The process of respiration has three components. Pooraka is inspiration of air, kumbhaka means retention, and rechaka is expiration. It can be said that kumbhaka is pranayama and pranayama is kumbhaka, not pooraka and rechaka, which are natural processes. Kumbhaka is again of three types. Bahir kumbhaka is retention of breath at the end of expiration. Antar kumbhaka means holding the breath after inspiration of air, and kevala kumbhaka or sahaja kumbhaka implies holding the breath with no particular state of respiration in consideration. Kevala kumbhaka is one of the final stages of yoga parallel with the state of samadhi. Bahir kumbhaka is not used very often. Hence we shall consider antar kumbhaka i.e. retention or holding the breath after fully inspiring or taking in air.
The physicochemical process of diffusion is dependent mostly on the extent of surface area available for the process to take place, the condition of the membrane in between, and the pressure of gases on either side of the membrane. The process of diffusion, especially of gases as occurs in respiration, is not so much dependent on the time factor. Once the pressure of gases is equalised on either side of the membrane, diffusion comes to a standstill. Hence, withholding the breath for a longer time does not afford any advantage as far as the exchange of gases is concerned. What then could be the advantages derived from kumbhaka?
The rate of the heart is slowed in inspiration. With a slower rate, the resting period of the heart- the diastole- is prolonged. Not only does the heart muscle receive more rest, but the cavities of the heart are also better filled with blood. During the next pumping action of contraction (systole), more blood is pushed into circulation with a better force. Thus general circulation is improved.
During kumbhaka no new air is entering the lungs, so no more oxygenation is taking place. The oxygen tension in the blood is reduced. Up to a certain level this has an advantage. The brain is most sensitive to this lowered oxygen tension, as its needs for oxygen are the greatest. If the quality of the blood is below par, the brain tries to get more blood in quantity.
In the brain and even elsewhere in the body, all the capillaries are not functioning at all times. Some of them are lying dormant in a collapsed or closed state. In order to receive a greater quantity of blood, these capillaries are opened up. The effect is more marked in the brain. Thus cerebral anoxia leads to cerebral vasodilation, more capillaries open up and circulation improves.
It must be emphasised that this effect is beneficial up to a certain optimum level only. Beyond this level it is distinctly harmful. Hence, it is always stressed that the practice of kumbhaka must be undertaken with the guidance of an experienced teacher. The practice of pranayama has fallen into disrepute in the eyes of the public, mainly because of the malpractice of breath retention. This explanation of cerebral anoxia, causing cerebral vasodilation, applies equally well to the practice of bahir kumbhaka.
The third phase of respiration is expiration. Expiration is a passive act. For stretching a rubber band one needs a conscious effort, while once the active action is released the rubber automatically assumes its original position. The same principle applies to the act of respiration. But the yogic act of rechaka is a slow, guided and controlled process. It should take double the time taken for inspiration.
The first advantage of slow respiration is mechanical. With a sudden release the rubber or the elastic tissue in the lungs will snap back violently, but with a slow release it will maintain its elasticity. The major advantage of slow rechaka, however, is in the brain and psyche. The conscious effort required for slow release needs the help of the cerebral cortex of the brain. The cerebral cortex sends inhibitory impulses to the respiratory centre in the midbrain. These inhibitory impulses from the cortex overflow into the adjoining area of the hypothalamus concerned with emotions, and quieten this area. Hence, the soothing effect of a slow expiration.
It also helps the next stage of ashtanga yoga i.e. pratyahara. Pratyahara means drawing in of the senses and the thought processes. The human mind is like a child. If it is asked not to do a certain thing, it will deliberately try to do it. Hence it is better to give a positive suggestion to a child as well as to the human mind. Instead of asking it to stop thinking, it is given the positive suggestion of observing the respiration. Thus the senses and the thought processes are automatically switched off.
Throughout our life, we are breathing continuously, and involuntarily, day in and day out, during waking and sleeping states. The very first instruction in the teaching of pranayama is to observe this breathing process as it is going on naturally, without trying to modify it. Even this simple act has a physiological implication. Automatic respiration is controlled by the respiratory centre, situated in the midbrain. But once we become aware of the process of respiration, its control shifts to the cerebral cortex. This involvement of the cerebral cortex causes the cortex to develop. Further development of the cerebral cortex leads to a higher stage of the evolutionary cycle.
Bhastrika or the bellows type of pranayama expels the gases from the stomach. One feels like belching while performing bhastrika. This is entirely a mechanical effect.
The recti and the other anterior abdominal wall muscles are well exercised during bhastrika. If these muscles are properly developed, the intestines and other organs in the abdominal cavity get proper support from the front. These organs are attached to the spinal column and are loosely hanging in the abdominal cavity. If they have no support in front, they cause a stretch on the lumbar spine leading to low back pain. But by developing the front muscles, and affording a support to intestines from the front, this strain on the spine is lessened, and the back pain is relieved. Due to this frontal support, the circulation of the intestines improves and hence they function better.
There is a lot of stagnant blood collected in the splanchic venous pool of the intestines. This stagnant blood is pumped out thus increasing the amount of blood in circulation.
Bhastrika exercises the diaphragm, which is a major component in the process of respiration, and renews the residual air in the lungs. Bhastrika is a process of hyperventilation, leading to respiratory alkalosis, which has a soothing effect on the respiratory centre. Hence it is observed that we can perform a better kumbhaka after doing bhastrika. Bhastrika also has certain yogic influences on the anahata and manipura chakras.