Cerebral Autoregulation in Carotid Artery Occlusive Disease Assessed From Spontaneous Blood Pressure Fluctuations by the Correlation Coefficient Index

Abstract

Background and Purpose-Estimation of dynamic cerebral autoregulation from spontaneous fluctuations of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) is an attractive monitoring option for cerebral hemodynamic impairment. We evaluated the correlation coefficient index method in patients with severe obstructive carotid disease and compared it with transfer function analysis (frequency domain approach to cerebral autoregulation) and CO 2 vasomotor reactivity. Methods-In 139 patients with severe unilateral carotid stenosis (Ն70%) or occlusion, CBFV (transcranial Doppler) and ABP (Finapres method) were recorded over 10 minutes. Correlations between systolic pressure, diastolic pressure, and mean ABP and CBFV oscillations over 1-minute epochs were averaged over 10 minutes to form the correlation coefficient indexes (Sx, Dx, Mx, respectively). Transfer function parameters (phase shift and gain between ABP and CBFV oscillations) were determined from the entire 10-minute period. CO 2 reactivity was assessed by inhalation of 7% CO 2 . Results-The correlation indexes Dx and Mx were significantly higher ipsilateral to stenosis and increased with degree of stenosis, indicating increasing dependence of CBFV on ABP and thus impairment of cerebral autoregulation.

Optimising the assessment of cerebral autoregulation from black box models

“…In [27] a broadband filtered impulse (generated by applying a Gaussian window to a cosine wave at 0.08 Hz - Figure 2B and Figure 3A) was proposed as an alternative test input. This is visually similar to spontaneous fluctuations observed in recorded ABP signals ( Figure 3B), and has a centre frequency in the range previously used in the assessment of CA from gain or phase [5,8,19]. The response to this input will be denominated as the pressure-pulseresponse (PPR).…”

“…The correlation of the ABP and CBFV time series [18] known as the Mx index, has also been very extensively used (e.g. [19]). The majority of published studies have considered one or two measures of CA for the analysis of cerebral blood flow control from spontaneous variations [10,14], and no single parameter has become accepted as a gold standard.…”

Critical Closing Pressure: Comparison of Three Methods

“…A correlation around 0.6 may seem to be low, but in clinical brain monitoring it is not uncommon to interpret such a value as indicating a reasonable agreement (Reinhard et al, 2003;Steiner et al, 2003). In the clinical scenario, estimated values can be calculated repetitively and time-averaged, thus improving the signal-to-noise ratio.…”

Near-Infrared Spectroscopy can Monitor Dynamic Cerebral Autoregulation in Adults

“…2). The Mx index has previously been validated by comparison to the static rate of autoregulation [15], the transient hyperemic response test [16], the leg-cuff test of cerebral autoregulation [14], the autoregulation index ARI [17], the pressure-reactivity index PRx [18], the phase shift between slow waves of FV and ABP [19], and the CO 2 reactivity test [20]. Using the same principle, a moving correlation coefficient between 10 s averages of ABP and TOI signals (Tox) was calculated.…”

“…We did not include a control group of healthy volunteers to compare Tox and Mx. A correlation between a new index of autoregulation (Tox) and Mx, an established index of autoregulation [9,15,[19][20][21][22] requires comparisons of the variables across a group of patients with both good and disturbed autoregulation. Patients with sepsis are ideal for this purpose, as they have a large spectrum of autoregulatory depletion.…”