Q: inhaled nitric oxide is given/measured as parts per million (ppm). What does it mean?

Answer: This is the expression of diluting the concentrations of substances. Parts per million (ppm) means out of a million.

INO (nitric oxide) is a pulmonary vasodilator and is a gaseous blend of nitric oxide and nitrogen (0.01% and 99.99%, respectively for 100 ppm). It is supplied in aluminum cylinders as a compressed gas under high pressure (2000 pounds per square inch gauge [psig]).