Hey Shaun,

Good question and it looks like you've received a good set of answers.  Glad to hear oxygen therapy is working well.

Most folks understand oxygen therapy well enough to know we need to breathe enough oxygen to saturate our hemoglobin to 100% and achieve hyperoxia (an excess of oxygen in the arterial blood).

What isn't fully understood is while it's important to achieve hyperoxia as an abortive for cluster headaches, it's equally important to reduce CO2 levels below normal (hypocapnia) in order to achieve aborts even faster and more reliably.

The only way to reduce CO2 levels below normal is to hyperventilate...  Breath faster and/or more deeply than normal.

If you think of hyperventilation in terms of minute-volume (the volume of air inhaled in one minute) instead of flow rate or respiration rate, this gets a little easier to understand. 

As you're sitting there at rest and reading this post, you're likely to have a minute volume of 9 liters (That's based on a Respiration Rate of 13 and tidal volume of 0.7 liters). That's the minute volume needed to keep CO2 in the normal range if you're breathing air or 100% oxygen.

It only takes a slight increase in physical activity to cause the minute volume to climb to 15 liters...  And if you're doing the cluster two-step cha-cha or pacing in circles, or seated bouncing your legs up and down and rocking hunched over your knees, or sitting in a fetal position while pounding on your head, the minute volume is likely near 20 liters...  Again, that's just to keep your CO2 level in the normal range breathing normal air or 100% oxygen.

In order to pump out CO2 faster than you're generating it through normal metabolism plus the metabolism associated with the increased physical activity, you need a minute volume of lung ventilation greater than 20 liters. 

The higher the minute volume, the faster you pump out CO2 and the sooner you pump it below the normal level tp achieve hypocapnia.  This is why an oxygen flow rate of 25 liters/minute (a minute volume of 25) is the minimum flow rate that supports effective hyperventilation and why higher flow rates pump CO2 out even faster.

There are a number of breathing techniques that can be used in hyperventilating, and the more effective of these in aborting cluster headaches involves the basics of exchanging as much exhaled breath as possible with 100% oxygen.

When you look at the mechanics of hyperventilation you need to consider the average adult lungs hold a volume of 5 liters. 

The maximum tidal volume of air or 100% oxygen inhaled or exhaled with one breath is 3 liters.  That leaves 2 liters of residual breath basically trapped in the lungs at all times...

That makes the most effective hyperventilation technique one that attempts to squeeze as much of the residual lung volume into exhaled breath as possible. This also removes the most Nitrogen as fast as possible.  Ventilating the lungs with 100% oxygen to the greatest extent removes the inert Nitrogen and also dilutes the residual lung volume to remove the most CO2.

I've done some tests that show inhaling to the maximum extent possible followed by a forceful exhale to the maximum extent possible followed by an abdominal crunch like you're doing a sit up and doing a coughing maneuver holding it for at least a two- or three-count. 

Coughing constricts the intercostal muscles in the ribcage and also forces the diaphragm up into the chest cavity to reduce lung inflation more than normal. 

If I do this correctly I'll hear a wheezing sound during the three count.  BTW, I've had my wife try this and she wheezes just like me and she has never smoked...

As soon as I've squeezed out as much breath as possible, I repeat the procedure again inhaling as deeply and as fast as possible.

The mantra I use is "Squeeze till I wheeze."

This works for me at a flow rate of 25 liters/minute and even better at a flow rate of 40 liters/minute.  If I do this correctly, 4 to 5 times, I start feeling the symptoms of respiratory alkalosis.  This is called paresthesia...  That's a sensation of slight dizziness combined with a tingling of the fingertips and the back of my neck.

If you follow my logic, if I'm feeling paresthesia, I'm hyperventilating.  And If I keep up that level of lung ventilation, I know I'm going to get the fastest abort possible...

Hope this helps.

Take care,

V/R, Batch