Unlike the nose, which harbors many types of bacteria, the sinuses--the air-filled cavities in the skull surrounding the nose--remain curiously free of intruders. The sinuses, like the rest of the body, are a warm, bacteria-friendly environment. It should be perfect for bacteria to live there, says Jon Lundberg, a physician at the Karolinska Institute in Stockholm. Lundberg and his colleagues have discovered one way that the sinuses stay sterile: they produce nitric oxide, a gas considered a pollutant in the atmosphere and one that is lethal even in small doses to bacteria and viruses.
Lundberg and his colleagues used a syringe and a catheter to remove air from the sinuses of dozens of healthy, nonsmoking subjects. When they analyzed the air samples, they found nitric oxide levels that were close to the highest permissible atmospheric pollution levels. They later removed small pieces of the membrane lining the sinuses, which consist largely of epithelial cells, and found that these cells were the source of the nitric oxide. Nitric oxide, says Lundberg, binds to vital enzymes in microbes, stopping their growth and reproduction and thus protecting the vulnerable sinuses from infection.
But NO has another important role, Lundberg says, one that doctors have known about for some time: it is a powerful vasodilator, a substance that dilates blood vessels. Since the sinuses create high concentrations of NO, when we breathe through our noses, NO probably travels down the airway to the lungs. By then it is so diluted that it isn’t harmful--and according to Lundberg may even be beneficial: it may dilate blood vessels and increase blood flow specifically in areas of the lung that are well supplied with oxygen. That would increase the amount of oxygen in the blood. This is kind of a new physiological principle, says Lundberg.
Doctors already use NO to open up the blood vessels of patients on ventilators suffering from high blood pressure in the lungs. Lundberg thinks it could also help such patients in another way. Typically, ventilator patients receive air directly from their trachea, so they miss out on the NO being generated in their sinuses. In a small trial, Lundberg has found that he can increase the oxygen content of his patients’ blood by nearly 25 percent by simply pumping their own nasal air into their ventilators. Not only is the treatment effective, but it is also less risky than externally administered NO might be. You can never give too much, explains Lundberg, because you only give back what is taken away.