Assessment of the Thigh Cuff Technique for Measurement of Dynamic Cerebral Autoregulation

Abstract

Background and Purpose-Dynamic methods of measuring cerebral autoregulation have become an accepted alternative to static evaluation. This article aims to describe a set of data collected from healthy volunteers by a dynamic method, the purpose being to qualify and quantify expected results for those who may be designing a study using this technique. Methods-Cerebral blood flow velocity (CBFV) (measured by transcranial Doppler) and arterial blood pressure (Finapres) were recorded in 16 normal subjects before, during, and after the induction of a blood pressure drop (release of bilateral thigh cuffs). This procedure was repeated 6 times for each subject. A mathematical model was applied to the data to generate an autoregulatory index (ARI) with values between 0 and 9. Results-The ARI values for this sample population follow a normal distribution, with a meanϮSD of 4.98Ϯ1.06 (nϭ15).Analysis of the cumulative mean ARI values of all subjects showed an exponential-type convergence of ARI toward the sample mean as the number of test iterations increased. The population average blood pressure drop on thigh cuff release was 26.4Ϯ7.1 mm Hg (nϭ16), occurring in 4.6Ϯ1.7 seconds. The corresponding population average drop for CBFV was 15.6Ϯ5.8 cm/s, taking 2.5Ϯ1.0 seconds. No significant trend was noted in the measurements as the number of test iterations increased. The correlation between the predicted and actual CBFV, having a mean value of 0.76Ϯ0.19, showed evidence of a nonlinear relationship to ARI values. Significant correlation was also found between ARI and (1) arterial blood pressure before cuff release and (2)

S(+)-ketamine/propofol maintain dynamic cerebrovascular autoregulation in humans

“…25 Studies in humans have shown that ARI is constant in the order of 5 ± 1 in neurologically healthy, awake patients. 11,24 The patients studied in the present investigation did not present with a medical history or clinical signs of cerebrovascular disease. We, therefore, assumed intact autoregulation in these patients and baseline measurements in awake patients were considered avoidable in order to reduce the preoperative psychological strain.…”

“…For example, any recovery of CBFV independent of MAP results in incremental steps of the CBFV curve and translates to an ARI of 4-6 indicating intact cerebrovascular autoregulation. 11 A pressure passive CBFV-pattern equals no difference between the CBFV and the MAP curve and translates to an ARI of 0 (=no autoregulation).…”

Phase dynamics in cerebral autoregulation

“…However, this transient effect stems naturally from the phase dynamics and does not have a pathological origin. The insight provided by the synchrony analysis may also allow to put in different perspective the reports of the very low values of ARI autoregulation index in healthy individuals (18). The low values of this index would suggest the absence of autoregulatory response in physiological condition.…”

Optimising the assessment of cerebral autoregulation from black box models

“…Previous studies have shown considerable intra-subject variation for repeated thigh cuff tests [33], repeated recordings with spontaneous fluctuations [22,25] as well as recordings with controlled breathing where a sliding window was used to estimate short-term variability [25].…”

“…Previous analyses that concentrated on the performance of the ARI [25,32,33] have shown large variations over time and sudden drops to zero of this index. Although rigorous studies have not been performed to understand the source of this variability, this may be due to the constraint that the Aaslid's model [15] imposes on the index as it only uses a set of ten filters [25].…”