Cutting off food mildly (fasting), is considered by some to be a healthy practice. Similarly, cutting off the oxygen supply to the organs and brain, for a short while, is considered by some, to have health benefits and may also influence the depth of meditative activity, in a positive way.
A simple cutoff is achieved by retaining the breath after inhaling or retaining the breath after exhaling. As time passes, while holding the breath, we get an indication from our body that oxygen supply is going low (higher CO2 level in the blood) and we start to get an unpleasant choking feeling. Instinctively at this point we inflate our lungs, which ultimately leads to the continuation of the breathing cycle thus relieving the choking-feeling.
As levels of CO2 rise in the blood, the body prioritizes the brain and directs more of the remaining oxygen to the brain. The brain gets oxygen through the artery going through the neck. By tilting the head backwards, then tilting the head to one of the sides and holding this posture, we can narrow the artery, restricting the blood flow and thus restricting oxygen supply to the brain.
If the head is kept tilted to the side in a particular angle for long enough, dizziness is experienced and ultimately loss of conscience.
Combination cutoff breathing
This breathing exercise is a combination of retaining the breath and narrowing the artery that supplies blood to the brain.
We start by sitting down watching the breath with the eyes closed. After fully exhaling, breath is held, head tilted to the back and then to the right. This position is held for 5 seconds ( I count 21, 22, 23, 24, 25) and then the head is straitened. While head is strait up, we inhale fully. At the last stage of abdominal exhalation, breath is held again, head tilted to the back and then to the left. This position is held for 6 seconds. This sequence continues by alternating between tilting to the left and tilting to the right, every time adding one second to the count.
As an example, counting may get up to 12 seconds (counting 21, 22, 23 ….. 32) which is in total 4 tilts to the right and 4 tilts to the left.
On the last count, 32, we retain the breath as long as we possibly can and then we inhale for relief.