pressure barometric 101Qc325 oncotic Pmax atm mmHg kilopascals mb psia pO2 QQNH freestream psi megapascals MPa LUP pascals pascal lithostatic mPa Barotrauma hydrostatic fsw Diastolic Hg barg Treprostinil ARMED psig pQpsQpi Intraocular GPa SAAMI pitot kbar