1. Reflections of the pulse wave Occur whenever there is a change in vessel cross section or stiffness. Local hydraulic impedance

2. + - + - Less stiff Stiff Less stiff Big Small Big Small Less stiff Stiff Less stiff Stiff Positive and negative wave reflections Pressure increases Flow decreases Pressure decreases Flow increases Pressure increases Flow decreases Pressure decreases Flow increases

3. Reflection coefficient Z c =  c/a

4. How to separate forward and backward traveling waves Multiple measurements of pressure/flow diameter and numerical processing of data Total occlusion methods Impulse methods

5. Total occlusion method Measure pressure in region of interest Apply a total occlusion distal to the region and re-measure pressure Substitute for P

6. How to separate forward and backward traveling waves Multiple measurements of pressure/flow diameter and numerical processing of data Total occlusion methods Impulse methods

7. Impulse method Generate a sharp spike of pressure/flow and track its movement at different points. If sharp enough its reflection can be observed in isolation from the incident wave

8. Measurement of pulse transmission in vivo

9. Measurement of pulse transmission in vitro

10. In-vivo or in-vitro

11. Propagation and reflection in a uniform tube 50 ms 20 kPa 0 150 300 0 100 200 Distance

12. Wave propagation in arterial models Normal artery Stenosed artery

13. Reflections at the aorto iliac trifurcation

14. Reflections in vivo Vasoconstriction PmPm Newman DL & Greenwald SE Cardiovascular Research 113: 595-600. (1979) Bertram, CD et al. (1997). Medical Engineering and Physics 19: 212-222. PfPf PbPb Vasodilation PmPm PfPf PbPb

15. Do negative reflections occur in the “healthy” vascular system?

16. Effect of age on aorto-iliac reflection coefficient Post mortem measurements of velocity and area ratios 46 subjects aged between 3 months and 88 years Velocity of pressure wave from catheter Dimensions of junction from radiography Catheter tip manometer Abdominal aorta Greenwald, S.E. et al. (1990) Circulation 82, 114-23.

17. Effect of age on area & velocity ratio y = -0.0023x + 0.95 R = 0.92 or VR

18. Effect of age on aorto-iliac reflection coefficient

19. YoungOld/Hypertensive PbPb PmPm PbPb PfPf Aortic pressure wave Late reflection augments diastolic pressure Early reflection augments systolic pressure PfPf PmPm Time scale