Tone, valsalva, CO/Q, types of pressure, assumptions of Poiseuille's law, resistance to blood flow, Reynold's number

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Biomedical Science
BMS 420
Charles Miller

27 August ΔP BF (blood flow) = R ΔP = BF x R ΔP is relatively constant Series – left heart and right heart, kidney Parallel – organs CO (cardiac output) = VR (venous return) Tone Arterioles – affects local flow or overall BP Veins – changes capacitance thus blood volume, venous return Valsalva ↑ thoracic pressure Compressed vena cava (circular to oval) ↓ venous return → ↓ CO RV → ↓CO →LV blood flow to brain → syncope possible Driving pressure is difference between downstream and upstream pressures Generally decreases farther along the vessel Q (blood flow) = Velocity x cross-sectional area Can be used for diagnosis of narrowing in a vessel Narrowed = less cross-sectional area → greater velocity Velocity in aorta vs vena cava Definitions Blood flow: volume of blood/unit time Cardiac output: SV x HR Blood velocity: distance traveled by blood element/unit time Pressure: force/unit area (Torr, mm Hg, Dynes/cm )2 Cardiac Output (CO) or Total Blood Flow (Q) CO =LVO RV (Principle of Continuity) Poiseuille-Hagen Law (ΔPxπr ) 4 Q = 8ηL 8ηL R = 4 πr η = blood viscosity; L = vessel length Types of Pressure Pressure gradient (ΔP vs. absolute) – relatively constant, R and blood flow change ΔP ~ blood flow (swinging door example) Types of pressure Driving pressure (ΔP) or axial pressure Transmural pressure (ΔP across vessel wall) – also called radial or di
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