Physiology of Bhastrika
Understanding the Bellows Exercise
David Coulter
Students of yoga hear many mysterious statements about breath that cannot be explained by modern biochemistry and physiology: Breathing absorbs prana into the body; prana controls the universe; prana is the vehicle of cosmic consciousness. Even though biomedical science stands helpless before such statements, scriptures from all over the world echo with similar mystery. The Prashno-panishad says, “Prana springs from the Atman and is as inseparable from the self as the shadow is from he who casts the shadow.” Genesis 2:7 reads, “God formed man from the dust of the ground, and breathed into his nostrils the breath of life, and the man became a living being.” We find in John 20:22 “He breathed on them, and said ‘Receive the Holy Spirit.’”
Breathing is also one of the most remarkable functions of anatomy and physiology. It is the only biological activity which can be brought under full conscious control and
yet functions semi-automatically 24 hours a day. It operates between two biological features of our being: (1) the conscious operation of the skeletal muscles, and (2) the unconscious operation of internal organs and the autonomic nervous system.
Controlling the Breath
Our practical concern here is the control of willful, habitual, and semi-automatic actions of the skeletal muscles of respiration. These are the same kinds of muscles that we use for walking, running, and speaking. By contrast, the lungs are internal organs—delicate, spongy receptacles for the breath of life. They are passive and can receive and expel air only because the surrounding skeletal muscles of respiration expand the semi-rigid chest cavity for inhalation and permit its contraction for exhalation.
Centers in the brain stem and spinal cord act to control the muscles of respiration. Many physical and mental factors have an effect on those centers. Some of the factors are environmental, such as altitude, humidity, and airborne noxious agents. Some are mental, such as excitement, anxiety, and boredom. Some factors feed back directly from the internal environment of the body, such as levels of oxygen and carbon dioxide in the blood and cerebrospinal fluid. Other factors, such as volition and long-established habits of breathing and posture, link the motor centers of the cerebrum directly to the brain stem and spinal cord.
Of the various factors that influence the control centers, volition is always at our disposal. Just as we can choose how many times to chew a bite of food or how to adjust our stride walking up a hill, we can also choose how we breathe. Although most of the time we run on automatic (allowing input from internal organs to regulate the rate and depth of our breathing), yogis emphasize choice. They have discovered the value of learning to regulate respiration consciously, to breathe evenly and diaphragmatically for meditation, to hyperventilate for bellows breathing, and to suspend the breath at will. In this column we will try to resolve at least part of the mystery surrounding bellows breathing by looking at some of its physiological aspects.
Oxygen and Carbon Dioxide
If you were swimming underwater, or trying not to breathe exhaust fumes when bicycling, or running short of air in a collapsed mine shaft, your main problem would be getting enough oxygen. The reason is simple. If the supply of oxygen to your brain is interrupted, the brain will suffer cellular damage in less than a minute and death of the tissue in about five.
Hyperventilation brings extra oxygen into the lungs and expels more carbon dioxide than usual. This raises the blood content of oxygen and lowers the blood content of carbon dioxide. Except for special circumstances, the extra oxygen obtained from hyperventilation is not harmful. So why do we hear of hyperventilation causing panic attacks? Why not have as much oxygen and as little carbon dioxide as possible?
The problem is that hyperventilation creates a paradoxical situation. Although it increases the level of oxygen in the blood, it results in a decreased supply of oxygen to the actual tissues of the brain and spinal cord. This occurs indirectly. The decrease in blood carbon dioxide that accompanies hyperventilation causes constriction of the small arteries and arterioles of the brain and spinal cord. (An arteriole acts something like an adjustable nozzle on the end of a garden hose. The nozzle can open to emit a lot of water, or clamp down to permit only a fine spray.) The decreased carbon dioxide causes the encircling smooth muscle cells of arterioles to contract. The blood supply is choked down, and if blood cannot get to the brain tissue it doesn’t matter how well it is oxygenated.
Decreases in blood levels of carbon dioxide could cause you to pass out, which is why lifeguards do not let swimmers hyperventilate vigorously before swimming underwater. Lowered carbon dioxide and cerebral vasoconstriction are also the main reasons hyperventilation causes obvious neural and neuromuscular symptoms such as increased excitability of nerves and muscles, tingling, numbness, twitching, and muscle cramps. Hyperventilation can also cause general symptoms such as fatigue, irritability, light-headedness, inability to concentrate, and panic attacks. (The folk remedy for panic attacks is to breathe into a paper bag; this increases carbon dioxide levels and opens the cerebral circulation.)
If beginning students start to practice the bellows exercise excessively they are likely to experience at least some of these symptoms—especially irritability. Over time, however, it is possible to expand your practice and gradually become less sensitive to
decreased carbon dioxide. To understand how this comes about, we need to look at two of the many reflexes that control breathing.
The Chemoreceptors
One reflex originates from peripheral chemoreceptors, specialized receptors in the carotid arteries. These monitor oxygen in arterial blood and are one connecting link between the internal organs and the skeletal muscles of respiration. They send sensory information to the brain, but instead of feeding into autonomic nervous system circuits that regulate internal organs, they feed into the controlling circuits of the nervous system that regulate breathing. The peripheral chemoreceptors do not respond significantly to small decreases in blood oxygen, but they become extremely sensitive as values for blood oxygen plunge. For example, if you hold your breath long enough to cut your arterial oxygen in half, your subsequent rate and depth of breathing will quadruple the amount of air delivered to the lungs.
A second reflex originates from central chemoreceptors on the surface of the brain that are sensitive to carbon dioxide in the cerebrospinal fluid. These strongly stimulate the rate and depth of respiration in response to increased levels of carbon dioxide. Because it takes a while for the carbon dioxide in cerebrospinal fluid to come to a state of equilibrium with the carbon dioxide in the blood, the stimulating effects of holding your breath or the retarding effects of hyperventilation are not felt as quickly as when the carotid artery chemoreceptors react to severely diminished supplies of oxygen.
High Altitude and the Bellows Breath
We can best understand responses to breathing exercises such as bhastrika if we look at our responses to high altitudes. Sudden exposure to high altitudes can be dangerous because: (1) There is less oxygen in the atmosphere. (2) Levels of inspired and arterial oxygen are decreased. (3) Hyperventilation results from the stimula- tion of peripheral chemoreceptors; this compensates for decreased blood levels of oxygen, and would be fine but for one serious problem. (4) Hyperventilation soon lowers the partial pressure of carbon dioxide in the cerebrospinal fluid, and the sorely needed continuing hyperventilation (for the sake of oxygen) is reduced because of decreased carbon dioxide. (5) To make matters worse, cerebral vasoconstriction accompanies the lowered blood carbon dioxide and causes ischemia (insufficient blood flow to the brain). (6) Finally, one can die before cerebral ischemia causes the buildup of enough carbon dioxide in the brain to dilate the arterioles and increase the oxygen supply to the cells.
If you acclimatize to high altitudes gradually over a period of days, however, bicarbonate levels in the cerebrospinal fluid are reduced, thereby increasing its acidity. This has an effect that is similar to elevating the level of carbon dioxide—it restimulates the central chemoreceptors and causes hyperventilation to continue. With gradual acclimatizing to high altitudes the cerebral arterioles also become less sensitive to lowered carbon dioxide and permit adequate perfusion of blood to the capillary beds of the brain.
This same mechanism will operate if you practice the bellows exercise at ordinary altitudes. It also will enable you to breathe faster and more deeply at high altitudes and at the same time allow you to handle decreased carbon dioxide gracefully. Carrying these and other compensatory mechanisms to their limits, a few people have now climbed Mount Everest (altitude 29,000 feet) without bottled oxygen, and they were able to continue
extreme hyperventilation—in an atmosphere containing the equivalent of only 5 percent oxygen at sea level (rather than the usual 21 percent)—while their arterial carbon dioxide dropped to one-fifth of its normal value. This appears to be about the limit of human ability to adapt to high altitudes. The untrained subject who has not developed this capacity to handle greatly decreased levels of carbon dioxide will lose consciousness at an altitude of 29,000 feet in less than two minutes.
Bhastrika, the Bellows Exercise
Now we can understand some of our responses to an exercise such as bellows breathing. Try taking 40 moderately vigorous bellows breaths in 15 seconds. Your blood oxygen rises and your blood carbon dioxide drops. When you stop, your rate and depth of breathing will decrease for a few moments in response to decreased stimulation of the peripheral chemoreceptors. This will be a minor reaction, but you can still feel it.
If you try six rounds of this exercise, with 15 seconds intervening between each round over a period of three minutes, it will lower carbon dioxide not only in your arterial blood but in your cerebrospinal fluid as well, and you will notice a decrease in the rate and depth of your breathing for a longer time. There is probably little point in bothering with the exercise unless you stimulate this much reaction. If you do it once a day you will not need to worry about acclimation, but if you overdo the practice in the beginning you may start causing the same problem that occurs with sudden altitude changes. Until the bicarbonate levels in your cerebrospinal fluid adjust, your central chemoreceptors will retard your breathing in response to lowered carbon dioxide. In time, you will be able to hyperventilate vigorously without creating problems for yourself.
Besides helping us acclimatize to high altitudes, the bellows exercise can give us many everyday benefits. If you are chronically sleepy and short on energy, for instance, it may be because you are surviving with less oxygen and more carbon dioxide than is optimal. (Remember, the peripheral chemoreceptors are not very reactive to small decreases in blood oxygen, and you may not notice that you could use more.) If you would like to remedy this by using conscious habits of breathing, practicing the bellows exercise will increase the level of oxygen in your blood and accustom you to decreased levels of carbon dioxide. This will give you the benefits of greater alertness as well as a new sense of well-being, thus resetting your standards for energy and enthusiasm.
Yoga International, now Yoga + Joyful Living
Jan/Feb 1995
Issue 22