Cardiac Output Regulation

Pagina 1

SYSTEM/((/RCULA T/①Nma = PERIPHERALcircolatori 285%totalbloodV 15%totalbloodV ', / " MICROCIRCULATION " " \ :| I HLUI / 'a ARTERIES: VEINS: theMAJORRESISTNE theMAJORRESERVOIR COMPONENT forbloodvolume Pa E - t.EE?IvIIFsi:niricantsP)oo-FPra(orPf) Ra Ru FILUNGPRESSORE Ca Cv BIGGERCompliance: /BigAVvs scuoleAPF- ÷ ELECTRICALMODEL forSYSTEMICCIRCULATION ⊥thisis WHYthe % Co= VR [a= 2%(v Mechanism isPOSSIBLE Ra=170%Rv HOWEVERisgodtotake intoconsiderationtheFact that(vempiricalyresultedtobeNOT LINEAR VESSELS' RESISTANCE REE-µ%e theRESISTANCE sinceAP= RQ, thepressoredrop. inVESSELSdramatically- additionalby→ invesselsdraunaticallyincreaseas Poiseuiue'slaw INCREASESas thevessel's theresistance(R)increases, wrt µ RADIUSDECREASES tuesaune flow(Q)ButactuallyitisSupposedtohadanyforlarge COMPLIANCEplaysanImportant|tlbes. RoleinpressoreREGULATION pormodernesofELASTICITA COMPLIANCE((p)= DP YOUNG'SMODULUS(e)is howmucuavessechamgesitsvolumeresuetingin agmaaaapaggunearopwreamywpy.pagfanimd.caforoftheSTIFFNESSofanelasticSolidMaterial theHIGHERE,thetessthe elongatiom(all)Underthe semePRESSORE(Fla)→ It is an example of NON LINEAR model that works around an EQUILIBRIUM POINT (or Working Point) in this case determined by the balance of 2 interacting steady-state curves: 1. CO, which is determined by the heart properties2. VR, which depends on the peripheral circulation It is not just CO = VR, which is the trivial consequence of the constant total blood volume (VT, alias, volemia) that circulates. It is by far more than this! “The cardiac output (CO) in a compensated heart is equal to and determined by the amount of blood flowing into the heart (VR), and may be increased or diminished within very wide limits according to the inflow.” (Starling, 1918) This mechanism is important since it…