Hey Ronkh,

Thanks for bringing up the topic of oxygen flow rates...  You're quite right...  a flow rate of 15 liters/minute 100% oxygen will saturate blood hemoglobin...  in fact, it only takes a flow rate of 7 to 9 liters/minute with 100% oxygen to do this when using a fully functioning non-rebreathing mask and remaining motionless...

Unfortunately, neither flow rate provides sufficient lung ventilation to remove excess CO2 that will build up when using a non-rebreathing mask with any physical activity...  such as doing the cluster two-step dancing around the oxygen cylinder, rocking back and forth in a fetal position, or headbanging... 

I'm sure with your knowledge of respiratory physiology, that you already know what happens when CO2 levels climb above normal...  that elevated CO2 levels results in the hypercapnia that stimulates among other things, increased respiration, elevated heart beat and vasodilation as the result of the body's homeostatic mechanism that controls arterial pH... and that under these conditions even while breathing 100% oxygen, the cerebral vasodilation is so great that an abort of a cluster headache may not be possible... 

It's also likely you're aware of the respiratory alkalosis that occurs during hyperventilation, where the pH of arterial blood climbs above normal when CO2 is cast off faster than it's generated by normal metabolism, and that hemoglobin has an increased affinity for oxygen when arterial pH is higher than normal...  Remember the Bohr Effect?  This is where hemoglobin can actually attract and carry more oxygen molecules than at a normal arterial pH of 7.35 - 7.45. 

But then you're probably also aware that most of the finger pulse oximeters are only calibrated to .99 or 99% SpO2 like the MD300C1 I've owned for over four years... so it's impossible for them to measure any higher level of oxygen saturation...  That requires BGA - blood gas analysis...  a far more invasive procedure with sophisticated equipment that measures the partial pressure of blood oxygen (PO2) and carbon dioxide (PCO2) concentrations in mm Hg. 

There are several studies that have shown that breathing 100% oxygen under normocapnic conditions (normal respiration with normal CO2 levels) results in a PO2 of 570 mm Hg and that breathing 100% oxygen under hypocapnic conditions (hyperventilating to reduced CO2 levels) results in a PO2 of 585 mm Hg.  If you converted that PO2 to an equivalent pulse oximetry value it would equal an SpO2 of 1.03 or 103%.

It's also interesting to note that the hypocapnia and increased arterial pH associated with the respiratory alkalosis that results from hyperventilation stimulates a level of cerebral vasoconstriction similar to that stimulated by sumatriptan succinate (imitrex), but greater in magnitude than the cerebral vasoconstriction induced by hyperoxia at normocapnic levels... 

Moreover the combination of hyperoxia, hypocapnia associated with respiratory alkalosis with symptoms of paresthesia resulting from voluntarily hyperventilating with 100% oxygen can produce a very rapid increase in cerebral vasoconstriction with cluster headache aborts up to three times faster at better than 95% efficacy, than oxygen therapy at a flow rate of 15 liters/minute.

I do want to thank you again for bringing up the topic of oxygen therapy flow rates.   We wouldn't want perspective or current oxygen therapy users to avoid using the more effective oxygen flow rates of 25 to 40 liters/minute that can abort their cluster headaches so much faster and more reliably than the lower oxygen flow rates.

Too many physicians and neurologists who prescribe the lower oxygen flow rates for cluster headache sufferers thinking it's sufficient to achieve the hyperoxia needed to abort a cluster headache have apparently forgotten their course in Respiratory Physiology 101 they took in med school. 

In addition, unless they served prior military service as a pilot or flight surgeon, it's also likely they were never exposed to aviation physiology or aerospace medicine so it's understandable that they're unaware that repeated exposure to breathing 100% oxygen at flow rates much higher than 25 liters/minute is quite safe...  In fact, Navy and Marine Corps pilots flying the F/A-18s do this routinely up to three times a day/night breathing oxygen from takeoff to landing on missions lasting 2 hours.

Oh yes... one last point...  as a CH.com Newbie, you might want to attend a few of the conventions and meet some of the regulars who routinely provide assistance to fellow CH'ers in need before you opine that we're jaded or selling something.  I don't know anyone who comes here to make money and all of us volunteer our time freely...  We also make donations to CH.com and OUCH.  Have you made yours?

Take care,

V/R, Batch