Hey Robb,
Go with the Rx for oxygen inhalation therapy... At flow rates that support hyperventilation (≥25 liters/minute), you'll get very fast aborts and great efficacy... Even at a flow rate of 15 liters/minute, the highest flow rate most physicians will prescribe, you won't be sorry.
I put up a post on how to get a properly prepared prescription for oxygen inhalation therapy at the following link:
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It contains suggested wording for your Rx for oxygen therapy and there are printouts you can download to take along when you see your neurologist or PCP for the Rx.
The important thing for you and your physician to understand is you are using oxygen inhalation therapy as a cluster headache abortive... not a supplement for low arterial oxygenation. You need the increased oxygen flow rate to support a lung ventilation high enough to cast off excess CO2 that can easily build up at too low an oxygen flow rate administered with a non-rebreathing oxygen mask.
Excess CO2 is a powerful vasodilator and it can easily overpower the beneficial vasoconstriction made possible with oxygen at high concentration. Too much arterial CO2 makes aborts very lengthy if not impossible at the higher pain levels where the increased physical activity of doing the CH two-step dance, rocking back and forth, or banging the head generates more CO2.
If your doctor won't prescribe the higher flow rates you can always order a regulator capable of these higher flow rates over the Internet. Getting one of the $27.50 O2PTIMASK™ kits from the CH.com store at the left is also a good idea. The 3-liter reservoir bag on the O2PTIMASK™ is far superior to the 1-liter reservoir bag used on all the disposable oxygen masks the home oxygen therapy folks provide.
The higher oxygen flow rates are very safe. Navy and Marine Corps pilots flying tactical fighter and attack aircraft have been breathing 100% oxygen at flow rates over 40 liters/minute for over 70 years with no ill effects... I've got over 3000 hours flight time in Navy fighters and all of it was spent breathing 100% oxygen from takeoff to landing at flow rates over 40 liters/minute on missions lasting over two hours. I've also been using oxygen inhalation therapy at these flow rates for over 5 years and I'm still here doing just fine at 65...
Take care,
V/R, Batch