Abstract 17734: Pulsatility of Pressure and Flow Waveforms in Cerebral Arteries: Origin and Significance
Arterial blood flow into the brain comprises a mean and pulsatile component, whereas flow out is near continuous. High mean flow is needed for normal cerebral function while high pulsatile flow is a consequence of the LV pumping intermittency and aortic elasticity. Cerebral microvascular damage is causally linked to pulsatile flow. Hence factors contributing to flow pulsatility need be recognised. Aortic pressure and flow waveforms from carotid siphon (S), anterior (A) and middle cerebral (M), vertebral (V) and basilar (B) arteries were obtained in 200 subjects (21-76 y, 94 males) referred for diagnostic 24-hour BP recording to Ruijin Hospital. Aortic pressure waves were generated from radial tonometric recordings using SphygmoCor; flow waves were recorded using transcranial/ transvertebral Doppler ultrasound. Flow waveforms were similar on right and left sides for S, A, M and V arteries. Mean and pulsatile velocities were high in all (S: 45, 34; A: 54, 41; M: 61, 47; V: 35, 25; and B: 38, 28 cm/s, respectively). Both flow and pressure waves showed evidence of two impulses which contributed to pulsatility, the first from LV ejection and second attributable to wave reflection from the lower body. The relationship was quantified as flow augmentation index (FAIx=F2÷F1), generated in similar way as for aortic pressure (PAIx=AP÷(P1+AP)). FAIx, in all waveforms and all arteries was closely related to PAIx (overall FAIx = 1.5 PAIx + 59; R2=0.5) and both increase with age (figure). Wave reflection from the lower body becomes a major contributor to flow pulsatility when FAIx exceeds 100%, adding to the initial wave generated by the heart, and approaches magnitude of this initial impulse in older subjects. Study of flow pulsatility in cerebral arteries together with aortic pressure pulsatility show that both increase with age, are partly attributable to aortic stiffening and early wave reflection from the lower body, and may account for cerebral microvascular damage in older subjects.
- © 2012 by American Heart Association, Inc.