Abstract TP446: Independent Measures of Cerebral Blood Flow in Asymptomatic Carotid Artery Disease.

Background: Cerebral blood flow (CBF) regulation is a critical element in cerebrovascular pathophysiology, particularly in large vessel disease. Different methods to assess hemodynamics may represent different aspects of blood flow regulation, however, uniquely affecting outcomes and management. We examined 4 different blood-flow related measures in patients with high-grade unilateral carotid disease, assessing asymmetry between the occluded vs non-occluded side, and the correlations among the measures. Methods: Thirty-three patients (age 50-93, 19M) with unilateral 80-100% ICA occlusion but no stroke underwent: 1) quantitative resting CBF using continuous arterial spin labeling (CASL) MRI, 2) mean flow velocity (MFV) in both middle cerebral arteries (MCAs) by transcranial Doppler, 3). Vasomotor reactivity (VMR) in response to 2 minutes of 5% CO2 inhalation, and 4) Dynamic cerebral autoregulation (DCA) using continuous insonation of both MCAs for 10 minutes at depth 56mm with a standard head frame. Phase shift (PS) between spontaneous oscillations in blood pressure (measured with finger photoplethysmography) and MCA MFV at frequencies .06-.12 Hz was calculated for each hemisphere using transfer function analysis. Lower PS indicated worse autoregulation. Paired T-tests and Pearson correlations were used to look for side-to-side differences within each measure, and correlations between measures (SPSS v.22). Results: CASL CBF (p=.001), MFV (p<.001), VMR (p=.008), and DCA (p=.047) all showed significantly lower values on the occluded side. The 4 measures were independent of each other on correlation analysis, even when controlling for age and anterior circle of Willis collateral (correlation coefficients all <0.40, p-values >0.09). Conclusions: These 4 measures showed high sensitivity to the occluded carotid artery, but appear to represent independent aspects of cerebral blood flow (CASL: resting gray matter CBF; MFV: whole-hemisphere CBF; VMR: cerebrovascular reserve, and DCA: homeostatic blood flow regulation) suggesting that any given measure only partially characterizes hemodynamic state. Further investigation will use these 4 measures to predict outcomes including vascular cognitive impairment.

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Frequency response characteristics of cerebral blood flow autoregulation in rats

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00794.2006 ◽

2007 ◽

Vol 292 (1) ◽

pp. H432-H438 ◽

Cited By ~ 14

Author(s):

Brittany Kolb ◽

Diane L. Rotella ◽

Harald M. Stauss

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

Carotid Artery ◽

Cerebral Perfusion Pressure ◽

Cerebral Perfusion ◽

Perfusion Pressure ◽

Transfer Functions ◽

Function Analysis ◽

Cerebrovascular Autoregulation ◽

Transfer Function Analysis

Transfer function analysis of blood pressure and cerebral blood flow in humans demonstrated that cerebrovascular autoregulation operates most effectively for slow fluctuations in perfusion pressure, not exceeding a frequency of ∼0.15 Hz. No information on the dynamic properties of cerebrovascular autoregulation is available in rats. Therefore, we tested the hypothesis that cerebrovascular autoregulation in rats is also most effective for slow fluctuations in perfusion pressure below 0.15 Hz. Normotensive Wistar-Kyoto rats ( n = 10) were instrumented with catheters in the left common carotid artery and jugular vein and flow probes around the right internal carotid artery. During isoflurane anesthesia, fluctuations in cerebral perfusion pressure were elicited by periodically occluding the abdominal aorta at eight frequencies ranging from 0.008 Hz to 0.5 Hz. The protocol was repeated during inhibition of myogenic vascular function (nifedipine, 0.25 mg/kg body wt iv). Increases in cerebral perfusion pressure elicited initial increases in cerebrovascular conductance and decreases in resistance. At low occlusion frequencies (<0.1 Hz), these initial responses were followed by decreases in conductance and increases in resistance that were abolished by nifedipine. At occlusion frequencies of 0.1 Hz and above, the gains of the transfer functions between pressure and blood flow and between pressure and resistance were equally high in the control and nifedipine trial. At occlusion frequencies below 0.1 Hz, the gains of the transfer functions decreased twice as much under control conditions than during nifedipine application. We conclude that dynamic autoregulation of cerebral blood flow is restricted to very low frequencies (<0.1 Hz) in rats.

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