Rightheart pressuredoesnotequalpericardial pressureinthepotassium chloridearrested canine heartinsitu

Recently proposed concepts ofpericardial surface pressure,asopposed toliquid pres- sure,haveadvanced ourunderstanding oftherelationship between pericardial andheart chamber pressures.However, thesubsequent suggestion that right heart intracavitary pressureequals, ornearly equals, pericardial surface pressureisnotstrictly consistent withthephysiology ofpericardial con- straint. Ifright heart pressureequals pericardial surface pressure,thentransmural right heart pressure equals zero.Because ofthedifficulty inmeasuring pericardial pressuredirectly inthebeating heart we designed anexperiment intherecently arrested canine heart insitu tomeasure pericardial pressure indirectly andtotestthehypothesis that right heart transmural pressureiszero underreasonably physiologic, static equilibrium conditions. According toastatic equilibrium analysis ofthepressures acting acrossthewalls oftheheart, ata given volume thechange inright heart pressurecaused by removing thepericardium isequal tothepericardial pressurewhenthepericardium isintact. We found that this dropinpressurecaused bypericardiectomy didnotequal right heart pressureandtherefore that right heart transmural pressuredoesnotequal zero. Circulation 76,No.2,357-362, 1987.