1. Hemodynamics

2. Objectives Define resistance and understand the effects of adding resistance in series vs.in parallel in total resistance and flow. Describe the relationship between pressure, flow and resistance in the vasculature. Explain how Poiseuille’s law influences resistance to flow and define the factors that determine resistance. Describe the change in pressure along vascular tree and explain how flow to any organ is altered by change in resistance to that organ. Explain types of flow, laminar versus turbulent and the transition between them; Reynold’s number.

3. Distribution of Cardiac Output at Rest Blood is constantly reconditioned so composition remains relatively constant Blood is constantly reconditioned so composition remains relatively constant Reconditioning organs receive more blood than needed for metabolic needs Reconditioning organs receive more blood than needed for metabolic needs Digestive organs, kidneys, skin Digestive organs, kidneys, skin Adjust extra blood to achieve homeostasis Adjust extra blood to achieve homeostasis Blood flow to other organs can be adjusted according to metabolic needs Blood flow to other organs can be adjusted according to metabolic needs Brain can least tolerate disrupted supply Brain can least tolerate disrupted supply

4. Hemodynamics: Factors affecting blood flow How much blood flow and what determines how much? Blood Flow: Volume of blood flowing through any tissue in a given time period (mL/min)

5. Relations of pressure, flow and resistance Flow = Change in Pressure Resistance F = PP R Flow is: Directly proportional to pressure gradient Inversely proportional to resistance

6. ( the greater the ∆P, the greater the flow) Flow  ∆P Flow  ∆P P1 = 90 mmHg P2 = 40 mmHg ∆P = P1 – P2 = 50 mmHg Pressure gradient is pressure difference between beginning and end of a vessel Blood flows from area of higher pressure to area of lower pressure

8. Path of Blood Flow in the Circulatory System Heart (left ventricle) aorta arteries arterioles capillaries venules veins vena cava Heart (right atrium)

9. Resistance to BF Resistance is measure of opposition of blood flow through a vessel   Resistance arises due to   interactions between the moving fluid and the stationary tube wall   interactions between molecules in the fluid (viscosity)   (the higher the R, the smaller the flow). Flow  1/R   Factors determining the resistance:   Vessel length   Vessel radius   Blood viscosity

10. 1. Blood vessel length Resistance to Flow is directly proportional to the length the longer the length  the higher the resistance the longer the length  the higher the resistance e.g. Obesity e.g. Obesity

11. 2. Blood viscosity Resistance is directly proportional to blood viscosity depends on:  ratio of RBCs to plasma vol.  conc. of proteins in plasma.  conc. of proteins in plasma. -  viscosity ( dehydration, polycythaemia) -  viscosity ( dehydration, polycythaemia) -  viscosity (  RBCs or  Plasma prot.)

12. The resistance to flow is inversely proportional to the fourth power of the radius R  1/d 4 ( the smaller the diameter the greater the resistance ------ if the diameter  by ½, the resistance  16 times) 3. Size of the Blood vessel lumen (vessel radius) Therefore vessel radius is a major determinant of resistance to flow (happen in arterioles-vasoconstriction and vasodilatation)

13. Poiseuille’s Law } r l F R = 8  l  r 4 DIFFERENCE IN PRESSURE RADIUS VISCOSITY (FLOW)F (FLOW)F = (  P ) r 8nL 4 LENGHT F = PP R

14. Some Implications of Poiseuille’s Law 8  l  r 4 (  P) F = PP R = If  P is constant, flow is very sensitive to tube radius r(10 - r/10)*100 Q/X[1 - (Q/Q r=10 )]*100 10 0%10,000 0% 910% 6,561 35% 550% 625 94% 190% 1 99.99% % decrease in flow % decrease in radius

15. What Can the Body Regulate to Alter Blood Flow and Specific Tissue Perfusion? 8  l  r 4 (  P) F = PP R =  P = Mean Arterial Pressure – Mean Venous Pressure  P, not subject to significant short term regulation R = Resistance R = 8  l  r4 r4 8, , l,  are not subject to significant regulation by body r 4 can be regulated especially in arterioles, resistance vessels

16. Arteriolar Vasoconstriction and Vasodilation

17. SERIES AND PARALLEL CIRCUITS Organization in the Circulatory System

19. RESISTANCE TO FLOW IN SERIES VS IN PARALLEL Rt = R1 + R2 + R3…. SERIES RESISTANCE 1/Rt = 1/R1 + 1/R2 + 1/R3… PARALLEL RES. SERIES R1R2R3 R1 PARALLEL R3 R2

20. If: R 1 = 2; R 2 = 4; R 3 = 6 PRU’s Then a series arrangement gives: R T = R 1 + R 2 + R 3 R T = 12 PRU’s But a parallel arrangement gives: R T = =1.94 PRU’s 1 1 R 1 1 R 2 1 R 3 ++

21. WHAT REALLY HAPPENS IN THE CVS? ARTERY ARTERIOLES CAPILLARIES LOWER RHIGHER R LOWER R

22. Flow is a measure of volume per unit time Velocity is a measure of distance per unit time Velocity = Flow/Cross sectional area Velocity of blood flow

23. CROSS SECTIONAL AREA AND VELOCITY F=10ml/s A= 2cm 2 10cm 2 1cm 2 V= 5cm/s 1cm/s 10cm/s V = F / A abc

24. Blood Vessel Diameter and Blood Velocity

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