"Daily Humming is Good For You
During humming, the gas exchange between the nasal passages and the sinuses is 98 percent, almost a complete exchange. During normal exhalation, without humming, the gas exchange rate is only 4 percent.
Poor gas exchange and poor circulation in the sinus cavities create a good environment for bacterial growth. Researchers suggest that daily humming could help reduce the incidence of sinusitis and upper respiratory infections.
Also, sinuses are major producers of nitric oxide, which helps dilate capillaries and increase blood flow. When nitric oxide levels are measured during humming, researchers find that they are 15 times higher than during normal breathing."
- Am J Respir Crit Care Med 02;166(2):131-2