effective as a preventative and it carries some onerous side effects... If you think about the risk vs benefit ratio... the choice of preventatives becomes obvious...
Take care,
V/R, Batch