The Science of Yoga

misunderstandings about fastbreathing, once stark, have grown more subtle over the years and decades. Yoga authorities who look into the science of respiration now tend to contradict one another on whether it can disrupt the carbon dioxide metabolism and result in harm. Some issue stern warnings about hyperventilation and caution new students to take Bhastrika in small increments so the body can adjust gradually to the challenge. Others argue that fast breathing—if done right, especially with methods they advertise as superior—does nothing to upset the carbon balance.
    The evidence of the classroom suggests that fast breathing can indeed pose a threat. Many a beginning student of yoga has fainted, and even intermediate students can feel dizzy or pass out. The science on the topic is rather limited. It does, however, suggest that advanced students can adapt to the respiratory push or learn to do Bhastrika and other varieties of fast breathing in ways that lessen the dangers.
    In 1983, three scientists in Sweden reported on a study of three highly trained yogis who did “high frequency breathing” for anywhere from thirty minutes to an hour. The scientists began the experiment by fitting the subjects with catheters to ease the sampling of blood. The arterial tap was meant to open a window on how the changing atmosphere of the lungs was affecting the rejuvenation of the blood and the release of carbon dioxide. The scientists took blood samples as the yogis rested—to create a basis for comparison—and after they had performed fast breathing for at least ten minutes.
    The results showed relatively modest drops— 4 percent, 11 percent, and 30 percent. Interestingly, the most experienced of the yogis, a man who taught the other two as well as regular classes in breath control, exhibited the modest decline. His was the decrease of 11 percent rather than 4 percent. That suggested that factors other than proficiency and experience in pranayama could limit the release of carbon dioxide. Overall, the scientists reported that none of the advanced yogis developed symptoms of respiratory alkalosis—the blood disturbance that can result in light-headedness and collapse.
    The overall repercussions for mood and respiratory physiology are radically different if the yoga breathing is slow rather than fast. The process starts with such varieties as Ujjayi—the kind that Behanan did. He was breathing about ten times slower than a resting adult.
    The consequences again centeron carbon dioxide—only this time its rise in the bloodstream, not its fall. Modern investigations echo Paul’s studies of more than a century ago. Today, a standard figure is that cutting lung ventilation in half prompts blood levels of carbon dioxide to double. And the ensuing dilation of cerebral blood vessels means the brain now gets more oxygen, not less.
    Slow breathing turns out to have deep mental ramifications, with increases in calm alertness and raw awareness. Behanan called the state “an extremely pleasant feeling of quietude.”
    Scientists who study animal behavior have linked slow breathing to heightened vigilance. When an animal is ready to protect itself, its exhalations slow. Its heart rate tends to fall. The animal carefully assesses its surroundings to see if it can relax or needs to flee or fight.
    As Paul suggested, many aspects of yoga reinforce slow breathing and limit the exhalation of carbon dioxide, including the repetition of mantras and chants. In 2001, Luciano Bernardi, a medical internist at the University of Pavia, in Italy, reported on a study of nearly two dozen adults. His team found that the repetition of a mantra cut the normal rate of respiration by about half, reinforcing mental calm and producing an enhanced sense of well-being.
    In short, science over the decades has learned a lot about how yoga breathing affects a person’s mood and underlying metabolic state. Fast styles tend to excite and slow ones to calm.
    And it has nothing to do with getting more or less oxygen into the practitioner’s body, contrary to innumerable yogis and gurus, video discs and yoga books, blogs and newsletters. Nevertheless, some yoga authorities go so far as to issue delusional warnings.
    “You’re not used to so much oxygen pouring into your system!” Choudhury, the guru of hot yoga, cautions students who do his deep breathing and begin to feel dizzy. He says nothing of big carbon dioxide drops, the real cause of blackouts.
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