US 7025869 B2 abstract inhalation of low levels of nitric oxide can rapidly and safely decrease pulmonary hypertension in mammals precise delivery of nitric oxide at therapeutic levels of 20 to 100 ppm and inhibition of reaction of nitric oxide with oxygen to form toxic impurities such as nitrogen dioxide can provide effective inhalation therapy for pulmonary hypertension application_number US 22902602 A description various nitric oxide precursors can be used in a nitric oxide delivery system nitric oxide precursors can include a nitrogen containing compound with a structure x nitric oxide when x is an organic residue or a precursor salt for example the nitric oxide precursor can include an alkali metal nitrite an alkaline earth metal nitrite a transition metal nitrite or an ammonium nitrite for example potassium nitrite sodium nitrite rubidium nitrite strontium nitrite barium nitrite calcium nitrite copper nitrite zinc nitrite or mixtures thereof the nitric oxide precursor can include nitrogen containing acids such as nitric acid physical characteristics of the nitric oxide precursor such as the dissolution rate can be used to control delivery of nitric oxide the nitric oxide precursor can be dissolved in a solution in which the precursor can dissociate to form anions including nitrite anions and cations the solution can include a buffer solution a buffer solution can include a ph buffer combination which is a solution containing either a weak acid or a weak base at a concentration that renders the solution resistant to change in ph the buffer solution provides a source of hydrogen cations which.