Humming increasing nitric oxide production is well documented. Here is one journal article but there are others: https://erj.ersjournals.com/content/22/2/323 h

Humming increasing nitric oxide production is well documented. Here is one journal article but there are others: https://erj.ersjournals.com/content/22/2/323 https://erj.ersjournals.com/content/22/2/323 Nitric Oxide dilates the nasal passages and is also a vasodilator as well. A simple n=1 test is to do nasal humming and test blood pressure before and after. I can typically get a (temporary) 10 point drop. Nitric Oxide is also anti-bacterial and humming may help clear sinus infections.