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CIRCULATION

CIRCULATION. MEDICAL PHYSICS PRESSURE FLOW RESISTANCE. Distribution of blood to the body organs. Figure 15-13: Distribution of blood in the body at rest. Blood vessel functions: overview. Strong and elastic arteries. Arterioles control blood flow and pressure.

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CIRCULATION

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  1. CIRCULATION MEDICAL PHYSICS PRESSURE FLOW RESISTANCE

  2. Distribution of blood to the body organs Figure 15-13: Distribution of blood in the body at rest

  3. Blood vessel functions: overview Strong and elastic arteries Arterioles control blood flow and pressure Caps: thin and with large area for diffusional exchange Compliant, large, low R veins with valves assures blood return Figure 15-1: Functional model of the cardiovascular system

  4. Pulse and Mean Arterial Pressures Figure 15-5: Pressure throughout the systemic circulation

  5. Systolic pressure Mean pressure Diastolic pressure Large arteries Left ventricle Arterioles Capillaries Venules and veins Fig. 10-8, p. 283

  6. Some Physics of Fluid Movement: Blood Flow • Flow rate: (L/min) • Flow velocity = rate/C-S area of vessel Figure 14-6: Flow rate versus velocity of flow

  7. Flow proportional to P Resistance reduces flow Reduce vessel diameter Increase viscosity or tube length With constant flow, R can affect P Poiseuille’s Law Flow = P/R R = length · viscosity / radius4 CO = art.bp/TPR Figure 14-4 c: Pressure differences of static and flowing fluid

  8. Arteriolar constriction alters blood flow

  9. Arterioles: large and variable R Flow = P/R R = P/Flow Parterioles and Rarterioles largest in CV system Figure 14-2 : Pressure gradient in the blood vessels

  10. Lowest velocity Largest total cross sectional area Hydrostatic pressure drops slightly Capillary Blood Flow Figure 15-17: The velocity of flow depends on the total cross-sectional area

  11. Velocity of flow (mm/sec) Anatomical distribution Total cross-sectional area (cm2) Blood flow rate (liters/min) 6,000 0.5 500 4.5 5 Aorta Arteries Arterioles Capillaries Venules Veins Venae cavae Fig. 10-14, p. 291

  12. P1 > P2 P1 FLOW P2 mm Hg P = FLOW x R P R FLOW = P FLOW R = L/min or ml/sec mm Hg ml/sec Peripheral Resistance Units (PRU)

  13. POISEUILLE’S LAW GOVERNING FLUID FLOW(Q) THROUGH CYLINDRIC TUBES (Pi - Po) r 4 • (FLOW)Q = 8nL DIFFERENCE IN PRESSURE VISCOSITY LENGHT RADIUS

  14. LAMINAR VS TURBULENT FLOWTHE REYNOLD’S NUMBER LAMINAR FLOW TURBULENT FLOW p = density D = diameter v = velocity n = viscosity Nr = pDv / n laminar = 2000 or less

  15. RESISTANCE AND BLOOD FLOW 1.RESISTANCE 2.CODUCTANCE =1/ RESISTANCE 3.DIAMETER OF THE BLOOD VESSELS 4.CRITICAL CLOSING PRESSURE

  16. Total peripheral resistance Blood viscosity Arteriolar radius Concentration of plasma proteins Number of red blood cells Local (intrinsic) control Extrinsic control Myogenic responses to stretch Vasopressin Heat, cold application (therapeutic use) Angiotensin II Histamine release (involved with injuries and allergic responses) Epinephrine and norepinephrine Local metabolic changes in O2, CO2, other metabolites Sympathetic activity (exerts generalized vasoconstrictor effect) Fig. 10-12, p. 290 Major factors affecting arteriolar radius

  17. 1.DISTENSIBILITY=^VOL/^P x ORIGINAL VOL 2.VASCULAR COMPLIANCE(CAPACITANCE)=^VOL/^P 3.DELAY COMPLIANCE 4.VOLUME PRESSURE CURVE 5.ARTERIAL PRESSURE PULSATION 6.TRANSMISSION OF PRESSURE PULSES 7.DAMPING OF THE PRESSURE PULSES

  18. CLINICAL METHOD FOR MEASURING BP 1.PALPATION METHOD 2.AUSCULTATORY METHOD(KORTKOFF SOUNDS) A.SYSTOLIC BP B.DIASTOLIC BP C.MEAN ARTERIAL BP

  19. Pressure-recording device Stethoscope Inflatable cuff Fig. 10-7a, p. 282

  20. When cuff pressure is between than 120 and 80 mm Hg: Blood flow through the vessel is turbulent whenever blood pressure exceeds cuff pressure. Intermittent sounds are heard as blood pressure fluctuates throughout the cardiac cycle. Fig. 10-7c (middle), p. 282

  21. Cuff pressure Blood pressure Fig. 10-7b, p. 282

  22. Effects of gravity on arterial and venous pressures. Each cm of distance produces a 0.77 mmHg change. Veins Arteries 0 100 mm Hg 190 mm Hg Sphincters protect capillaries VENOUS PUMP keeps PV < 25 mm Hg

  23. Pressure = 0 mm Hg Pressure = 100 mm Hg 90 mm Hg caused by gravitational effect 10 mm Hg caused by pressure imparted by cardiac contraction Pressure = 90 mm Hg Fig. 10-26, p. 301

  24. VEINS AND THEIR FUNCTION 1.VENOUS PRESSURE 2.RIGHT ATRIAL PRESSURE 3.EFFECT OF GRAVITY ON VENOUS PRESSURE 4.PRESSURE REFERENCE 5.BLOOD RESERVOIRS

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