The Science of Yoga

situation was no anomaly or medical oddity but instead a new kind of danger. Healthy individuals can seriously damage their vertebral arteries, they warned, “by neck movements that exceed physiological tolerance.” And yoga, they stressed, “should be considered as a possible precipitating event.” In its report, the Northwestern team cited not only Nagler’s account of his female patient but Russell’s early warning. The concern was beginning to ripple through the world of medicine.
    The next case showed its global spread. In Hong Kong, a woman of thirty-four practiced yoga faithfully. One day, shortly after doing a Headstand for five minutes, she developed a sharp pain in her neck and numbness in her righthand. A surgeon made an incorrect diagnosis and prescribed neck traction and physical therapy. Her symptoms got worse. The attacks of nausea and dizziness grew in severity. Eventually her troubles came to the attention of a medical team at the University of Hong Kong and Queen Mary Hospital.
    By this point—some two months after the neck pain—the doctors found that the woman showed signs of disorientation and paralysis on the left side of her body, as well as an inability to feel sensations of touch. Her eyes displayed the jerky movements typical of a rear-brain stroke, and the physicians made that the provisional diagnosis.
    The doctors repeatedly scanned the woman’s brain with imaging devices over the next few days. But they found nothing, even as her consciousness began to ebb. Finally, the team located a region of tissue that appeared dead from lack of blood. It ranged over the pons, the thalamus, and the occipital lobe. The doctors sought to pinpoint the cause of the stroke by injecting dye into the woman’s neck arteries and taking X-rays. The diagnostic images showed no problems in the vertebral arteries but a severe blockage in the basilar artery.
    The doctors had put the woman on blood thinners and clot-dissolving drugs after the provisional diagnosis. Eventually she underwent intensive physical therapy as well. After a year, she regained strength on the left side of her body. But she still exhibited clumsiness in her left hand.
    Jason K. Y. Fong, a young neurologist, led the analysis. In 1993, he and his colleagues reported that the woman’s problems had probably begun when vertebral arteries in the C1–C2 region suffered a tear or a severe reduction in blood flow. That produced a clot, the doctors wrote in Clinical and Experimental Neurology , that eventually worked its way into the basilar artery and blocked the blood supply to her inner brain. They attributed the lack of visible damage in the vertebral artery to the likelihood that the exceptionally long period between the Headstand and the hospital admission “may have allowed sufficient time for spontaneous healing.”
    The delay in uncovering the woman’s stroke and its likely cause bore lessons for the medical community, Fong and his colleagues argued. The main one was the importance of learning the inconspicuous details of case history, which if taken seriously could speed diagnosis and treatment. Their warning echoed Russell’s observation about overlooking the origin of brain damage.
    The gravity of theHong Kong case, the team concluded, showed that yoga could pose extraordinary risks to human health. The doctors cautioned that postures in which the neck came under great strain could be “potentially dangerous or even lethal.” The latter word is one that physicians, steeped in a culture of cautious optimism and dry understatement, tend to avoid if possible.
    The spike in clinical reports made yoga strokes a common feature of medical concern. The danger was judged to be at least partly due to underlying weaknesses in the vertebral arteries of some individuals. But it was difficult if not impossible to know who was at risk. So the warnings spread. They appeared not only in medical journals but in textbooks as health specialists gained new appreciation of the threat.
    Science of Flexibility , whose first edition appeared in 1996, featured a section called X-Rated Exercises. It linked strokes to poses that stretched the neck far backward, including the Wheel and the Cobra. In summarizing the medical findings, the book’s author called the value of the postures too small “to justify the potential, although rare, risk of vertebral artery occlusion.” He suggested avoidance.
    Injuries due to yoga turned out to range far beyond