The Science of Yoga

reaction to his newfound discipline. Yoga, he said, had remade him.
    Before, he had frequent headaches, felt run down, and lacked what he called pep. But his days at the ashram gave him new energy and “emotional stability.” Behanan saw the same in his ashram colleagues.
    “They were the happiest personalities that I have known,” he recalled. “Their serenity was contagious.”
    If only he had stopped there. In his book, Behanan went on to describe experiments he had done at Yale in respiratory physiology (a very different field with very different methods and measurement techniques that in many respects are more difficult). He reported that Ujjayi caused a spike in oxygen consumption—more than any other breathing style that he investigated. To allappearances, the oxygen boost seemed to be the secret of yoga serenity.
    But it was only the myth, yet again. Behanan had left India before Gune cast doubt on the popular doctrine of the surges, and the research of the Yale investigator proved to be flawed.
    Unfortunately, his false report added to the unshakable durability of the oxygen myth, which still haunts popular yoga. And his misapprehension neglected what turns out to be one of yoga’s main sources of leverage over the unruly currents of human emotion—the manipulation of the body’s relationship with carbon dioxide, which both Paul and Gune had begun to glimpse.
    Today, after many decades of research, it is fairly easy to distinguish between fact and fiction, despite the complexities of respiratory physiology. The big picture is the best place to start.
    The atmosphere of our planet is 21 percent oxygen. That’s a lot. In comparison, the levels of carbon dioxide are five hundred times smaller. The human body exploits this ocean by means of hemoglobin—the remarkable protein inside our red blood cells that soaks up oxygen like a sponge and carries it from the lungs to the tissues. Typically, the refreshed hemoglobin of a resting person is nearly saturated with oxygen, holding virtually as much as it possibly can. The usual figure for the level of absorption is 97 percent.
    For yoga, the glut of oxygen in the air and the saturation of hemoglobin in the lungs mean that fast or slow breathing does little to change the levels that enter the bloodstream—as Gune found at his ashram and as I found at the University of Wisconsin. The vital gas is available in large quantities no matter what.
    The body’s consumption of oxygen does go up and down. But science demonstrates that it does so in response to changes of muscle activity, metabolism, and heart rate—not breathing styles. As we saw in the last chapter, cardiovascular fitness can raise peak oxygen consumption.
    The story with carbon dioxide in the bloodstream is dramatically different and variable. Consider a person breathing in a relaxed way. Fresh air mixes in the lungs with stale air, creating an inner environment where carbon dioxide levels remain fairly high. This person, in typical fashion, ventilates the lungs so inefficiently that each relaxed inhalation replaces less than 10 percent of the gas.
    Now consider what happensif that individual starts to breath fast. Blasts of fresh air with extraordinarily low concentrations of carbon dioxide (three-hundredths of 1 percent of the atmosphere) rush into the lungs, lowering the inner levels. Nature seeks to equalize the concentrations. So diffusion quickly draws more carbon dioxide out of the bloodstream and into the lungs. The result is that the body’s levels plunge.
    This view is anything but contentious. It is the standard account found in hundreds of medical textbooks as well as official pronouncements of the U.S. Navy. Its responsibilities for thousands of professional divers make it a global authority on human respiration. Fast breathing “lowers body stores of carbon dioxide,” the Navy’s diving manual states, “without significantly increasing oxygen stores.”
    The common name for fast breathing is hyperventilation, and the common danger is passing out. It can also result in dizziness, headaches, light-headedness, slurred speech, and numbness or tingling in the lips, hands, and feet. The drop in carbon dioxide influences mood in many ways. One is through respiratory alkalosis. It heightens the excitability of nerves and muscles—so much so that many circuits short out, producing tingling in the hands and spasms in the muscles.
    Yogis often feel such sensations after doing many