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1、PathogenicMechanismofPulmonaryHypertensionRoleofCa2+andIonChannelsandNO1Certainproblemsrelatedtodistributionofbloodflowandotherhemodynamicsarespecialtothepulmonarycirculationandareespeciallyimportantforgasex-changeinthelungs.Thepresentdiscussionisconcerne
2、dspeciallywiththesespecialfeaturesofthepulmonarycircu1ation2PHYSIOLOGICANATOMYOFTHEPULMONARYCIRCULATORYSYSTEM3PulmonaryvesselsThepulmonaryarteryextendsonly5centimetersbeyondtheapexoftherightventricleandthendividesintotherightandleftmainbranches,whichsuppl
3、ybloodtothetworespectivelungs.4Thepulmonaryarteryisalsothin,withawallthicknessabouttwicethatofthevenaecavaeandonethirdthatoftheaorta.Thepulmonaryarterialbranchesareveryshort,andallthepulmonaryateries,eventhesmallerarteriesandarterioles,havelargerdiameters
4、thantheircounterpartsystemicarteries.5This,combinedwiththefactthatthevesselsareverythinanddistensible,givesthepulmonaryarterialtreealargecompliance,averagingalmost7ml/mmHg,whichissimilartothatoftheentiresystemicarterialtree.Thislargecomplianceallowsthepul
5、monaryarteriestoaccommodateabouttwothirdsofthestrokevolumeoutputoftherightventricle.Thepulmonaryveins,likethepulmonaryarteries,areshort,buttheirdistensibilitycharacteristicsaresimilartothoseoftheveinsinthesystemiccirculation6BronchialVesselsBloodalsoflows
6、tothelungsthroughsmallbronchialarteriesthatoriginatefromthesystemiccirculation,amountingtoaboutlto2percentofthetotalcardiacoutput.Thisbronchialarterialbloodisoxygenatedblood,incontrasttothepartiallydeoxygenatedbloodinthepulmonaryarteries.Itsuppliesthesupp
7、ortingtssuesofthelungs,includingtheconnectivetissue,septa,andlargeandsmallbronchi.7PRESSURESINTHEPULMONARYSYSTEMPulmonaryarterialpressureaveragesabout25mmHginthenormalhumanbeing;thediastolicpulmonaryarterialpressure,about8mmHg;andthemeanpulmonaryarterialp
8、ressure,15mmHg.Pulmonaryarterialpressure8PulmonaryCapillaryPressureThemeanpulmonarycapillarypressure,hasbeenestimatedbyindirectmeanstobeabout7mmHg.Theimportanceofthislowcapillarypressureisrelatedtofluidexchangefunct
