1. Hemodynamics Purpose of control mechanisms of blood flow? Maintain homeostasis Purpose of blood flow? Nutrient and waste exchange Blood flow to brain and heart must be maintained Insufficient blood volume to perfuse all tissue simultaneously Blood flow must match metabolic needs of tissue AJ Davidoff

2. MAP = CO x TPR Important to maintain adequate perfusion pressure in order to control blood flow Sherwood Fig 10-1 HR x SV MAP = mean arterial pressure TPR = total peripheral resistance CO = cardiac output

3. Sherwood Capillary exchange is the sole purpose of the circulatory system Blood flow depends on pressure gradients and vascular resistance

4. Relationship between blood flow, pressure and resistance Ohm's Law:V = I*Ror I = V/R V = voltage (potential difference) I = current R = resistance Blood Flow:  P = Q*Ror Q =  P/R Q = flow (mL/min)  P = pressure gradient (mm Hg) R = resistance (mm Hg/mL/min) The major mechanism for changing blood flow is by changing arterial resistance (e.g., TPR or in a single organ)

5.  Pressure gradients Pressure difference affects flow not absolute pressure Sherwood Fig 10-3

6. Resistance to Blood Flow Poiseuille equation R = 8  L  r 4 R = resistance  = viscosity of blood L = length of blood vessel r 4 = radius of blood vessel raised to the fourth power If radius decreases by one half, resistance increases by 16-fold (= 2 4 )!!! (  r 4 = area)

7. Radius profoundly affects blood flow Sherwood Fig 10-4 R~ 1/r 4 Q =  P/R Flow ~ r 4

8. Costanzo Fig 4-5 Q = P/R Total resistance equals the sum of the individual resistances Total flow is the same at each level, but pressure decreases progressively (93 mm Hg)(4 mm Hg) Why? Series Resistance

9. Parallel Resistance Flow in aorta is equal to the flow in the vena cave (steady state) Flow to each organ is a fraction of the total blood flow Total resistance is less then any of the individual resistances, therefore no significant loss of arterial pressure to each organ 5 L/min Needs work

10. Velocity of Blood Flow v = Q/A v = velocity of flow (cm/sec) Q = flow (ml/sec) A = cross-sectional area (cm 2 ) Costanzo Fig 4-4

11. Costanzo Fig 4-3 Total cross sectional area of systemic blood vessels v = Q/A

12. Laminar flow and Turbulence Laminar flow is parabolic, highest velocity in center (least resistance), lowest adjacent to vessel walls Turbulent flow is disoriented, no longer parabolic, energy wasted, thus more pressure required to drive blood flow. quiet noisy Costanzo Fig 4-6

13. Ganong Fig 30-8 Turbulence is  velocity of blood flow diameter of blood vessel 1/ viscosity of blood Mohrman and Heller Fig 6-6

14. Bernouilles Principle (in a single vessel) Total energy = distending pressure (P D ) + kinetic energy (K E ) Higher velocity through a constriction PDPD KEKE Bad for plaque regions Why? Total energy is actually not conserved completely because of heat loss

15. Bad for aneurysms Why? KEKE PDPD Bernouilles Principle

16. Cardiovascular Physiology Concepts http://www.cvphysiology.com/Blood%20Pressure/BP004.htm Compliance of blood vessels C = compliance (mL/mm Hg) V = volume (mL) P = pressure (mm Hg) C =  V/  P Compliance is a slope At low pressures, veins have a greater compliance than arteries At high pressures, compliance is similar in veins and arteries (but volume is much greater in veins)

17. Compliance changes related to vasocontraction or aging With vasocontraction: Venous volume decreases and pressure increases Venous compliance decreases Similar effects in arteries with aging

18. Martini Fig 21-2 Arteries Conduits Blood Vessels

19. Pressure reservoir Sherwood Fig 10-6 & -7 Elastic recoil continues to drive blood toward arterioles during diastole

20. B&B Fig 17-11

21. MAP = diastolic pressure + 1/3 pulse pressure (at rest) 2/3 time in diastole 1/3 time in systole 80 mph for 40 min 120 mph for 20 min Sherwood Fig 10-7

22. G&H Fig 15-6 Dampening pulse pressures Arterial pulse pressure influenced by: elasticity rigidity resistance  resistance,  pulse pressure

23. What does systolic pressure tell you? What does diastolic pressure tell you? CO & TPR TPR Cardiac Output (CO) = MAP TPR Sherwood Fig 10-9

24. G&H Fig 15-4 and B&B Aortic pressure changes rigid

25. G&H Fig 15-4 Aortic pressure changes

26. G&H Fig 23-4

27. Mean arterial pressure (MAP) is the main driving force for blood flow through capillaries G&H Fig 14-2

28. Basis of auscultatory method for measuring BP (Sounds of Korotkoff) Mohrman and Heller Fig 6-9 Turbulent flow is noisy

29. Why should cuff be placed at heart level? What effects on BP measurement would the presence of obesity cause?